Big Carnivores

Have you ever encountered a big predatory dinosaur in a book, museum, movie, etc., and ventured to identify said dinosaur as a Tyrannosaurus, only to be informed by some dino-obsessed little know-it-all (like your humble author) that what you thought was good old T. rex is actually Carcharodontosaurus saharicus, or Tarbosaurus baatar, or some other unheard of prehistoric beast? When did paleontologists name so many other dinosaurs? A lot of us grow up learning only the ‘fundamental’ dinosaurs of kid’s books and Spielberg movies. You have Brontosaurus as the long-necked one, Triceratops as the horned one, Stegosaurus as the weird spikey one, throw in some generic hadrosaurs bathing in the background for scenery, and T. rex as the big nasty bad guy.

I would probably blame the ‘quiet years’ of paleontology from the 30’s to the 70’s for instilling pop culture with this fundamental core of dinosaur diversity. But we’re now living in a true golden age for paleontology, and new dinosaurs are being named at an exponential rate, so quickly in fact that paleontologists are struggling to keep up with each other’s work. This includes a whole roster of big, scary predators that give Tyrannosaurus a run for its money in the size department. Now as we discussed in the ‘Biggest Dinosaur’ article, one of the things paleontologists spend the least amount of their time and effort on is ranking dinosaurs from biggest to smallest. There’s a whole list of reasons why this is, and I like to think of the size of animal species as more of a spectrum than a clear-cut ranking system. All the same, the diversity of big predatory dinosaurs out there is fascinating, so let’s take a look at a few of them.

In the pre-Tyrannosaurus days (yes, there was such a time), there was a very different set of big predators that haunted the imaginations of the public. The first dinosaur to receive a scientific description, as a matter of fact, was a medium-sized yet fragmentary theropod from England called Megalosaurus, a creature that stalked the dark recesses of Victorian minds before the word ‘dinosaur’ was even coined (Buckland, 1824). With the opening of late Jurassic quarries in the American frontier, other large predator bones were uncovered in the late 19th century. The best known of these is Allosaurus, described in 1877 by the J. D. Rockefeller of paleontology himself, Othniel Charles Marsh (Marsh, 1877). By the standards of some giants, Allosaurus was a little more modest in size, averaging still a respectable 30 feet in length or so. With several good specimens of this dinosaur known, Allosaurus became fairly well known as the ‘definitive’ large theropod around the turn of the century, with skeletal mounts in several museums around the world, and even starring as a minor villain in Arthur Conan Doyle’s The Lost World. With its big triangular skull, large hook-like claws, and prominent orbital horns, Allosaurus is still one of the most recognizable non-Tyrannosaurus theropods. Allosaurus belongs to a lineage of advanced predatory dinosaurs called the carnosaurs, sister-group to the more birdlike coelurosaurs, and it’s in the Carnosauria that many giant predators are found.

Within the allosaur family itself, there’s a similar yet even larger creature from western North America called Saurophaganax, which clocks in at one of the longest theropods at about 35-45 feet in length (Chure, 1995). Close cousins to this family are the carcharodontosaurs, a group of true giants from the Cretaceous that would have been a sight to behold in life. These dinosaurs tend to have big, triangular-shaped skulls with bladelike teeth. All of them rivalled or exceeded Tyrannosaurus in length, with some species growing to around 45 feet or more. However, these beasts were lightly built for their size, with some less than half the weight of the biggest known Tyrannosaurus. Their jaws may have worked like giant meat-shears, useful for slicing a hefty chunk out of the large herbivores these animals shared their habitats with. Their hunting and killing style would have likely differed from the bone-crushing bite-and-smash method of tyrannosaurs, though they were certainly no less dangerous in their own right.

The carcharodontosaur family gets its name from the dinosaur Carcharodontosaurus of Egypt. This creature’s name translates to ‘shark-toothed reptile’, and like the Great White (Carcharodon carcharias) itself, Carcharodontosaurus had big, serrated, bladelike teeth. The first skeletal material of this dinosaur was described in 1931 by German paleontologist Ernst Stromer, but was tragically destroyed during WWII- and this wasn’t even Stomer’s most tragic loss during those events (Stromer, 1931). Luckily, a fairly complete skull was found in Morocco in the mid 90’s by the leading expert in North African carnivores, Dr. Paul Sereno of Chicago. The massive skull of this dinosaur with its arsenal of teeth is truly stunning.

Carcharodontosaurus had some similar looking relatives from South America that have also bolstered the ranks of giant predators, all of whom were roughly its equal in length, pushing 40-45 feet or so and equivalent to a big elephant or two in weight. Giganotosaurus, the ‘southern giant’, was described in 1995 in Argentina (note that the name is ‘Giga-noto-saurus, not Giganto-saurus), with its close relatives Mapusaurus and Tyrannotitan following it from the same country in the mid 2000’s (Coria & Salgado, 1995)( Coria & Currie, 2006)( Novas et al., (2005). Mid-Cretaceous South America was a land of enormous carnivores with huge triangular skulls and slicing teeth. Until the discovery of these predators, it was believed that the only predatory theropod to achieve gigantic sizes was Tyrannosaurus, but this parade of carnosaurs from the mid 90’s onwards left T. rex fans feeling more than a little insecure. Further down the carcharodontosaur family tree, a massive yet bizzare theropod was found in early Cretaceous rocks from Oklahoma. Described in 1950, this dinosaur had noticeably long vertebral spines forming a sort of ridge or short sail down the back (Stovall & Langston, 1950). The creature was named Acrocanthosaurus, and up until fairly recently had largely flown under the radar in the pop culture dinosaur fandom. Numerous trackways from the American Midwest have been tentatively assigned to Acrocanthosaurus, and one particular one from the Paluxy River in Texas might hint at hunting behaviour, as the theropd tracks follow along a set of sauropod prints (Bird, 1941)(Farlow, 2001). Similar footprints from early Cretaceous rocks of northern British Columbia might have also been left by ‘Acro’, or something like it.

The high-backed giant Acrocanthosaurus with the contemporary Deinonychus. By Nicholas Carter

Further down the theropod tree, branching off before the more birdlike coelurosaurs and carnosaurs, was a group called the megalosauroids, a very diverse clade full of big predators. The megalosauroids themselves are split into two very different families- the megalosaurs and the spinosaurs. The megalosaurs, which included the first known dinosaur Megalosaurus, were mostly medium-sized carnivores from the Jurassic with big, square-shaped skulls. One species though, known as Torvosaurus, is found in late Jurassic rocks from Colorado and Portugal. With deep jaws and short but powerful arms, Torvosaurus managed to coexist with the more common Allosaurus, as well as Saurophaganax and the horned Ceratosaurus. It may have been more of a deep-brush ambush hunter, with Allosaurus living as an open-plains pursuit predator (Bakker & Gary, 2004). Though Torvosaurus wasn’t quite in the same size league as a lot of these other big carnivores, it’s another very neat dinosaur that’s been tragically ignored in media so far.

Sister group to the square-jawed megalosaurs were the bizzare crocodile-headed spinosaurs, named for the largest and easily most famous species of this family, Spinosaurus. This dinosaur is a rare example of a massive theropod that many people nowadays can recognize with little trouble. Spinosaurus was a fairly big mystery to paleontologists for decades. Found and described by Stromer in 1915 from Egypt (Stromer, 1915), what material he had suffered the same fate as the original Carcharodontosaurus fossils- destroyed by bombings during WWII (apparently the director of the museum was a Nazi, Stromer was not, and so his material was not taken to a safe location during the war. Talk about being punished for doing the right thing). Today Stomer is as well known for what he lost as for what he found. Since then paleontologists, including Dr. Sereno, have been trying to figure out what exactly Spinosaurus was, and this dinosaur has morphed in our collective understandings from a fairly ‘generic’ theropod in its initial description (with a its characteristic sail as flair) to the radically slow-slung, stumpy-legged swamp dweller of Nizar Ibrahim and colleagues’ 2014 reassessment after the discovery of more spinosaur fossils (Ibrahim, 2014). This most recent interpretation of the shape of Spinosaurus is still a matter of great contention amongst paleontologists, as are the specifics of its lifestyle, but one thing’s for sure- it was big. Certainly longer than Tyrannosaurus, with some of the largest specimens suggesting a length of nearly 60 feet. This makes it easily the longest predatory dinosaur known to science. But Spinosaurus wasn’t the only member of its family, as other less extreme species have been uncovered in different parts of the world. Some of these, such as the Nigerian Suchomimus and the English Baryonyx, could grow to pretty respectable sizes. While the spinosaurs all had their little quirks (check out the bizzare sail of Ichthyovenator), they’re all distinguishable by their hefty claws and long, narrow jaws full of pointed, conical teeth. These, along with thickened bones and broad toes, have led many paleontologists to suspect that spinosaurs lived in or alongside bodies of water, and specialized in snapping up large fish like big prehistoric herons (Sereno et al., 1998).

I sometimes get asked whether Spinosaurus or T. rex would come out the victor in a fight. Since these species were separated by each other by vast stretches of time and distance, it’s impossible to say. Dinosaurs were not gladiators. By Nicholas Carter

Moving back up the theropod tree, we get to the most derived group of theropods, the coelurosaurs. This is a group of extremes, including some of the largest and smallest predators that ever lived. The most famous of the coelurosaurs would naturally be the tyrannosaurs, and the biggest species in this family is, of course, Tyrannosaurus. T. rex was hyped as the biggest, baddest, most dangerous predator to ever live as soon as the first skeleton of this dinosaur was mounted in New York, and this touting has kept it in the spotlight for over 100 years. Not a bad legacy for something that died 66 million years ago. While Tyrannosaurus was far from the longest predatory dinosaur, at nearly 20 tonnes in some of the biggest specimens, it very well could have been the heaviest (Campione et al., 2014). A close look at the teeth of Tyrannosaurus shows that, while huge (noticeably bigger than in other theropods), they weren’t all that sharp at the tips. It seems as though this dinosaur did not evolve the slicing side-bite strategy of other large predators, and invested instead in big, powerful teeth and jaws, adapted for crushing bone (Gignac & Erickson, 2017). It’s also worth noting that there were many types of tyrannosaurs that came and went throughout the Cretaceous. The relatively primitive Yutyrannus of China, one of the few tyrannosauroids to sport evidence of feathers, was a respectable 25-30 feet long. The advanced tyrannosaurs were split between the sleek, long-legged albertosaurines (including Alberta’s own Gorgosaurus and Albertosaurus, both roughly the same size as Yutyrannus) and the bulkier, powerfully built tyrannosaurines. T. rex is obviously in this subfamily, and is joined by its somewhat smaller cousins including the North American Daspletosaurus, and Asia’s Tarbosaurus and Zhuchengtyrannus, among many others. These dinosaurs picked up as the dominant land predators in the northern hemisphere where the carnosaurs and megalosauroids, mostly extinct by the late Cretaceous, left off.

A highly simplified tree showing the evolution of theropods from small predators to the big, weird forms we know and love. By Nicholas Carter

And finally, we get to what were probably the weirdest big theropods of them all. The closer you get to birds along the coelurosaur clade, the stranger some of the dinosaur families become. Herbivory, for example, is something that begins to be experimented with to great success, and many advanced coelurosaurs lose their teeth in favour of birdlike beaks. One example of this is seen in the ostrich-like ornithomimosaurs, with their long slender necks, sprinting legs, and skulls that, at first blush, look eerily like that of big flightless birds. Most ornithomimosaurs were roughly ostrich-sized as well, and include things like Ornithomimus, Struthiomimus, and Jurassic Park’s own Gallimimus. One species, however, takes things to another level. Deinocheirus of late Cretaceous Mongolia is estimated to be over 30 feet long and 5 tonnes in weight. It’s a truly strange creature too, with long arms ending in big blunt claws (the first part of the creature discovered, earning it its name ‘terrible hand’), wide bulky hips, tall yet irregular vertebral spines forming some sort of hump or sail, and a long, deep skull with a flaring beak making it look like an ornithomimid trying its best to be a duck-billed hadrosaur (Lee et al., 2014).

The holy trinity of weird giant herbivorous theropods of Asia. Left-to-right: Gigantoraptor, Deinocheirus, and Therizinosaurus. By Nicholas Carter

Deinocheirus shared its habitat with another large, unusual herbivorous theropod called Therizinosaurus. Also known from a set of partial forelimbs, Therizinosaurus looked something like a giant sloth crossed with the world’s biggest chicken. Like other (smaller and more complete) members of the therizinosaur family, this pot-bellied, wide-hipped, stumpy-tailed oddity likely had a small, beaked skull with leaf-shaped teeth reminiscent of plant-eating ornithischians. Also from late Cretaceous Gobi rocks is the giant oviraptorosaur called Gigantoraptor. While most of this dinosaur’s relatives were cassowary-sized beaked and crested herbivores, this particular species is estimated to have towered at nearly 13 feet tall and over 25 feet long (Xu et al., 2007). Not terribly impressive compared to some of the other big theropods we’ve looked at, but that’s still a honking big oviraptorosaur!

As far as modern theropods go, outside of Sesame Street, no birds really get to super-sized dimensions anymore. The fossil record has several examples of pretty large flying avians, such as Pelagornis with its 16 foot wingspan. There’s also many cases of big, flightless birds that dwarf the modern ostrich. More famous examples include New Zealand’s giant moa (Dinornis) and the elephant bird of Madagascar (Aepyornis), both of which died out well within the time of modern humans. Other big prehistoric birds worth getting to know include Gastornis of the early Paleogene (often restored as a vicious carnivore but most likely a harmless fruit-eater), the dromornithid “demon ducks” of Australia, and the predatory phorusrhacid “terror birds” of South America. Again, none of these post-Cretaceous theropods come close to the size of the great carnosaurs, spinosaurs, or tyrannosaurs, but they would’ve been wonderful to see in life all the same.

This list could go on and on to encompass the wide variety of medium to large-ish theropods out there. I’ve criminally left out the strange nub-armed, bulldog-faced abeliosaurs, and their horned cousins the ceratosaurs. There’s also the crested dilophosaurs, the enigmatic piatnitzkysaurs, the exotic metriacanthosaurs, and a small handful of dromaeosaurs that rivaled polar bears in size. Maybe one day we’ll be able to give more of these dinosaurs their due attention. I suppose it’s fitting that the most beloved giant predatory dinosaur was also the last. Blessed must be the T. rex, for it inherited the earth.

By Nicholas Carter

References:

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Nicolás E. Campione, David C. Evans, Caleb M. Brown, Matthew T. Carrano (2014). Body mass estimation in non-avian bipeds using a theoretical conversion to quadruped stylopodial proportions. Methods in Ecology and Evolution

Chure, Daniel J. (1995). “A reassessment of the gigantic theropod Saurophagus maximus from the Morrison Formation (Upper Jurassic) of Oklahoma, USA”. In A. Sun; Y. Wang. Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota, Short Papers. Beijing: China Ocean Press. pp. 103–106.

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Farlow, James O. (2001). “Acrocanthosaurus and the maker of Comanchean large-theropod footprints”. In Tanke, Darren; Carpenter, Ken. Mesozoic Vertebrate Life. Bloomington: Indiana University Press. pp. 408–427.

Gignac, P. M.; Erickson, G. M. (2017). “The biomechanics behind extreme osteophagy inTyrannosaurus rex“. Scientific Reports7 (1): 2012.

Ibrahim, Nizar; Sereno, Paul C.; Dal Sasso, Cristiano; Maganuco, Simone; Fabri, Matteo; Martill, David M.; Zouhri, Samir; Myhrvold, Nathan; Lurino, Dawid A. (2014). “Semiaquatic adaptations in a giant predatory dinosaur”. Science345 (6204): 1613–6.

Lee, Y.N.; Barsbold, R.; Currie, P.J.; Kobayashi, Y.; Lee, H.J.; Godefroit, P.; Escuillié, F.O.; Chinzorig, T. (2014). “Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus“. Nature515 (7526): 257–260.

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Sereno, Paul C.; Beck, Allison L.; Dutheil, Didier B.; Gado, Boubacar; Larsson, Hans C. E.; Lyon, Gabrielle H.; Marcot, Jonathan D.; Rauhut, Oliver W. M.; Sadleir, Rudyard W. (1998-11-13). “A Long-Snouted Predatory Dinosaur from Africa and the Evolution of Spinosaurids”. Science282 (5392): 1298–1302.

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Xu, X.; Tan, Q.; Wang, J.; Zhao, X.; Tan, L. (2007). “A gigantic bird-like dinosaur from the Late Cretaceous of China”. Nature447 (7146): 844–847.


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