The critters in this page pertain to groups of "biota" (= living beings) that have by old-fashioned biologists been quoted as "lower-ranking" than the so-called "higher animals" (mammals and birds). note
However, modern scientists do not accept such an unfairly "racistic" distinction. Furthermore, "lower animals" often show biological traits and behaviours traditionally considered typical of mammals and birds: social attitudes, parental care, intelligence, even some "warm-blood" abilities. On the other hand, in popular media they may be treated as stupid/unfeeling brutes even to this day. Documentaries not excluded: within the Walking With series, for example, Walking with Dinosaurs and Walking with Beasts show dinosaurs and mammals as smart/social/caring creatures, while the meaningfully-named Walking With Monsters and Sea Monsters focus mainly to non-dino reptiles and to all the animal groups listed below, with only animals with bones shown as being smart/social/caring (Artistic License Biology).
We humans should be more grateful to extinct "lower beasts" however: several of them gave rise to many modern animals, and some did that to Mankind itself (yes, there were not only APES among our ancestors!). And don't think they were boring, uninteresting creatures: anything but, as you'll see soon.
Lissamphibians excluded, prehistoric amphibians are traditionally called "labyrinthodonts" ("labyrinth tooth") or "stegocephalians" ("roof-head"), but these terms shouldn't be used today, just like "thecodonts" for basal archosaurs or "pelycosaurs" for basal synapsids. They don't indicate any natural grouping of animals, but are instead catch-all words with little scientific significance in modern phylogenetic systematics. Labyrinthodonts means labyrinth-teeth because many of these animals had convoluted, labyrinth-like internal patterns inside their teeth, but this isn't a fundamental thing. Their importance was much, much greater than this and lies upon another aspect. They were, simply, the links between fish and truly terrestrial vertebrates, a keystone group for mankind's evolution. And yet, just like synapsids and Mesozoic mammals, they have not gained much attention in pop culture. If they appear at all in fictional works, they'll be simply described as "giant amphibians".
- The only real amphibians in modern taxonomy, lissamphibians (frogs + salamanders + caecilians) appeared in the Triassic together with the first dinosaurs, but their deepest origins and their relationship with extinct amphibian groups are still unclear. The first frogs (Triadobatrachus, meaning the "triassic frog", is the most cited example) were already like the modern ones, only with shorter hind legs less adapted for hopping. Frogs have possibly been the most evolved amphibians ever, with their complex social behaviours and the ability to produce loud vocal sounds (this ability is atypical for a non-mammal / non-archosaur vertebrate). On the other hand, extinct salamanders have retained the primitive crawling shape of early amphibians. It's curious the case of Andrias scheuchzeri (a close relative of the modern Japanese Giant Salamander) which was initially believed a man dead during the Biblic Great Deluge! ("Andrias" just means "man" in Greek). About the legless worm-like caecilians, they are as little known in palaeontology as they are in Real Life. Their fossils are extremely rare, but they are believed to have had small limbs at the start of their evolution (ex. Eocaecilia, "dawn caecilian").
Malagasy giant frog: Beelzebufo
- This guy deserves his own section. Beelzebufo was an enormous relative of modern horned frogs that lived in Madagascar during the Cretaceous period, alongside the herbivorous crocodile Simosuchus. It could grow up to sixteen inches in length, and weight over nine pounds, making it larger than any modern frog, including the already gigantic goliath frog of Africa. It's also known as the "devil frog" (which is basically what its name means). Given the eating habits of its modern relatives (which will devour mice) this amphibian could have easily eaten baby dinosaurs. With that said, it still would have lived in fear of large carnivorous dinosaurs such as Majungasaurus that also lived in the area.
- Lepospondyls were among the most numerous and diversified "amphibians" in the Carboniferous. They could have been the closest relatives of lissamphibians, and perhaps their ancestors. Usually with long bodies and weak limbs, they lived mainly in water or in soil. Some were like salamanders, ex. the whip-tailed Urocordylus; other were limbless and eel-like, ex. Phlegetontia. But the most interesting one is certainly Diplocaulus, who can be found on the Stock Dinosaurs (Non-Dinosaurs) page.
- The most successful and diversified group of prehistoric amphibians, temnospondyls are often described in documentary media as "croc-like": however, their jaws and teeth were smaller and weaker than a crocodile's, but they should nonetheless be efficient predators. The most famous is the 8 ft long, alligator-like Eryops from Early Permian North America (the Dimetrodon's place), but there's also Prionosuchus ("saw crocodile") from Early Permian Brazil, which resembled an enormous gharial and one reported specimen is estimated to have grown up to thirty feet, making it the largest known temnospondyl. Other Permian relatives were more terrestrial: the dissorophids Cacops and Platyhystrix had an armor on their back to protect them from land predators. Cacops is remarkable for its large head respect to the body and stronger limbs than the more water-living Eryops; Platyhystrix ("flat porcupine") was similar, but with striking dorsal spines very similar to a Dimetrodon's or an Edaphosaurus, maybe sustaining a "sail". Even though not a temnospondyl is also worthy of note Crassigyrinus scoticus ("Scottish fat tadpole"), as an example of how paleo-amphibians were diversified to each other: living in the Carboniferous, it was a very specialized water-loving animal with tiny limbs, just like what happened to some modern salamanders (the olm, the mudpuppy, the amphiumas, the sirens).
- Temnospondyls survived well the huge Permian mass extinction and made their way in the Triassic: only competition with croc relatives at the end of the period caused their decline and their nearly total extinction before the Jurassic. The most famous Triassic amphibian has been Mastodonsaurus (improperly meaning "mastodon lizard", and sometimes misspelled "Mastodontosaurus"). It was one of the very first "giant amphibians" discovered to science, in the first half of the 1800 century (and portrayed in the London Crystal Palace Park as "Labyrinthodon"). Lived in Early Triassic Europe before true dinosaurs like Plateosaurus. 5 m long, it was one of the biggest paleo-amphibians ever, remarkable for its massive body and 4 ft long head with a couple of strange protruding teeth. Also very large was Trematosaurus, more similar to a gharial in shape. Aphaneramma looked like the latter, though was not as big. On the other hand, Gerrothorax was much smaller than the mastodonsaur, and a bit similar to the unrelated arrow-headed Diplocaulus; interestigly, it shows neoteny (that is, adults retained the external gills of their larval stage, like the modern axolotl). Another known neotenic paleoamphibian was Branchiosaurus ("gill lizard", nothing to do with the dinosaur Brachiosaurus, "arm lizard"). Few temnospondyls reached the Late Triassic: among them, the North American Metoposaurus was able to see Coelophysis in Real Life. In 1997 a new temnospondyl was unexpectedly discovered in Cretaceous terrains: Koolasuchus ("Koola's croc") was probably an isolated Australian late survivor which managed to resist the competition with freshwater reptiles. It shows both in Walking with Dinosaurs and in Disney's Dinosaur (rather incorrectly in the latter, in truth).
- The "amphibians" cited here are collectively called reptiliomorphs ("reptile-shaped"), were more related to amniotes (reptiles + mammals) than to every amphibian mentioned above: indeed, many of them were once variably classified as reptiles or amphibians depending on the scientist. More terrestrial than the latter, they progressively evolved the typical traits of amniotes, but we don't know when these traits appeared exactly: waterproof skin, water-storing lungs and kidneys, and egg shells. The latest invention was crucial for vertebrate evolution: embryos inside shelled eggs were able to develop and to hatch out of water, and the descendants of the reptiliomorphs became able to survive in arid environments. Traditionally the most known reptiliomorph has been Seymouria baylorensis (the genus name comes from the surname Seymour), which was once mentioned in textbooks the "missing link" between reptiles and amphibians, or alternatively the very first reptile appeared. 2 ft long, it lived in Early Permian North America like Dimetrodon, and was possibly one of its most frequent preys. Well-known are also the Anthracosaurs or Embolomers, the biggest "amphibians" in the Carboniferous (some reached 9m in length!): Eogyrinus ("dawn tadpole") and the croc-sized Proterogyrinus ("first tadpole") are among them. Also in the Carboniferous lived Westlothiana lizziae, a tiny lizard-like animal that was briefly considered "the first reptile" in the 1990s (and familiarly nicknamed "Lizzie"). Last example, the Early Permian Diadectes ("crosswise biter"): similar to an iguana, it was possibly one of the first land vertebrates that evolved (partial or total) vegetarianism.
- Sarcopterygians, aka "lobe-finned fish" or "lobefins". They should better be called proto-amphibians rather than fish: their blood circulation is double like land vertebrates, not simple like typical fish; their fins are bony and fleshy, and their nostrils are connected with their mouth (those of fish aren't). And some can even breathe air like us, other than absorbing oxygen in water with the usual gills. The latter are meaningfully called lungfish, they have one or two true lungs which originally were simple protrusions of the digestive tube. Lungfish are very few today: the most archaic is the Australian one, Neoceratodus, with robust paired "fins". Its name means "new Ceratodus": Ceratodus ("horned tooth") is the most abundant prehistoric lungfish, and was virtually identical to Neoceratodus. The other modern lungfish are African Protopterus and South American Lepidosiren. Among the very first Paleozoic lungfishes there were Dipterus ("two wings") and Scaumenacia; the first one was already in the Devonian. However, the most famous modern lobe-finned fish is Latimeria, the only surviving coelacanth. Prehistoric coelacanths, too, were virtually identical to their modern descendents: one of the most common in fossil record is Macropoma from the Mesozoic; the namesake of the group Coelacanthus ("hollow spine") lived earlier in the Paleozoic. Mawsonia was Cretaceous and the biggest of the group, 12 ft long and one of the largest freshwater fish ever (and a possible prey of Spinosaurus). Unlike lungfish, coelacanths (also known as actinists) have been exclusively aquatic: unable to breathe air, they are the most "fishy" among the lobe-finned fish. It's worthy to note that during the Dinosaur Age lungfish and coelacanths were very abundant: coelacanths swam in great numbers in the sea, while lungfish lived in oxygen-poor swamps, sometimes obligated to walk out of water when the water pools dried out just like modern lungfish.
- Even though more closely related with US than with true fish, lungfish and coelacanths were less close to terrestrial vertebrates than some fossil lobefins, the basal tetrapodomorphs (called "rhipidists" or "Osteolepidotes" in older sources). Among them, there was the common ancestor of all tetrapods aka land vertebrates, but we don't know which was really the ancestor. The traditionally most cited is Eusthenopteron ("well-thin fin"). Its shape recalled a bit that of the famous ur-amphibian Ichthyostega, but smaller (60 cm), with fleshy paired fins instead of true legs, classically fishy dorsal and anal fins, and a curious three-lobed caudal fin reminiscent of Poseidon's trident. Its lifestyle was probably like a lungfish's, and was also able to breath air with primitive lungs and get occasionally out of water to escape drought. Its almost-identical relative Hyneria was much bigger (3-4 m long), and because of its size was chosen by Walking With Monsters producers instead of Eusthenopteron as the representative of Sarcopterygii (and it was oversized). However, it is shown only to give a predator to the early tetrapod Hynerpeton, and with no mention at all about its role as one of the tetrapods' forerunners (in effect it was eating its descendant!). Other relatives of the eusthenopteron included Holoptychius and Osteolepis, both with a more normal-looking, non-"trident" tailfin. In the 1990s/2000s some new animals were discovered, which appear evolutionarily in the middle between a Eusthenopteron and an Ichthyostega: excellent examples are Panderichthys, Tiktaalik, and Acanthostega. The latest one was very similar to the ichthyostega, but had eight digits on each "hand" instead of seven.
- Actinopterygians, aka "ray-finned fish" or "rayfins". Or, more simply, "the fish". They are by far the most common fish today (95% of all fish species!), but in the Dinosaur Age they were only one of the several fish groups roaming the seas and fresh waters. The most evolved rayfins, the Teleostei, became widespread only in the Cretaceous. Almost all modern ray-finned fish are teleosts. However, most familiar teleostans appeared only after the K-Pg extinction, in the Age of Mammals. There were no goldfishes, swordfishes, seahorses, piranhas, ocean sunfishes or deep sea anglers in the Cretaceous (only herrings, tarpons, and a few others). However, non-teleostan rayfins were already common in the Mesozoic, among them gars, sturgeons and their relatives. And then, there were things such as Leedsichthys ("Leeds fish"), a Jurassic fish with no modern relatives that was as big as a humpback whale, maybe the largest fish of all times. note Another non-teleostan fish was Lepidotes ("the scaly one"). It was one of the most common fish, with more than 100 species that lived during the whole Mesozoic timespan. Similar to a carp, it was actually not related with any modern fish: its primitiveness is revealed by its heavy scales similar to an armor. These scales are sometimes found inside the rib cages of other animals, e.g. the fishing dinosaur Baryonyx. Since the Cretaceous all these early forms have been outcompeted by teleosts, which were more agile thanks to their lighter scales. One of the most common of them was Leptolepis ("thin scale"), an ancient herring-like fish . Another, Enchodus is nicknamed the "saber-toothed herring" but was not a clupeiform (the herring group). Perhaps the most famous Cretaceous rayfin is Xiphactinus ("sword ray"): also similar to a herring but with teeth, it was 5-6m long (like a great white shark), and a voracious predator in competition with the giant sea reptiles of the time. Xiphactinus (called "Portheus" in older media) is most famous for a fossil in which a 4m-long specimen was preserved with a 2m-long fish in its gut. Among the Mammal-Age rayfins, the most common in fossil record is Knightia, an ancient true herring.
- Together, ray-finned fish and lobe-finned fish make the traditional Osteichthyes, aka bony fish. Indeed, a bony skeleton was their main invention - all the earlier fish groups had cartilaginous skeletons, while their bones were only outside their body in the form of scales and teeth. Bony fish (both lobefins and rayfins) appeared in the Paleozoic era, 200 million years before the first dinosaur.note Among the earliest ray-finned fish, Palaeoniscum (traditionally called "Palaeoniscus") and the Devonian Cheirolepis ("hand scale") resembled a cross between a shark and a modern bony fish: mouth placed downwards and asymmetrical caudal fin like the sharks'; fins, opercula, and smooth scales like the bony fish's. Curiously some extant archaic rayfins like the sturgeon still preserve this mixed look. In the Paleozoic there was also a unique fish group that went totally extinct before the Mesozoic: the acanthodians (so-called from their namesake Acanthodes, "the spiny one"). They were externally similar to the earliest ray-finned fishes above, but with a cartilaginous inner skeleton like a shark. Their name means "spiky" from their spiny fins, and have been nicknamed "spiny sharks", but they were actually closer to bony fish than to sharks. Among the other acanthodians we can mention Climatius. Together, sharks, acanthodians, bony fish and placoderms (see below) have one thing in common: jaws. See also "Tough Guys" below.
- If you ask a paleontologist what are the most common vertebrate fossils, (s)he'll answer you "shark teeth". However, these teeth are usually found isolated - ironically, the remaining skeletons are among the rarest fossil finds (sharks' cartilage don't fossilize well, unlike bone). Even though sharks made only a small percentage of the modern fish species (about 5%), they were a very successful group in the past, even more diversified than they are today. But stop a moment. What is a shark, exactly? In common sense, sharks are things like the great white or the bull shark; but zoologists often use this word to indicate every cartilaginous fish, or more technically, every Chondrichthyian. Palaeontologists usually give the same meaning to "shark", too. So, the first ever sharks appeared in the Devonian period 400 million years ago, and since then have changed very little: sharks are often cited as "living fossils". More precisely, the modern kinds of shark appeared in the Cretaceous: earlier sharks were only distantly related with them. Examples are Cladoselache, Stethacanthus, and Xenacanthus (all from the Devonian period), and also a little known modern fish, the deep sea chimaera (also called ratfish or rabbitfish). The latter has preserved to this day the mixed shark/bony fish anatomy of the acanthodians and the earliest rayfins. Cladoselache ("branch shark") was more like a true shark, with uncovered gills and tooth-like scales covered in enamel (its fossils have preserved prints of soft tissues), but its mouth was strangely placed at the top of its head like the modern unrelated whale-shark. Xenacanthus and Stethacanthus were more bizarre. The former had an eel-body and a long filament protruding from its head (its name means "strange spine"); the latter is nicknamed "ironing-board shark" from its flat head prominence with many dentines on the top. Maybe only males had these things, which resemble the much smaller tubercle of the male chimaera (if so, they would have been courtship devices). But the perhaps weirdest "shark" ever is Helicoprion ("helix saw"), whose teeth were placed in a spiral line inside its mouth!note . Other early chondrichthyans, Falcatus, Harpagofutator, and many others, also showed strange prominences above their heads.
- Triassic and Jurassic sharks were still primitive, but with a more modern look. One of the most common was Hybodus, whose shape recalls a typical predatory shark but with small "horns" on its head, like the modern bull-head shark. Other relatives became flatter and similar to a ray: Ptychodus is one example. If we imagine to swim in Cretaceous waters, however, we'll see sharks virtually identical to the modern ones. Cretoxyrhina (nicknamed "the Ginsu Shark") was very similar to a great white shark. It was one of the top predators of the Late Cretaceous North American inland sea, in competition with mosasaurs, plesiosaurs, and the bony fish Xiphactinus above. But we could also encounter another kind of fish which little resembles a shark, but technically is a true shark: rays and skates. They appeared in the Cretaceous, in the same time of the commonly intended "sharks", and also little changed their anatomy during the times.
- The Devonian is rightly called "the Fish Age". Almost every main fish group was present in Devonian waters: lobe-finned fish, ray-finned fish, cartilaginous fish, acanthodians, and several jawless fish (see further). But the perhaps most typical Devonian fish group is another: the Placoderms. Their name means "skin with plates", and are nicknamed "armored fish"; their scales were notably thick and broad and covered their forebody like a true armor. However, this armor was still flexible and didn't make a "shell", making these fish more agile than their armored predecessors, ostracoderms; unlike the latter, they were active predators. There were two main placoderm groups: antiarchs and arthrodires. The former had bizarre pectoral fins more similar to crustacean legs than fins, and lived near the bottom of the seas: Bothriolepis and Pterichthyodes are the most known example. The latter had strange scissor-like teeth for cutting meat, and probably lived in more open waters. Ex. Coccosteus and Dunkleosteus. Another interesting placoderm is Lunaspis, with its crescent-shaped body. There is a curious thing about the evolutionary origin of jaws and teeth: the former arose from the first pair of gills of the earliest jawless fish; while the teeth had the same origin of scales. After all, modern sharks still have enamel-covered scales on their body, the same shape of their teeth (only smaller). note In a sense, you could even say teeth are the only fish scales we human still preserve.
- Welcome to the Aspis family. Most "ostracoderms" ("shelled skin") have this suffix. Despite this, they don't make a real fish group: every armored fish devoid of jaws is traditionally called with this name, but they are actually distinct lineages, some closer to jawed fish than to other ostracoderms. Compared with placoderms, ostracoderms' armor was more complete, covering the whole body, and formed a true shell at the head level. Despite their badass look they were very harmless creatures; their size was from a thumbnail up to a human hand, and with their jawless mouths they could only have feed on tiny food items like algae, small invertebrates, etc... They often fell victim to predators like the eurypterids ("sea scorpions"), cephalopods and jawed fish that were strong enough to go through their thick armored skin. One successful ostracoderm lineage is the osteostracans ("bony shell"), whose prototype is the flat-headed Cephalaspis ("head shield") but include also Hemicyclaspis ("semicircle shield") among the others. Another is the anaspids ("with no shield"), more streamlined and with a lighter armor. The heterostracans ("different shell") had often long snouts; Pteraspis ("winged shield") is their prototype, Drepanaspis was a round-shaped example of them. Finally, the Thelodonts, which where the most closely related with jawed fish (and maybe their ancestors).
- However, ostracoderms were not the most primitive fish; they were already very evolved animals, with complex brains, fins, and keen senses (Cephalaspis seemingly shows even electric sensors!) Their anatomy is unusually well-known because the inner portion of their head shows the prints of the brain, nerves, inner ear, and other soft tissues. note Actually ostracoderms descended from unarmoured fish, among them the very first fish appeared. Sadly, as soft tissue don't usually fossilize, they are virtually unknown by science. Two exceptions are Haikouichthys (improperly "Haikou's fish") and Yunnanozoon ("Yunnan's animal") from the Cambrian period, similar to the famous invertebrate lancelet, or also to the larval stage of the modern lamprey (the so-called ammocoetes). Haikouichthys was a tiny animal the size of a human nail, and was probably a harmless filter feeder. Incredibly, Walking With Monsters managed to transform even this unconspicuous critter in a "terror": here, a shoal of Haikouichthys is seen feeding on the flesh of a wounded Anomalocaris like modern lampreys and hagfish would do. Actually, lampreys and hagfish (aka the cyclostomates) are very evolved parasitic animals capable to feed on large items despite their lacking of jaws; their evolution is very poorly known. Finally, we could not forget the enigmatic conodonts. These tiny fossils similar to toothed jaws (conodont means "cone tooth") have been a real headache for scientists (invertebrates? early vertebrates? worms?). Today we know they belonged to early jawless fishes that lived during the whole Paleozoic, but their lifestyle is still uncertain; maybe they were the ancestors of the lampreys.
A 50-year old mystery: Tullimonstrum, aka the "Tully Monster".
- What was this thing? Found in 1966, and very common in the Carboniferous Mazon Creek Beds of Illinois, it looked like nothing paleontologists had ever seen before. It had a jaw like a crab claw, the body plan of a cuttlefish, and two weird stalked lumps on both sides of its body. The only thing anyone could classify this as was as an invertebrate, probably some kind of worm.
A study by Yale University revealed the Tully Monster's true identity, and it was the least expected identity. They noticed the remains of a primitive notochord in the creature (meaning it was a vertebrate), and the weird lumps turned out to be eyestalks. Using these, and other parts of the fossil, they came to the conclusion that it was a jawless "fish", closely related to the lamprey.
When thinking about animal fossils, our mind usually goes on the petrified bones of dinosaurs. But dinosaurs in paleontology are extremely rare finds compared to other vertebrate groups, such as sea reptiles, Cenozoic mammals and fish. And yet, vertebrates as a whole are in turn only a very small part of the total. Indeed, more than 90% animal fossils that Earth left to us are from invertebrates. Some invertebrate groups like ammonites and trilobites are so common they're object of collection by many paleo fans; while it's unlikely dinosaur bones will receive this trade although some trade of dinosaur bones do exist as well, but it's highly debated if it's a right thing to do, since dino fossils are such a rarity.
- Today, crustaceans are by far the most abundant water arthropods. Their prehistoric relatives were like the modern ones, and have always been an important group. Examples of Mesozoic crustaceans include the shrimp Aeger, the crab Eryon, and the enigmatic Thylacocephalans. However, in the Paleozoic another group of aquatic arthropods were even more diversified: the early chelicerates, more related with spiders than to crabs. The most spectacular water chelicerates were the so-called sea scorpions (see the following paragraph); the smaller xiphosurans were just as abundant. Like the coelacanth and the nautilus, they have classically been mentioned as "living fossils". Indeed, the modern Limulus (the horseshoe crab) is just the only surviving xiphosuran, and the only surviving aquatic chelicerate (except for the little-known sea spiders or Pantopods). All the other chelicerates became terrestrial, forming the arachnids (true spiders, true scorpions, whip-scorpions, pseudoscorpions, soliphugans, harvestmen, ticks, mites and others). Xiphosura means "sword tail". Contrary to what is believed, the "sword" at the end of the horseshoe crab is not venomous or dangerous at all (you could probably lightly prick your foot if you step on it, but that's pretty much it), is only a mechanical device to overturn again the animal when capsized. Many extinct xiphosurans were identical to our modern Limulus, and probably behaved the same; our horseshoe crab lives mainly in the bottom of the seas like trilobites, feed only on small items, but comes ashore to lay its eggs. Curiously, its young are very similar to an adult trilobite.
- When talking about evolution, the superpredators are usually described as a sort of foe that try to destroy our distant ancestors, almost as their precise purpose was to delete Man's modern presence on Earth. Just see Walking With Monsters for an egregious example. When the portrayals are about Mesozoic life this treatment is typically reserved to dinosaurs (see The origin of Mammals); in Paleozoic settings, however, the classic choice has been the eurypterids (also called Gigantostracians, "giant shellfish"), better known as the sea scorpions. They were indeed related with modern scorpions (and maybe their ancestors), but technically they were not scorpions, and not all were marine (some became freshwater dwellers). They hadn't the venomous sting, and resembled more slender lobsters than scorpions. Their had big composed eyes like insects, scorpion-like pincers, and their rear pair of legs were flattened and used to swim; they arguably lived both in the bottom and in open waters. We don't know if they came on land to lay their eggs. Eurypterids were active predators, and the biggest ones were among the apex predators especially in the Silurian period; in the following Devonian they were outcompeted by jawed fish like Dunkleosteus, but managed nonetheless to survive until the Permian. Eurypterus ("broad wing"), the namesake of the group, is the most common eurypterid in fossil record; but the most famous is Pterygotus ("the winged one"). It was one of the biggest gigantostracians (the length of a human), and one of the biggest arthropods of all times along with the extinct millipede Arthropleura and the modern Giant Japanese Crab. Pterygotus is the sea scorpion traditionally most portrayed in media, because of its size of course. Ironically, however, its even larger cousin, Jaekelopterus was the largest known eurypterid, and yet has still not appeared in broad-audience media.
- Within the evolution of animal life, it is universally agreed that arthropods and vertebrates have been the two animal groups which reached the best results. Cephalopod molluscs, too, are very complex creatures; but they never managed to come on land. Arthropods and vertebrates did that, but it was the former which made the first step on dry land, in the Silurian period. Vertebrates joined them only later in the Devonian. Even when out of the liquid element arthropods and vertebrates have continued to co-exist and to co-evolve, and this competition has made both more and more perfected. It's actually unfair to declare arthropods have been the vertebrates' worst enemies, and that the latter had to fight a "war" against spider-scorpions-insects (as said in the preface of Monsters); indeed, arthropods have unwillingly helped us vertebrates to became those successful beings we are. Among the very first land arthropods were the first TRUE scorpions and the first myriapods (millipedes and centipedes). Critters such as Palaeophonus were already identical to a modern scorpion; the same about the earliest myriapods like Euphoberia. Spiders appeared a bit later, in the Carboniferous (ex. Arthrolycosa); the first non-insect hexapods (hexapod = six legs) evolved in the Devonian (Rhyniella), but the first winged TRUE insects took their first flight in the Carboniferous forests: they were the very first flying animals ever, and the only flyers until pterosaurs made their appearance in the Triassic, followed by birds and finally bats. In the Carboniferous, land arthropods became often huge; two in particular have become a staple in paleo-books and documentaries: Arthropleura and Meganeura. They have even made some appearances in fiction, too. note Walking With has also popularized other critters: the huge true scorpions Brontoscorpio from Silurian and Pulmonoscorpius from Carboniferous, the alleged giant spider Megarachne (it was actually a spider-looking freshwater eurypterid, also from Carboniferous) and the Early Cenozoic giant ants seen in Beasts. All, more or less, affected by Rule of Cool in the show.
Bugs Everywhere! TRUE INSECTS
- Insects. The most abundant, diversified, biomechanically efficient, and last but not least, by far the most studied animals by modern fauna zoologists. Sadly, in paleontology this is not the same. Their fossil record is extremely poor, for understandable reasons: their tiny body isn't precisely the most adapt to turn into stone, and their terrestrial habitat doesn't help either - most fossil animals discovered so far were aquatic indeed, just because water helps a lot the process of fossilization. However, if we know something more about the ancient relatives of modern insects, we have to thank pines, firs, spruces and larches. Remember Jurassic Park, and those fossilized mosquitoes in amber from which dinosaurian DNA was extracted? The DNA extraction thing was obviously fictional, but the amber thing itself is Truth in Television. Insects preserved in amber are perhaps the most marvelous fossil a palaeontologist could wish in its life. Not only they are perfectly preserved in every detail, included external anatomy and even color (an almost unique example among fossils); they have their original tissues preserved, single cells included. And they can provide an extraordinary clue to understand the entire ecosystem in which they lived in indirect ways. Unfortunately, most insects fossilized in amber come from the Cenozoic era (the Mammal Age), a period in which insect were already similar to their modern relatives. But we still know little about their Mesozoic ancestors, still less about the Paleozoic ones - except for those living in the Carboniferous (such as the aforementioned Meganeura) because many of them did preserve well in coal.
Anyway... we know some things with a good grade of certainty. The first insects appeared in the Devonian note , later than scorpions and millipedes: they were still wingless as modern springtails and silverfish still are, but then the Carboniferous saw their success: the very first flying animals appeared, among them the now-extinct Palaeodictiopterans with six wings. In this period they reached large size up to the four-winged Meganeura and starting their radiation destined to continue even today: not only dragonflies, but also cockroaches, grasshoppers and beetles appeared first in the Carboniferous. Other groups began their history in the Triassic: moths, wasps, flies and true bugs appeared at that time or a bit later, as well as parasitic kinds like fleas and lice. Insect evolution has always been related with that of terrestrial plants. It's worth noting, however, that this relationship has always been far more strict than one may think: biologists talk about a veritable co-evolution between insects and seed-producing plants, especially the flowering ones (angiosperms). This partnership reached its climax in the Cretaceous, when flowering plants became the new dominant group, just because of the relationship with two new kinds of insects barely appeared: the pollinators and the social ones. The former include butterflies, bees, wasps, flies and even some beetles, while the latter include ants, bees, wasps, and termites. Both ensembles began to affect dramatically their ecosystem, conditioning indirectly the evolution of all the other terrestrial animals, dinosaurs included. Many paleontologists think if modern birds and placental mammals are today the most diversified land vertebrates, they have to thank the insect-plant mutualism which has created well-suited habitats for their (initial) small size and eating versatility. Think about those birds and bats who feed only upon nectar, anteaters and pangolins which feed upon nothing but social insects, or the infinite insectivorous/"angiospermivorous" modern animals. And think about all the plant-related products we humans utilize today. Keep this in mind, every time you crush a bug.
No other animal group has had a greater importance in paleontology than molluscs. Their fossils are extremely abundant, to the point that many rocky formations are mainly made of cemented mollusc shells. Among molluscs cephalopods deserve a mention apart, being much more "evolved" than the others. Together with arthropods, cephalopods are the extinct invertebrates you have more chances to see in media - at least, the documentary ones: you hardly can see a trilobite, an ammonite, a sea scorpion or a nautiloid in Fictionland. If it happens, they would be simple "ambient critters", and good luck if the animal is mentioned.
Stony arrows?: Belemnites and extinct octopuses and squid
- Extinct cephalopods have given fuel to many legends, even before paleontology itself was "invented" by Georges Cuvier at the end of the 1700 century. Before that, those strange things today called fossils were believed to be Nature's jokes, the Earth's flowers, or other things (Only Leonardo da Vinci recognized correctly their nature, but his discovery was long ignored). And then, there are more specific legend about cephalopod fossils. Ammonites were believed stony horns ("ammonite" comes from Amun, an often ram-horned/headed Ancient Egyptian deity), or petrified snakes. note The less-known belemnites (technically the belemnoids), with their straight pointed shape, were believed stony arrows, or even the Devil's fingers! Belemnites were cephalopods living in the Mesozoic era together with ammonites, and probably gave rise to squid. Like ammonites, only their shell is usually preserved. This shell was inside the animal's body and invisible in life; belemnites would resemble simple squid or cuttlefish if alive today. Their lifestyle was more active than ammonites, and probably they were able to do the same things modern squid do (spraying ink, swimming using the lateral "fins", catching preys with their suckers, seeing images with their eyes). True modern squid became widespread in the Cretaceous, and the first octopuses (Proteroctopus for example) were already around in the Middle Jurassic; these mollusks (called "coleoids") usually have no shell inside, or at least only a remnant of shell (ex. the famous cuttle-bone). Some Cretaceous squid were as large as a modern giant squid.
"Finding Nemo": Orthoceras and the other "nautiloids"
- Some fossil animals' names recall literary characters, rather than mythical things: nautiloids (literally "similar to the Nautilus") are so-called from the modern Nautilus, whose name (meaning "sailor" in Greek) incidentally recalls Nemo's submarine (we're talking about the human captain, NOT the cartoon fish!). Actually, nautiloids are an artificial assemblage of all cephalopods which were neither ammonoids (ammonites) nor coleoids (octopodes, squids, belemnites etc.). They include both the modern nautilus and the most ancient cephalopods, widespread in the Paleozoic. Their traits were probably like those of the nautilus: their shell was divided in sections which could be filled alternately with water or with air like in a submarine. This allowed them to regulate their buoyancy (ammonites had a similar inner-shell anatomy and probably did the same). As the nautilus' eyes are simple chambers lacking any lens and incapable of forming images, this was probably true for other nautiloids as well. They should have had dozen of sucker-less tentacles, and were probably slow swimmers. However, many Paleozoic nautiloids had straight conical shells, not curly like the nautilus; Orthoceras ("straight horn") is the classic example. Its shell shows even traces of its original colors. Rhizoceras ("root horn") had a slightly curved but still conical shell. Rayonnoceras was more similar to Orthoceras, but was longer than a human and lived in the Carboniferous. The Walking With series has popularized another straight-shelled nautiloid, the Ordovician Cameroceras (named the "giant orthocone"), chosen as the prototypical Paleozoic cephalopod only because it was 10m long and the biggest known nautiloid so far (and one of the largest Paleozoic animals at all).
There is not much to say about the portrayal of extinct non-arthropod / non-cephalopod invertebrates in media: they rarely appear even in books/documentaries, much less in Fictionland, and when they do, they are almost never named (except sometimes for the names of each group, but only in popular science works). As an example, the original Disney's Fantasia showed several modern critters to symbolize the early evolution of invertebrates, but few or nothing among the really prehistoric ones. The Walking With series did the same: only modern jellyfish, sponges and sea urchins appear, all live-acted. Indeed, many modern invertebrate groups have populated our seas since the Cambrian Period, but many others are extinct today. Among modern land arthropods expect to see dragonflies, scorpions, centipedes, spiders, cockroaches, beetles, and sometimes crickets. They would be oversized: roaches the size of a rat, scorpions as big as cats, and so on. Finally, let's not forget a staple in every Paleozoic or Mesozoic sea: a Jellyfish, used as the symbol of the most ancient Forms of Life.
- Gastropods, scaphopods, bivalves, brachiopods, chitons, monoplacophorans: who's the intruder? All these invertebrate groups were "shellfish", and all but one were molluscs: brachiopods weren't. They were only distant mollusc relatives, and more related with the coral-like bryozoans (see "sessile invertebrates" below). As a whole, molluscs and brachiopods are extremely abundant in fossil record of all ages, from early Paleozoic up to the modern era. However, while molluscs are still a dominant group in modern seas, brachiopods are nearly extinct today, and thus cites as "living fossils". The most representative is probably Lingula ("small tongue"), a clam-like, filter-feeding animal that lives anchored to the sea floor with a fleshy protrusion (the "tongue"); prehistoric Lingula have been identical to the modern one since the Early Ordovician! Among extinct non-cephalopod molluscs are worthy of note the Rudists like Hippurites. Exclusively Cretaceous, these clams are notable both for their often great size (some were as tall as a human), and for their unique shape. They can be described as giant cups with a lid: the lower valve (the one attached to the sea bed) was conical and much bigger than the flat upper valve. Like Lingula, rudists were probably almost motionless creatures that filter-fed on tiny organisms.
- Crinoids, echinoids, asteroids, note ophiuroids, holoturoids, blastoids, cystoids, carpoids: who's the intruder? To some extent the carpoids (see the following paragraph); all the others were confirmed echinoderms. The asteroids ("star-like") are the starfish; ophiuroids are nicknamed "brittle stars" or "serpentine stars"; the echinoids ("husk-like") are the sea urchins and sand-dollars; while the holoturioids are the sea cucumbers or trepang. Thanks to their hard "skeleton", all these groups (except for the soft-bodied sea cucumbers) are common fossils, and have roamed the seas since the start of the Paleozoic. However, we're going to talk more about other three less familiar groups of echinoderms: crinoids, blastoids and cystoids. Crinoids ("sea lilies") are the only ones still living, but are today a rarer sight than the four groups above; like brachiopods, they are considered "living fossils". They have been not-very-movable filter feeders, and like all echinoderms they resemble more plants than animals: symmetrically rayed and with several "arms" that make them looking like ferns or flowers (hence "sea lily"). Adult echinoderms lack eyes, limbs, heads (but have a mouth nonetheless) and they usually lack a right/left side of their body - however, their tiny planktic larvae do have bilateral symmetry. The astonishing thing is, echinoderms are among the closest relatives of vertebrates, being Deuterostomes like us and not Protostomes (like most invertebrates). About blastoids and cystoids, they are exclusively fossil, were similar to crinoids but without the "arms"; their lifestyle was probably like the sea lilies'. Also worthy mention were the (exclusively fossil as well) edrioasteroids, perhaps similar to sand dollars or sea urchins.
- In Prehistory, some odd-looking invertebrates were even closer relatives of us vertebrates than echinoderms themselves: graptolites and calcichordates (or homalozoans). Graptolites are among the most common fossils in the Paleozoic, and used as index fossils alternatively to trilobites. They resembled floating water plants, but the "plant" was not the whole organism. They were colonial animals like modern corals, and the single individuals were actually inside the colony. Like brachiopods and crinoids, graptolites too were passive filter feeders. About calcichordates (remember, they are the carpoids above), they have been variably classified as primitive echinoderms, graptolite relatives, or even true chordates (that is, the group including sea-squirts & relatives + lancelets + vertebrates aka US). Calcichordates lived in the bottom seas, were movable animals (and bilaterally symmetrical unlike a typical echinoderm), with an armor and a sort of "tail". note However, one of the most depicted calcichordate, Cothurnocystis elizae, lost the bilateral symmetry altogether for inexplicable reasons.
Survival of the toughest: Prehistoric sessile invertebrates
- This is a merciless law even in palaeontology. Only hard parts of the organisms' bodies usually fossilized: bones, shells, armors, jaws, teeth, and whatnot. Many modern invertebrate groups which haven't tough elements left little fossil record (if they did). For examples, most "worms" (annelids aka segmented worms, nematodes aka round worms, platyhelmintes aka flatworms, nemertheans aka ribbonworms, and many others) are virtually unknown in paleontology, and their evolution is only a guess. This is also true for coelenterates - that is, the cnidarians (jellyfish, sea anemones, hydrae, siphonophores) and the ctenophores (comb jellies). At least, the totally soft ones; fortunately, corals (which are also cnidarians) build tough external skeletons that fossilize well, and their extinct relatives are well-known since the start of the Paleozoic. The same about the unfamiliar bryozoans (moss animals), very similar but not related at all with corals but with the brachiopods. Finally, the enigmatic sponges (which many zoologist hardly consider real animals) are also frequent fossils. They too have had an inner "skeleton" made of limestone (and sometimes glass-like silicon or a horny material, but they usually don't fossilize); one extinct group of possible sponge relatives were the archaeocyathans, which became the planet's first reef-building animals in the Early Cambrian.
- Foraminifers ("forams" for friends) are really a treasure in the rock, in all senses. They have contributed to confirm the deep impact theory about dinosaur extinction; their shells have contributed to form several sedimentary rocks around the world; and they are cool on their own, with their immense variety of shapes. The biggest forams, the nummulites, look often like literal COINS emerging from the rocks ("nummus" means coin in Latin); they are used as index fossils for the Cenozoic era, and have also created the material for the Egyptian pyramids! But wait: what are actually the foraminifers? Originally, scientists thought they were molluscs or mollusc-like critters; today we known they weren't even real animals. They were "protozoans", aka single-celled organisms with animal traits. Most other one-celled "animals" have left very few fossil material (if they did); the ancestors of Amoeba, Paramecium, Euglena, Vorticella, and so on are a mystery. Even the radiolarians: their shell is siliceous, and silicon usually dissolves before fossilising.
Once upon a time... CAMBRIAN ANIMALS
- Cambrian. The first Paleozoic period, in which the famous Cambrian explosion of life happened. The less known thing is, we humans are unbelievably lucky if we know that remote event. At that time, animals just were starting to achieve hard parts in their body, and we already know that, usually, soft-bodied organisms do not preserve at all. The astounding luck is, one of the greatest exceptions of this rule are just some deposits from the Cambrian period. : it almost seem Ol'Mother Nature has done this deliberately for ourselves.... The most famous and historically relevant is the Burgess Shale in British Columbia, but still others are also known (for example in China). For obvious reason, our curiosity now reaches the top: which were the first animals (not counting protozoans) that thrived in our oceans? Well, the answer is not simple: we can divide them in two ensembles. One is made from those groups either still alive today or extinct several ages after the Cambrian: among the former, most non-arthropod / non-cephalopod invertebrate groups already seen; among the latter, the trilobites. We'll talk here about the second ensemble: many Cambrian invertebrates were indeed exclusive of the Cambrian and didn't survive long enough, not even to reach the following period, Ordovician - in which the most famous Paleozoic critters: sea scorpions, nautiloids, ostracoderms etc. appeared. Thus, is easy to imagine many of them were really bizarre-looking to our limited point of view. We still know very very few things about their lifestyle, but their appearance is extraordinarily well-known, because these Cambrian deposits have preserved soft bodies; not only that, they have preserved them very well! It would be too long to mention all the members of the Cambrian fauna: see the image here for having an idea. The bizarre shrimp-like animal in the center is immediately recognisable, by far the biggest creature in this fauna, and arguably the top predator. It is called Anomalocaris (meaning "bizarre shrimp" indeed — it's a coincidence as the name was invented for one "arm", that was mistaken for separate organism), and was a distant relative of arthropods with no articulated legs but with the same compound eyes of the trilobites. Of course it is the most portrayed Cambrian animal in documentaries and illustrations, classically mentioned as "the first prehistoric monster ever appeared on Earth". Actually, if alive today, the "terrible" anomalocaridid would appear as a really narmy thing, a sort of 3 ft long, shell-less, pincer-less (it does have Combat Tentacles and a Lamprey Mouth, though) lobster note , nothing dangerous for a tough-boned, tough-muscled, tough-skinned mammal we are in comparison. Nonetheless, anomalocaridids were highly specialized predators, with a mouth build for prey around 1/12 to 1/6 of their own size. However, at the Anomalocaris time, every other organism was very small: the other creatures you see in the linked image are not longer than your hand, all possible prey for anomalocarids. note Anomalocaris canadensis (the largest known species) would have ignored them, focusing on larger prey. Creatures like Hallucigenia and Pikaia were hunted by smaller predators, such as Opabinia and Anomalocaris saron. The later was the species shown in Walking With Monsters, though ridiculously oversized (6 ft. on a A. saron!?) and prone to attack its own kind, even though neither its mouth nor grasps could injure an equally sized specimen in the way it was depicted, let alone possibly eating it. Anomalocaris also deserves a mention as the first active, intelligent predator capable of dismemberment, and quite possibly setting up the important role of predators in ecology and evolution. Apart from Anomalocaris, we can mention at least other three invertebrates which are stock in drawings: Hallucigenia, Opabinia, and Pikaia. The first has a so strange look that its name means "hallucination generator"! It was a sort of "worm" with long paired spikes for uncertain purpose, and long soft paired legs: the reconstruction of Hallucigenia has had an astounding Science Marches On tangle for many years (it was believed overturned, with the dorsal spikes believed actually legs, and the legs pointing upwards ending with one small mouth each!), and it still remains one of the most enigmatic Cambrian animal: nobody knowns exactly in which phylum it has to be placed. Opabinia was related to Anomalocaris, but had an even weirder look: maybe no other fossil animal resembles a fiction-related extraterrestrial thing more than Opabinia. It had five eyes put in circular fashion on its head, and a pincer-like grasp at the end of a long, flexible proboscis, often mistaken for the mouth which was actually located behind the proboscis. But the most important find is the third guy, Pikaia: despite its rather insignificant slug-like appearance, it is the most well-known vertebrate ancestor, a sort of prehistoric relative of our lancelet (the closest extant vertebrate relative). This relevance has made Pikaia one of the unofficial symbols of evolution, just like the ur-amphibian Ichthyostega, the ur-bird Archaeopteryx and the ur-horse Eohippus. But wait... have you see these critters in TV at least once? A hard thing, even if you watched Walking With Monsters. In this Rule of Cool-filled show, the only real Cambrian invertebrate to appear is... Guess what? Well, the superpredator Anomalocaris of course! The other two invertebrate guys shown up are... a modern jellyfish and an anachronistical phacopid trilobite - remember that phacopids first evolved in the Ordovician, while Cambrian trilobites looked very differently to the classic image we have when thinking about these animals. The absence of such awesome animals like Opabinia and Hallucigenia (and still others, like Wiwaxia, Marrella, Aysheaia, Aminskwa, Sydneya etc.) makes another egregious example of a missed opportunity. Talking about Pikaia, this time it's missing is no problem for us: the aforementioned proto-vertebrate Haikouichthys did perform its role. Still another thing: if you watch the list of creatures from the Burgess Shale, you'll note almost all animals (the main exception being Anomalocaris) have uncommonly short scientific names, most of them ending in -a'. A rather amusing thing to read, and - let's face it - a true oasis of happiness among so many other unutterable, absurdly-difficult names.
- The most familiar plants today are the angiosperms aka flowering plants, including most modern trees, bushes, herbs, but also apparently non-flowering critters such as grass, palms, bamboos, and even some "seaweed" (Posidonia). But as a group, they appeared only in the Cretaceous. Or, at least, became widespread only in that period. In modern taxonomy the angiosperms are called magnoliophytes (literally magnolia plants). Indeed, the magnolia was one of the earliest flowering plants ever appeared, in the lower Cretaceous. This is the most commonly shown angiosperm in paleo works, which often portray herbivorous dinosaurs like Iguanodons and Triceratopses eating magnolia leaves. note . Among the other earliest angiosperms are water lilies. The first palm trees also appeared in the Cretaceous (but note that most Cretaceous palm-looking trees were NOT palms, see further). However, most modern flowering greens - roses, apples, figs, oaks ad infinitum - appeared (or became a main component of the vegetation) only AFTER the dinosaur extinction. The angiosperms' success is tied to their relationship with pollinating animals, especially insects (see in the Arthropod section above), but also to those mammals/birds which still aid them to disperse their seeds by eating their fruits, or by other means. However, some flowering plants returned again to traditional strategies, using the WIND to disperse their pollen like the more archaic pines/firs do. Among them, ironically, are the most evolved and successful ones: the Poaceae, aka the grasses. See below.
Grasslands, at last!: Prehistoric grasses
- In the Early Mammal Age landscapes were already similar to those surrounding us today... except for one thing: grasslands were still totally missing. Prairies and savannah appeared only 30-20 million years ago in the middle of the Cenozoic. Grasses were already living in the Cretaceous, but they still didn't form grasslands, they grew isolated within the undergrowth. Grasslands have had a crucial role in Earth's ecosystems: all modern herbivorous mammals living in the modern African savannah (just to make one example) were able to evolve just thanks to grass. They developed special teeth to cope with this especially harsh green food, and thanks to the scarcity of trees, they were able to become bigger and faster. We humans have to be grateful to the grasses, too. All cereals and most fodder belong to this family of plants, as well as bamboo and sugar cane, other than the common grass naturally. However, their importance has been even greater than what you might think: if the grasses didn't evolve million years ago... you would not be here to read this. Simply, without grasslands, the human race still would look like big apes. (see in the Mammal section).
Dinosaur trees: Prehistoric ginkgos
- In the Dinosaur Age, however, most land plants had no flowers. Non-flowering plants belonged to two main ensembles: those reproducing with seeds, and those reproducing with spores. The former are traditionally called "gymnosperms", but are actually more than one group of plants not particularly closely related to each other. The most familiar gymnosperms are, obviously, the conifers (see below). In paleo-books, however, you can often read the name "Ginkgo biloba". This is, indeed, the only surviving member of a whole group of seed plants (the Ginkgophyta) that was among the dominant greens in the Mesozoic. Its special status makes the ginkgo often cited as a living fossil. However, it doesn't look like a pine or a fir: with its wide leafs and fruit-like seed, it resembles a normal-looking flowering plant. Indeed, ginkgophytes are probably the closest angiosperm relatives. Even though the modern ginkgo is widespread around the world as a ornamental tree, its wild ancestor lives only in Eastern Asia.
- Fictional media typically make us believing the trees from the Mesozoic were all palm-shaped. If non-palmlike tree appear, they usually have the shape of an angiosperm. Pines, firs, spruces, larches, cypresses and cedars are usually unseen in Fictionland... maybe because are usually associated with cold in the writers' mind (while 1 Million B.C. is always a very hot world filled with volcanoes....). However, in Real Life things were very different. Conifers were among the dominant plant groups in the whole Mesozoic, and a common food for camarasaurs, camptosaurs, centrosaurs, cetiosaurs, chasmosaurs, corythosaurs, and so on. However, there were not only pines and firs note at the time: more common were some kinds of conifers which are rare or extinct today. For example, the araucarians (monkey puzzles), the podocarps, the yews, and the more spectacular of all, the sequoia trees. note If you think sauropods were the real titans of the Jurassic, think again: a Giraffatitan near a redwood would appear like a house cat near a fully grown man.
- These are the Mesozoic seed plants that more resemble the ones seen in the fictional Dinosaur Age. They did resemble palm trees, but were NOT related at all with them. Cycads are the only ones still living, often used to embellish our cities. Bennettitales or cycadeoids ("pseudo-cycads") went extinct at the end of the Mesozoic. These two groups were very abundant at the dinosaur times, but were already present before the Triassic (as well as the little-known Cordaitales, maybe the ancestors of the conifers). About pteridosperms (the "seed ferns"), they are so called because of their external look, but were not true ferns: ferns do reproduce with spores. Seed ferns were among the very first seed plants ever appeared, in the Devonian, and survived until the Cretaceous. One of them, the Triassic Glossopteris, has been used to demonstrate the Pangaea hypothesis: its fossils have been found in every southern continent, showing landmasses were still united at the start of the Dinosaur Age (see also Mesosaurus in another page).
- One of the worst errors in popular media (sometimes even the documentary ones) is to portray grasslands in the Mesozoic. Arguably, writers think grass is the simplest kind of plant ever... thus, the first ever appeared on Earth. As seen above, grass are actually the most evolved plants and among the latest to become widespread on our planet. In the Dino Age, the dominant small-sized land plants were much, much more primitive: ferns, fern relatives and horsetails. These are collectively called pteridophytes and their modern descendants still make a wide portion of the undergrowth in many forests. In the Mesozoic, ferns and horsetails already made the forests' undergrowth, but also made true "prairies" where trees were absent. Only in the Mammal Age fern prairies were definitively substituted by grass prairies. But don't think ferns and horsetails were always small: in Prehistoria there were also giant horsetails and tree ferns, both deceptively similar to trees. In some places, they still live today: the 10m tall Equisetum giganteum is still growing in tropical landscapes. And tree ferns are still present in Australia and New Zealand — to the point that in the latter country they have become a national symbol, just like the kiwis. Indeed, the Land Down Under and its neighbor archipelago are a real mine of "living fossils": not only the platypus, the kiwi, or the tuatara...
- After all, Mesozoic vegetation wasn't so different than ours. Right, most land plants at the dinosaur times were mostly pine-like, palm-like or fern-like, and flowering plants were still a minority... but widespread conifer forests are still present today in northern territories. But if our time machine could bring us to the Carboniferous (aka the Coal Age, 100 million years before the Triassic), landscapes would appear REALLY a sorta Otherworld. At the time, all the plant groups cited so far were either a small portion of Earth' vegetation, or they haven't still appeared. The dominant plants were the so-called lycopods — named after Lycopodium (lit. "wolf foot"), a tiny plantlet which is one of the few kinds surviving today. Many of them would resembled extraterrestrial trees if alive today: Lepidodendron (lit. "scaly tree") and Sigillaria are two often cited examples. Their trunk was indeed scaly, they sometimes had only two branches; and some were huge, taller than a building! Despite their powerful look, they were quite fragile giants: giant lycopods easily fell down during the frequent Carboniferous storms. The rotting logs then carbonized, becoming the fossil coal we burn today (hence "Carboniferous", meaning "coal-making"). It's worth noting lycopods, ferns and horsetails have always been strictly tied with water; their spores can develop in adult individuals only in humid habitats, and this explains why they were so common in the Carboniferous swamp world. Then, in the following Permian period the Earth mostly dried out, and giant lycopods weren't able to survive the change. It was seed plants that have become the more successful plant groups since that: seeds are a bit like the reptiles' and insects' shelled eggs, well-adapted to sprout in arid environment.
The "first tree": Archaeopteris
- Sometimes it seems paleontologists have fun making unwilling jokes with scientific names. While the traditional "first bird" is called Archaeopteryx, one of the first land plants ever appeared is the almost homonymous Archaeopteris! But wait, Archaeopteryx means "ancient wing", Archaeopteris means "ancient fern". This plant lived in the Devonian (before the Carboniferous), just when the proto-amphibian Ichthyostega made the first step on dry land; it was one of the first terrestrial plants to develop the size of a tree. Since at the time land animals were very few and mostly carnivorous or detritivorous, Archaeopteris and its relatives were able to spread worldwide but never far from water, just like amphibians did. Their appearence was that of a tree fern: indeed, the fern-like is considered one of the most primitive body plans among terrestrial plants.
The "first shoot": Cooksonia
- However, plants went on land before the amphibians. In the Silurian period (before the Devonian) there were already some aquatic plants (ex. the Psilophytes) emerging out of water; Cooksonia is an often cited example. These tiny plantlets had their roots still underwater, but their "branches" grew out of the water level, capturing extra light. Terrestrial plants are actually very evolved creatures and have done a hard work to create their adaptations to survive outside the liquid element. Among them, a vascular system (that is, tiny vessels for the flow of the lymph), waterproof "skin", and fibres to make their stalks more robust against gravity.
Fungus Humongous: Prototaxites
- This species was first described in 1843, and for the longest time experts couldn't decide what it was. Many thought it was a conifer tree (its name means "First yew"), others thought it was a giant aquatic alga. It wasn't until 2007 that scientists confirmed it was indeed a giant terrestrial fungus! Since this thing grew up to 8 meters, it would've been the tallest organism of its time. Many are still confused as to how such an organism could grow like that without photosynthesis.
- These so-important living beings in modern world are very little known in paleontology. Their "bodies" fossilize very rarely, but they surely have been main components of both water and dry land ecosystems since the Paleozoic. However, only bryophytes (mosses, hornworts and liverworts) can be called "plants" without going in error. Algae (seaweed) and fungi (mushrooms, toadstools, moulds, yeasts) are NOT true plants in modern systematics (fungi cannot even perform photosynthesis!). And lichens are not even true organisms: they are the results of a symbiotic relationship between a fungus and an alga.
The creatures here are from the Precambrian, and lived/originated before the other organisms listed in all the other "Prehistoric Life" pages. Talking about them is hard matter even for the most skilled biologists. Our mind has trouble to imagine how the first living beings actually looked, even more how they lived... However, not everything is unknown to us.
Animals, or plants?: The Ediacara creatures
- We are so accustomed to divide the visible-to-the-naked-eyes creatures between plants and animals (and fungi), it's hard imagining critters that were neither. The Ediacaran biota (often improperly called "Ediacaran fauna") match all this. They lived even BEFORE Anomalocaris and the other Cambrian animals, and their body plans are even more enigmatic to us. One of the most mentioned is Spriggina, similar to a fern; another is the elliptical Dickinsonia. Like the Burgess Shale, is a very lucky thing that some fossil deposits have preserved these soft-bodied creatures to our days. However, we could recognize some modern invertebrate groups: for example, one of these Ediacarans is a very archaic mollusc. This would mean modern invertebrate groups were still living before the famous Cambrian explosion of life. Maybe, even our earliest vertebrate ancestors, but this is unproven.
The first Earthlings: Prehistoric Stromatolites and other bacteria
- One-celled organisms are usually not preserved in fossil records (the aforementioned foraminifers are a well-known exception). However, we're sure the first Earthicans were bacteria. note They have been the simplest form of life, even lacking the nucleus which is the hallmark of the Eukarya - that is, animals + plants + fungi + algae + protozoans + other less-known organisms, all with nucleate cells. Some bacteria, the photosynthetic cyanobacteria (improperly called "green-blue algae") have built strange rocky structures called stromatolites (they produce them still today); the most ancient stromatolites are from 2,000 million years ago, three times earlier than the first multi-celled organisms. They are among the most ancient form of life that has left some fossils. It's worthy noting that parasitic bacteria (those that carry diseases) could only have appeared after multi-celled organisms: otherwise which creature could have they infected? The same about the non-living viruses: note they should have appeared only after true living things for the same reasons (Some viruses infect bacteria, mind this). How life as a whole has originated is one of the most fascinating fields within human knowledge, but here we're outside paleontology and science in general. This is mainly speculation and philosophy, even though molecular biologists are doing great efforts to found the answer.
- The RNA world is about as far as we can look back. The RNA world is a well founded hypothesis - it has enough evidence to be generally believed, but insufficient to be considered proven. In the modern world, DNA codes genes. Genes are copied to messenger RNA. Messenger RNA is read by ribosomes to create proteins. Almost all the functions of the cell are performed by proteins, including duplicating DNA, copying DNA to RNA, and most of the ribosome is protein. This works great, but how could it start? DNA can't replicate without proteins, and proteins can't be made without the instructions in DNA. However, RNA can both store information and catalyse reactions. Although it would be grossly inefficient by modern standards, life based on RNA with no DNA and no proteins is quite plausible. The RNA world hypothesis is that such RNA life existed, and is ancestral to modern life. Evidence for this is functional RNA (RNA which does stuff directly, rather than simply being instructions to ribosomes) performs just a few cellular functions, but very central critical ones. Most central is that RNA forms the reactive core of the ribosomes.