Allosaurus, a large predatory dinosaur from the Late Jurassic Period, is the most common theropod genera. Unfortunately for poor Allosaurus, the shadow of Tyrannosaurus rex looms large over other predatory dinosaurs.
It’s a shame that most news articles about Allosaurus find a way to relate it to Tyrannosaurus rex. For example, the webpage about Allosaurus for the museum of Utah State University Eastern states that it “lived 83 million years before Tyrannosaurus rex.” Perhaps more annoying are websites that say Allosaurus was an “early relative” of Tyrannosaurus, an inaccurate statement that I will discuss in this article. While some of these references help contextualize Allosaurus to the public, many are misleading and reduce it to a lesser version of Tyrannosaurus.
Today I will attempt to avoid the omnipresent impetus of Tyrannosaurus rex and instead focus on Allosaurus. Easier said than done, am I right? Perhaps not. After all, Allosaurus is a dinosaur that somehow connects feuding paleontologists with creationism, cannibalism, and injured toes. I’ll bet you’ve never heard those things associated before. Yet Allosaurus somehow does, and I promise that all these topics (and more) will be discussed today.
First, a few points about Allosaurus. At approximately 9 meters long and weighing an average of 2 tonnes, Allosaurus was amongst the largest theropods alive during the Late Jurassic Period. Fossils of Allosaurus are found throughout the midwestern United States (between Wyoming and Oklahoma) and in Portugal. Allosaurus had three species: A. fragilis, the original and most common species; A. Jimmadseni, a rarer species found only in small areas of the U.S.; and A. europaeus, the European species.
The most recognizable feature of Allosaurus are two horns located above each eye. Like all theropods, the arms of Allosaurus weren’t all that impressive, forcing Allosaurus to rely on its serrated, dagger-like teeth to take down prey. Such deadly instruments were needed in its late Jurassic home, given the abundance of large predators and herbivores at the time. Allosaurus lived in a dangerous and hostile world, yet still became a successful predator that lived for almost 10 million years.
A Product of War…
During the last 25 years of the 19th century, two American paleontologists battled for supremacy. The conflict between Othniel Charles Marsh and Edward Drinker Cope – later dubbed the bone wars – involved fossils, sabotage, angry letters to newspapers, and heads placed on tails. Though the bone wars created a complicated legacy, their impact on North American paleontology was immense.
Famous dinosaurs such as Triceratops, Stegosaurus, and Diplodocus are some of the species discovered during the bone wars. Allosaurus was another product of the feud, described by O.C. Marsh in 1877 based on fossils from Colorado. The name Allosaurus, which translates to “different lizard” in Greek, stemmed from the vertebrae of Allosaurus that Marsh perceived to be “distinguished from any known dinosaur”[i]. Reading Marsh’s initial publication perfectly summarizes the research of the bone wars: rushed, with the only goal being naming new species. Talk about sloppy…
Voyage Across the (Infant) Atlantic
During the Late Jurassic Period, the Atlantic Ocean was in its infancy. South America and Africa had yet to separate, and the gap between Europe and North America was a fraction of what it is today:
Nonetheless, a substantial gap was present between North America and Europe. Despite this, fossils of Allosaurus are found on both continents, with specimens being well documented in Portugal[ii]. Allosaurus wasn’t the only dinosaur found on both continents, as the large theropods Torvosaurus and Ceratosaurus – and potentially Stegosaurus and the sauropod Supersaurus – have been found in Portugal and the USA.
The presence of these dinosaurs could indicate a few things. The first explanation is that they swam across the fledgling Atlantic to Portugal, Europe’s most western nation. Although Portugal (which at the time was a large island) was close to North America, it was likely too substantial of a voyage for the dinosaurs. The next theory is that they used a raft to travel across the ocean. This theory may explain how monkeys and rodents – relatively small animals – journeyed across the Atlantic to South America in the Eocene, but not multi-tonne dinosaurs in the Jurassic.
The most logical theory is that land bridges formed periodically between the two continents during the Jurassic, allowing dinosaurs and other animals to cross[iii]. Tectonic events and fluctuating sea levels may have occasionally created island chains for animals to cross, only to close sometime after. We know that closure must have occurred, given that there is enough difference between European and American dinosaurs to justify assigning different species. After the Jurassic, the Atlantic continued to grow, meaning that Allosaurus was amongst the last group of terrestrial organisms to cross the Atlantic for the next 100 million years.
Troublesome Eating Habits…
We all make mistakes in the heat of passion sometimes. Or should I say during feeding frenzies?
Allosaurus bite marks are found on dinosaur bones throughout the United States. Some of these bites are ordinary interactions between predator and prey, such as a fossil of a Stegosaurus plate with an Allosaurus bite on it[iv]. Nothing strange to look at here! However, other bite marks are far more sinister…(if you can say that about 150-million-year-old fossils).
In 2020, an analysis of dinosaur bones from the Mygatt-Moore quarry of Colorado revealed something shocking: Allosaurus was a cannibal. Of almost 3,000 bones discovered at Mygatt-Moore, nearly a third had evidence of Allosaurus scavenging upon them, including those of sauropods, an ankylosaur, and 83 bones of other Allosaurus[v]. To say Allosaurus was a picky eater couldn’t be farther from the truth…
Cannibalism is common in nature and has been identified in at least two other predatory dinosaurs. In the case of Allosaurus, cannibalism was likely a response to the harsh climate of the Late Jurassic. The Morrison Formation, the geologic area in which Allosaurus fossils are discovered, was a hot and dry area that experienced long periods of drought[vi]. During these droughts, food was a rare commodity, meaning that any food you could sink your teeth into – whether your kind or not – would have been valuable.
Allosaurus wasn’t the only dinosaur forced into cannibalism by droughts. Paleontologists believe that cannibalism in another dinosaur, the abelisaurid Majungasaurus, was caused by droughts too. More than anything, this may be a sign that living in Jurassic North America wasn’t a cakewalk by any stretch of the imagination…
Lion of the Jurassic, or rather Hyena?
Allosaurus’ nickname, the “lion of the Jurassic,” originated in the 1999 BBC documentary Walking with Dinosaurs. The name makes sense given the comparison between the Jurassic Morrison and the African Savanna, both dry, semi-arid habitats littered with large prey and predators. While I’m fine with the Morrison-savanna association, the casting of Allosaurus as lions has always seemed off to me. Instead, I believe a more fitting comparison lies in the Lion’s arch-nemeses: the Hyena.
Let’s start with population. Hyenas are the most common predators on the African Savanna, outnumbering lions 3:1[vii]. As for Allosaurus, look no further than a ratio of theropod dinosaurs discovered throughout the Morrison Formation. Keep in mind that this graphic encompasses 10 million years of geologic time:
Like Hyenas, Allosaurus wasn’t the biggest carnivore of the Jurassic Morrison. While Hyenas must contend with lions and leopards, Allosaurus had to deal with Torvosaurus and Saurophaganax, two predators that dwarfed Allosaurus. In this analogy, cheetahs and canines can be compared to Ceratosaurus and Marshosaurus, two other predators that were smaller and more specialized than Allosaurus.
Next, we have social behaviours. Hyenas practise complex social behaviours around female-dominated clans. Though nothing concrete has been discovered, social behaviours in Allosaurus have been inferred based on the remains of the scavenged sauropod Camarasaurus at Wyoming’s Dinosaur Centre. The remains were found with bite marks, scratch marks, teeth, and footprints that match Allosaurus[viii]. What’s more interesting is that the teeth comprise individuals of different ages, showing these dinosaurs either lived together or at least cooperated for the sake of an easy meal.
Lastly, we have diet. Though Hyenas are cast as scavengers, they are generalist predators and eat just about anything that comes in front of them. Sound familiar? As discussed earlier, evidence of Allosaurus munching on everything from Sauropods to Stegosaurus (to itself) demonstrates it wasn’t particular about its diet. Studies on its tooth structure reinforce this, with general tooth structure aligning with generalist predators[ix]. This broad diet may have fueled their success, as they could take advantage of many kinds of prey available in the Late Jurassic.
Though this analogy isn’t perfect – Hyenas are bone-crushers, while Allosaurus were slashers – it seems more fitting than calling Allosaurus lions.
“Big Al” and the Downsides of Being a Predatory Dinosaur
Naming dinosaurs is always fun. Take “Big Al” for instance, an exceptionally complete specimen of Allosaurus Jimmadseni and the star of his own BBC program, The Ballad of Big Al. Housed at the Museum of the Rockies, Al is 95% complete, an exceptional amount for any large theropod. Al has revealed a lot about Allosaurus, especially the pathologies associated with carnivorous dinosaurs.
19 of Al’s bones exhibit serious injury[x]. The most pronounced is swelling to the middle toe on Al’s right foot, caused by the growth of bone overtop an existing layer (ouch)[xi]. Other injuries are found on Al’s feet, vertebrae, and ribs[xii]. Al isn’t the only Allosaurus specimen reported to have multiple injuries either.
An Allosaurus specimen from Wyoming may have been even worse off than Al. Pathologies were noted on its jaw, multiple vertebrae and ribs, the left shoulder blade and humerus, hip, and toes[xiii]. Remarkably, both Big Al and our Wyoming specimen lived with seemingly debilitating injuries for months, if not years! Their resilience was driven by advanced bird-like immune systems, which prevent pathogens from spreading and instead localize pathologies to their source[xiv].
It has been speculated that social behaviours helped injured Allosaurus survive, though they could have just scavenged. Though Big Al and others suffered in their life, their fossils have helped paint a fuller picture of the lives that carnivorous dinosaurs endured.
The Specimens Gone, but not Forgotten…
Since Allosaurus fossils are so common, it’s not surprising that some are possessed by…undesirable individuals. Some specimens have been sold to private collections, where they may never see the light of day again. Then there is “Ebenezer,” one of the best preserved and most complete specimens of Allosaurus…that is on display at a creationist museum. Unfortunately for paleontologists, Ebenezer isn’t going anywhere, meaning that a crucial fossil for researchers will be left with people who don’t know how valuable it is.
No relation to Tyrannosaurus
Allosaurus and Tyrannosaurus rex are not related. While Allosaurus dominated Late Jurassic savannas in North America and Europe, the earliest relatives of Tyrannosaurus lived in the forests of China. These early tyrannosaurids, such as the species Guanlong, grew no bigger than three meters and would have been dwarfed by allosaur cousins such as Yangchuanosaurus. As the Jurassic turned to Cretaceous, Allosaurids were soon replaced in the Northern hemisphere by the Tyrannosaurids, giving way for Tyrannosaurus rex to arrive at the end of the age of dinosaurs.
Allosaurus’ dominance in the Jurassic was incredible. In a hostile world full of dangerous predators, Allosaurus emerged as the most successful. A fearless predator that cowered away from nobody – not Stegosaurus, Brontosaurus, or even its relatives – it’s about time Allosaurus dissociates from Tyrannosaurus and gets the respect it deserves.
Thanks for reading todays article! If you enjoyed learning about Jurassic North America and would like to know how a dozen sauropods lived together in the Morrison, I suggest you read about The Morrison’s Giant Conundrum here at Max’s Blogosaurus!
I do not take credit for any images found in this article.
Header image courtesy of @Alloverasaur on twitter, found here
Allosaurus courtesy of TheMingau on DeviantArt, found here
Allosaurus Fragilis skull courtesy of the Carnegie Museum of Natural History, found here
The Bone Wars found here
Jurassic Earth courtesy of the Encyclopedia Brittanica, found here
Adrift Allosaurus courtesy of Dmitry Tokalchik, found here
Face-biting Allosaurus courtesy of FredtheDinosaurman, found here
Allosaurus cannibalism courtesy of Johnnykcage, found here
Morrison Formation theropods courtesy of Brad Shelby on twitter, found here
Allosaurus vs Barosaurus courtesy of FredtheDinosaurman, found here
Big Al courtesy of Katon Callaway, found here
Big Al toe courtesy of Ben Miller on twitter, found here
Ebenezer skull courtesy of…*sigh* the Creation Museum, found here
Lounging Allosaurus courtesy of FredtheDinosaurman, found here
[ii] Malafaia, E., et al. “Vertebrate Fauna at the Allosaurus Fossil-Site of Andrés (Upper Jurassic), Pombal, Portugal.” Journal of Iberian Geology, vol. 36, no. 2, 2010, pp. 193–204., https://doi.org/10.5209/rev_jige.2010.v36.n2.7.
[iii] Black, Riley. “Portugal’s Giant Jurassic Predator Gets a New Name.” Science, National Geographic, 4 May 2021, https://www.nationalgeographic.com/science/article/portugals-giant-jurassic-predator-gets-a-new-name?loggedin=true.
[iv] Carpenter, Kenneth. “Evidence for Predator- Prey Relationships Examples for Allosaurus and Stegosaurus.” The Carnivorous DInosaurs, edited by Kenneth Carpenter, Indiana University Press, 2005, pp. 325–350.
[v] Drumheller, Stephanie K., et al. “High Frequencies of Theropod Bite Marks Provide Evidence for Feeding, Scavenging, and Possible Cannibalism in a Stressed Late Jurassic Ecosystem.” PLOS ONE, vol. 15, no. 5, 2020, https://doi.org/10.1371/journal.pone.0233115.
[vi] Turner, Christine E., and Fred Peterson. “Reconstruction of the Upper Jurassic Morrison Formation Extinct Ecosystem—a Synthesis.” Sedimentary Geology, vol. 167, no. 3-4, 2004, pp. 309–355., https://doi.org/10.1016/j.sedgeo.2004.01.009.
[vii] “Lions vs. Hyenas: Competing Interests.” National Geographic Society, https://education.nationalgeographic.org/resource/lions-vs-hyenas-competing-interests.
[viii] Lomax, Dean R., and Bob Nicholls. Locked in Time: Animal Behavior Unearthed in 50 Extraordinary Fossils. Columbia University Press, 2021.
[ix] Testinet, Jason J. et al. “Dental Morphology of Allosaurus Fragilis (Dinosauria: Theropoda) from the Upper Jurassic Morrison Formation of Western North America: Is Dentition More Indicative of Taxonomy or Feeding Niche?” Nov. 2011.
[x] Wilkin, Jack. “Review of Pathologies on MOR 693: An Allosaurus from the Late Jurassic of Wyoming and Implications for Understanding Allosaur Immune Systems.” 2019, https://doi.org/10.31233/osf.io/f3rh6.
[xi] See Above
[xii] See X
[xiii] Foth, Christian, et al. “New Insights into the Lifestyle of Allosaurus (Dinosauria: Theropoda) Based on Another Specimen with Multiple Pathologies.” PeerJ, vol. 3, 2015, https://doi.org/10.7717/peerj.940.
[xiv] See Above