NOTE: The original article concerning Torvosaurus was published on August 8, 2015. It was completely overhauled and re-published on December 9, 2020, with more information and new artwork.

Introduction

The Morrison Formation of western North America, dated to the late Jurassic Period approximately 155 to 145 million years ago (MYA), is one of the richest fossil beds anywhere on Earth. Ever since the 1870s, the rocks that make up this formation have been intensively studied by paleontologists, geologists, environmental scientists, and amateur fossil hunters. It is from these rocks that hundreds of thousands of dinosaur bones have been uncovered, including the skeletons of some of the most famous dinosaurs ever like Allosaurus, Stegosaurus, and Diplodocus. Their skeletons are on display in museums around the world, and both their names and their physical appearance are instantly recognizable. For some species, so many specimens have been uncovered that we know practically everything that there is to know about their anatomy.

However, not all dinosaur species are so richly attested. There are several species from the Morrison Formation which are known only from one skeleton, or from partial remains, and in some cases from just a single tooth. One of these is a creature which has increasingly gained attention in popular media for the past ten or so years – a large meat-eating dinosaur named Torvosaurus.

Torvosaurus was one of the largest carnivorous dinosaurs that lived in the Morrison Formation. It measured 35 feet long, the same size as its contemporary Allosaurus, nicknamed “the Lion of the Jurassic”. However, there were many anatomical differences between these two species. Torvosaurus and Allosaurus may have lived in the same location at the same time, but Allosaurus was clearly the most numerous theropod within that environment. In fact, we have more fossils of Allosaurus than any other carnivorous dinosaur anywhere in the world. By contrast, very few remains of its competitor Torvosaurus have been found.

Discovery, Phylogeny, and Geographic Diversity

The first fossils of this animal were discovered in 1899 by Elmer Riggs in the “Freeze-out Hills” of southeastern Wyoming, located about eleven miles northwest of the town of Medicine Bow. The material consisted of bones from the left foot and right hand of a meat-eating dinosaur. These fossils were taken to the Field Museum of Natural History in Chicago, Illinois…where they remained untouched, collecting dust in storage, for nearly eighty years, until they were “found” and re-examined. The fossils were officially described in 2013 (Hanson and Makovicky, 2013). It is a tale that is unfortunately common in the realm of natural history museums: specimens are collected in the field, they are brought back to the institution, they are put on a shelf, and then they are completely forgotten about for decades until somebody finds them again. I have personal experience in this.

In 1971 at a place called Calico Gulch Quarry, located in northwestern Colorado, a single gigantic thumb claw was seen sticking out of the ground. Unfortunately, a search of the surrounding area resulted in a dead end – there were no other associated bones nearby (Galton and Jenson, 1979).

A Torvosaurus hand claw. Photo by Matt Heaton, FossilEra (June 3, 2015). Image used with permission. https://imgur.com/ppceR6a. https://www.fossilera.com/blog/torvosaurus-king-of-the-real-jurassic-world-unearthed.

Afterwards, this claw was shown to Prof. Jim Jensen of Brigham Young University in Provo, Utah. In response, the following year in 1972, he and a team of paleontologists turned their attention to a place called Dry Mesa Quarry, a very rich bonebed dated to the late Jurassic which was located in west-central Colorado, in an attempt to find anything that could match the claw that had been found a year earlier. There, they found the partial remains of a large meat-eating dinosaur which Jensen assumed (and that’s the key word here) belonged to the same animal as that enormous claw. The bones which were uncovered were remarkable in many respects, and the team were confident that they had discovered a new species. In 1979, Jim Jensen and his colleague Peter M. Galton published an article concerning this previously-unknown dinosaur, which was officially named Torvosaurus tanneri (“Nathan E. Tanner’s savage lizard”) (Galton and Jenson, 1979).

Fossils of Torvosaurus discovered at Dry Mesa Quarry, housed at Brigham Young University. Photo by Jim Kirkland, posted to Twitter (April 24, 2015). Image used with permission.

A preliminary description of Torvosaurus tanneri was given in Galton and Jenson’s original 1979 report, and subsequent descriptions were published in 1985 and 1991. The last of these studies claimed that the large thumb claw which had been found in 1971 should not be included with the rest of the Torvosaurus remains because it was isolated and found over 150 miles away from the rest of the fossils, and it could not be stated with absolute certainty that they belonged to the same species (Jenson, 1985; Britt, 1991).

Torvosaurus was obviously a meat-eating theropod dinosaur, but where exactly did it fit into the dinosaur tree? In 1985, Jim Jensen assigned this animal to its own family, Torvosauridae, which was intended to include any heavily-built theropod which possessed short-but-powerful arms as well as finger claws that were unusually large in proportion with the overall size of its arms (Jensen, 1985). However, by the late 1980s, it was recognized that Torvosaurus’ hip bones looked remarkably similar to those seen in Megalosaurus, a theropod from the middle Jurassic Period of Europe, and people began to wonder if Torvosaurus itself was a megalosaur; I know of one children’s book dated to 1989 which definitely says that it was (Sattler, 1989). In 1991, Brooks Britt stated that since many of Torvosaurus’ bones were similar to those in Megalosaurus, it therefore ought to be officially re-classified as a megalosaurid (Britt, 1991). It has remained within that theropod family ever since.

By the early 1990s, at least three individuals were identified as belonging to Torvosaurus (two adults and one juvenile) with the remains having been discovered in Wyoming, Utah, and Colorado. No complete specimen of Torvosaurus has been found, so it is difficult to precisely determine its length. However, most sources that I have seen place it as being somewhere between 30 to 35 feet long. Reports which gave a larger measurement of 40 feet or more are believed to have exaggerated its size (Bakker et al, 1992).

My Drawing

Within this article is a detailed drawing which I made of the North American species Torvosaurus tanneri. The drawing was made with No.2 and No.3 pencil on printer paper in 1:20 scale, and it measures 21 inches long, which would make the real-life animal 35 feet long. This illustration is actually the third iteration that I have made of this animal. The first drawing was made back in the middle 2000s when I was an undergrad in college. I knew nothing about Torvosaurus’ anatomy at the time, and all I did was stick a Megalosaurus head onto an Allosaurus body. Not very scientific. My second drawing which I made in 2015 was more in-line with what the animal looked like. However, it was based very heavily on Scott Hartman’s skeletal drawing of this animal, in particular its widely splayed legs, and I definitely did not want to be accused of artistic plagiarism. So, the time came for me to update my work once again. The image that you see here is the finished result based upon what we presently know of the creature’s anatomy.

Torvosaurus tanneri. © Jason R. Abdale (December 5, 2020).

I have also made a colorized version of this animal. I’ve always associated Torvosaurus with the color brown, which I blame on being impressioned by that 1989 children’s book that I read when I was a kid. Consequently, I’ve given it a color scheme of medium brown with a light tan underside and decked out with a camouflage pattern of light tan diamonds framed with black. I’ve also put black feet on it just for some added color contrast.

Torvosaurus tanneri, colorized. © Jason R. Abdale (December 5, 2020).

Torvosaurus comes from a more ancient lineage than Allosaurus. My Allosaurus drawing, which you can see here, was done in a sort of stippling effect to replicate the tiny round scales which have been found associated with Allosaurus skin impressions. Since Torvosaurus comes from an earlier and more primitive line of theropods, I decided to have its primitive nature reflected by giving it large crocodilian-like polygonal scales and rows of decorative dermal scutes. So far, no skin impressions have been found with Torvosaurus, or indeed with any megalosaur to my knowledge, so I cannot be certain if this scale texture is accurate or not.

The scutes on the feet were also changed. I have seen numerous posts on the internet claiming that the rectangular bird-like scutes which are traditionally seen in paleo-art, arranged in rows along the toes and metatarsals of dinosaurs is, in fact, very inaccurate. Therefore, I made these foot scutes smaller, and in so doing, they have taken on a somewhat crocodilian appearance. I must say that it fits with the overall appearance of the animal.

Torvosaurus Fossils in Europe and Africa

For nearly three decades, Torvosaurus fossils had been found exclusively within North America. Then in the year 2000, the bones of a large meat-eating dinosaur were found in Portugal’s Lourinha Formation, also dated to the late Jurassic Period. These fossils looked very similar to those that had been discovered in North America, but there were some slight differences in the anatomy. In 2014, it was officially named Torvosaurus gurneyi. Although known from incomplete remains, it’s evident that the European species has a more boxy skull than its North American counterpart (Hendrickx and Mateus, 2014).

Elsewhere in Europe, isolated fragments which were discovered in England within clay dated to about 155-150 MYA are believed to have come from a megalosaur. Although it was proposed that these fragments might belong to Torvosaurus, it could not be stated with any degree of certainty (Benson & Barrett 2009; Carrano et al. 2012).

In the 2010s, a partial maxilla (one of the bones that forms the upper jaw) was discovered in the Ornatenton Formation in northwestern Germany, at a spot which is not far from the ancient Teutoburg battlefield. An examination of this bone revealed that it was almost identical to the maxillae of Torvosaurus. However, there was one glaring red flag – the Ornatenton Formation occurred millions of years earlier than both the Morrison Formation of the United States and the Lourinha Formation of Portugal. The rock layers of both the Morrison and Lourinha are dated to the Kimmeridgian and Tithonian Stages of the late Jurassic Period, about 155-145 MYA. However, the rocks of the Ornatenton Formation of Germany are dated to the Callovian Stage of the middle Jurassic Period, approximately 166-161 MYA. During this stage, other megalosaur species roamed Europe such as Wiehenvenator, a megalosaur which lived in Germany during that same stage (Rauhut et al, 2016). Therefore, it is possible that this maxilla, which was identified as belonging to Torvosaurus, might be mis-identified. However, a tooth was also discovered within this maxilla, and it is this tooth which is diagnostic. This tooth, in particular the size and pattern of its serrations, does not match those known from either Megalosaurus or Wiehenvenator. A closer examination of the skull fragment showed features which were present in Torvosaurus, but which were absent in other megalosaur genera. Therefore, it is likely that these German fossils belong to an as-yet unconfirmed species of Torvosaurus. This adds further evidence to the idea that megalosaurs like Torvosaurus originated in Europe and then radiated outwards, spreading into North America, Africa, and Asia. It is also possible that the genus Torvosaurus originated in Europe during the middle Jurassic, and then migrated into North America during the late Jurassic. (Rauhut et al, 2020).

In Africa, fossil bones of a large meat-eating dinosaur were found in the Tendaguru Formation of Tanzania, dated to the late Jurassic Period. In 2011, these bones were ascribed as belonging to the super-family Megalosauroidea – it was unclear as to whether it was a megalosaur or a spinosaur (Rauhut, 2011). In 2020, theropod teeth that had been discovered in the Tendaguru Formation, which had formerly been given the unofficial classification of “Megalosaurus ingens”, were ascribed to Torvosaurus, thus potentially creating a third species, Torvosaurus ingens. However, more specimens would need to be collected before this can become officially recognized (Soto et al, 2020)

Torvosaurus in Popular Culture

From its official naming in 1979 up until the early 2010s, Torvosaurus was an obscure species that not many people knew about. Most dinosaur books didn’t even mention it, and the few that did didn’t have that much to say – scarcely a single paragraph in most cases – and much of it was general information that could be given to any theropod dinosaur.

Then in 2011, that changed. That year, the Discovery Channel released a mini-series entitled Dinosaur Revolution, which was intended to be a docu-drama series in the vein of Walking with Dinosaurs, but having a more comic book like feel to it. The second episode, “The Watering Hole”, takes place in Portugal during the late Jurassic Period, and Torvosaurus appeared on screen for the first time. It was portrayed as a massive terrifying beast with a huge head and enormous teeth and was the top predator in its environment. Virtually overnight, Torvosaurus got thrown into the spotlight and its notoriety sky-rocketed.

Comparative Anatomy: Allosaurus fragilis versus Torvosaurus tanneri

Torvosaurus tanneri lived alongside Allosaurus within the Morrison Formation of western North America, but Torvosaurus came from a more primitive line of theropods, the megalosaurs. During the middle Jurassic Period, about 170-160 MYA, these animals ruled the world as the dominant carnivores of their environments. They were the top predators in Europe, Africa, and as far away as China. However, by the late Jurassic, five million years later, these animals were being phased out by newer and more advanced theropods, such as the allosaurs. The megalosaurs had become outdated obsolete relics of a bygone era. By 150 MYA, only a couple of megalosaur species still remained worldwide, Torvosaurus being one of them – all of the others had gone extinct – and it seems that it too was just barely hanging on. By the end of the Jurassic Period five million years later, the last of the megalosaurs would die out.

Both Torvosaurus tanneri and Allosaurus fragilis had the same maximum length of 35 feet or thereabouts, but they possessed different physical proportions. These anatomical differences no doubt drove these two species to develop different hunting styles. Below is an overlay of an Allosaurus (blue) with a Torvosaurus (red) which shows the difference in body proportions. I will be getting into specifics as we go on.

Color contrast between Allosaurus fragilis (blue) and Torvosaurus tanneri (red) © Jason R. Abdale (December 5, 2020).

As a member of the family Megalosauridae, Torvosaurus retained some anatomical features that were primitive compared to more advanced theropods living at that time like Allosaurus. It was also probably less intelligent than Allosaurus as well, although not by much apparently, since Allosaurus wasn’t exactly the brightest bulb either, according to studies of its brain (Allosaurus: A Walking With Dinosaurs Special).

Torvosaurus’ head was much larger in proportion to body size than Allosaurus’ head was. In fact, Torvosaurus’ head was 1.5 times bigger than the biggest Allosaurus skull that we have found. Torvosaurus’ teeth were also freakishly huge, so big that it’s hard to imagine how they could even fit into its mouth. I should state, however, that most museum mounts show Torvosaurus as having much longer teeth than it had in reality because the teeth are extended out of their sockets and half of the root is exposed. Yet even if you were to shorten the teeth to their correct length, the sight is still a fearsome one to behold. Its demonic grinning maw of over-sized steak knives reminds me of the ape-beast “Fluffy” from the 1982 movie Creepshow. By contrast, Allosaurus had very small teeth in proportion to skull size. However, the one thing that both of these animals had in common was the fact that they had flat skulls with sideways-facing eyes. These animals had NO depth perception at all, and they would almost assuredly have to slightly bob their heads back-and-forth from side-to-side, like a shark swimming or a dog scent-tracking, in order to get an alternating left-right-left-right picture of what was in front of them.

Of course, a big heavy head needs a strong neck to hold it up. As such, Torvosaurus’ neck was short and thickly muscular, while Allosaurus’ neck was longer and more sinuous. Allosaurus had the ability to flex its neck to a great degree, especially in an up-down motion (this is known as “ventral flexion”), but the thick layers of muscle on Torvosaurus’ neck would have greatly reduced its mobility.

Torvosaurus had short squat arms and small hands, but the claws are mind-bogglingly massive. When your head is so large and weighs so much, and the majority of your killing power is centered on your jaws, your arms become rather un-necessary. It seems that Torvosaurus was a Jurassic analog of a tyrannosaur, since it had an unusually large head and unusually small arms in proportion to its body. By contrast, Allosaurus also had huge claws, but it also had longer arms and huge hands to go with them; obviously these were used for grabbing and ripping things. Why Torvosaurus, which possessed such short arms, would need such huge claws is beyond my comprehension.

Torvosaurus’ body was long and shallow and possessed an elongated trunk with a low back. By contrast, the body of Allosaurus was short and deep, with a compressed trunk, an arched back, and a deeper ribcage. This is a good body structure for an animal that has a large heart and lungs, indicating an active lifestyle. A small shallow body makes me wonder if a large heavy animal like Torvosaurus ran out of breath quickly. Allosaurus also had large well-built hip bones, which served as attachment points for the muscles that pull the legs back and forth. This means that Allosaurus’ legs were very strong and had the ability to run at full-tilt if it wanted to. By contrast, Torvosaurus’ hip bones were small and not as robustly built – not a design suitable for a runner.

Allosaurus had a tail that was slightly longer than what you would expect when compared with its overall body. This is often given as a definite feature of an agile runner, which needs a long tail to balance the body when it’s making quick tight turns. The tail of Torvosaurus, while long, would probably have to be very thick in order to balance out the weight of the front half of the body. The thick layers of muscle meant that it would not have been able to pivot back-and-forth as easily as the tail of Allosaurus. No tight turns for this beast.

On the whole, Torvosaurus seems to be rather front heavy (good for physically slamming its jaws onto prey) while the weight on Allosaurus appears to be more evenly distributed. Of course, an animal which weighed that much would need some seriously thick legs in order to hold up all of its massive bulk. As such, Torvosaurus’ legs were noticeably thick and robust, far more so than the legs of Allosaurus.

If you look at the detailed picture above, you may think that Torvosaurus’ legs look far too short in proportion with the rest of its body. Surely this was a mistake and the legs ought to be longer, right? Sorry, but the legs are indeed the correct size. It’s true that Torvosaurus’ legs were shorter than Allosaurus’ legs, but they were only slightly shorter. It’s just that Torvosaurus’ head, body, and tail are so utterly huge and massive that the legs look short and under-developed by comparison. It’s an optical illusion. The combination of thick legs, a shallow stretched-out ribcage, and unpronounced hip bones gives Torvosaurus a low-slung appearance. In fact, while I was looking at the entire body, I was struck that Torvosaurus’ build was reminiscent of a rauisuchid. The rauisuchids were a group of archosaurus from the Triassic Period which were related to modern-day crocodiles. Unlike their prestosuchid relatives such as Prestosuchus and Saurosuchus, which were exclusively quadrupedal, the rauisuchids might have been bipedal. The skeletons of rauisuchids such as Postosuchus show a large head, a heavily-built body, short stumpy arms, and short thick legs balanced out by a long tail. The rauisuchids were one of a few groups of non-dinosaurian reptiles which were experimenting with walking on two legs. Torvosaurus’ overall anatomy seems to harken back to an earlier time.

In total, one gets the impression that Torvosaurus was an animal that was not designed for the active chase. It seems that Torvosaurus was primarily an ambush hunter that was built for short-distance bursts, lunging forwards in a straight line, who relied upon its jaws to do most of the work and killing the prey through sheer impact force and by causing deep lacerations with its ungodly-sized choppers. By contrast, Allosaurus was a very active energetic predator who was capable of impressive speed and quick agile turns. If Allosaurus really was “the Lion of the Jurassic”, as it is commonly referred to, then Torvosaurus was the grizzly bear of the Jurassic.

Bibliography

Books:

• Sattler, Helen Roney. Tyrannosaurus Rex and its Kin. Illustrated by Joyce Ann Powzyk. New York: Lothrop, Lee, & Shepard Books, 1989.

Articles:

• Bakker, Robert T.; Siegwarth, James; Kralis, Donald; Filla, James. “Edmarka rex, a new, gigantic theropod dinosaur from the middle Morrison Formation, Late Jurassic of the Como Bluff outcrop region”. Hunteria, volume 2, issue 9 (1992). Pages 1-24.
• Benson, Roger B. J.; Barrett, Paul M. 2009: “Dinosaurs of Dorset: Part I, the carnivorous dinosaurs (Saurischia, Theropoda)”. Proceedings of the Dorset Natural History and Archaeological Society, volume 130 (2009). Pages 133-147.
• Britt, Brooks. “Theropods of Dry Mesa Quarry (Morrison Formation, Late Jurassic), Colorado, with emphasis on the osteology of Torvosaurus tanneri”. Brigham Young University Geology Studies, volume 37 (1991). Pages 1-72. http://geology.byu.edu/home/sites/default/files/geol-stud-vol-37-britt.pdf.
• Carrano, Matthew T.; Benson, Roger B. J.; Sampson, Scott D. “The phylogeny of Tetanurae (Dinosauria: Theropoda)”. Journal of Systematic Palaeontology, volume 10, issue 2 (2012). Pages 211-300.
• Galton, Peter Malcolm; Jensen, James A. “A new large theropod dinosaur from the Upper Jurassic of Colorado”. Brigham Young University Geology Studies, volume 26, issue 1 (1979). Pages 1-12. geo-stud-vol-26-part-2-galton-jensen.pdf (byu.edu).
• Hanson, Michael; Makovicky, Peter J. “A new specimen of Torvosaurus tanneri originally collected by Elmer Riggs”. Historical Biology, volume 26, issue 6 (2014). Pages 775-784. https://www.tandfonline.com/doi/abs/10.1080/08912963.2013.853056?scroll=top&needAccess=true&journalCode=ghbi20.
• Hendrickx, Christophe; Mateus, Octavio. “Torvosaurus gurneyi n. sp., the Largest Terrestrial Predator from Europe, and a Proposed Terminology of the Maxilla Anatomy in Nonavian Theropods”. PLOS One, volume 9, issue 3 (2014). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3943790/.
• Jensen, James A. “Uncompahgre dinosaur fauna: A preliminary report”. Great Basin Naturalist, volume 45, issue 4 (1985). https://scholarsarchive.byu.edu/gbn/vol45/iss4/8/.
• Rauhut, Oliver W. M. “Theropod dinosaurs from the Late Jurassic of Tendaguru (Tanzania)”. Special Papers in Palaeontology, volume 86 (2011). Pages 195-239.
• Rauhut, Oliver W. M.; Hübner, Tom R.; Lanser, Klaus-Peter. “A new megalosaurid theropod dinosaur from the late Middle Jurassic (Callovian) of north-western Germany: Implications for theropod evolution and faunal turnover in the Jurassic”. Palaeontologia Electronica, 19.2.26A (2016). Pages 1-65.
• Rauhut, Oliver W. M.; Schwermann, Achim H.; Hübner, Tom R.; Lanser, Klaus-Peter. “The oldest record of the genus Torvosaurus (Theropoda: Megalosauridae) from the Callovian Ornatenton Formation of north-western Germany”. Geologie und Paläontologie in Westfalen, volume 93 (2020). Pages 1-13. https://www.lwl.org/wmfn-download/Geologie_und_Palaeontologie_in_Westfalen/GuP_Heft_93_14_Seiten.pdf.
• Soto, Matías; Toriño, Pablo; Perea, Daniel. “A large sized megalosaurid (Theropoda, Tetanurae) from the Late Jurassic of Uruguay and Tanzania”. Journal of South American Earth Sciences, volume 98 (2020): 102458.

Videos:

• Allosaurus: A Walking With Dinosaurs Special. BBC, 2000.
• Dinosaur Revolution. Episode 2 – “The Watering Hole”. The Discovery Channel, 2011.

Categories: Paleontology, Uncategorized

Tags: allosaurid, Allosaurus, America, art, dinosaur, Europe, Jurassic Period, Late Jurassic, megalosaurid, Mesozoic, Morrison Formation, North America, paleo-art, paleontology, Portugal, reptile, theropod, Torvosaurus, tyrannosaurid