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- Geosternbergia (or Pteranodon sternbergi, depending on who you ask) lived in the coastlines of Late Cretaceous North America, just like its pop culture relative, Pteranodon longiceps, with which it is sometimes confused. Slightly larger than the latter, its name is a reference to early XX century palaeontologist Charles Sternberg. It also had a more striking look: its beak was curved upwards, and its crest was taller, shorter and more developed. Another pterosaur from the same habitat, Nyctosaurus ("night lizard"), was also similar to Pteranodon longiceps but smaller and straight-beaked, and had an extraordinary, two-branched crest. The two branches may have supported a flap of skin, though this is unlikely, and there is no evidence to support it. This was also the only pterosaur without non-wing fingers on each hand, making it the most aerial reptile ever discovered. Geosternbergia was briefly portrayed in Disney's Dinosaur (perhaps the only mostly correct pterosaur portrait ever made in fiction); while Nyctosaurus appears in the Walking With spin-off Prehistoric Park.
Return on Land: Azhdarcho and its relatives
- Azhdarchids were the only confirmed pterosaur family still alive at the end of the Cretaceous note when it was hit by the K-Pg extinction event. The largest pterosaurs known to science (Quetzalcoatlus and Hatzegopteryx) belong to this family, but there were also many other smaller-sized cosmopolitan members as well (like the Asian namesake Azhdarcho). Their heads were vaguely Pteranodon-like with toothless mouths, but they had small crests (if they had crests at all) and, in some cases at least, very long beaks. They were among the less aerial pterosaurs, with relatively short wings and very long neck and hindlimbs; now ptero-scientists think they were rather stork-like in habits, walking around, grabbing any animal they could swallow and eating them. Hatzegopteryx is an exception, as its much more robust body plan made it a big-game hunter (more details below). Alanqa, from mid-Cretaceous Morocco, may also be an exception, as that species has a specialized beak that could imply durophagy (feeding on hard-shelled organisms).
Giant Among Dinosaurs: Hatzegopteryx
- Quetzalcoatlus was not the only gigantic azhdarchid. Since the 90s, several others have been discovered with a similar estimated wingspan, e.g. Arambourgiania. But at an estimated 250 kg, Hatzegopteryx was the heaviest of them, and quite possibly the biggest pterosaur (and flying animal in general) of all time, a real "Badassodactylus". Hatzegopteryx lived on and was named after Hateg Island in Romania. It's a peculiar creature for many reasons; while the island was home to dinosaurs that were subject to island dwarfism, Hatzegopteryx went the opposite direction and was subject to island gigantism. This would have put Hatzegopteryx on the top of the island's food chain. Additionally, unlike most other azhdarchids, Hatzegopteryx likely had an extremely thick and muscular build and a relatively short neck. This implies that Hatzegopteryx hunted significantly larger prey than other azhdarchids (potentially up to the size of a cow). Despite all this, Hatzegopteryx hasn't become stock just yet. But as its existence becomes more well-known, it's edging ever closer to that point. Its current claim to fame is a memorable appearance in the documentary Planet Dinosaur, which was made before the species' robust body plan was known.
- Dsungaripterus ("wing from Junggar") lived in Early Cretaceous Asia. Smaller than Pteranodon but larger than Rhamphorhynchus, it's easily recognizable thanks to its robust and unusually-shaped skull - the toothless beak curves upwards, robust teeth are present further back in the jaw, and a sinusoidal crest is present on the top of the head. The sturdy build of the jaws indicates a diet of hard objects; traditionally believed to be a shellfish specialist, it's also been proposed to have crushed bone. Similar but earlier and more primitive than Dsungaripterus was Germanodactylus from Late Jurassic Germany: this one lived alongside two of the most famous flying reptiles, Ptetodactylus and Rhamphorhynchus, and also the true dinosaurs Archaeopteryx and Compsognathus.
Flying Duckbill: Istiodactylus
- Istiodactylus was once called Ornithodesmus, although that name turned out to be from a dromaeosaurid. It was a fairly large European pterosaur from the Early Cretaceous, flying above Iguanodon and other dinosaurs from the same fauna. It was characterized by a spatula-like bill similar to the modern bird called spoonbill, but lined with small teeth. It might have been a scavenger, as the teeth are serrated and tightly-interlocking, unlike the long, conical teeth of piscivorous pterosaurs. Indeed, the several pterosaurs from the Cretaceous had very diverse head shapes and different food habits, just like modern birds.
A Whale of Pterosaur: Pterodaustro
- Pterodaustro was perhaps the most specialized of all pterosaurs. Its name means "southern wing": it was the first discovered among the numerous South American pterosaurs. It is often seen as a sort of Cretaceous flamingo, and for good reason: its lower jaw was filled with hundreds of long, narrow, baleen-like teeth - probably used to filter microscopic plankton out of the water in a similar manner. Its upper jaw had many tiny teeth as well. Unlike flamingos, the jaws were curved upwards. Thanks to all this, the pterodaustro could even be considered as a flying version of baleen whales. Pterodaustro is a Ctenochasmatid, closely related to other filter-feeding but less specialized pterosaurs, such a the Late Jurassic European Ctenochasma ("comb jaw"), Gnathosaurus ("jaw lizard"), and Cycnorhamphus ("swan beak"), once named "Gallodactylus" ("rooster-finger"). Other members of the group include the Chinese Moganopterus and Gegepterus.
- Ornithocheirus ("bird with hands", once also known as "Criorhynchus", "keeled beak") was one of the first pterosaurs discovered, being named in 1869 for a fragementary snout tip from early Cretaceous England. Since then, it's been involved in massive taxonomic quagmire, with dozens of species formerly assigned to it - including its close relative Tropeognathus, the species portrayed in Walking with Dinosaurs (albeit well oversized and portrayed as "the biggest pterosaur ever" -the true record holder among known pterosaurs is Quetzalcoatlus or Hatzegopteryx). When someone refers to Ornithocheirus, they probably mean Tropeognathus - Ornithocheirus itself is a much smaller animal and much less well-known. Even including Tropeognathus, though, it's interesting that Ornithocheirus has not become a stock animal, despite its memorable appearance and how the similarly-oversized marine reptile Liopleurodon became stock. Like many pterosaurs, the two had specialized heads - with sharp pointed teeth suited for catching fish, and keel-like crests on both jaws probably used for display ("Tropeognathus" means "keeled jaw"). It was once believed that these round "keels" were used to cut through the water to better catch fish, and portrayed in such a way in classical illustrations.
- Unlike South American dinosaurs that have mostly been found in Argentina, most South American pterosaurs have been found in northern Brazil - especially in the Early Cretaceous site named Chapada do Araripe: Cearadactylus and Anhanguera were among them. Anhanguera was a close relative of Ornithocheirus, with the same keeled jaws but with smaller "keels". Multiple species are known, some from very complete remains. Studies done on Anhanguera fossils have revealed much information about flight mechanics. Cearadactylus ("finger of Ceara": Ceara, a small northern Brazilian province, has one of the greatest pterosaur fossil deposits in the world) was also a close relative; in life, it would have looked like an Anhanguera or Tropeognathus with a very low, nearly invisible crest. Both had very large, recurved teeth, used for catching fish. Cearadactylus was chosen as "the pterosaur" in the first Jurassic Park novel: needless to say, in the airborne terror role, while Anhanguera is most well known for starring in Dinosaur Revolution.
- Tapejara was also found in Brazil in the Araripe Formation, like Tropeognathus and the two examples above. Again a large-sized animal, it was unusual among Early Cretaceous pterodactyloids because of its short and toothless beak; toothless pterosaurs were mainly in the Late Cretaceous, among them two stock animals, Pteranodon and Quetzalcoatlus. Some scientists hypothesize Tapejara was a fruit-eating, toucan-like animal, a rare example of a non-carnivorous flying reptile. Its most striking feature was once a huge crest, taller than the head itself (the popular Pteranodons is unpretentious in comparison). However, the owner of the crest has since been separated into a new genus, the new pterosaur Tupandactylus. Tapejara/Tupandactylus appears in the same episode of Walking With featuring Ornithocheirus. The similarly-named Tupuxuara was a close relative, lived in the same places, and had similar features. On the other hand, a similar but not closely related toothless pterosaur was Thalassodromeus, once thought to be a meager skimmer like modern, well, skimmers - hence the name "sea runner". Now it's known to not have been able to skim after all, and was actually was a terrestrial predator like azhdarchids. With its large, robust beak, it was potentially capable of tackling comparatively larger prey than azhdarchids.
Toy Pterosaur: Ludodactylus
- Here's Ludodactylus, a recently-discovered pterodactyloid which, strangely, lived in Early Cretaceous South America. It has gained some notoriety, and it's easy to tell why: with its long crest paired with toothed jaws, it's the very first discovered pterosaur which looks just like fictional versions of Pteranodon, transforming mere fiction in some kind of reality. Its prefix Ludo- derives from a Latin root meaning "play" or "toy", as a sort of Real Life Lampshade Hanging. Its species name, sibbicki, honors renowned paleoartist John Sibbick — the illustrator of the Great Dinosaur Encyclopedia of 1985 which also depicts many stock and non-stock pterosaurs other than true dinosaurs.
Missing Link?: Darwinopterus
- Darwinopterus ("Darwin's wing") was a pretty big deal to the paleo-community; it was the very first pterosaur to show traits of both rhamphorhynchoids (long tail, elongated toe) and pterodactyloids (long head, long wings), making it a possible transitional species between the two groups. These little guys were insect eaters from China, and likely lived alongside little feathered dinosaurs during the Jurassic Period. Darwinopterus and its relatives may have been sexually dimorphic, with males and females differing in crest size - and one crestless specimen of Kunpengopterus (nicknamed "Mrs. T") was discovered to have died while in the process of laying an egg. Related with Darwinopterus were other pterosaurs like Cuspicephalus.
- Now we get really out of the "true pterodactyls" world and enter the "rhamphorhynchs". Eudimorphodon from Late Triassic Italy is one of the most ancient pterosaurs. Despite its earliness, it already had all features of a typical pterosaur. But it was still small: all Triassic/Jurassic flying reptiles were small, at least compared to the Giant Flyer pterosaurs of the Cretaceous. Eudimorphodon was similar to the similar-named Dimorphodon, with the typical long, rigid tail of a "rhamphorhynchoid", but with a smaller, thinner head with complex dentition (its name means "well two-shaped teeths"). Its contemporary Peteinosaurus (also found in the same site) was actually more Dimorphodon-like; it has appeared in Walking with Dinosaurs to represent the start of pterosaur evolution. However, it's not the most archaic pterosaur known: this record may pertain to another Italian Triassic "rhamphorhynchoid", Preondactylus, already with all the adaptments for flying typical of pterosaurs. Other Triassic rhamphorhynchs were discovered in the 2000s: Caviramus and Raeticodactylus (the latter named after a portion of the Alpine range), which showed the first bony head-crests ever appeared on pterosaurs.
- Anurognathus was one of the tiniest pterosaurs ever, just larger than a sparrow! It lived in Late Jurassic Europe, alongside many other pterosaurs and Archaeopteryx. Anurognathus ("frog jaw") and its relatives, including the Asian Batrachognathus (also meaning "frog jaw") and Jeholopterus are exceptional pterosaurs - short-tailed like pterodactyloids, but with short wings and robust legs more like "rhamphorhynchoids". Most notably, however, their skulls are blunt and wide-mouthed, almost froglike in appearance, with gigantic eyes. They were probably insectivorous, possibly living and brooding on trees. Despite having been one of the most harmless Mesozoic creatures in Real Life, not even Anurognathus has managed to escape the pop-cultural fate which hits all its relatives: Primeval has show to us a sort of Zerg Rush flying piranha, while the more benevolent Walking with Dinosaurs has make it a Jurassic oxpecker (which there is also no evidence of).
- These guys were also rhamphorhynchoid pterosaurs, all from the Jurassic Period. Scaphognathus was a small generalist contemporary of the more well-known Rhamphorhynchus and Pterodactylus. Dorygnathus was likely adapted to a life at sea, with its long narrow wings and sharp, interlocking teeth, perfect for keeping a hold on slippery fish, while the also Early Jurassic "Campylognathus" (today renamed Campylognathoides) was probably more terrestrial and Dimorphodon-like. note Campylognathoides is unusual for its long and heavily-muscled forelimbs, almost "gorilla-armed" in comparison to other pterosaurs. Harpactognathus was one of the few pterosaurs discovered in Late Jurassic North America (in the Morrison Formation, where pterosaur fossilization is not easy): another is Mesadactylus. Harpactognathus was quite possibly the only pterosaur that remotely resembled the "Ptero Soarer" trope in any way, shape or form; it had a long tail, a (low) head crest, and teeth. It was also quite large; with an estimated wingspan of eight feet, it is the biggest known rhamphorhynchoid pterosaur — but still much smaller than several "mid-sized" pterodactyloids. It's thought to have been omnivorous like its relative Scaphognathus, although potentially more predatory of small vertebrates due to its size.
A Revolutionary Guy: Sordes
- Among pterosaurs, last but not least: Sordes pilosus ("hairy devil"). Very similar to Rhamphorhynchus, this small Late Jurassic "rhamphorhynch" from Central Asia has had an enormous relevance in ptero-science; it was the first pterosaur ever discovered with fur-like covering (20 years before the description of the first feathered non-bird dinosaur), and thus led the start to the "Pterosaur Renaissance" briefly described in Stock Dinosaurs (Non-Dinosaurs). Today, many scientists believe all ornithodirans (= dinos + pteros + their common ancestors) were originally covered in filamentous skin structures - feathers and proto-feathers in the case of dinosaurs, "pycnofibres" in the case of pterosaurs. Both dinosaurs and pterosaurs could have inherited this trait from their earliest Triassic ancestors like Lagosuchus and Scleromochlus. The other main archosaurian lineage, the pseudosuchians (crocs and their extinct relatives) never developed these filamentous elements on their skin during their evolution. See also "Triassic archosaurs" below.
Non-Stock Marine Reptiles:
Mesozoic Dolphins: Stenopterygius
- The small (2.4 m) namesake Ichthyosaurus is the pop culture member of the ichthyosaur group because it was the first ever discovered (1821, before the first dinosaur): lived in Early Jurassic seas, but has been used as a "wastebin taxon" for undetermined/generic small ichthyosaurs (a bit like what happened to the dinosaur Megalosaurus). With its dolphin-like shape, Ichthyosaurus had no particular traits compared to other ichthyosaurs, as well as the contemporary, almost-identical Stenopterygius. The latter is worth of note, however, because is the species from which the famous "mother-with-young-inside" skeleton comes from. That mother died just when its child was going out of its body. This fossil probably inspired the WWD producers who depicted a scene of a mother killed with a still-not born young, but attributing it to another ichthyosaur, Ophthalmosaurus (see further).
- Most ichthyosaurs were Early Jurassic just like Ichthyosaurus and Stenopterygius, and some had some specialization. Eurhinosaurus ("well-nosed lizard"), for example, had a swordfish-like head plus tiny teeth on its "sword"; the same about its relative Excalibosaurus. They were middle-sized ichthyos, and could have used their prominence like a modern swordfish or maybe a sawfish, but there are no sure indications.
Mesozoic Orcas: Temnodontosaurus or "Leptopterygius"
- There were also bigger guys in the Early Jurassic seas: Temnodontosaurus was much larger than Ichthyosaurus, reaching 8 m in length, as a modern killer whale. It was once called Leptopterygius ("thin flipper") and was one of the apex predators of its time, but its shape was that of a generic ichthyosaur. Its preys could have included smaller sea-reptiles like Ichthyosaurus proper and the original plesio, Plesiosaurus.
- However, the largest ichthyosaurs known to science were surprisingly the earliest, Triassic ones: Shonisaurus reached 18m or even more and weighed about 30 tonnes, as large as a sperm whale, and likely occupied a similar ecological niche. Found in North America in 1976, the shonisaur was traditionally considered the biggest ichthyosaur, but Shastasaurus sikanniensis has recently revealed to be even larger at over 20m and weighing almost 70 tonnes! Another smaller (but still very big) close relatives of both was Himalayasaurus found in the Himalayas (still covered by seas at the time: they emerged out of water only in the Cenozoic). These early giant ichthyosaurians had also several specializations: their four flippers were long and plesiosaur-like, all of similar length (unusually for ichthyosaurs); their body was stockier than most other ichthyosaurs, and their jaws were partially or totally toothless — just like the modern sperm whale, beluga whale etc. compared with other more toothed cetaceans like orcas and typical dolphins. We don't know if they had a dorsal fin or not, but almost surely did they have the typical caudal fin of the Jurassic ichthyosaurs, although more primitive and less-developed. These ichthyosaurs are candidates for "the biggest marine reptile ever" title, along with the biggest mosasaurs; and yet, have not received much attention even in TV documentaries, perhaps because they were nearly toothless and likely only hunted unshelled cephalopods and fish. In 2016, fragmentary jawbones of possibly much larger Shastasaurid were discovered in England. Without enough remains yet found to name the species, it's known for now as simply the "Lilstock ichthyosaur", and if its proportions are comparable to the rest of Shastasauridae then it could have been 26 to 30m long and weighed around 200 tonnes, making it the only known animal to rival the blue whale in size.
- On the other hand, the very un-ichthyosaur-like Cymbospondylus has received a "better" treatment, showing up as the "biggest ichthyosaur" in the Triassic seas in Sea Monsters. Even though it was large as well, reaching 9m/27ft, it was far smaller than Shonisaurus and Shastasaurus (the series' accompanying book got this right). Unlike the latest two, Cymbospondylus was one of the most basal ichthyosaurs known, being more similar to large evolved mosasaurs like Plotosaurus (see further), with only a hint of caudal fin and a very elongated body: it may have even been too primitive to be an ichthyosaur proper. However, its head was already ichthyosaurian, and had no visible neck. Interestingly, the famous model of Ichthyosaurus in the Crystal Palace Park in London incidentally resembles a bit a Cymbospondylus. Other giant confirmed ichthyosaurs known from the Triassic were discovered more recently. Besanosaurus was found in the Alps (the highest mountains of Europe, that emerged only during the cenozoic Mammal Age 200 my after: at the time there were shallow seas instead) in the 1990s and was 6 m long, not much smaller than Cymbospondylus; Thalattoarchon ("ruler of the seas") found in the 2010s was as large as the latter, and one of the top predators of the Triassic seas as well.
- In dinosaur books, the traditional prototypical Triassic ichthyosaur has been Mixosaurus. Even smaller than a human and with a still underdeveloped caudal fin, it had already the classic fish-like form of more advanced ichthyosaurs, showing how the ichthyosaurs' strong adaptations to water were already achieved well before the success of, say, the land-living dinosaurs and the flying pterosaurs. Californosaurus (found in California) and Grippia were other relatively small basal ichthyosaurs from Triassic. The two animals' preys might have included ammonites, fishes of every kinds, crustaceans etc. Like what happens with modern sea-mammals different kinds of ichthyosaurs arguably ate different sources of food, even though none of them was probably a filter-feeder like the modern baleen whales.
- Ichthyosaurs reached their prime in the Jurassic. But, surprisingly, in the Late Jurassic they had already become rare. Ophthalmosaurus is the most well-known among these Late Jurassic kinds. Unusual for having toothless jaws, its name means "eye lizard" because of its enormous orbits: it's often said to have had "the largest eyes of all vertebrates ever" (in respect to the whole body). Even though it was actually a specialized ichthyosaur, Ophthalmosaurus shows up in Walking with Dinosaurs' episode dedicated to marine reptiles as the icon of the whole ichthyosaur group - at least averting Stock Dinosaurs by not showing Ichthyosaurus in this role. Very few ichthyosaurs survived in the Early Cretaceous: among them, the toothed and quite unspecialized Platypterygius. Ichthyosaurs went to extinction far before the asteroid/comet, about 100 million years ago: since they were the best adapted to sea among all Mesozoic reptiles, the reason of this remains still unclear. They may have been outcompeted by sharks and bony-fish, which started to diversify just in that period.
Heads or Tails?: the Elasmosaurids
- Plesiosaurs are divided in two main lineages: plesiosauroids (the "plesiosaurs" sensu stricto) and pliosauroids (the "pliosaurs"), which separated from plesiosaurs in the Triassic. Other than the spectacular Elasmosaurus, there were many other animals in the plesiosauroid subgroup. The closest Elasmosaurus relatives are called "elasmosaurids" from their namesake, among them Styxosaurus, Mauisaurus, and Hydrotherosaurus: some of them were as large as the latter and sometimes even more. They generally lived in the Late Cretaceous, and were among the last sea reptiles before the Cretaceous-Palaeogene boundary. Let's talk a bit more about the prototypical Elasmosaurus: it was victim of an astonishing paleontological blunder in the middle of the 19th century, when it was first discovered. Before the notorious Bone Wars began in the USA, Edward Cope (one of the two "warrior" scientists) discovered its first skeleton, but its skull was found separated by the rest. Looking at the unbelievable length of its neck and the comparatively short tail, Cope decided, after infinite second thoughts, to put the skull... on its tail-tip. The other paleontologists obviously laughed at Cope when the mistake was cleared, and the legend says that Othniel Marsh (his future rival) was among them; and this would have caused the hate between the two, and thus, the upcoming Bone Wars.
- Among non-elasmosaur plesiosauroids, Cryptoclidus and the prototypical Plesiosaurus are the most portrayed. The former was medium-sized and the classic Late Jurassic plesiosauroid, with a typical look but a not-so-oversized neck as the elasmosaurs; some remains show stones in its ribcage, whose purpose is uncertain. It could have been a prey of the famed Liopleurodon. Plesiosaurus was even smaller and even shorter-necked, and lived in Early Jurassic along with many ichthyosaurs. The relatively large Muraenosaurus lived in a time between Plesiosaurus and Cryptoclidus, in the Middle Jurassic.
- Even though are little-known compared with other relatives, Polycotylids are interesting because they were the only short-necked plesiosauroid subgroup. They lived in the Late Cretaceous, and achieved a shape deceptively similar to pliosauroids (see below), but were far smaller, often man-sized. However, one National Geographic Special featured one polycotylid (Dolichorhynchops) as the main character. Another example of polycotylid is Trinacromerum, whose name recalls that of Trinacria (the ancient name of the italian island of Sicily, meaning "three-corners" because of its triangular shape).
- Unlike plesiosauroids, pliosaurs hadn't a great variety in the Mesozoic: most of them had the same size and the same appearance of the two stock members, the gigantic Kronosaurus and Liopleurodon (although the former is about 20 ft smaller than first thought). There were smaller pliosaurs as well, though: the Late Jurassic Peloneustes ("mud swimmer") is a good example. Some giant pliosaurs (ex. Brachauchenius) managed to reach the end of the Cretaceous and lived alongside Elasmosaurus, Tylosaurus and Archelon, but are rarely considered unlike their earlier predecessors, suffering the rivalry of the aforementioned stock sea reptiles. However, the earliest, Early Jurassic pliosaurs were very different-looking than a Liopleurodon: Macroplata ("big plate") and Rhomaleosaurus (once often confused with "Thaumatosaurus", "wonder lizard"), had a long neck and a small head. At the Early Jurassic, plesiosauroids and pliosauroids weren't still differentiated from each other: Plesiosaurus and Macroplata may easily get confused (and people are still arguing about the Late Triassic Thalassiodracon, "sea-dragon"). Late Jurassic forms were well-defined, Liopleurodon and Cryptoclidus looked very differently.
"Antediluvian" Sea Reptiles
- When non-bird dinosaurs were still unknown, sea-reptiles were already well-known to science. Mosasaurs in particular have had a crucial role in vertebrate paleontology: their namesake, Mosasaurus has been the
very firstsecond "antediluvian reptile" ever discovered, at the end of the 18th century in Netherlands (the record-holder is Pterodactylus). The "mosasaur" was described by the Father of Paleontology, French naturalist Georges Cuvier, and its first found remains were object of an awesome tangle, with the jaws that were lost during the battles of the european Napoleonic Era. One detail is astounding: the mosasaur was ultimately discovered... thanks to some bottles of wine offered as a reward for who would have ultimately found them.
- All mosasaurs lived in the Late Cretaceous, and thus were short-lived compared to other sea reptiles. The gigantic Tylosaurus and Mosasaurus are the two stock genera, often confused each other in paleo-art. Among other "mosas", we can mention: the huge Hainosaurus, believed by some the largest mosasaurian; the rather ichthyosaur-like Plotosaurus ("swimming lizard"), a specialized mosasaur which was as large as Tylosaurus or even more; the much smaller, more traditional-looking Platecarpus and Clidastes, both primitive kinds very common in the famous inland sea that covered central North America at the time (which was also home to Tylosaurus); Halisaurus ("saltwater lizard") and Goronyosaurus; and the unusual ammonite eater Globidens ("globe tooth"), with a typical mosasaur shape but uniquely blunt teeth. Perhaps the first mosasaurian was the amphibious Dallasaurus (named after Dallas city), which had functioning legs. While some scientists speculated that mosasaurs evolved from the same ancestor as snakes, the discovery of legless snakes predating Dallasaurus has debunked that, and it is now known that they are varanoids, making them the badass marine cousins of monitor lizards such as the Komodo dragon and Megalania. More recently a freshwater mosasaur been discovered, named Pannoniasaurus and it wasn't a small animal like Dallasaurus, it had a length considerable to the largest living crocodilians and likely took a niche similar to them, ambushing dinosaurs as they came to drink.
- For decades, it was assumed that Mosasaurs swam like crocodiles or sea snakes: undulating with their tails and paddling with their flippers. In 2010, fossils of Prognathodon ("protruding tooth") turned this assumption on its head by showing a striking example of convergent evolution with Metriorhynchid crocodylomorphs (the "marine crocodiles", see below) and Ichthyosaurs: at least some species of mosasaurs - like the aforementioned evolved Plotosaurus - had developed shark-like tail-flukes, a far more efficient method of swimming than the previously assumed undulation. Whether all species of mosasaurs possessed this adaptation or whether they gradually evolved from undulating to using only their tails is currently unknown.
Color me Black-and-White
- In 2014, paleontologists discovered melanosomes (black pigments) in fossil remains of a number of prehistoric marine reptiles - including not just mosasaurs but pliosaurs, ichthyosaurs, and even turtles. The study determined that - like many extant marine animals - prehistoric sea animals were counter-shaded, with a dark back and a light belly that would have served as a form of camouflage.
There were many other groups of sea reptiles in the Mesozoic other than the previous ones. Among them, giant turtles in the Cretaceous (such as Archelon); sea crocodiles in the Jurassic, some of them very fish-like (such as Metriorhynchus); while the Triassic was represented by two primitive, still partially terrestrial groups: placodonts and nothosaurs.
- Placodonts and Nothosaurs were the two main groups of Triassic sea reptiles, both relatively small compared to the most famous Jurassic-Cretaceous marine reptiles, but still large animals compared with other basal Triassic reptiles. Both are still partially terrestrial and with functioning limbs: if compared with plesiosaurs, they were like seals or otters compared with whales or manatees. Placodonts were the most specialized. They were bulky animals with strong jaws and crushing teeth specialized to eat shellfish; the most evolved of them (ex. Placochelys, Psephoderma, Cyamodus, and Henodus) had an armor and were very turtle-like, with a beak, weak tails, and swum with their limbs like turtles. Henodus was particularly turtle-like, with its flat broad shell and stubby tail. Psephoderma was also peculiar, because of its armor divided in two pieces. However, the most basal placodonts (ex. the namesake Placodus) were almost armor-less, with "incisor"-like teeth and a long, robust tail for swimming, resembling a bit the modern Galapagos islands' marine iguana. Placement of placodonts in the reptilian phylogenetic tree is still uncertain, but are traditionally regarded as distant plesiosaur relatives, thus probably not related with turtles despite their resemblance. However, as recent evidence indicates that plesiosaurs themselves may have been distant turtle relatives, placodonts may have been as well.
- Nothosaurs were very different-looking than placodonts: slender fish-eaters with streamlined bodies, flat tails, long necks and long, thin jaws with pointed teeth. Some of their features were plesiosaur-like: this because nothosaurs were close plesiosaur relatives, and some of them might have even been their ancestors. However, nothosaurs still swum using their tails like modern crocodilians, while their possible descendants the plesiosaurs had rigid body and used their flippers to propel themselves through the water. Nothosaurus is considered the prototype of the nothosaur group and was 4m/12ft long, but the most basal nothosaurs were much smaller, like Neusticosaurus and Pachypleurosaurus. The most evolved nothosaurs were practically plesiosaurs: ex. Pistosaurus. Other examples of nothosaurs include the large evolved Ceresiosaurus and the small more primitive Lariosaurus, whose names are a reference to some alpine lakes (the Lake of Lugano and the Lake of Como respectively), between Switzerland and Italy, where their fossils were dug out. Another group of Triassic aquatic reptiles, Thalattosaurs — lit. "sea lizards", for example Askeptosaurus italicus ("italicus" = Italian) and Endennasaurus, also found near the aforementioned alpine lakesnote , resembled miniaturized nothosaurs, but weren't related with them. Others, like Helveticosaurus, were perhaps related with placodonts. Still others, the hupehsuchians like Hupehsuchus and Nanchangosaurus, looked like a cross between an ichthyosaur and a placodont, and were perhaps the ancestor of ichthyosaurs. One recently-discovered, Eretmorhipis, had unusually seven digits in its hands and six in its feet, like some ichthyosaurians and the earliest land-vertebrates (Ichthyostega, Hynerpeton etc.). In the Permian, one of the earliest aquatic reptiles was Claudiosaurus (see also in another section), a sort of small but bulky-bodied swimming lizard: some think it could be a distant ancestor of turtles (see below), but this is unproven.
Successful Underdogs: the Choristoderes
- While technically not exclusively marine, choristoderes (better known as champsosaurs) are thought to have been fully aquatic, even in freshwater ecosystems - to the point that in some species only the females had limbs that were strong enough to move on land. Originated in the Triassic period, champsosaurs were once considered "eosuchians" (see below). They were often similar to miniaturized crocodiles (but not related at all with them), and are of particular interest as they managed to survive beyond the Mesozoic and into the Cenozoic where most of its brethren went extinct at the K-Pg extinction event. They are the only now-extinct group of reptiles that lasted after the end of the Mesozoic era. The Late Cretaceous Champsosaurus is the namesake of the group: croc-shaped, it was only 5 ft long, a perfect underdog when compared with its neighbour, the 45 ft long "true crocodilian" Deinosuchus. Among Cenozoic choristoderes Lazarussuchus is named after Lazarus, the character resuscitated by Jesus (a reference to its Science Marches On story, see the link above)
Split Jaw?: Atopodentatus
- One of the strangest marine reptiles ever discovered, this Triassic creature had a body structure similar to that of the aforementioned Placodus. But that's not what so strange about this guy. The name means "Unusual dentation", and for good reason: it was originally assumed that the creature's upper mandible was split into a strange zipper-like structure.◊ Two new specimens described in 2016 showed that the processes of the mandible thought to form a zipper-like structure actually faced laterally, giving the animal's head a hammerhead-like shape. Before 2016 it was interpreted as likely a filter feeder instead of an active predator, swimming into shallow waters to prey on small microscopic organisms. The 2016 discoveries suggest it might have actually been a herbivore, scraping algae off the substrate underwater.
Extant Reptile Groups:
Contrary to what many shows make to believe, dinosaurs, pterosaurs, Dimetrodon and sea reptiles were not the ancestors of any modern reptile; instead, some of them were at the origin of bird and mammal groups. However, there were true relatives of modern reptilian species in the past as well, and they have existed since the beginning of the Age of Dinosaurs or even before that time (except snakes, which are a rather young group evolutionarily speaking). Some of these animals were rather similar to their modern relatives, while other were quite different (remember that every animal group does evolve during the time). In general, most media and even documentaries will go with the larger species of each group. The smaller relatives are almost never mentioned because they are not spectacular enough, even though they were more abundant that their gigantic versions, just like what happens to modern animals in general.
An Enduring Success: Prehistoric Crocodilians
- Here we're going to talk about crocodilians, the only surviving members of the clade Pseudosuchia. They are the only extant reptiles that it wouldn't be too wrong confounding them with dinosaurs. OK, they aren't dinos in a strict sense, but they were their closest non-avian relatives, and shared with dinosaurs much more traits it may seem at first glance. Both dinosaurs and crocs have/had alveolate teeth with a bit of heterodonty: to make things clear, their teeth were more similar in their structure to the mammalian ones than, to say, those of lizards. Both dinos and crocs show complex parental care, again just like mammals and unlike lizards/turtles. And both dinos and crocs did descend from bipedal ancestors. Quite so. The first common ancestors of both dinos and crocs, the Triassic archosaurs (see further), were a sorta mix-up of dinosaurian and crocodilian features, and some ancient croc relatives were deceptively dinosaur-like - the most striking case is the Struthiomimus-like Effigia. But at the Jurassic, their evolution diverged more, and since then, separating crocs from dinos becomes an easier task. However, don't think ancient crocs were boring things: it's anything but. Within their enduring success, they were almost as diversified as dinosaurs, and their size and body plan was very variable. Some were as small as a chameleon, others larger than T. rex. Some were powerful predators of large land animals; other became fish-lovers or insect-hunters; and some were even aquatic filter-feeders. As a group, they roamed all the three main Earth environments: land, oceans and freshwater - even though the latter was their favourite, because here they didn't suffer any competition, unlike dinosaur-ruled lands and sea reptile-ruled seas. Some examples of ancient crocodylomorphs are following.
- Let's start with giant freshwater crocodylomorphs, for obvious reasons. Sarcosuchus ("meat-eating croc") was not an Eusuchian like Deinosuchus and modern crocodilians, but only a crocodylomorph distantly related with true crocodilians. note Its shape was that of a gigantic gharial, with long thin jaws and numerous needle-like teeth. First found in Cretaceous Northern Africa in the same habitat of Spinosaurus, it was recently found also in South America, where Giganotosaurus roamed. 15 m long, Sarcosuchus was basically the same bulk of these giant theropods. Recently CGI documentaries have popularized the Deino- and the Sarco- -suchus with the nickname supercrocs. Given their size they could have eaten giant dinosaurs if theyd the chance, and some portraits show them defeating even the biggest theropods (tho the point they could be renamed "Badassosuchus"). In Real Life, it's more likely such powerful predators tried to avoid each other, but at least Deinosuchus is known to have attacked living tyrannosaurs, shown by a leg bone that healed after the bite. Not everyone knows, however, that two enormous crocs lived just few million years ago, in full Mammal Age, when the first hominids just started their evolutionary journey: the giant graham Rhamphosuchus ("sharp-snouted croc") from India and the giant alligator Purussaurus ("Purus lizard") from South America. And they were at least as big as (if not bigger than) the two dinosaur-eating docu-stars. Stomatosuchus ("mouth-croc") despite its large size (10 m or so) was a sort of ducklike or whalelike crocodylomorph, because its wide but weak jaws bear small crammed teeth maybe apt to an inoffensive filter-feeding. The recently (2012) discovered Aegisuchus might have been even larger: measurements of its only remain, a skull (which was larger than a human by itself) suggest an animal over 20 metres long, making Aegisuchus the longest non-marine predator to ever live — although it's much more probable that its skull was larger in comparison to its body than other crocodylomorphs.
- Most known crocodylomorphs had the suffix -suchus on their name (meaning "croc" in Greek), but this isn't always the case — after all, not every dino ends in -saurus, not every prehistoric mammal ends in -therium, and not every pterosaur ends in -dactylus. And dont forget that most prehistoric freshwater crocodylomorphs were not bigger than ours, either. The Late Jurassic/Early Cretaceous Goniopholis is one of the best known examples, and was not bigger than a modern alligator or cayman. It was closely related with the Eusuchians (aka the "modern" crocodilians), and lived alongside Iguanodon among the others. The same about Bernissartia, a tiny (only 2 ft long) relative of Goniopholis whose name is due to being discovered in the famous Belgian coal mine in which the 40 Iguanodons described by Dollo were found. Among Cenozoic crocodilians, Diplocynodon was widespread in Europe: only 4 feet long, was virtually identical to a modern alligator.
- And now, let's discover the opposite end: the smallest crocodylomorphs ever lived were land-loving, long-legged, agile things with a bit of dinosaur inside. Early Jurassic Protosuchus ("first croc") has been perhaps the most portrayed, and was found by the same discoverer of Tyrannosaurus rex, Barnum Brown; closely related with it was Orthosuchus. Most land crocodylomorphs weren't related to each other however: several croc lines reached this body plan independently. Among the Late Jurassic ones, the tiny Atoposaurids were not bigger than a cat! It's simple to understand why many "land-crocs" remained small: competition from dinosaurs was too strong in dry land, and they could survive only occupying the niche of small, fast-reproducing hunters, just like proto-mammals which shared the same niche. Some scientists hypothesise that the nocturnal adaptations mammals underwent during the Mesozoic (inherited by all modern mammals, even the diurnal ones like humans) were not determined by dinosaurs' predation, but rather by the competition of the (arguably) diurnal land crocs. Some of the latter were even partially bipedal: for example the Jurassic sphenosuchians (the most primitive crocodylomorphs known so far, ex. Hallopus), which were smaller than Compsognathus and could become their prey. Hallopus was found during the Bone Wars in North America and, significantly, was originally believed a tiny dinosaur. Some land crocs became larger however, expecially in Cretaceous South America and Australia, and were powerful predators in competition with theropod dinosaurs. The most extreme example known of a running croc appeared just after the mass extinction (that wiped out many crocodylomorphs as well): the large, "hoofed" Pristichampsus. This one was one of the top-predators within its Paleocene world, populated mostly by much smaller creatures. The last group to take to the land was the Mekosuchines (a subfamily of the modern true crocodiles), but they were wiped out by humans, first in Australia and much later in New Caledonia —- maybe even in historical time in the latter island, but before the first European settlers managed saw the animals alive.
- As said above, while most terrestrial crocodiles were small animals, others reached larger size. Some of them were almost mammal-like. While mammals hid in the dinosaurs' shadows, the croco-mammals were actively competing with them, at times growing to enormous sizes that directly competed with theropod dinosaurs and mammals; some species may have even driven them out of their own niches. They were also highly diverse; with the cat-like Pakasuchus (whose name even translates into "cat crocodile"), the herbivorous Simosuchus, the sabre-toothed Kaprosuchus (nicknamed the "boar-croc", maybe the most famous of them), the armadillo-like Armadillosuchus, the pig-like Notosuchus (the official prototype of the group), and the hyperpredator Baurusuchus, which even dethroned the theropods as top predator. Not only did they successfully compete with dinosaurs for over 35 million years, they actually outlived them: the last forms did not die out until the Middle Miocene only 11 million years ago. Most of them were part of the suborder Notosuchia or were otherwise related to them.
- Initially, crocodiles were land animals. Then, many of them became amphibious, as they still are today. But some of them went even further, trying to colonize open seas. Here, they have always had trouble, because of the strong competition with the classic sea reptiles (ichthyosaurs, plesiosaurs, mosasaurs). But a group of them did manage to coexist with the latter: the mainly Jurassic thalattosuchians (literally "sea crocodiles", once classified within the "mesosuchian" suborder, see the note in the "supercroc" paragraph above). The most-archaic ones were still gharial-like, the most known being Teleosaurus portrayed in the Crystal Palace Park in London, and Steneosaurus; the most evolved didn't even resemble crocs. Rather, they looked like slender ichthyosaurs or small mosasaurs, because they developed the same identical caudal fins of an ichthyosaur, lost their armor altogether, and transformed their limbs in paddles (but still not true "flippers"). They were probably the only fully-marine archosaurs ever, maybe they didn't even lay eggs and gave birth to alive newborn, just like ichthyosaurs, mosasaurs and (perhaps) plesiosaurs. Metriorhynchus and the ironically-named Geosaurus ("land lizard") are the two most portrayed examples. Another, the recently-discovered Dakosaurus andiniensis, was an especially bizarre example as it possessed a theropod-like skull and teeth, earning it the nickname "Godzilla".
- Turtle Power is Truth in Television. Turtles have literally been among the longest lived reptiles ever, since appeared 230 million years ago and are still living today. But their origin has long been really mysterious. The very first turtles ever discovered, among them Proganochelys (also called Triassochelys) from the Triassic, had already the classic turtle shape, shell and toothless beak included; since then, they have not changed their body plan at all for 250 million years. Mesozoic turtles were very similar to ours. They have had a great success, colonizing all three main habitat just like crocs, terrestrial, marine, freshwater (but unlike crocs they frequent all these environments still today); however, like crocs, freshwater has been the favourite one, while terrestrial and seagoing species have always been a minority. Marine turtles reached gigantic sizes in the Cretaceous: the aforementioned Archelon was 20 ft long and weighed several tons: the contemporaneous Protostega ("first roof", the prototype of the archelon's family, Protostegids) was very similar to it and not much smaller, while the more obscure Calcarichelys was pretty small (about one foot in length) but developed a spiny shell to defend it against predators, like some modern freshwater turtles. Chelonians or Testudines (the correct names for turtles/tortoises) were the only group of Mesozoic sea reptiles which managed to survive the K-Pg mass extinction: unlike saltwater crocs, venomoud sea-snakes, and Galapagos marine iguana (which returned in the sea during the Mammal age), modern marine turtles do descend from some ancestors already present before the cataclysm happened, though not from Archelon or Protostega which went eventually extinct without leaving descendants. The fossil record of chelonians is extremely abundant (like that of crocodilians and unlike those of lizards and snakes) since freshwater aid the fossilization, and hard-boned shells / bony armors do preserve very well. Most non-marine turtles were small, just like today, but the freshwater-dweller Stupendemys ("wonderous turtle") reached 3 m and was perhaps the biggest turtle that ever lived - rivalling the famous Archelon. Astonishingly, it lived only 6 million years ago, not much before the first hominids. Much earlier (living just after the dinosaur extinction) was another large recently-discovered freshwater turtle, Carbonemys. There were also two large land-living species just 1 million years before modern history: Colossochelys atlas the "Atlas tortoise" from India was very Galapagos tortoise-like but as large as a small car; the Australian Meiolania (nicknamed "horned tortoise") was smaller but with a cooler look: it had small bovine-like hornlets on its head. Extra note: recent research seems to show turtles were not Anapsids as traditionally said, thus not descending from the "near-reptiles" (see the last folder of the page). Before that, they were believed the most ancient still living reptiles, but lizards and tuataras were perhaps more basal, and turtles (together with plesiosaurs) make probably the archosaur's sister-group: that is, they're closer to birds than to lizards, just like crocodiles. Recent fossils found in The New '10s like Odontochelys semitestacea ("toothed turtle with half shell") belong to stem-turtles even more ancestral than Proganochelys itself, having true teeth and still incomplete shells. These "missing links" has connected turtles with Diapsids even more than the former genetic research made in the 2000s upon living species. A traditionally possible candidate for the "ancestor of turtles & tortoises" title has been Eunotosaurus because of the shape of its ribs, but this is not sure. In short, the real origin of turtles has been an age-old discussion among paleontologists. Everything Is Long-Living With Turtles, literally.
- Contrary to turtles and crocodilians, lizards' fossil record is extremely poor: their gracile skeletons do not usually fossilize. Ironically, the best preserved lizard remains known so far were discovered... into other creatures' rib cages. It's particularly famous the case of Bavarisaurus, a small Jurassic lizard found into the first discovered Compsognathus skeleton. We don't know exactly which kind of modern lizards lived already in the Age of Dinosaurs: we're sure there were at least geckos like Ardeosaurus, monitors like Estesia, and proto-iguanas like Paliguana; while chameleons seem to be a recent evolution, after the non-avian dinosaur extinction, derived from iguana-like ancestors. Lizards occupied the same niche ruled by mammals and the apparently similar land crocs, as small insectivores or omnivores. Many modern lizards are still compared with dinosaurs, or even passed off as "mini-dinosaurs", in documentaries and pop books; ironically, just because they were used in the past as a model for the early dinosaur paintings and models. This spread the popular notion that all prehistoric reptiles were nothing but "giant lizards": a notion then adopted by films, comics and whatnot, which has given to us the Slurpasaur trope. But lizards actually pertain to a very different group of reptiles than dinosaurs and even crocodiles (both archosaurs); this group is called the squamates (literally "the scaly ones"). Together with the sphenodonts (see below), squamates form in turn the Lepidosaurs. One may even hear the largest modern lizards literally passed off as dinosaurs in documentaries or other non-fictional works; the predestined victim is, obviously, the large monitor lizard called Komodo dragon. The astonishing thing is, our Indonesian "dragon" did have in the recent past a close Australian relative much, much larger than itself: Megalania prisca (also known as Varanus priscus) was 20 ft long, twice as long as its Komodo kin; like its contemporary (this was a modern animal that lived with and was wipe rout by humans) it was highly intelligent, as smart as most carnivorous mammals, was a fast runner, had shark-like teeth, produced venom, and lived just 50000 years ago. It was, arguably, one of the most powerful predators of its habitat (but don't forget the contemporary marsupial lion: though not larger than a lion, some scientists think it was the most efficient mammalian predator ever, maybe even capable to kill a fully-grown Megalania if it was lucky!). Megalania is by far the largest lizard that ever lived. But wait... have we forgotten something? Yeah, the mosasaurs. It's so easy to forget this, but they were true lizards, and evolved from monitors to boot; with more than 30 ft in total length, the ultimate size-record belongs definitively to them. Along with Megalania and the Komodo dragon, mosasaurs are the only "giant lizards" which are Truth in Television. But wait we've still forgotten something: yeah, anacondas and reticulated pythons. See below.
- Snakes are the great exception among extant reptiles: they are a very recent thing, appearing only in the Late Cretaceous, just before the mass extinction. But their success was obtained only since the beginning of the Mammal Age 65 million years ago, and venomous species appeared even later, 30-20 million years ago. The most ancient extant snakes are probably boas and pythons, or at least their closest relatives: the most common kind of snakes, the colubrids (the garden snake and relatives), appeared in fully Cenozoic settings. As birds are nothing but winged dinosaurs, snakes are nothing but legless lizards. They descend from a still unknown kind of Cretaceous lizard which did elongate its body loosing the limbs at the same time. Curiously, the lizard group closer to snakes in phylogeny is not to be searched among the small slithering ones, like blind worms or amphisbaenians. One hypothesis suggests snakes evolved from burrowing monitor-like lizards, or shared an ancestor with the gigantic mosasaurs instead, although recent genetic analysis and the discovery of Najash, a genus of two-legged snakes, is calling that relationship into question. The mosasaurs' reputation as the Cretaceous "sea serpents" is thus not totally unwarranted. Prehistoric snakes are not much portrayed in books or paleo art: this is probably because their remains are very, very scant, even more than those of their lizard ancestors: all that we often have are few isolated vertebrae, which don't allow to understand even how long they were. Hence, speculation and exaggerations tend to be common. Gigantophis (lit. "gigantic snake", which lived just after the dinosaur extinction) is a prime example: only known for fragmentary remains, it may get described as twice the length of an anaconda despite it more probably was only a bit longer than the latter, if it was. If dealing with Cretaceous species, it'll probably be a Dinilysia ("terrible destroyer"). A very recent discovery, right after the extinction of non-bird dinosaurs, has been the 40-foot long, one-ton Titanoboa: its name means "titanic boa" for obvious reasons. Titanoboa, despite being a recent discovery, has already shown up in a number of documentaries and even an episode of Primeval: New World. Another interesting guy is Palaeophis ("ancient snake"), a marine boa that, like the aforementioned champsosaurs, survived the Cretaceous mass extinction and made it up to the Eocene. A real life sea serpent, this creature has an estimated length of up to 30 feet, but is yet to be seen even in educational media. What about venomous snakes? Well, they never approached the size of the largest boas and pythons, but they still got impressively big. The largest venomous snake ever was Laophis, a 13-foot note viper from what is now Greece. It was related to the Gaboon viper of Africa, which can swallow animals nearly its own size. If Laophis was like that, it could have taken prey the size of a small deer or a time-traveling human child!
- The tuatara is the modern reptile more often cited for being a "living fossil", and with reason. It is the most ancient and primitive extant amniote (amniotes = reptiles + birds + mammals), a survivor which has miraculously managed to be alive today, while all its relatives went extinct before the end of the Mesozoic. The tuatara group is called the sphenodonts, a sibling group of the squamates. Once called "rhynchocephalians", the sphenodonts' natural history is completely distinct to lizards and so on. Sphenodonts are lepidosaurs just like lizards, but have retained more primitive traits still present in our tuataras; they appeared in the Triassic, like almost all the main reptilian lineages. Dinosaurs (both ornithischians and saurischians), pterosaurs, ichthyosaurs, plesiosaurs, crocodylomorphs, chelonians, lizards, even mammals: all these appeared in the Triassic. And sphenodontians as well. Like turtles, they didn't change much since then; fossils show that prehistoric tuataras were almost identical to their modern relative; and lived around the world, while they are limited only to New Zealand today. Like komodo dragons, tuataras are often cites as "living dinosaurs" in pop-books. Once the "rhynchosaurs" (see "Triassic non-archosaurs") were considered early tuatara relatives (they are now considered closer to archosaurs): this explains why tuataras used to be called rhynchocephalians in the past. The latter means "beaked head", and yet nobody'll ever see a tuatara with a beak! This term was actually referred to the parrot-billed rhynchosaurs, which were once considered rhynchocephalians as well. And this explains why the term rhynchocephalian has fallen in disuse for indicating the tuatara lineage. While "sphenodont" has always been referred only to tuataras, never to rhynchosaurs: thus, scientists now use only this more correct term when referring to our spiky New Zealander and its ancestors.
Triassic reptile groups:
In this field terminology has changed recently. Traditionally archosaurs were divided into dinosaurs, pterosaurs, crocodiles and thecodonts, but the last name has fallen out of fashion as paraphiletic and is called by cladistics "artificial assemblage of basal archosaurs". Besides, only crown group (descendants of last common ancestor of birds and crocodiles, i.e. only living members) are called archosaurs, and others are Archosauriformes. Among thecodonts are the ancestors of crocs, dinos and pteros. Actually some of them (Teratosaurus, Ornithosuchus, and others) were once believed true dinosaurs, precisely the very first large carnivorous dinosaurs, but most belong to the clade Pseudosuchia, today represented only by crocodilians. Basal archosaurs, often being somewhere between crocodylomorphs and dinosaurs, tend to get token appearances more in art and documentaries than anywhere else, and are rarely named.
- Rauisuchians are the most commonly represented Triassic archosaurs, as they were the apex predators of Late Triassic and the competition for the early dinosaurs. Rauisuchians were more related to crocodilians than to dinosaurs, but their look was more that of a small, four-legged tyrannosaur rather than a crocodile, and their skull was very theropod-like. In fact, some of them, like Teratosaurus (also mentioned in the Theropod list) and Zanclodon suevicus were long considered dinosaurs, often also because their remains were mixed with those of true dinosaurs like the contemporaneous "prosauropods". Today the 18 ft long Postosuchus has become the new unofficial prototype of the group (the official one is Rauisuchus), expecially after its memorable appearance in Walking with Dinosaurs as the competitor of Coelophysis. Other rauisuchians, like the small European Ticinosuchus (which could have been the author of some footprints often cited in old textbooks as belonging to "Chirotherium") and the South American Saurosuchus (lit. "lizard-crocodile", the biggest ever discovered, 25 ft long) make one rauisuchian subgroup, the prestosuchians; another, very specialized subgroup is the poposaurs (see later). Controversial is the placement of Smok from Poland: it could be a rauisuchian, but also an early theropod.
- The only "thecodont" group that was entirely herbivorous, with small jaws and teeth, aetosaurs looked like ankylosaurs crossed with crocodiles: they had a heavy armor covering not only their back but also their underbelly, making them the most armored archosaurs that ever lived. Like rauisuchians, aetosaurs reached large sizes (5 m the most) and had pillar-like limbs. Despite this, these animals were not dinosaurs, and their erect limbs were obtained by other means than those of dinosaurs. Desmatosuchus is the most portrayed, because has the coolest-look among them with its long shoulder spikes surprisingly similar to those of certain ankylosaurs, and lived alongside Coelophysis in Triassic North America, while Stagonolepis was devoid of these spikes and looked more like a stocky crocodile.
- Despite many of the creatures above may superficially look dinosaurs, the only true basal archosaur related to dinosaurs (and pterosaurs) was the tiny Lagosuchus and its relatives, called Dinosauromorpha. Together, dinosauromorphs and pterosaurs make one of the two main archosaur subgroups, the ornithodirans - literally "bird-necked", because many had flexible bird-like necks, contrary to the almost always short-necked pseudosuchians (the other great archosaur subgroup). Only one foot long, Lagosuchus could stay on an adult man's hand without problems - hence its fanciful name, "croc-rabbit"! It was a long, thin animal, a bit like a miniaturized Coelophysis but also capable to walk on all fours - complete bipedalism was reached only by its descendants, dinosaurs, thanks to the shape of their hips. However, Lagosuchus has been classified as a dinosaur in the past just because its dinosaurian appearance, but its skeleton is too primitive to make it a proper dinosaur. Lived in Triassic South America alongside the gigantic rauisuchian Saurosuchus and the very first true dinosaurs, such as Eoraptor and Pisanosaurus. It's worth noting however, some partially bipedal croc relatives, such as Ornithosuchus and Saltoposuchus (both European and living alongside Plateosaurus), were believed the real ancestors of dinosaurs because they too had a dinosaur-like appearance. Both animals are very common in old dino books: Ornithosuchus ("bird-crocodile") was 4 m long and was once considered the ancestor of the "carnosaurs" (the big-robust theropods in the older meaning, see also Stock Dinosaurs Saurischian Dinosaurs); other less-known ornithosuchids include the South-American Venaticosuchus ("hunting croc") and Riojasuchus ("La Rioja croc", not to be confused with the equally south-american sauropodomorph dinosaur Riojasaurus, also from Triassic). Saltoposuchus ("foot-hopping crocodile") and North-American Hesperosuchus ("western crocodile"note ) were much smaller (1 m long) and were once considered the common ancestor of dinosaurs, birds and crocodilians; they are actually simple crocodylomorphs, more precisely early members of the sphenosuchians (see above). An then, there's Scleromochlus (also European), a tiny (only one foot long) animal that was also considered a proper dinosaur once, and could actually be the ancestor of the pterosaurs. Science Marches On has been a very common thing when coping with dinosaur ancestry.
- Poposaurs are perhaps the least known among Triassic archosaurs, but perhaps the more interesting. They were the most dinosaur-looking among all pseudosuchians, (but until few years ago you'll read more often the name "Crurotarsan" for the archosaurs more closely related to crocs than to dinosaurs, instead of "Pseudosuchian"). Many of them had sail backs resembling Dimetrodon (ex. Arizonasaurus), and the most specialized were toothless and beaked (ex. Lotosaurus). The most surprising one are the shuvosaurids like Effigia and Shuvosaurus: if you take a look on them, you'll surely say they're ostrich-mimic dinosaurs!
As was stated in previous folder, some traditional thecodonts are no more called archosaurs through nothing has really changed in beliefs about their phylogeny (with exception of phytosaurs). Here they are:
The First Runners: the Euparkeriids
- There were several archosaur offshoots as well in the Triassic. Some of them are closely related and very similar to the archosaurs above, and lived mainly in the Early Triassic (while true archosaurs were mainly Middle and Late Triassic): among them, the most iconic is surely Euparkeria. Discovered in South Africa in the Early Triassic, it was contemporary to the two stock cynodonts Cynognathus and Thrinaxodon. This merely 3 ft long insectivore resembled a bit a theropod dinosaur in shape, but is thought to be only partially bipedal, and with slightly sprawling legs unlike dinosaurs and Lagosuchus above. Euparkeria has been perhaps the most commonly portrayed "thecodont" in classic sources, sometimes misinterpreted as "the first ancestor of dinosaurs" (like in Walking With Monsters). Once, it was also considered "the first animal that could walk on two legs"; but now it seems having lost this record in favor of the near-reptilian Eudibamus (see the last folder).
The High-Nosed Crocodiles: the Phytosaurs or Parasuchians
- Phytosaurs have a very weird name: "plant lizards". A much more apt name for this group is Parasuchians, "near crocodiles". Phytosaurs indeed were the most crocodile-like among all Triassic reptiles, and occupied the freshwater predator niche outcompeting temnospondyl amphibians. But then, true crocodylomorphs took their place in turn, after the Triassic-Jurassic extinction event wiped the phytosaurs out.note Phytosaurs could reach large size (5 m the most), but had very short limbs and long, thin jaws often similar to a modern gharial. However it's easy separate them from crocs, by one feature: their nostrils were just in front of their eyes, a bit like whales. Though once thought to be croc-line archosaurs (pseudosuchians), new analyses have shown that phytosaurs are likely outside of crown Archosauria altogether. Rutiodon is one of the most portrayed, because it lived alongside Coelophysis and was a potential predator of the latter.
- Proterosuchus (not to be confused with the early Late Triassic crocodylomorph Protosuchus) and its relatives were the first archosauromorphs which reached the mixed croc-dino shape of Triassic archosaurs. Indeed proterosuchians may be the most basal thecodonts/archosauriformes. Also called chasmatosaurs (nothing to do with the horned dinosaur Chasmosaurus except for their names, both meaning "cleft lizard"), they were medium-sized reptiles with long heads and croc-like shape, but had also a strange overbite which, along with the lack of armor and longer legs, made them distinctive. We don't know if they were semi-aquatic as usually stated: being so basal, they could still have been terrestrial. Another croc-shaped group of basal archosauriforms is very rarely portrayed in books: the gharial-like proterochampsids. Interestingly, both Proterosuchus and Proterochampsa mean "ancient crocodilian" (champsa is another Greek word for crocs, other than the more familiar suchus), but Proterochampsa seems to be more closely related to crown group. Archosaurus was a proterosuchid that interestingly bears the same name of the Archosaurs reptiles in general.
The Crimson Crocs: the Erythrosuchids
- The most spectacular basal archosauriforms were the large, bulky, carnivorous Erythrosuchus, Shansisuchus, Garijania, and their relatives: the erythrosuchians, lit. "red crocodiles". Nicknamed "crimson crocs", with their one-meter long head (as large as an allosaur head) filled with robust teeth and with forward-facing eyes like a tyrannosaur, they occupied the top predator niche in the Early Triassic, substituting the mammal-like gorgonopsians (see further). However, they were stocky and armor-less animals arguably slower-moving than the more evolved rauisuchians, and finally get replaced by the latter in Late Triassic. Unfortunately, erythrosuchians didn't appear in any piece of the Walking With TV series. They were also classified as proterosuchians until paraphyletic groups felt out of fashion.
Note that while recent evidence indicates that plesiosaurs, placodonts, and turtles may be basal archosauromorphs like them, they are still in seperate folders just for differentiation.
- Even though unfairly forgotten by the Walking With TV series as well, rhynchosaurians are perhaps the most interesting basal reptiles from the Triassic. Indeed, they were the most successful groups of herbivores in this period, thanks to their parrot-like beak (their name means "beaked lizards") and powerful grinding jaws which allowed them to chew even the toughest vegetation, as efficient as ceratopsian jaws. Like horned dinosaurs, rhynchosaurs were four-legged, plant-eating reptiles with a bulky body and relatively short tail, but lacking any "horn". They were only distant archosaur relatives; once they were thought to be in the same group of the modern tuatara (see above). Rhynchosaurs were rather small compared to other Triassic reptiles, lived worldwide, and shared their habitat with the very first dinosaurs such as Plateosaurus and Coelophysis. In the Middle Triassic they became the most successful land herbivores in the whole planet, and were perhaps the favorite prey for the first carnivorous dinosaurs like Herrerasaurus. They went to extinction only at the end of the Triassic (like rauisuchians and the other basal archosaurs above) probably outcompeted by the first plant-eating true dinosaurs. Hyperodapedon (also known as Scaphonyx: once the two were considered two distinct animals) is the most portrayed rhynchosaur. It had a very bizarre look: its head was flat, its upper bill had a deep slit which served to accomodate the lower bill like in a Swiss Knife, and its eyes pointed forwards like an owl — remember herbivores have usually lateral eyes to see nearly at 360 degrees: primates and sloths are among the rare exceptions. Other than the rhynchosaurs, in the Triassic there were other terrestrial herbivorous archosauromorphs. One of the most classic is Trilophosaurus ("three-crested lizard", nothing to do with Dilophosaurus "two-crested lizard"), similar to a rhynchosaur but with a round beak. Expecially worth of note is the recently-discovered (2014) Shringasaurus. This one was 3-4 m long, had a head similar to a bull with two small "horns", and longer forelimbs than hindlimbs, resembling a cross between a bull and a lizard — a bit like the famous horned theropod Carnotaurus.
- Living in Triassic Europe, Tanystropheus was one of the most enigmatic among all prehistoric reptiles. 15 ft long, its body was lizard-like but its neck was the longest respect-to-the-body that any creature known (even more than sauropods or Elasmosaurus), to the point it almost challenges physical laws. We haven't any precise idea how Tanystropheus lived: but it was almost certainly a partially aquatic creature. Its neck was particularly stiff, having only few very elongated vertebrate: since its neck was flexible only at the base, some hypothesised Tanystropheus used it as a fishing-rod for catching fish from ashore. Indeed, the neck vertebrae of Tanystropheus are so different-looking than the other vertebrae, the scientist who first described the animal though the neck and the remaining body were from two completely different animals! Interestingly, recent research has shown sauropods and even plesiosaurs too had stiff necks despite their higher number of neck vertebrae: this would make the comparison between Tanystropheus and sauropods/plesiosaurs rather apt. In the early 2000s, a close relative of Tanystropheus was found. Called Dinocephalosaurus ("terrible-headed lizard"), this reptile probably sucked in fish like a vacuum. But Tanystropheus and Dinocephalosaurus are only highly specialized members of their own group of basal non-archosaurs: the Prolacertiforms or Protorosaurs. Most of them were small and more lizard-like than their specialized cousins (ex. the namesakes Prolacerta and Protorosaurus, but also Macrocnemus), but with very long hind limbs and also quite elongated necks. Another very specialized prolacertiform is Sharovipteryx, which looks very similar to and has similar adaptions to the gliding reptiles mentioned in the next section.
Protruding Ribs, Flaps of Skin, and Pseudo-Wings: Icarosaurus and other "gliding lizards"
- Even though are often nicknamed "gliding lizards", these reptiles were not lizards. They were small and lizard-shaped nonetheless, except for one thing: they were able to glide, just like a modern lizard species called "flying dragon". They weren't related to each other, and adopted several different gliding structures and mechanisms: North American Icarosaurus ("Icarus lizard") and European Kuehneosaurus (belonging to Eolacertilia, a group closely related to lizards and tuataras) had elongated ribs which sustained a skin membrane acting as a parachute, just like that of the "flying dragon"; Asian Sharovipteryx had membranes extending from limbs to the body, in a way rather similar to pterosaurs. note While the most enigmatic of all, the hard-to-classify Longisquama (its name means "long scale") had two rows of long scales protruding from each side of its body. However, nobody knows what these things exactly were (Real scales? Proto-feathers? Or a simple fossilization artefact as it seems according to recent research?) Despite this, Longisquama is perhaps the most portrayed "gliding lizard" in documentary media, and has even made an apparition in Dinosaur, wrongly shows as an active flier capable to flap its "wings". Another "gliding lizard" appeared in Primeval: Coelurosauravus (see below).
- Among the most basal diapsids - that is, the group containing all reptiles sensu stricto (except anapsids and maybe turtles), most looked like simple lizards, for example the Permian Araeoscelis and the Early Triassic Youngina. But other were more specialized. The small tree-specialists avicephalans for example, also living in Early Triassic (nowadays the word 'avicephalan' is generally disused as it's probably contains unrelated animals). Some avicephalans were gliding forms similar to those already mentioned above: ex. the deceptively dinosaur-sounding Coelurosauravus (literally "coelurosaur ancestor") had elongated ribs like those seen in Kuehneosaurus and Icarosaurus, but was not related with them, being more primitive. One species of Coelurosauravus was once considered a distinct genus, "Weigeltisaurus". Another subgroup, the drepanosaurs, was more similar to chameleons but with a neck of a bird, ex. Megalancosaurus and Hypuronector. Even though they are very rarely portrayed note , drepanosaurs were among the most specialized and weird-looking reptiles ever; to give an example, Megalancosaurus had chameleon-like forearms, a bird-like beak, a large hump across its shoulders, and a prehensile tail with a claw at the end of it. It's worth noting that many basal diapsids that don't belong to any of the main reptilian groups were once put in their own group, the Eosuchians ("dawn crocs", not to be confused with the Eusuchians which are the real crocs). They were believed related with lepidosaurs, or lepidosaurs altogether: among former Eosuchians there are many animals mentioned in this folder, but also the aquatic thalattosaurians like Askeptosaurus and even the long-surviving croc-like champsosaurians.
This section talks about both "mammal-like reptiles" (not actually reptiles in a cladistic sense), and their descendants the Mesozoic mammals. However, if you're searching only for Dimetrodon and nothing else, see Stock Dinosaurs (Non-Dinosaurs).
- We traditionally call "pelycosaurs" the most basal synapsids (the correct name for the mammal-like "reptiles"). They were the dominant group of land animal in the Early Permian (for the record, the Permian period was just before the Mesozoic era), until they were replaced in the Middle Permian by their descendants, the therapsids. "Pelycosaurs" were still lizard-like in general body shape but showed already mammalian traits: their head was laterally flattened and high-settled above the ground, and their teeth started to show some resemblance with ours. By far the most popular are Dimetrodon and, to a lesser degree, Edaphosaurus, because both shared a similar crest (the so-called "sail") on their back substained by elongated neural spines, still for uncertain purpose: a solar panel/radiator as traditionally said? A courtship device? Or both things? Most other "pelycosaurs" didn't have such a sail: these seem not to receive any attention, even in books. However, from little animals like the Carboniferous Archaeothyris, several big, cool-looking animals originated, not only the sailbacks. The plant-eating Cotylorhynchus, for example, was not only the biggest pelycosaur known so far, but also one of the oddest-looking, with its disproportionately small head compared to the bulky body; the more normal-looking Ophiacodon ("snake tooth") was one of the very first amniotes to reach large size (it was already living at the end of the Carboniferous); Varanosaurus (literally "monitor lizard") and Varanops ("monitor face") were even earlier than the latter. While Sphenacodon was a sort of sail-less Dimetrodon, and gave its name to the Dimetrodon's family, Sphenacodontids, which includes also other "sailed" members such as the croc-headed Secodontosaurus. If you see old paleo art, expect to see scaly-skinned mammal ancestors. This is due to a long-standing Taxonomic Term Confusion: since they are classically called reptiles in Linnaean systematics, most old-fashioned artists use to draw them using actual modern reptiles as model. But horny scales are a exclusive thing of the diapsids aka true reptiles (and possibly anapsids aka near-reptiles). It's very unlikely that Dimetrodon and its kin developed horny scales only to lose them altogether after becoming mammals. On the other hand, modern birds still retain the old reptilian scales on their hind limbs... indeed, cladistically speaking, birds are true reptiles.
- Scientific names are often misleading. Tetraceratops, for example, means "four-horned face" but is not a middle-way between a Triceratops ("three-horned face") and a Pentaceratops ("five-horned face"): it was a synapsid, thought by some a "missing link" between "pelycosaurs" and true therapsids, but with four small horns above of its head. Tetraceratops could actually belong to the most basal group of therapsids, the obscure Biarmosuchians, whose Biarmosuchus is the prototype. Only a bit more advanced was Eotitanosuchus: despite its name, it was not related with the dinocephalian Titanosuchus (see just below).
- "Therapsid" is the classic name for the most advanced mammal-like "reptiles"; cladistically speaking, however, it contains mammals as well, so we humans are therapsids in this sense. We'll use this term with the traditional meaning. It's worth noting that most therapsids have been discovered in two precise places in the world: South Africa and Russia. Dinocephalians ("terrible head") included the largest therapsids. They were bulky-bodied and large-headed, and lived in the Middle/Late Permian, but were wiped out by the Permian-Triassic extinction event. Some of these were herbivorous, like Moschops and Tapinocephalus ("humble head"); and others were more likely carnivorous: Anteosaurus note and Titanophoneus ("titanic murderer") or omnivorous (Titanosuchus, meaning "titanic croc"). The meat-eating ones were the apex predators of the Middle Permian, but were later substituted by another therapsid group, the gorgonopsians. The most awesome-looking among dinocephalians is probably the Russian herbivore Estemmenosuchus ("crowned croc"), with its bony, almost moose-like protrusions on its head whose purpose is uncertain. Despite their diversity, all dinocephalians shared common traits in their dentition. Curiously, Anteosaurus has often been depicted in drawings with a literal lion mane around its neck!
- Recently popularized by Walking With Monsters in the 2000s, gorgonopsians ("monstrous face") were the top predators of the Late Permian, but they too were deleted by the aforementioned mass extinction. More slender and usually smaller than dinocephalians, they are nicknamed "sabretooth" just like their mammalian namesakes; however their upper canines, though longer than most therapsids, were far less developed than those of a sabretooth-cat. The prototypical Gorgonops, the wolf-sized Lycaenops ("wolf face") and Sauroctonus, and the cow-sized Inostrancevia (named after a Russian geologist, and perhaps the biggest of the group) are among the most portrayed. Gorgonopsians, Cynognathus and other carnivorous therapsids are often described as dog-looking; indeed, in modern depictions, this resemblance is even more evident than in the older, more reptilian-like portraits.
- Dicynodon has given his name to the Dicynodonts, the most successful group of herbivorous therapsids. They appeared in Late Permian as small diggers such as the tiny Diictodon ("two weasel teeth", portrayed in Walking With Monsters), Robertia broomiana (which honors Robert Broom, one of the greatest therapsid experts, which described in early XX century many south-africans mammal-ancestors), and the toothless Cistecephalus; flourished in the Early Triassic with Lystrosaurus; and then become bulky and vaguely elephant-like at the end of the Triassic: Russian/South African Kannemeyeria (named after Kannemeyer), Chinese Sinokannameyeria (meaning "Kannemeyeria from China" indeed), and the Walking with Dinosaurs-famed North American Placerias ("broad body") are three main examples. Traditionally thought to have disappeared at the Triassic-Jurassic border, a recent discover seems indicating some Australian dicynodonts managed to make their way even in the Cretaceous. One thing does unify dicynodonts: their jaws. They had only two teeth at all, the upper canines vaguely Dracula-like, while the tip of their mouth was a sort of tortoise-like beak for cutting vegetation. Some species however lacked even these teeth, but still they made their way very well.
The Biggest known Mammal-Ancestor: Lisowicia
- Described only in 2019 (at the end of The New '10s), Lisowicia bojani was found in Europe, precisely in Poland near the town of Lisowice — hence the name. It's not only the last confirmed dicynodont known, living at the very end of the Triassic (even later than the former record-holder, Placerias); reaching the size of a modern elephant, it is now by far the biggest known "mammal-like reptile" ever, as heavy as the biggest contemporaneous "prosauropods" like Riojasaurus, but still half the length and height of them because of the absence of the typically long neck and tail of the sauropods and their relatives. Marking its similarity with an elephant even more, Lisowicia had also erect pillar-like limbs covergently like a proper dinosaur or elephant, not splayed like most other mammal-predecessors of the Triassic. And had elephantine feet, and unusually for a mammal-ancestor also almost-lacked external tail, resembling several true mammals in this. Lisowicia is destined to gain attention in the next decade, possibly becoming as common in paleo-books as other more traditional therapsids such as Cynognathus, Lystrosaurus, Thrinaxodon, Dicynodon, and Moschops.
- The closest-to-mammals cynodonts were very diverse in habits, and often not predatory at all: traversodonts (Traversodon, Massetognathus, and others), for example, were omnivores or even herbivores; tritylodonts (so-named from their prototype Tritylodon) even developed rodent-like teeth for gnawing. However, both achieved their traits independently from modern herbivores, and were not direct ancestors of mammals. However, the last common mammal ancestor has surely to be searched among cynodonts. In the Late Triassic, cynodonts were the only successful therapsid group: dicynodonts were still surviving but were rare at that point. Non-mammalian cynodonts survived until the Early Jurassic (the tritylodont Oligokyphus) and perhaps even in the Early Cretaceous (the enigmatic Xenocretosuchus, "strange cretaceous croc"), but they made a minor part of the synapsid fauna after Triassic: their true mammalian descendants were dominant at this point.
- Among the least portrayed among the main therapsid groups, therocephalians ("mammal-head") were similar in size and shape to the cynodonts, but less mammal-like, and only distantly related to mammals. Therocephalians began in the Permian and survived until the Early Triassic, but then were replaced by their more evolved relatives, cynodonts indeed. Just like the latter, they were initially carnivores (ex. Lycosuchus "wolf-croc", and Pristerognathus, "saw-jaw"), but then some of the last forms became vegetarian (Bauria, once considered in a distinct group, the Bauriamorphs), while others became more similar to lizards (Ericiolacerta: "lacerta" just means lizard in Latin). One unidentified predatory therocephalian appears in Walking With Monsters, portrayed with a totally speculative venomous bite; it could be Euchambersia.
Thank You Dinosaur! MESOZOIC MAMMALS
The boundary between mammals and non-mammals has always been a hard issue for paleontologists. Since typical mammalian features such as hair, milk glands, etc... do not fossilize most the time, the key to separate the two ensembles lays in their skull. True mammals have a mandible made by a single couple of bones, and three ossicles in the mid-ear. Non-mammalian synapsids have several pairs of bones in the lower jaw and a single ossicle in the ear. It's also worth noting that mammalian features probably didn't appear all in the same instant: perhaps some therapsids already produced milk, though they didn't have erect limbs yet, unlike modern mammals (except platypus and echidna, aka the Monotremes, that still have splayed limbs). Some quasi-mammals (more correctly called mammaliaforms) began in Late Triassic and were tiny, very shrew-like, and insectivorous: Morganucodon and Megazostrodon are the two most portrayed. Both were once classified as "triconodonts", but today this term only indicates some more evolved true mammals from the Jurassic and Cretaceous, like the cat-sized Triconodon indeed. Another group of mammaliaforms were the omnivorous docodonts, which managed to reach the Late Jurassic with species such as the namesake Docodon. The first true mammals appeared in the early Jurassic, and were shrew-like just like their Triassic mammaliaform ancestors. They remained so for all the Mesozoic... at least this is what scientists used to think. Traditionally, fossils of Mesozoic mammals are extremely rare and fragmentary due to their smallness; but some very interesting new mammal fossils have been discovered since the 2000s, and we now know mammals were already very diversified at the Age of Dinosaurs. Some were mole-like diggers (Fruitafossor), some were beaver-like swimmers (Castorocauda), and some were even gliders (Volaticotherium). If you'll read a paleo book you have good chance to see Mesozoic mammals described as "insignificant little creatures ruled by the mighty dinosaurs". Actually, thanks to their possibly dense populations, mammals could have affected their ecosystem the same way dinosaurs did; and remember that small animals are often key species in their natural environments. Another unexpected discovery from the 2000s showed Mesozoic mammals not being necessarily preys for dinosaurs as well: the badger-sized Repenomamus was discovered with baby dinosaur remains in its stomach. Another commonplace to debunk is that Mesozoic mammals were all insectivores. Actually, a whole group, the multituberculates were rodent-like and herbivorous: their name "multi-tubercled tooth" is due to an unique couple of protruding cheek-teeth. They were the most abundant early mammals at the end of the Cretaceous, and managed to survive after the mass extinction. At the beginning of the Cenozoic they became even more successful, until true rodents replaced them in the Oligocene. Multituberculates were the longest living mammalian group ever before gone extinct. The largest one, Taeniolabis from the Palaeocene, weighed 100 kg (the bulk of a giant panda). The direct ancestors of modern mammalian groups (placentals, marsupials, and monotremes) appeared in the Early Cretaceous but became widespread only in the Late Cretaceous. We can mention: the platypus-like Steropodon, an early monotreme portrayed in Walking with Dinosaurs as a scavenger; the early otter-like "marsupial" Didelphodon, also portrayed in WWD as an opportunist; and the oddly-named placental Purgatorius, which is often considered the first known ancestor of primates, or at least, a close relative. Together, eutherian mammals (the placentals) and metatherians (the marsupials) make their own group: the Therians (literally "the beasts" in Greek). Monotremes, on the other hand, are much more primitive than the former, and are traditionally called prototherians ("the first beasts"). You could also read the names "allotherians" and "pantotherians" especially in older texts. "Allotherians" included the multituberculates; "pantotherians" included the common ancestors of marsupials and placentals. As you'll see in the following mammal section, -therium is the common suffix for most extinct mammals, a bit like -saurus for extinct reptiles. In the 2000s two animals discovered from the famous Early Cretaceous deposits of China were object of some sensationalism: Sinodelphys the "first marsupial ever", and even more Eomaia "the first ever placental" and thus "the first Man's ancestor" ("Eomaia" meaning "dawn mother"). However, as mammal fossils from the Mesozoic are such a rarity, it's virtually impossible understanding which one was really the most basal placental / marsupial. Both are very precious, though, because they have preserved their fur — before that, the oldest fossilized furs were from the Early Cenozoic (the famous Messel tar pits of Germany). Finally, let's debunk another tenacious myth about mammal evolution: we must thank if non-avian dinosaurs went extinct, otherwise humans couldn't have appeared on Earth. Maybe we could have appeared just the same, maybe a bit later... It's more probable that dinos actually guided mammal evolution in an indirect way. Being competitors of and preying upon our ancestors, they selected actively the most adapted, most evolved traits us mammals are proud of: among them, intelligence and parental care. If you are here to read this now, you have to thank dinosaurs. Everything has always been better with dinosaurs!
The animal listed here were once called "cotylosaurs", but this word is now fallen in disuse. This was a catch-all term for all most primitive "reptiles" which couldn't be placed in another well-defined groups. However, some of them still make a natural grouping: Anapsids. They were a successful group of animals which make a group on their own, intermediate between true reptiles (the diapsids) and the mammal-like synapsids: hence their alternate name: parareptiles ("near reptiles"). Most anapsids were even more ancient than diapsids: they lived mainly in the Permian period alongside Dimetrodon and the other mammal ancestors. Like therapsids, they were mainly discovered in Russia and South Africa. Whether turtles are just surviving anapsids or not has long been matter of discussion: today they're considered true diapsids, though still of uncertain placement in the tree (see Still-living reptile groups above).
- Pareiasaurs were the only anapsids which reached great size, almost like a small rhinoceros at the extreme (but there were also smaller species though). They resembled a bit some plant-eating therapsids in shape (Moschops, Placerias, Lisowicia ), with their bulky frame, short tails, strong semierect limbs, and an armored skull. Indeed, pareiasaurs occupied their niche during the Late Permian, substituting dinocephalian therapsids (which were dominant in the Middle Permian); but were wiped out by the mass extinction and substituted in turn by other therapsids (the dicynodonts) and the non-therapsid rhynchosaurs in the Triassic. An early theory said pareiasaurs could have been the ancestors of turtles and tortoises. Now this seems disproved, as turtles anatomy is very specialized and very different to that of a pareiasaur. Scutosaurus ("scute lizard") was one of the largest pareiasaurs and the most armored, with a "horned" skull and bony plates on its back (a sort of archaic version of an ankylosaur). Of course, this is the pareiasaur most common in media. Other examples are the namesake Pareiasaurus (as large as the former but armor-less), the more primitive Anthodon ("flower tooth") and the small spiky Elginia, with no armor-back but head horns like some ankylosaurs and the "horned tortoise" Meiolania.
Near-Reptilian Crocodiles: the Mesosaurs
- As already seen, the croc-like body plan was independently reached by several primitive extinct reptiles (phytosaurs, proterosuchians, champsosaurs...), and also by a group of near-reptiles, the Mesosaurs (do not confound them with mosasaurs!). They were among the most basal anapsids, but perhaps the most specialized. Semi-aquatic, they were a bit like unarmored gharials, with a croc-like shape and long jaws filled with strongly-crammed teeth. As these teeth look weak and needle-like, the mesosaurs diet is uncertain: they could have been either fishers or filter-feeders. Mesosaurs were small-sized (3 ft long) and arguably werent strong swimmers: they are known to be freshwater dwellers. However, their remains have been found in several Southern continents. Since they couldnt be capable to cross open seas, they were used as a demonstration of the Pangaea hypothesis. In their time (Permian) continents were still linked together, and this allowed mesosaurs to go across landmasses with ease without leaving freshwater. Mesosaurus ("middle lizard") and Stereosternum are among the best-known kinds in this group. Interestingly, the oldest currently known fossilized amniotic embryos are mesosaur embryos, and it seems that mesosaurs were the oldest group of amniotes known to evolve vivipary.
- Most other anapsids had a very generic look, classically described as "lizard-like"; for example, Millerosaurus and Milleretta. But the most successful ones were the procolophonids. They were the only anapsid group which managed to survive the awful mass extinction at the end of the Permian, and survived long enough to see the first dinosaurs; only the Triassic-Jurassic mass extinction deleted them definitively. Procolophon is the namesake of the group, resembled an iguana in shape, and could have been omnivorous; another, Deltavjatia, was once considered a pareiasaur. One of the latest procolophonids was Hypsognathus, which developed spikes on its head convergently with some pareiasaurs. Once considered anapsids, Captorhinus and Labidosaurus from Middle Permian have revealed to be diapsid relatives; this has happened as well to another animal, Hylonomus (see just below). Finally, let's not forget the tiny anapsid Eudibamus, found in 2000. Living at the start of the Permian period, this is the guy which has taken over the title to the Triassic Euparkeria for being the first animal ever capable to run on two legs.
- The very first amniotes appeared in the Carboniferous, the Paleozoic period with huge swamp forests populated by giant bugs and large amphibians. Traditionally we quote Carboniferous "reptiles" as "lizard-like" because were similar to 1 ft long lizards in shape, but some weren't even reptiles sensu stricto. The most cited has been Hylonomus ("law of the forest"), because it was long believed the most ancient of all; some hylonomes have been found inside fossilized logs so abundant in the Carboniferous. Another is Petrolacosaurus, which lived slightly after Hylonomus and was a full diapsid - contrary to the latter which was only a relative of diapsids. Walking With Monsters chose to show Petrolacosaurus as "the very first reptile": only.... for some weird reason, it magically reveals to be the ancestor of mammals in this show. This is even more unbelievable if you think that the true first known mammal ancestor was available for a Carboniferous setting: Archaeothyris. Put together, these three animals make the most archaic common ancestors of all land vertebrates that lived from Permian up to now (amphibians excluded, which originated before these and remain only partially terrestrial even today). Among their descendants there are indirectly birds and mammals as well, and thus mankind itself. Recently, another Carboniferous animal has been found in Scotland, which could be the real first amniote: Casineria kiddi.