One of the coolest dinosaurs.
"If Dorothy Gale had been swept by the whirlwind to some Mesozoic glade instead of to the Haunted Forest of Oz, she might have observed, 'Lions and tigers and bears are one thing, but these predatory dinosaurs are way out of hand!'"
— Gregory S. Paul
This section talks about "carnosaurs". We will begin with a word about its meanings. In old sources, this term included all large theropods, from Tyrannosaurus to Allosaurus, from Ceratosaurus to Megalosaurus, to Baryonyx, Spinosaurus, and sometimes even Dilophosaurus. Science Marches On however, and now “carnosaur" has a much narrower meaning, indicating only the natural lineage including Allosaurus and its closest relatives, which make together the most advanced and bird-like giant theropods after the tyrannosaurs.
But this change has happened only at the beginning of the 1990s (ceratosaurs and Dilophosaurus were removed earlier). That’s why pre-Jurassic Park dino-fans still have the habit to call “carnosaurs” all the big meat-eaters in the dino-world - and let’s admit it, “carnosaur” is a very apt name, just meaning meat(-eating) lizards. Thus, to avoid Taxonomic Term Confusion, we’ll use here the term “allosauroids” instead of “carnosaurs” to indicate Allosaurus relatives. Note, however, that megalosaurids and spinosaurids are sometimes considered non-allosauroid carnosaurs. Also, Friedrich von Huene, who named Carnosauria in 1920, recognized right away that ceratosaurs & tyrannosauroids were not carnosaurs.
Of course the most portrayed large predatory theropods in documentary media are the stock ones: the seven classic "carnosaurs" above, already common in dino-books since The '80s or even before, plus Carnotaurus & Giganotosaurus that joined them in The '90s, when the word "carnosaur" had already assumed its current meaning. Other big meat-eaters, however, have also been common sights. Among the North-American ones, it's especially common the "small" tyrannosaur Albertosaurus — or alternatively Gorgosaurus or Daspletosaurus. Though less-frequent, the sail-backed allosaur Acrocanthosaurus can appear in Early Cretaceous reconstructions, and Torvosaurus in the Late Jurassic ones. The tyrannosauroid Dryptosaurus is noted for a painting made by Charles R. Knight at the early 1900.
In Europe, a frequent choice is the megalosaur Eustreptospondylus, see Walking with Dinosaurs for an example. Among Asian carnivores, the tyrannosaur Tarbosaurus is the classic guy for Cretaceous settings, while the allosaur Yangchuanosaurus and the hard-to-classify Gasosaurus are for the Jurassic ones. Among the African theropods, the allosauroid Carcharodontosaurus, the spinosaurid Suchomimus and the Malagasy ceratosaur Majungasaurus have become common since the 1990s. Among South-American kinds, the allosauroid Mapusaurus and the allosauroid or tyrannosauroid Megaraptor have become popular since the 2000s. No especially relevant large theropod has been found yet in Australia (except Australovenator and more fragmentary remains like those of the "Australian Allosaurus" of Walking With Dinosaurs and others), while Antarctica has given to us the curly-crested Cryolophosaurus, the animal of the image.
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Tyrannosaurus Relatives
The Appalachian Dinosaur: Dryptosaurus
- Not all tyrannosauroids were tyrannosaurids, remember this. Basal tyrannosauroids were often very different animals: smaller, slenderer, with three fingered hands. Not exactly T. rexes… only their skull structure was analogue to the tyrannosaurids. The most long-standing basal tyrannosauroid is Dryptosaurus aquilunguis ("eagle-clawed wounding lizard"), the first theropod discovered in North America from not-only-teeth, in 1866, before the Bone Wars. Because of its apparently untyrannosauroidian nature and scant remains, Dryptosaurus was long considered a hard-to-classify theropod (for example, a late-surviving megalosaur). After the discovery of North American forms like Appalachiosaurus (from the Appalachian mountains), Dryptosaurus has consistently been placed in the tyrannosauroid realm. However, it was more slender than true tyrannosaurs, and we don’t know if it had two- or three-fingered hands (they have never been found, apart from some isolated phalanxes). Dryptosaurus has also the distinction to be one of the few dinosaurs discovered in eastern USA, contrary to the quasi-totality of North American dinosaurs. Edward Cope called it "Laelaps", from a mythical dog turned into stone while jumping; Othniel Marsh, however, renamed it with its current name. Dryptosaurus was also the dinosaur ever depicted by the famous paleo-artist Charles R. Knight (when the dinosaur was still called “Laelaps”), with two individual fighting and one jumping over the other.
Feathered Tyrant: Yutyrannus
- In 2012, a new and important find about the tyrannosaur lineage came to light: Yutyrannus (lit. "feathered tyrant": Yu = "feathered dragon" in Chinese, tyrannus = "tyrant" in Latin) from the Early Cretaceous of China. Iy was Proceratosaurid, an early group of tyrannosauroids that had three fingers and a much more gracile body-type. From the same Liaoning site in which other much smaller feathered dinosaurs have been found, Yutyrannus was much bigger than them (30-foot long, only slightly smaller than Tarbosaurus) - but it too bears a complete covering of feathers. This suggests that even large true tyrannosauroids were feathered, not just their smaller ancestors. Despite its size Yutyrannus was very basal among tyrannosauroids, believed related with the 9-foot Guanlong and thus more distantly related with true tyrannosaurids than Dryptosaurus and Appalachiosaurus were. In 2015, the "feathered tyrant" made its first appearance in mainstream media by playing a major antagonist in The Land Before Time 14. It may be on its way to becoming a Stock Dinosaur in the near future.
Dwarf Rex?: Nanotyrannus
- A much smaller animal was Nanotyrannus. In year 1988, Bob Bakker described it as Nanotyrannus lancensis, “dwarf tyrant from Lance Creek”; merely 18 ft long, it has been celebrated it as "the smallest tyrannosaur ever discovered in North America", living alongside the much bigger cousin T. rex. But its only remain is a fragmentary skull, which could have been actually based on a juvenile of what very likely is Tyrannosaurus rex. The "nanotyrant" has nonetheless appeared in several popular dino-books as a truly dwarf tyrannosaur living alongside the Tyrannosaurus rex. Originally, before 1988, Nanotyrannus was believed a juvenile Gorgosaurus. The closest thing there was to a "dwarf tyrannosaur" was Daspletosaurus horneri, Alioramus, and Nanuqsaurus, all of which were under 25 feet long.
False T. rex?: Daspletosaurus
- Over the decades, there have been multiple tyrannosaurid specimens coined as a species of Tyrannosaurus, with the biggest examples arguably being Tarbosaurus and Daspletosaurus. Some even believed that Daspletosaurus evolved into T. rex through anagenesis (which is a controversial concept in biology). However, with discoveries of tyrannosaurids more similar to T. rex like Lythronax, Teratophoneus and Bistahieversor, this theory came into question. This led to some analysts coming to the conclusion that Daspletosaurus was much more basal than previously thought, and that its superficial similarities to T. rex were a result of convergent evolution (due to them living in very similar niches). Another analysis argued that Daspletosaurus was a closer relative of T. rex than Lythronax, but couldn't have been a direct ancestor. With Tarbosaurus, things are a little less complicated. While Tarbosaurus was T. rex's closest relative, they still had too many skeletal differences to be considered the same genus. The discovery of a second Asian tyrannosaurid of similar size (but from millions of years before), Zhuchengtyrannus, led to the idea that these three genera came from Asia, and that Tyrannosaurus was invasive to North America.
Asian Cousins: Alectrosaurus
- Alectrosaurus, was perhaps the first-found large theropod in Asia, and is more probably a basal tyrannosauroid like Dryptosaurus. Several undetermined tyrannosauroid remains found in Asia have been assigned to Alectrosaurus, but are too undiagnostic. The alectrosaur's closest relative; Xiongguanlong, was quite a bit older than it. Among other Asian findings, the small "Shanshanosaurus" and "Maleevosaurus" are now regarded as juvenile Tarbosaurus, while "Raptorex" (whose name is a Portmanteau of "raptor" and "rex"), was originally thought to be a highly advanced Early Cretaceous form, but now appears to be the juvenile of a true Late Cretaceous tyrannosaurid that simply died falling into a lower strata layer. Given the time period this specimen came from, this may have even been the ancestor of T. rex in juvenile form.
Strange Muzzle: Alioramus
- Alioramus literally means "the other branch" (of the tyrannosaurs) and was once thought the juvenile of Tarbosaurus, but has revealed a truly small tyrannosaurid, whose long narrow skull shows small hornlets along its muzzle. It lived alongside the much bigger Tarbosaurus in Late Cretaceous Asia. Both the alectrosaur and Alioramus arguably occupied the role of the smaller and more agile predator in respect to Tarbosaurus. Recently Alioramus was placed in its own tyrannosaurid subgroup, the Alioramines, alongside the similar but slightly younger Qianzhousaurus.
The Other Tyrants
- "Aublysodon", described as early as the 1860s, is known mainly from unusually-blunt teeth found in North America and others were found later in Asia, and it may be just represent juveniles from known tyrannosaurids like what is possible for Nanotyrannus. "Dinotyrannus" ("terrible tyrant") and "Stygivenator" ("Hunter from the Death-River"), both described in 1995, are today regarded as proper T. rex specimens. Unfamiliar North American tyrannosaurids have been named in recent years, often with badass names, such as Bistahieversor ("New Mexican destroyer", it was originally considered a southern species of Daspletosaurus) in 2010, Teratophoneus ("monstrous assassin", a short-snouted form) in 2011 and Lythronax ("gore king", more broad-snouted) in 2013, Dynamoterror (Dynamic Terror) in 2018 and in 2020, Thanatotheristes (Death-Reaper, the oldest known so far). 2014 saw the discovery of truly unusual North American Tyrannosaur, this one from the same time period (the very end of the Cretaceous, about 68-66 million years ago) as T. rex itself. However, there's no chance that the two could have met, because Nanuqsaurus ("polar-bear lizard") lived above the Arctic Circle, in Alaska — hence the name. It was also small, only about half the size of T. rex. It was initially believed to be a late-surviving species of Gorgosaurus, but was later reclassified as its own genus. This means that the tyrannosaur villains in the 2013 Walking with Dinosaurs movie, though labeled as Gorgosaurus, could actually be Nanuqsaurus.
Dawn Tyrannosaur: Eotyrannus
- Most of the dinosaurs listed above were Late Cretaceous, either Asian or North American, but some basal tyrannosauroids have been found elsewhere: Eotyrannus “dawn tyrant” lived in Early Cretaceous Europe along with Iguanodon. Known since 2001, its find in England made sensation both because of its earliness, and because was small: 10 ft long, even though it too could be a juvenile. It was similar to a large “coelurosaur” with a tyrannosaur-like head, and long, three-fingered forelimbs. Eotyrannus adds additional support to the notion that tyrannosaurs were more related to birds than to the other “carnosaurs” in traditional sense (allosaurians, etc). Other basal tyrannosauroids or possible basal tyrannosauroids have been discovered in Northern continents: among them, the European Aviatyrannis ("bird tyrant") and Juratyrant ("Jurassic tyrant") were named with a different suffix than -tyrannus. Of note also Moros intrepidus, described only in 2019 but already chosen in 2022 as one of the seven new dinosaurs/Mesozoic reptiles within Jurassic World: Dominion. Other basal tyrannosaur relatives are listed in the “small theropods” section, for example Proceratosaurus and Stokesosaurus.
The First-Found: Deinodon
- Few people today are aware of this practically unknown dinosaur, described only from teeth. Nonetheless, “Deinodon horridus” ("terrible tooth") has been the very first carnivorous dinosaur described in North America, in 1856, when dinosaurs were still only-European things. Its describer, Joseph Leidy, didn’t realize that he named the first tyrannosaur, but only because Tyrannosaurus rex and its relatives had not been found yet. Now scientists think the “Deinodon” teeth pertain to another better-known tyrannosaurid, perhaps Daspletosaurus. However, “Deinodon” has left one memory: once, the tyrannosaurid family used to be called “deinodontids”... or rather, this should be the correct name for tyrannosaurids: but is obscured by how ingrained the term "tyrannosaurid" now is.
The Giant Claw: Megaraptor
- Some think this dinosaur and its relatives (the Megaraptorans) are basal tyrannosauroids as well, but others do not agree. Discovered in the late 1990s and initially thought to be a large dromaeosaurid (hence its name), this South American Late Cretaceous theropod was variably classified in the past, from a small spinosaurid to an allosauroid, or even a large noasaurid – all groups characterized by some sort of oversized claws. Indeed, a one-foot-long claw was the first discovered Megaraptor fossil; and, wrongly, palaeontologists put on its foot, describing it like a giant-dromaeosaur critter. But then a complete hand including the same enormous claw of the original specimen was discovered, and we now know this claw was on its thumb instead. Baryonyx too had enormous thumbclaws, the same size of those of Megaraptor; however, since Megaraptor was a smaller theropod, this means its claw could be the biggest among all dinosaurs in respect to the overall body size. How Megaraptor used those weapons (and they most certainly were weapons) is still a mystery; for obvious reasons, many have fun to imagine incredible massacres of herbivores, including severed throats, disemboweled bellies and whatnot...but the more likely options are hooks to hold prey close and enable the creature to inflict more wounds with its jaws, or, more likely, slashing tools for cutting flesh with the sharp blade at the inside curvature of the talons, ripping out chunks and causing fatal wounds, but nothing as extreme as complete disemboweling or decapitation. Megaraptor got a fair bit of publicity back when it was discovered— no doubt boosted by the Jurassic Park-inspired "raptor-mania" of the 1990s. It appeared in Warpath: Jurassic Park and Dinosaur King, portrayed in both as a giant dromaeosaur. The newer version with the claws on the hands has yet to appear in pop culture.
Allosaurus & Giganotosaurus Relatives
Runner of the Nile Delta: Deltadromeus
- In 1996, a smaller but still big theropod similar in shape to a slender Allosaurus was found in Africa alongside the huge Carcharodontosaurus one year later: Deltadromeus, which was possibly an allosauroid or not. Around 30 ft long, nearly as big as an Allosaurus, Deltadromeus had long, unusually slender hind limbs for its size: this suggests it was one of the fastest-running giant theropods, like the horned Carnotaurus, and a predator as efficient as its bigger but clumsier neighbors Spinosaurus and Carcharodontosaurus (although others think it was an herbivore). Its name just means “delta runner” - a reference to the Nile's delta. Originally considered a giant primitive coelurosaur, it is more likely a ceratosaur (possibly a synonym of the giant but poorly-known Bahariasaurus). Still another African theropod was originally thought by Ernst Stromer (Spinosaurus' Trope Namer) a second species of his famous dinosaur. However, it was later found that its bones actually came from two different dinosaurs: the limbs from Carcharodontosaurus, and the vertebrae from a new dinosaur, which was renamed Sigilmassasaurus ("Moroccan reptile") in 1996. Some thought Sigilmassasaurus would end up being the same as Carcharodontosaurus, but it now seems to be Spinosaurus after all (vindicating Stromer's suggestion).
Sail-Backed Guy: Altispinax
- Spinosaurus was not the only theropod with a ridge on its back made by elongated neural spines: there were others as well. Acrocanthosaurus is the most well-known among “these others”. Other two less-known “sailbacks” of smaller size and with an even less-evident crest were Altispinax and Metriacanthosaurus, both European. Once placed in the “Megalosaurus wastebasket”, both are now considered allosauroids of some sort. Altispinax was renamed “Becklespinax” in the late eighties, because its first remain was an isolated tooth found in the XIX century. It's worth noting that Altispinax's crested backbone was used in the middle XIX century as a model for the famous "Megalosaurus" sculpture in the Crystal Palace Park in London; this explains why the megalosaur model shows a humped back. Just as surprisingly, in spite of being a very obscure dinosaur, Metriacanthosaurus' long name appears on one of the embryo-containing vials in the first Jurassic Park film. However, the name probably was referred to another better-known large theropod, the Chinese Yangchuanosaurus (which was by Gregory Paul synonymized with Metriacanthosaurus in 1988).
Feathers. Or maybe Not: Concavenator
- In 2010, Europe has gifted us a new sailback, Concavenator from Early Cretaceous Spain. This carcharodontosaurid is maybe one of the greatest dino-discoveries of the year, with not only a small “hump” on its hips made by elongated neural spines; its arms show possible attachment points for filament-like structures. This would mean Concavenator could be a non-coelurosaur theropod found with feathers or feather-supporting structures. Now our imagination can travel further and further, imagining feathered Allosaurus, feathered Spinosaurus… but wait: don’t get too excited. Other researchers have pointed out that these attachment points are more similar to those for muscles in crocodiles than feathers in birds, so this supposed evidence for feathers in Concavenator may not be valid at all. See also Sciurumimus in Prehistoric Life - Other Small Theropods .
Allosaurs vs Tyrannosaurs: Saurophaganax
- One of the reasons behind the Poor Man's Substitute role Allosaurus has played in pop-culture is probably its smaller size compared to Tyrannosaurus rex. But this is true only if you count the most known allosaurid species, Allosaurus fragilis (the second term, ironically, means “fragile”). Another species, Allosaurus maximus (“maximus” just means “the biggest” or ”the greatest”), has recently been thought distinct enough to be classified once more in its own genus, Saurophaganax (originally "Saurophagus", "reptile-eater", but the name was preoccupied). Nonetheless, the latter was so similar to the classic Allosaurus, it might well return to the genus Allosaurus again. Saurophaganax maximus though, sounds much cooler and it means "The greatest king of the reptile-eaters" opposed to Allosaurus maximus, which means "The largest different lizard"". Other dubious synonyms of Allosaurus include "Creosaurus" (which some thought had a longer snout than Allosaurus proper) and "Labrosaurus" (based on an astonishingly deformed jaw). Saurophaganax was about the size of a T. rex and most of the really large Allosaurus depictions, which are really misnamed Saurophaganax from the days when the two were considered the same animal.
Immense Allosaur: "Epanterias"
- Still another close kin has been described as a really huge animal, up to 15 m long, even bigger than an average T. rex: "Epanterias amplexus". The astonishing thing is, "Epanterias" is known to science since as early as year 1878, 25 years before T. rex was discovered! This awesome oversight is due to its extremely scant remains (to the point it was originally considered a sauropod). But the main point is another: "Epanterias" is very likely another overgrown Allosaurus species as well. If true, then our Allosaurus would deserve to be considered a real rival of Tyrannosaurus rex, Giganotosaurus, and Spinosaurus for the King-Of-The-Dinosaurs title.
New Hunter: Neovenator
- Since 2009 or so, Megaraptor is classified as an allosauroid, more precisely as a very specialized member of the family Neovenatoridae (here called "megaraptorans"). However, some workers think that megaraptorans may be coelurosaurs and possibly even tyrannosaurs. This recently-created family is based on Neovenator (“new hunter”), a much more normally-looking 7.5 long theropod which lived in Early Cretaceous England alongside former Iguanodon species Mantellisaurus as well as Iguanodon itself. Discovered in the 1990s, Neovenator unwillingly made a Hilarious in Hindsight case. It has indirectly made Truth In Books a classic in old dinosaurian portraits: that is, the battle between Iguanodon and an anachronistic Megalosaurus, which in Real Life lived in the Middle Jurassic. The 2009 discovery in Australia of the megaraptoran Australovenator, "southern hunter", has likely revealed the true identity of the mysterious 'dwarf Allosaur' seen in Walking with Dinosaurs. Also of note is Fukuiraptor, one of the rare Japanese dinosaurs. Initially known from the claw, this Early Cretaceous megaraptoran was initially considered a large deinonychosaur (again, the claw actually went on the hand). Perhaps the most interesting member of the neovenatorid family is Aerosteon: discovered in Argentina in 2008, this allosauroid shows prominent air sacs in its bones, providing more evidence that birds are dinosaurs. Also notable is the fact that lived in the Late Cretaceous, in a time tyrannosaurids and abelisaurids (see further) were believed the only large predatory theropods still around. Also Argentinian but even younger than Aerosteon, Orkoraptor was initially considered a birdlike theropod; probable carcharodontosaurid teeth from Brazil that are still younger suggest allosauroids as a group may have survived until the very end of the Cretaceous. While with the 2013 discovery of a North American megaraptoran called Siats ("man-eating monster"), neovenatorids are now known from every continent except Africa & Antarctica. Living about 90 mya, Siats is to date the youngest North American allosauroid. The recent discovery of a Megaraptor skull lends credence to an idea proposed by F.E Novas...that megaraptorans were not allosauroids, but tyrannosauroids. However, this may simply be a case of convergent evolution. A real phylogeny chaos for Megaraptor and its relatives.
Exotic Names in China: Shaochilong
- Many allosauroids have been found in Asia, notably in China. This is evident if you read their names: just as an example, Yangchuanosaurus. One theropod related to Yangchuanosaurus was named Sinraptor (“Chinese robber”) in the nineties. The latter became the prototype of the allosauroid family also containing Yangchuanosaurus and the sail-backed Metriacanthosaurus, the sinraptorids, more basal than allosaurians (allosaurids + carcharodontosaurians); but in 2012 this family has changed name to Metriacanthosauridae, as Metriacanthosaurus has ended up a "sinraptorid" closer to Sinraptor than to Yangchuanosaurus. Interestingly, the hands and hips of metriacanthosaurids are more similar to those of the more primitive megalosaurs than to those of other allosaurs. Other Chinese allosauroids & possible allosauroids are known only from extremely scant remains, so their classification has subject of several shifts. Szechuanosaurus, one of the first large theropods found in China, is known only from teeth, while some good skeletons once assigned to it are probably Yangchuanosaurus instead. Xuanhanosaurus is now believed a metriacanthosaurid but may instead be a megalosauroid or a very primitive tetanuran. Curiously, some once thought Xuanhanosaurus was able to walk on four legs, thus making an exception among the exclusively-bipedal theropods (another large theropod once believed partially quadrupedal is Baryonyx). Kaijiangosaurus is known from bones that may actually come from more than one species. Shidaisaurus is another metriacanthosaurid, this one found crushed beneath a sauropod; the Early Cretaceous Kelmayisaurus is known only from jaws that likely came from a carcharodontosaurid. Last example, the Late Cretaceous Chilantaisaurus is a neovenatorid similar to Megaraptor, but was once considered a possible megalosauroid or an intermediate allosaur-tyrannosaur. Known from somewhat better remains is the Late Cretaceous carcharodontosaurid Shaochilong, which has a long and convoluted story. It was originally considered a second species of Chilantaisaurus when that dinosaur was named in 1964. Starting in 1998, it was found to be a coelurosaur (although whether it was a tyrannosauroid or maniraptoran was debatable) and informally named "Alashansaurus". In 2009, it was found to be a carcharodontosaurid—one of very few from Asia— and given its current name ("shark-toothed dragon"). Its recognition as a carcharodontosaurid also helped solve a mystery. Megalosauroids & allosauroids dominated the Jurassic lands, while tyrannosaurids held sway over the latest Cretaceous world. What happened between then, however, was a mystery. Did the more primitive theropods continue to rule, or did the tyrannosaurids "come to power" earlier than once thought? The presence of Shaochilong in Late Cretaceous rocks favors the former.
A Less Exotic Name: Gasosaurus
- As you can easily tell now after reading this page, many large theropods aren’t exactly the simplest things to pronounce. But there’s also a curious exception which comes just from China. This one makes a sort of comic relief among many huge theropod names, having one of the simplest, most obvious names one could imagine: Gasosaurus just comes from a gasoline company that funded the excavation of its skeleton. A smallish theropod, 4 m / 15 ft at the most, Gasosaurus constructus lived in Middle Jurassic, and its appearance was a sort of middle-way between a gracile “carnosaur” and a stocky “coelurosaur” (in the older sense of these words). Its classification remains uncertain, and suggestions regarding its phylogenetic position within Theropoda range from a metriacanthosaurid to the most ancient coelurosaur known to an early ancestor of both groups. The most recent large study of tetanuran theropods considers it "best regarded as having an uncertain position within Tetanurae and probably outside Coelurosauria".
Dilophosaur Cousin?: Monolophosaurus
- Another reasonably complete theropod from Middle Jurassic China is not an allosauroid (though it was once considered one) but a very primitive tetanuran: Monolophosaurus jiangi (“Jiang's one-crested lizard”), so-called because of its single cranial crest vaguely similar to each branch of the double-crest of the unrelated Dilophosaurus ("two-crested lizard"), but shorter and more robust. Named in 1993 and informally known as "Jiangjunmiaosaurus" before then, it is probably a late-surviving form that managed to make its way among the more evolved allosauroids, a bit like what Ceratosaurus did in North America. Chuandongocoelurus, known only from vertebrae and once considered a coelurosaur or ceratosaur, may be closest to Monolophosaurus; if the known specimen is an adult, it is the smallest tetanuran outside of coelurosaurs. Monolophosaurus appears in the 2021 TV animated series Jurassic World: Camp Cretaceous. The monolophosaur and the dilophosaur were about the same size and shape in real life, and the two theropods could be easily mistaken one for each other by non-experts.
Spinosaurus & Baryonyx Relatives
Croc Mimic: Suchomimus
- No other group of large predatory theropods was as specialized as spinosaurids. Their croc-like heads, their hook-like thumbclaws, and their flat crests on their backs make them immediately recognizable; even though some other theropods had sail-backs or hook-thumbs, no one had the crocodilian-like jaws. As a group, they lasted a long time, starting in the Late Jurassic with African Ostafrikasaurus (known only from a tooth that might actually come from another type of theropod) and ending with an unnamed form from the mid-Late Cretaceous of China. However, spinosaurids as a group are recognized only since the late 1980s/early 1990s; before, the only-two known members, Spinosaurus and Baryonyx, were believed so different that each was put in its own family: Spinosaurids and Baryonychids. In year 1998, a third spinosauroid was discovered in Early Cretaceous North Africa: Suchomimus, lit. “the imitator of the crocodile”. 11 m long, bigger than Baryonyx but smaller than the unbeatable Spinosaurus, has long been the only dinosaur ending in -mimus that is definitely not a bird-like coelurosaur. It was very similar to Baryonyx: indeed, it was at one point believed to be a member of that genus. Suchomimus had longer legs in proportion to its body than Spinosaurus or Baryonyx, meaning it probably spent more time on land than they did. Suchomimus was therefore the only spinosaur to have been the top predator of a terrestrial ecosystem, with the largest carnosaur in the area (Eocarcharia) being only about half its size. Despite its significance, Suchomimus is a rare sight in fiction compared to Spinosaurus and Baryonyx. It was mentioned in Jurassic Park III, alongside Baryonyx, when the heroes are trying to figure out what the Spinosaurus is.
Forgers of Dinosaurs: Irritator
- Another less-known spinosaurid has a name which reveals an astounding backstory: Irritator ("the irritating one"). Scientists are not robots: they too have feelings, and sometimes project them in their dinosaurs’ names. This Brazilian theropod is known only from one skull; sadly, this skull was badly affected by some fossil-poachers which rebuilt it making it longer than it originally was, even before the animal was named! When was found, scientists had hard time to rebuilt it correctly: when they finished the work, decided to call it Irritator, the “irritating one” indeed. Irritator probably includes Angaturama, another spinosaurid also discovered in Brazil (and the two could simply be the same specimen called two times with a different name!). Whether they're distinct or not, this mistreated skull pertains to a spinosaurid closer to Spinosaurus than to Baryonyx; for obvious reasons, we don’t know if it had a “sail” or not. Siamosaurus ("Siamese lizard") was first-found in Thailand and originally based on teeth, which some thought were from a fish. A skeleton announced in 2004 suggests it is a dinosaur, but it has yet to be described in the literature. In 2011, another spinosaurid was discovered in Brazil from skull remains, Oxalaia (named from a river deity); estimated to be 12-14 m in length, is now the second largest known spinosaurid and one of the biggest known theropods, maybe even bigger than Tyrannosaurus or Giganotosaurus. However, some paleontologists now think Oxalaia is simply a Brazilian specimen of Spinosaurus.
Double-Sail: Ichthyovenator
- Even newer than that is 2012's Ichthyovenator, a double-sailed Spinosaurus relative from Laos, about the size of Baryonyx. The discontinuity of its sail was upon the pelvis. Despite its name (literally "fish hunter"), neither the skull nor any other material that would indicate its diet are known. The few tail vertebrae found of Ichthyovenator indicate that at about half of its tail had long neural spines as well, indicating that it was partially flattened and paddle-like (whereas for Spinosaurus it was discovered in 2020 that the entire length of the tail had this adaptation), implying that while more primitive than Spinosaurus it was also highly adapted for swimming. Recently, it was hypothesized that even Spinosaurus had a double-sail like Ichthyovenator. Siamosaurus and Ichthyovenator are among the rare Asian dinosaurs found in the South-East of this continent (precisely in Indochina): another is Siamotyrannus — so-called because it was initially believed a kind of tyrannosaur, this Thai theropod is now classified as an allosauroid. In 2010, a comparative analysis of oxygen isotope ratios was conducted using teeth and bone samples taken from Spinosaurus, Baryonyx, Irritator, and Siamosaurus, as well as crocodilians, turtles, and contemporary terrestrial theropods like Carcharodontosaurus. The study found that spinosaurids' ratios were closer to those of crocodilians and turtles, indicating they were semiaquatic to varying degrees, with Siamosaurus possessing the greatest ratio difference from terrestrial theropods (remember, some thought it was a fish!) and Spinosaurus possessing the least difference. The study posited that this semiaquatic behaviour enabled the spinosaurids to avoid directly competing with other theropods for land-based prey and large crocodilians for aquatic prey.
Megalosaurus Relatives
Russian Dinosaur?: Piatnitzkysaurus
- Roughly fifty theropod dinosaurs have once been labeled Megalosaurus at one point. Most have yet to be renamed, due to them being based on isolated teeth & vertebrae that tell us little. Many of the renamed ones have revealed to be totally unrelated animals (Carcharodontosaurus, Dilophosaurus, Erectopus, Majungasaurus, Nuthetes etc.), but some were really cousins of the proper Megalosaurus: the most important is Eustreptospondylus. Among other "modern" megalosauroids, there is one which has received a deceptive name: Piatnitzkysaurus floresi was not discovered in Russia as it seems, but in Argentina. A smallish animal (4-5 m long), it is one of the few dinosaurs known from Jurassic South America (most dinosaurs from this continent are either Triassic or Cretaceous). It shared the habitat with the much larger primitive sauropod Patagosaurus; these two animal were found together in the 1970s and desribed by Jose Bonaparte, the Argentinian paleontologist who named most South American dinos between the 1970s and the 1990s; among the others, Saltasaurus, Carnotaurus, Amargasaurus, Riojasaurus, and the "mouse-lizard" Mussaurus. Piatnitzkysaurus has recently become the prototype of its own group, the piatnitzkysaurids, just placed outside the proper megalosaurians (megalosaurids + spinosaurids); interestingly, the group seems to be limited to the Americas and includes also the South-American Condorraptor and the North-American Marshosaurus.
African Hunter: Afrovenator
- Most megalosaurids belonged to one of two branches: the larger, more robust megalosaurines and the smaller, slenderer afrovenatorines (traditionally "eustreptospondylines", but Eustreptospondylus itself may not belong to the group). The first branch includes Megalosaurus itself, Torvosaurus and former Megalosaurus species Duriavenator ("Dorset hunter"). The second branch is much more diverse & widespread, containing five or six taxa. Afrovenator ("African hunter"), which lent its name to the group, has had an interesting Science Marches On story. When it was named in 1994, it was thought to come from the Early Cretaceous; however, work carried out in 2009 suggests it is far older, instead hailing from the Middle Jurassic. It has also been considered a megalosaur outside megalosaurids + spinosaurids (that is, a non-megalosaurian megalosauroid), a dinosaur closer to allosauroids and birds than to megalosaurs and even an allosauroid itself, but now seems to be a megalosaurid. The afrovenatorines also include the only Asian megalosaurid, Leshansaurus (originally considered a metriacanthosaurid allosauroid). These two, known from fairly good skeletons, are far more complete known than most other afrovenatorines. For example, Piveteausaurus ("Piveteau's reptile") is known only from a Ceratosaurus-like braincase, which has caused much confusion (some thought the entire animal was smaller than a man, while others thought it was actually Eustreptospondylus). The original skeleton of Poekilopleuron ("varying ribs") was lost in World War II, and the remaining specimens are also very fragmentary (in fact, it may even be an allosauroid); former Poekilopleuron species Dubreuillosaurus ("reptile of the Dubreuillo family") is known from a pretty decent skull. Interesting that Poekilopleuron was one of the very first dinosaurs described (before Owen coined the world "Dinosaur"), and that was also used as an early synonym of Allosaurus, just like what happened to "Antrodemus".
The Oxford Megalosaur: Eustreptospondylus
- Eustreptospondylus oxoniensis ("Oxford's well-curved vertebra") was from Middle Jurassic Europe and was more related with Megalosaurus than to Allosaurus. It was smaller-sized than Megalosaurus being 2 m shorter and slenderer, but was once believed a Megalosaurus species. Its well-preserved skeleton is actually from a juvenile: some have suggested it to be the same as the more poorly known Magnosaurus, also a former Megalosaurus species, but it may be more primitive (curiously, both Magnosaurus and Megalosaurus mean "big lizard", but magno- is Latin, megalo- Greek). As two-thirds of the skeleton of Eustreptospondylus is known, compared to about half for Megalosaurus itself, this makes the eustreptospondyl the most well-preserved European large Jurassic theropod. People have long tried to determine its exact affinities: some early workers thought it was an intermediate form between megalosaurs and allosaurs, but since the rise of more thorough analyses, it has consistently come out as a true megalosaur. Interestingly another megalosaur, Streptospondylus, was once considered a crocodile. Although Eustreptospondylus made a major media appearance in Walking with Dinosaurs, it has not made the same pop-cultural impact as other animals introduced in that series. This probably because in its own episode (the one dedicated to sea-reptiles) has only a rather minor role, as the token dinosaur - and the only true dinosaur here. Here, some individuals of Eustreptospondylus hang themselves in an insular world with usually little food available, and one of them is easily captured by surprise by the oversized sea-reptile Liopleurodon at the start of the episode.
Carnotaurus & Ceratosaurus Relatives
"Tyrannosaurs" in the Deep South: Abelisaurus
- The theropods here are not tyrannosaurs and didn’t live in the Deep South, but the definition works well. Even though much more basal than tyrannosaurids, abelisaurids shared with the latter some specializations: robust skulls, long hindlimbs and shortened forelimbs. But most were only 7 m long, much smaller than the largest tyrannosaurids as well as many megalosauroids and allosauroids. Even though some incomplete specimens had already been found before 1985, like Indosaurus, Indosuchus, Genyodectesnote , and Majungasaurus, abelisaurids were recognized as a group only in that year after the contemporary discover of its two prototypes: the unofficial one is the “horned” Carnotaurus sastrei; the official one, Abelisaurus, more precisely Abelisaurus comahuensis. The latter also has long detained the record of the 1st dinosaur in the alphabet list, now occuped by the prosauropod Aardonyx ("Aachenosaurus" was thought a dinosaur but was actually a piece of petrified wood; "Abdallahsaurus" is an informal name for Giraffatitan; Abdarainurus is an Asian titanosaur described in 2020, Abditosaurus a Spanish titanosaur described in 2022). Both from Late Cretaceous Argentina, these dinosaurs didn’t look so similar; Abelisaurus skull was long-snouted and totally horn-lacking, more similar to a miniaturized Giganotosaurus. However, the shape of the orbits, the narrow lower jaw, and other “small” things indicate that it was a close relative of Carnotaurus. Always remember that in systematics external appearance is usually a minor factor, even when coping with modern animals.note Unfortunately, the only thing we know from Abelisaurus is just the skull. Just one year after were found in Argentina the even scantier remains of the third abelisaurid recognized as such, Xenotarsosaurus ("strange-footed lizard").
An Unexpected Diversity
- But other relatives found in more recent years are much more known: for example, Aucasaurus (portrayed in Dinosaur Planet). Discovered in the 2000s also in Late Cretaceous Argentina, Aucasaurus was one of the smallest members of the family (only 5 m long). Despite not showing neither horns nor a shortened skull, it was one of the closest relatives of Carnotaurus, and, like the latter, had a strange look: forelimbs even more reduced than Carnotaurus itself, tiny stubs without any digits. The year 2002 saw the discovery of Ilokelesia ("meat reptile"), another South American abelisaurid (although it was originally considered a more primitive ceratosaur). In paleontology, it is all too common for creatures to be based on poor remains, which do little to set them apart from related forms. When more complete specimens are uncovered, or when the known bones are restudied, strange features may come to light. Such was the case with abelisaurid bones uncovered in a dynamite explosion in 2004. Initial study of these bones suggested their owner was similar to other abelisaurs, if different enough to warrant a genus of its own: Ekrixinatosaurus ("explosion-born reptile"). A 2011 reexamination suggests that it was far larger than previously estimated, at 11 meters in length. This makes it larger than most tyrannosaurs, and by far the largest of the abelisaurs.
Emigrating in Europe
- Most abelisaurids were Late Cretaceous and have been found in South America, but remains have been found in most southern continents (once one landmass, Gondwanaland). In the same period, tyrannosaurids roamed Laurasia (the northern landmass). However, Tarascosaurus (also portrayed in Dinosaur Planet) and at least three other abelisaurs (Betasuchus, Genusaurus, and Arcovenator) managed to reach Europe, more precisely France and the Netherlands. Europe was at the time isolated to the remaining Laurasia: due to lacking of competition from the more evolved tyrannosaurids (which were exclusive to Asia and North-America and absent in Europe), these four were able to survive and become the top predators of Late Cretaceous European islands, but not the famous Hateg island of Romania — here the role was assumed by a giant pterosaur, Hatzegopteryx. While Genusaurus and Tarascosaurus are primitive abelisaurids, Arcovenator seems to be most closely related to forms from Madagascar and India. Betasuchus (the "Beta crocodile") was originally thought to be another species of Megalosaurus and later an ornithomimosaur because of the slenderness of its only remain (a femur).
Strange Heads
- Many abelisaurids showed some kind of ornamentation on their skull, though none had the "bovine" horn of a Carnotaurus. Majungasaurus is an excellent example of this. Interestingly, the majungasaur seems to be closely related to Indian abelisaurs like Rajasaurus & Indosaurus, suggesting that these areas were connected at one point. Rajasaurus ("Raja lizard") is today the most well-known Indian abelisaur, and is notable for its unusually robust built compared with the prototypical Carnotaurus. Also related with Majungasaurus was Rugops ("wrinkled face"); known only from a skull, it nonetheless lived alongside Spinosaurus in Cretaceous Northern Africa. Dandakosaurus lived in Jurassic India, and according to some was a basal ceratosaur, like Ceratosaurus and Genyodectes.
How Did They Evolve?
- Ever since they were recognized as a group, the abelisaurids have posed many problems for paleontologists. Arguably the biggest of these was their relationship to other theropods. As noted before, they show some similarities to tyrannosauroids — indeed, the abelisaur Indosuchus (deceptively meaning "Indian croc", not to be confused with Indosaurus above) was once considered a tyrannosaur, and the mysterious large theropod Labocania (one of the few dinosaurs described in Mexico) is similar to both groups as well as the allosaurs. It was also briefly proposed that abelisaurs were late megalosaurids. However, since at least The '90s or so, they have been found to be ceratosaurs close to the typically much smaller noasaurids. With one mystery solved, however, another arose: when & where did the earliest abelisaurids live, and what did they look like? This question went unanswered for nearly twenty years. In 2012, the paleontological community apparently received the long-awaited answer in the form of Eoabelisaurus ("dawn Abelisaurus"). Hailing from the Middle Jurassic of Argentina, its arms were longer than those of the more advanced abelisaurids, but still shorter than those of the tyrannosaurids. However, science may have marched on for this fellow, as a 2013 analysis suggests that it is not a true abelisaurid, but a primitive relative of abelisaurids & noasaurids.
Dilophosaurus Relatives
Even Palaeontologists have Fun!
- Paleontologists are not necessarily those nerdy people one could believe. Some do fit more in the Adventurer Archaeologist and Badass Bookworm tropes - think about the famed Australopithecus specimen nicknamed Lucy; the cowboy-looking Bob Bakker; the “Bone Wars” fought by two arch enemies…. and above all, Roy Chapman Andrews. And yes, paleontologists do consume pop-cultural products just like all the other people. In the 1990s, even the most skeptical people were forced to change their idea about, in front of these two new-discovered theropods: Cryolophosaurus and Gojirasaurus. Because the uniquely curly shape of its crest, the former was initially named "Elvisaurus"; the latter has been named after “Gojira”, which is the Japanese name of Godzilla. And since Rule of Cool indisputably dominates every time dinosaurs are involved... some paleo-artists have been giving to our Godzillasaur unlikely features such as prominent/raised scutes along its back, just to make it look like its namesake! Talking more seriously, these two theropods are interesting because, along with Dilophosaurus and other less-known animals such as Halticosaurus (found in Germany and known since the start of the XX century from fragmentary remains), Liliensternus (also discovered in Germany, and originally believed an Halticosaurus species), Sarcosaurus (from England, whose name means "meat-eating lizard", the same meaning of the popular word "carnosaur", but carno- is Latin, sarco- is Greek), and still others like Dracovenator ("hunting dragon", found in South Africa), Saltriovenator (discovered in Italy and initially believed the first tetanuran), and Zupaysaurus (from Argentina, until recently the last member of the dinosaur's alphabetical list: since year 2017 has been the ankylosaur Zuul), they are among the earliest large-sized carnivores.
One of the Coolest Dinosaurs: Cryolophosaurus
- Cryolophosaurus means “crested lizard from ice”; this is because it was the third dinosaur found in Antarctica, and the first one named, in 1993. But wait, it has not been found enclosed in ice: even though it is cool to think, this is an impossible thing in Real Life. Not counting ice had formed on Antarctica only after the Cretaceous mass-extinction, bones cannot turn into stone when surrounded by solid water… Antarctic dinosaurs have been found encased in rocks like everywhere in the world, in the rare ice-free portions of Antarctica at its extreme “north”. Cryolophosaurus was an Early Jurassic theropod 5-6 m long, which (along with the Chinese Sinosaurus, "lizard from China") could be a very primitive tetanuran — some thought these two may be closer to Dilophosaurus, but this is questionable.
Named after a Kaiju: Gojirasaurus
- Found in Texas in 1997, Gojirasaurus was an ever more primitive theropod from Triassic: 15 ft long, was several times heavier than most carnivorous dinosaur from Triassic such as Coelophysis and Procompsognathus. Thus, it has received the same treatment of the “younger” Dilophosaurus, hailed as “the first big-sized meat-eating dino of North America" — even though the celebration of Gojirasaurus is more correct than the dilophosaur's one for obvious chronological reasons. Despite the interest surrounding Gojirasaurus, its look is quite inconspicuous, similar to a robust Coelophysis and lacking any known cranial crest — not exactly a Kaiju. Then, other similar theropods were already known before the description of the gojirasaur; for example, the aforementioned Halticosaurus from Late Triassic Europe has been known since 1908, and was just as big. Liliensternus from the same habitat was also of similar size. The latter has been known since 1934, but classified as Halticosaurus liliensterni before 1984. As the second word of a scientific name usually doesn't change when the first one does, the resulting full scientific name of this dinosaur has become Liliensternus liliensterni.
