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Useful Notes: Prehistoric Life - Large Theropods
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 

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 Eighties) plus Carnotaurus & Giganotosaurus that have become common since The Nineties (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 expecially common the "small" tyrannosaur Albertosaurus — or alternatively Gorgosaurus (mainly in older paleo-art) and Daspletosaurus (mainly in the newer one). Though less-frequent, the sail-backed Acrocanthosaurus can appear in Early Cretaceous reconstructions. 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 is for the Jurassic ones. Among the African ones, the allosauroid Carcharodontosaurus and the spinosaurid Suchomimus have become common since the 1990s.


The Myth's Twin: Tarbosaurus

Let’s start our long trip among non-stock dinosaurs with Tarbosaurus. If you want to describe it, don’t worry, it’s a simple thing: just say it was the Asian twin of T. rex, and you’ve given the idea.

To be more accurate, Tarbosaurus was slightly smaller than Tyrannosaurus, but shared the same familiar body-shape, with large head, huge teeth, short neck, tiny forelimbs with only two functional digits, and whatnot. Those forelimbs were even smaller than those of T. rex, sometimes cited as “the smallest arms in the dinosaur world” - even though the “horned” theropod Carnotaurus had even more reduced arms, as did the weird alvarezsaurids and many flightless birds. Obviously, Tarbosaurus shows up in books and documentaries as the king of the predators in its habitat, Late Cretaceous Asia, just like T. rex in North America. In fact, these two dinosaurs are so similar that some scientists have suggested that Tarbosaurus is another species of the genus Tyrannosaurus, but new studies seem to disagree. Tarbosaurus may be closest to Zhuchengtyrannus, an Asian tyrannosaur named in 2011. While the coolly-named "Jenghizkhan" (from the Mongolian Gengis Khan), described in 1995, is today just an invalid synonym of Tarbosaurus.

Tarbosaurus has been first discovered in 1955 in Mongolia, more precisely in the Gobi Desert. Mongolia, a sparsely populated Asian country bordered by Russia and China, has always had a major role in the brief history of paleontology: despite being much smaller than China, Canada or the USA, it has given us the same number of fossils of the latter, almost all from Late Cretaceous. Among them, most of the classic Asian dinosaurs: from the famed Protoceratops/Velociraptor battle to the first Mesozoic dinosaur eggs ever discovered, from Oviraptor to the huge forelimbs of Deinocheirus, from Gallimimus to the scythe-claws of Therizinosaurus. And Tarbosaurus as well.

Interesting that the succession of geological periods (Cretaceous-Jurassic-Triassic) of the Mesozoic era, have also a distribution in latitude which is amazingly specular in Asia and in North America. In both continents, the Cretaceous terrains are those in the northern part of the range (Alberta, Canada/Montana, USA, and Mongolia/Inner Mongolia/Northern China); the Triassic terrains are the most southern (Arizona/New Mexico, USA, and the province of Yunnan, southern China); while the Jurassic one were in the middle (Utah/Colorado/Wyoming, and the province of Szechuan, central China). Also note that most North American dinosaurs have been discovered in western USA and western Canada (not in the coastal region however, but only in the Mountains and Plains); while the Asian dinosaurs are concentrated in only two countries, Mongolia and China, both in the Far East. Some of the most astonishing recent discoveries about dinosaurs just come from China, especially the northern province of Liaoning (see “Birdlike theropods”).


Smaller Tyrants: Albertosaurus

Albertosaurus is the most abundant tyrannosaur in fossil record, and also the second big-sized theropod by wealth of fossil material, just after the unbeatable Allosaurus. And yet, Albertosaurus has not gained much attention in films and comics as Tyrannosaurus - tyrannosaurids are so similar to each other that if one appears in cinema, people will always call it T. rex. To compensate, Albertosaurus is a very common sight in many paleo-books, just as common as several Stock Theropods.

Naturally, it is portrayed as the superpredator of its time, North America 80-75 million years ago, 10 million years before T. rex. The menu of an Albertosaurus was probably not monotonous; several kinds of herbivores roamed North American plains at the time, from ceratopsians to hadrosaurs, from the armored ankylosaurs to small swift "hypsilophodonts" and ornithomimids. Even though tyrannosaurids are classically shown battling some powerful prey, they more probably hunted young individuals more often, to avoid the risk of fatal injuries or consequent infections.

Compared with the legendary Tyrannosaurus rex, Albertosaurus was like a leopard compared with a lion; smaller (25 ft long against the 40 ft of T. rex), it was also more slender, with longer, thinner jaws, smaller teeth, and more agile legs apt to higher top speeds than Tyrannosaurus. Even the herbivores which shared their world were conformed to these predators; those which lived alongside T. rex were bigger, slower and more powerful than those living with Albertosaurus.

Albertosaurus was also the first dinosaur ever discovered in Canada, at the end of the XIX century, but was named only in 1905 (incidentally, the same year as Tyrannosaurus) after the Canadian province of Alberta, where most of the abundant Canadian dinos have been discovered. Albertosaurus has also contributed indirectly to the popular image of tyrannosaurs. The forelimbs of Albertosaurus have been known since its very first find, while those of T. rex were first discovered only in the 1990s; for almost a century the well-known two-fingered hands of "rex" have been modeled upon those of Albertosaurus, debunking at the time the old pop-cultural Hand Wave about portraying three-fingered tyrannosaurs. note 


Smaller Tyrants 2: Gorgosaurus & Daspletosaurus

Discovered in 1914, Gorgosaurus is another North American tyrannosaurid which was long considered a distinct genus compared to Albertosaurus. Then, in the 1970s, Canadian paleontologist Dale Russell found the two animals so similar they had to been put under a single name: since the first created name always has priority, so was Albertosaurus. Only in recent years, scientists changed idea again separating "Gorgosaurus" from "Albertosaurus" note . There has also been a curious sequence in pop-portraits: Gorgosaurus has long been the most depicted non-"rex" tyrannosaur in classic paleo-art and old books; but its long-lasting synonimization with Albertosaurus has definitively harmed its relevance, and today Albertosaurus is the new prototypical “small” North American tyrannosaur.

In the 1970s, a third North American tyrannosaur was recognized as distinct: Daspletosaurus. The same size of the other two and living in the same epoch, Daspletosaurus was actually more similar to T. rex than to Albertosaurus in anatomy. Many scientists think the more agile Albertosaurus/Gorgosaurus specialized on relatively easier preys such as hadrosaurs, young ceratopsians, troodonts or ornithomimids, while the more powerfully-built Daspletosaurus hunted “armored” herbivores like adult ceratopsians and ankylosaurs, and possibly Albertosaurus and Gorgosaurus themselves! Other North American tyrannosaurids have been named in recent years, 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", the oldest true tyrannosaurid) in 2013. On the other hand, "Dinotyrannus" ("terrible tyrant") and "Stygivenator" ("Hunter from the Death-River"), both described in 1995, are today regarded as proper T. rex specimens.


Not exactly T. rexes: Dryptosaurus & Eotyrannus

Not all tyrannosauroids were tyrannosaurids, remember this. Basal tyrannosauroids were often very different animals: smaller, more slender, 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, 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. After the discovery of North American forms like Appalachiosaurus (guess where this one has been discovered), Dryptosaurus has consistently been placed in the tyrannosauroid realm. However, it was more slender than tyrannosaurids, and we don’t know if it had two- or three-fingered hands (they have never been found). 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. But the main distinction of Dryptosaurus is to be the first dinosaur ever depicted by the famous paleo-artist Charles Knight (when the dinosaur was still called “Laelaps”), with two individuals fighting each other.

Small tyrannosauroids are also known from Asia: Alioramus (lit. "the other branch" [of the tyrannosaurs]) was once thought the juvenile of Tarbosaurus, but has revealed a truly small tyrannosaurid (or another kind of tyrannosauroid), whose untyrannosaurian skull shows small hornlets along its muzzle. Another, Alectrosaurus (perhaps the first-found large theropod in Asia), 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.

Other small-sized tyrannosauroids are classified as tyrannosaurids, but many are (or could be) simple juveniles of other well-known tyrannosaurids: for example, "Aublysodon" (described as early as the 1860s) is known mainly from teeth found both in North America and in Asia, and it may be just represent juveniles from known tyrannosaurids. In year 1988, Bob Bakker described Nanotyrannus (“dwarf tyrant”); 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. Among 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.

All 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), 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.

In 2012, a new very important find about tyrannosauroids came to light: Yutyrannus (appropriately "feathered tyrant") from the Early Cretaceous of China. From the same Liaoning site in which other much smaller feathered dinosaurs have been found, Yutyrannus was much bigger than them (30-foot long); this suggested that even large true tyrannosaurids were feathered. Other basal tyrannosauroids or possible basal tyrannosauroids have been discovered in Northern continents: among them, the European Aviatyrannis and Juratyrant were named with a different suffix than -tyrannus. Others are listed in the “small/birdlike theropods” sections.


Missed Moment of Glory: Carcharodontosaurus

In 1995, an unexpected find deeply shook the paleontological world as well as the dino-fandom. The obscure-at-the-time Carcharodontosaurus has revealed not to be a midsized, unclassifiable theropod as always thought (it was originally considered a megalosaur, but others thought it was an allosaur, an intermediate form between allosaurs & tyrannosaurs or even a completely unique theropod that returned to the seas). It was a much more Bad Ass animal, whose name “great white shark lizard” has revealed stunningly apt. A predatory dinosaur even bigger than T. rex!

Obviously, popular media ballyhooed the discover a lot… totally forgetting that some other giant theropods were already Tyrannosaurus rex contestants for the “biggest” title much before 1995! Spinosaurus makes the most striking example, but there is also the obscure Epanterias (almost certainly just an overgrown Allosaurus); not to mention Deinocheirus and Therizinosaurus (see “Bird-like theropods”). But the glory of Carcharodontosaurus didn’t last a long time; merely one year later, it was surpassed by the just-discovered, almost-identical, only a bit bigger, and now stock, Giganotosaurus. Our “white shark dino” was a quite unlucky dinosaur, really.

However, in the 2000s, Spinosaurus has done justice to "Carcharo", taking in turn the popularity of Giganotosaurus out thanks to Jurassic Park III. The awesome thing is, in Real Life Carcharodontosaurus and Spinosaurus, living together in Cretaceous Africa where today is Sahara, maybe contended with each other the “top-predator” niche; while Carcharodontosaurus was better-weaponed with huge jaws, Spinosaurus was more enormous-bodied and could have been even twice its weight. They can be considered the “tiger” and the “grizzly bear” of their time respectively, and it’s not a thing to exclude that Spinosaurus sometimes chased away Carcharodontosaurus from their kills like modern bears do with big cats when they live side-by-side.

As a consolation prize, our Carcharodontosaurus has been chosen as the official namesake of its own family, a recently-identified group of gigantic Cretaceous allosauroids which were also among the most evolved carnosaurs: carcharodontosaurids. Other than Carcharodontosaurus, Giganotosaurus & Acrocanthosaurus (we'll get to that one in a few), they include animals discovered in the 2000s: among these, Mapusaurus

Found only in 2006 in Argentina, it was the closest relative of Giganotosaurus, and may have been its descendant in Real Life. Just as big as “Giga”, Mapusaurus was almost identical to it and to Carcharodontosaurus, with huge skull filled with crests and protuberances, and the usual powerful three-fingered hands of all allosauroids. However, the most interesting thing is that its fossils seem to show proof of gregarious behavior. Even though this doesn’t automatically indicate “pack hunting”, many have now fun to imagine awesome scenarios, with pack of Mapusaurus killing together the immense sauropods of the time like Argentinosaurus. This behaviour was also speculatively attributed to Giganotosaurus in the “Land of Giants” episode of the WWD series… four years before Mapusaurus was discovered!

Among other carcharodontosaurids, Tyrannotitan is worthy of note because of its name “titanic tyrant”, the most "rex"-like of all theropods, even though its owner, being an allosauroid, was not so closely related with T. rex. An early Cretaceous animal, it was more primitive than the examples above, but still with a fully carcharodontosaurian skull. Even more primitive are Sauroniops ("eye of Sauron"), Eocarcharia ("dawn carcharodontosaurid") and Veterupristisaurus ("old shark reptile"), all from Africa.

Another less-impressive but still formidable theropod was found in Africa alongside Carcharodontosaurus one year later: Deltadromeus. 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, 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 Maker) 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).


Sailbacks. Or maybe not: Acrocanthosaurus & Concavenator

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”. However, its “sail” was very different; only one foot tall, it extended from the neck to the tail-tip, while that of Spinosaurus was far higher but limited to the back. Actually, the sail of Acrocanthosaurus could have been buried in flesh in the living animal, making it looking even bigger when seen from the side, just like what could have been for Spinosaurus. Furthermore, Acrocanthosaurus was not a spinosaur relative at all (even though it and other sailbacks were classified as such in the past just because of their sails): actually was an allosauroid, traditionally classified as being between Giganotosaurus and Allosaurus phylogenetically. However, the most recent analyses support carcharodontosaurid affinities, making it closer to Giganotosaurus.

Acrocanthosaurus lived in Early Cretaceous North America, rather between Allosaurus and Tyrannosaurus in the time scale. Apart from the “sail”, it was similar to a robust Allosaurus in shape, and with its 12 m long body was as big as Tyrannosaurus rex, albeit of lighter build. One could even say Acrocanthosaurus combined the best powers of the four most popular giant theropods. The size of "rex", the overall robustness of “Giga”, the powerful three-clawed forelimbs of “Allo”, and a crested back like “Spino”. And yet, have you sometimes seen this dinosaur outside dino-books (apart from the pseudo-docu Monsters Resurrected)? Things get even worse if you think Acrocanthosaurus has been known since the 1940s from rather complete remains, was the top-predator of Early Cretaceous North America, and shared the same habitat with another famous (but much smaller) “killer dinosaur”, Deinonychus. However, Bob Bakker’s scientific novel Raptor Red does justice to Acrocanthosaurus, portraying it as the great predator of the world in which Utahraptor are the main characters.

Other two less-known “sailbacks” of smaller size and with a even less-evident crest were Becklespinax and Metriacanthosaurus, both European. Once placed in the “Megalosaurus wastebasket”, both are now considered allosauroids of some sort. Becklespinax was once called “Altispinax” (that name properly belongs to an isolated tooth); curiously, the word "altispinax" still survives scientifically as the specific name of this genus (the full scientific name of this dinosaur is Becklespinax altispinax). It's worth noting that Becklespinax'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, even though this detail has passed rather unnoticed. However, the name probably was referred to another better-known large theropod, the Chinese Yangchuanosaurus (which was by Gregory Paul synonimized with Metriacanthosaurus in 1988).

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. It not only had a small “hump” on its hips made by elongated neural spines; its arms also 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.


Allosaurs vs Tyrannosaurs: "Epanterias" & Saurophaganax

One of the reasons behind the Poor Man's Substitute role Allosaurus has played in pop-culture is surely 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 in its own genus, Saurophaganax. 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).

Still another close kin has been described as a really huge animal, 12 m long, around the size of a T. rex: "Epanterias". 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 T. rex, "Giga", and "Spino" for the “King of Dinosaurs” title.


Imitators and forgers: Suchomimus & Irritator

No other group of large 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. In year 1998, a third spinosaurid was discovered in Early Cretaceous North Africa: Suchomimus, “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 small bird-like coelurosaur. Very similar to Baryonyx (indeed, it and/or its fragmentary neighbor Cristatusaurus ["crested reptile"] may actually be species of that dinosaur), Suchomimus was probably a fishing specialist as well, but was distinct by spotting a noticeable spinal ridge analogue to Spinosaurus, though far shorter. Since its discovery this dinosaur has gained much consideration: as an example, both Suchomimus and Baryonyx are cited in Jurassic Park III, when the little boy asks Alan Grant about spinosaurids. There is also a debate among dino-fans about the true identity of Rudy (the villain of Ice Age 3), and many think is a Suchomimus; actually he's a Baryonyx, but he’s so modified that correct identification is hard without asking the Word of God.

Another less-known spinosaurid has a name which reveals an astounding backstory: Irritator. 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”. Irritator probably includes Angaturama, another spinosaurid also discovered in Brazil (indeed, 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; 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. Even newer than that is 2012's Ichthyovenator a double-sailed Baryonyx relative from Laos. Despite its name (literally "fish hunter"), neither the skull nor any other material that would indicate its diet are known. 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.


The modern megalosaurs: Eustreptospondylus

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 and Majungasaurus), but others were really cousins of the proper Megalosaurus. The most important is Eustreptospondylus.

From Middle Jurassic Europe like Megalosaurus but smaller-sized (being 2 m shorter and more slender), 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)note . As the most well-preserved European large Jurassic theropod (two-thirds of the skeleton is known, compared to about half for Megalosaurus itself), 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. Eustreptospondylus was also chosen as the go-to dinosaur in the episode of the 1999 docu Walking with Dinosaurs dedicated to marine reptiles… somehow living in the Late instead of the Middle Jurassic. Here our megalosaur is depicted as an inoffensive scavenger which has to hang on its world made by small islands, eating the occasional carrion the sea brings on the shore. But the most remembered scene is at the beginning: a specimen of Eustreptospondylus apparently described as “the most fearsome predator of the Jurassic”… only to be eaten alive by the gigantic… erhm… OVERSIZED marine reptile Liopleurodon.


The modern megalosaurs 2: Piatnitzkysaurus & Torvosaurus

Among other "modern" megalosauroids, there is one which has received a deceptive name: Piatnitzkysaurus 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.

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 (see below) 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", see Stock Dinosaurs).

The largest megalosaurid(s?), as well as the one most closely related to Megalosaurus itself, has been found in North America and maybe Europe: Torvosaurus (“savage lizard”, not to be confused with the tyrannosaurid Tarbosaurus) and its probable synonyms "Edmarka rex" (not that rex) and "Brontoraptor" (the latter name has yet to be officially published, and is therefore not italicized). 10 m long or more, the same size as Allosaurus but more powerfully-built, it shared the same habitat with Allosaurus and sometimes took some prey out of it. However, the fossil record seems to show that the giant megalosaurids didn’t make true rivals for allosaurs: they were much, much rarer than the latter, and this leads to speculation that allosauroids were more efficient hunters, and finally replaced most megalosauroids (the spinosaurids may have survived due to occupying a different ecological niche); however, a supposed megalosaur has been found in the Late Cretaceous of Antarctica.


Hook Hands and Phylogeny Hell: Megaraptor

Several theropods have evolved one enormous claw on their hands/feet which vividly contrast with the smaller ones: just think about Baryonyx and Deinonychus, whose names are just references to this condition. But the following one makes the Up to Eleven example: Megaraptor.

Discovered in the late 1990s and initially thought to be a large dromaeosaurid (hence its name), this smallish South American Late Cretaceous theropod was variably classified in the past, from a small spinosaurid to a large noasaurid – all families characterized by some sort of oversized claws. Currently, a possible clading puts Megaraptor and kin in with the tyrannosauroids (ie: T.rex, Albertosaurus and all the relatives thereof), albeit one of the more basal of the group. Indeed, an one-foot-long claw was the first discovered Megaraptor fossil; and, wrongly, palaeontologists put on its foot. But then a complete hand (including the same enormous claw of the original specimen) were 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 much smaller theropod, this means its claw could be the biggest among all dinosaurs in respect to the overall body size. How Megaraptor used those impressive 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 literal hooks (to hold prey close and enable the creature to inflict more wounds with it's jaws) or slashing tools (cutting flesh, but not disemboweling).

Late-Survivors: Neovenator & Aerosteon

Since 2009 or so, Megaraptor is classified as an allosauroid, more precisely as a very specialized member of the family Neovenatoridae (here called "megaraptorans").note 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 (and the aforementioned Valdoraptor) 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....or is it?

The recent discovery of a Megaraptor skull lends credence to a idea proposed by F.E Novas...that megaraptorans were not allosauroids, but tyrannosauroids.


Exotic names in China...: Yangchuanosaurus & Shaochilong

Many allosauroids have been found in Asia, notably in China. This is evident if you read their names: just as an example, Yangchuanosaurus. This one was basically the “Chinese Allosaurus”: only a bit smaller and with a shorter, taller skull with the usual Allosaurus-like crests on the snout; robust, three-fingered forelimbs, and perhaps a small ridge on its back. It was probably the top-predator of Late Jurassic Asia (155-145 million years ago), and lived alongside Mamenchisaurus “the Chinese Brontosaur” and Tuojiangosaurus “the Chinese Stegosaur”. 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, the first large theropod 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 piatnitzkysaurid 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 more famous 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.


...except two: Monolophosaurus & Gasosaurus

Another reasonably complete theropod from China is not an allosauroid (though it was once considered one) but a very primitive tetanuran: Monolophosaurus (“one-crested lizard”), so-called because of its single cranial crest vaguely similar to each branch of the double-crest of the unrelated Dilophosaurus, but shorted and more robust. Named in 1994 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.

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 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".


Tyrannosaurs in the Deep South: Abelisaurus & Majungasaurus

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 Majungasaurus, Indosuchus, and Genyodectes note ), 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; the official one, Abelisaurus. 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. 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. The year 2002 saw the discovery of Ilokelesia ("meat reptile"), another South American abelisaurid (although it was originally considered a more primitive ceratosaur).

But other relatives found in more recent years are much more known: for example, Aucasaurus. 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.

In paleontology, it is all to common for creatures to be based on poor remains, which do little to set them apart from related forms. When more compete 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.

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): hence “tyrannosaurs in the Deep South”. However, Tarascosaurus (portrayed in Dinosaur Planet) and at least three other abelisaurs (Betasuchus, Genusaurus, and Arcovenator) managed to reach Europe, which was at the time isolated to the remaining Laurasia: due to lacking of competition from the more evolved tyrannosaurids (which were absent in Europe), these four were able to survive and become the top predators of Late Cretaceous European islands. 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).

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. Found in Madagascar, it was not bigger than Carnotaurus and shared a similar overall look, but with shorter legs and one single horn atop of its head. This dinosaur has had a curious Science Marches On story: initially only its blunt horn was known, and because of its shape was thought to be the domehead of a tiny pachycephalosaur called “Majungatholus”. Then, this name was applied to the carnivore until few years ago; for example, in Jurassic Fight Club this theropod appears named “Majungatholus”. Here, two adults are shown cannibalizing a young of their own species; this was based upon some marks of teeth on the bones of young Majungasaurus specimens, whose shape match the teeth of adult Majungasaurus.

Interestingly, Majungasaurus 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.

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 Nineties 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.


Even palaeontologists have fun: Cryolophosaurus & Gojirasaurus

Paleontologists are not necessarily those nerdy people one could believe. Many 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 archenemical guys…. 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 sceptical 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 undisputly 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, Liliensternus, Sarcosaurus, and Zupaysaurus, they are among the earliest large-sized carnivores. Cryolophosaurus means “crested lizard from ice”; this because 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 is cool to think, this is an impossible thing in Real Life. Not counting ice has formed on Antarctica only after the Cretaceous mass-extinction, bones cannot turn in 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) could be a very primitive tetanuran — some thought these two may be closer to Dilophosaurus, but this is questionable. 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. Thus, it has received the same treatment of the “younger” Dilophosaurus, hailed as “the first big-sized meat-eating dino (even though the celebration of Gojirasaurus is more correct than the dilophosaur's one for obvious chronological reasons) . Despite all the popular interest surrounding Gojirasaurus, its look is quite incospicuous, similar to a robust Coelophysis and lacking any crest. Then, other similar theropods were already known before the description of the gojirasaur; for example, Liliensternus from Late Triassic Europe 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.


An only-historical relevance: Deinodon & Teratosaurus

We can also mention two virtually-unknown animals which have had nonetheless a great relevance in the past, but have lost it due to Science Marches On. Teratosaurus: (“monster lizard”) lived in Europe during the Triassic period. Discovered as early as the middle of the XIX century, it was 6 m long, and has long detained the record of “the first giant meat-eating dinosaur”. In old books, Teratosaurus was portrayed as a generic-looking “carnosaur” which hunted the neighboring prosauropod Plateosaurus. Then, in the mid 1980s, it was discovered that Teratosaurus was actually reconstructed upon very fragmentary remains mixed with bones belonging to Plateosaurus: these new studies showed it was not even a dinosaur, but a four-legged, non-dinosaurian archosaur related to Postosuchus.note 

The other example is "Deinodon" (“terrible tooth”). Few people today are aware of this pratically unknown dinosaur, described only from teeth. Nonetheless, “Deinodon” 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. 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.
Prehistoric Life - DinosaursTropesaurus IndexPrehistoric Life - Birdlike Theropods
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