Allosaurus was a meat-eating dinosaur that lived during the Late Jurassic Period, between 150 and 155 million years ago. Its bones have been uncovered in the Western United States, Portugal, and in parts of Africa. An adult Allosaurus, on average, measured about thirty feet long from snout to tail, but some have been found that were slightly smaller or larger. The genus name translates to "Other Reptile" because at the time of its original discovery in the late 1800s, its vertebrae were what paleontologists used to differentiate Allosaurus from "other" fossil dinosaurs they were finding in the area. (Underwhelming...I know.). In life, Allosaurus would have shared its habitat with (and probably ate) many other known dinosaurs, including, but not limited to Apatosaurus, Brontosaurus, Barosaurus, Diplodocus, Camarasaurus, Stegosaurus, Gargoyleosaurus, Torvosaurus, and Ceratosaurus.
There are actually three different known species of this Allosaurus that have been identified. Allosaurus fragilis, from North Ameirca, is the most commonly found, and therefore the most extensively studied. Allosaurus jummadseni, is also found in North America but was from a few million years before Allosaurus fragilis. There is also Allosaurus europaeus, which was from what is now Europe.
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Because there have been many specimens of Allosaurus that have been unearthed over the years, paleontologists know a lot more about it and often use Allosaurus as a model to compare to other, less complete dinosaurs for references. Allosaurus' skull, in particular, is subject to a lot of attention. The holes in its skull on either side of its eye sockets, called fenestrae, were large, and the bone walls of the skull, including those surrounding the brain case, were thin. In addition, Allosaurus also had hollow chambers in its other bones, including its vertebrae and its leg bones, like birds. This suggests Allosaurus was light for its size. It also suggests Allosaurus had an advanced, one-way respiratory system that birds, and some other kinds of reptiles have today, where air initially breathed in via the lungs, was more efficiently circulated around the body, including through some of the bones. This would have allowed Allosaurus to remain more active for longer periods of time without needing to rest. These same adaptations would have also helped to keep Allosaurus cool, with easy airflow within the body to shed excess warmth, and preventing the animal from overheating. It makes sense since we have evidence that the the environment Allosaurus was living in could get rather hot and arid during the Jurassic.
Allosaurus' teeth were curved, flat, and serrated. They were not extremely large compared to some of its contemporary meat-eaters, like Ceratosaurus or Torvosaurus, which means Allosaurus had a different feeding, and probably hunting style from them. Allosaurus' teeth were probably best for slicing and cutting, rather than crushing or piercing. These teeth were backed up by rather slender lower jaws, which means that there was less muscle attached to them in life, and therefore Allosaurus had a proportionally weaker bite when compared to many other meat-eating dinosaurs. (this does not mean Allosaurus had a weak bite! It just wasn't crushing solid bones with its jaws like some other more specialized dinosaurs could.) That being said, the jaws of Allosaurus were also able to open much wider than those of other dinosaurs, an impressive 79 degrees, to be exact. Also, the back of Allosaurus' skull and its neck bones suggest that there were very large muscle attachments there in life, and its skull, although having weak jaw muscles, was, as a structure, very strong when it came to sustaining impact. So what does all of this mean? Some paleontologists think that instead of using just bites to inflict damage or remove flesh from a carcass, Allosaurus likely would have used its strong neck to swing its open mouth to hack away at its target like an axe...with teeth.
It was also discovered that the muscles that would have been in Allosaurus' neck in life would have allowed for this dinosaur to move its neck in an up-and-down motion very quickly, taking many bites in a smaller amount of time. Scientists hypothesize that Allosaurus may have used its jaws and teeth like a saw, to hack away mouthfuls of meat off of bones as it fed. Adding to this, there are numerous sauropod bones from the same habitat as Allosaurus that were found with scrape marks that match Allosaurus teeth on them. We may never know if Allosaurus actually killed these plant-eaters first or if it was simply scavenging an already dead animal, but either way we can agree Allosaurus' neck, skull, jaws, and teeth were a great butchering adaptation!
Allosaurus' mouth wasn't its only weapon. This dinosaur is possibly most famous for its relatively long, strong arms, and three large, hook-shaped claws on each hand. The first finger of each hand possessed the largest claw, but all were more than capable of dealing substantial damage together and keeping struggling prey in place as the jaws did work on removing flesh from the bone.
Thanks to numerous well-preserved specimens of Allosaurus, scientists have been able to tell a bit about its lifestyle...and that its lifestyle was rough! Allosaurus specimens have been found with numerous stress fractures on both the front limbs and the hind limbs, that healed over. This tells us that Allosaurus was using its arms for something getting injured in the process sometimes. It is possible Allosaurus was attacking large prey, like sauropods, with its front limbs, holding on with its hook-like claws, and slashing with its teeth to inflict bleeding wounds until its prey was too weak to stand any longer. In addition to these injuries, Allosaurus have also been found with bite wounds from other Allosaurus on their skulls, which tells us that there was some intraspecies violence going on. Another Allosaurus specimen was discovered with a nasty puncture wound in its tail that had healed over. This wound matches the spike of a Stegosaurus, one of Allosaurus' contemporaries, suggesting that the two famous dinosaurs may have fought on occasion. Lastly, yet another Allosaurus was discovered with a puncture wound through its PELVIS, likely inflicted by yet another Stegosaurus tail spike which appears to have not healed fully and therefore was the death of the unlucky Allosaurus.
We also have juvenile specimens from Allosaurus, showing that this dinosaur was more slender, with proportionally longer legs when it was young, and bulked up as it matured into adulthood. Allosaurus also had two small bony crests, one in front of each eye. In life these crests likely had a layer of bony material, called keratin, making them even larger. These were probably display adaptations to communicate within the species who was mature and who wasn't. It is even possible that these crests were different sizes, or even colors between males and females. Some believe these crests may have also been weapons that Allosaurus would have used to shove each other with in life to establish dominance. We may never know for sure!
Lastly, paleontologists have discovered impressions of some of Allosaurus' skin! The skin would have been from the dinosaur's side, and had small, bumpy scales. It is unknown if this kind of skin would have covered the whole body, or if there were different kinds of scales or other kinds of body covering, like feathers, elsewhere.
References
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| Allosaurus fragilis mount on display at the American Museum of Natural History in New York. |
Allosaurus' teeth were curved, flat, and serrated. They were not extremely large compared to some of its contemporary meat-eaters, like Ceratosaurus or Torvosaurus, which means Allosaurus had a different feeding, and probably hunting style from them. Allosaurus' teeth were probably best for slicing and cutting, rather than crushing or piercing. These teeth were backed up by rather slender lower jaws, which means that there was less muscle attached to them in life, and therefore Allosaurus had a proportionally weaker bite when compared to many other meat-eating dinosaurs. (this does not mean Allosaurus had a weak bite! It just wasn't crushing solid bones with its jaws like some other more specialized dinosaurs could.) That being said, the jaws of Allosaurus were also able to open much wider than those of other dinosaurs, an impressive 79 degrees, to be exact. Also, the back of Allosaurus' skull and its neck bones suggest that there were very large muscle attachments there in life, and its skull, although having weak jaw muscles, was, as a structure, very strong when it came to sustaining impact. So what does all of this mean? Some paleontologists think that instead of using just bites to inflict damage or remove flesh from a carcass, Allosaurus likely would have used its strong neck to swing its open mouth to hack away at its target like an axe...with teeth.
 |
| Section of an Allosaurus leg bone on the left compared with that of a modern bird on the right. Note how there is a different fossilized mineral inside the Allosaurus bone, showing how it was hollow in life. |
It was also discovered that the muscles that would have been in Allosaurus' neck in life would have allowed for this dinosaur to move its neck in an up-and-down motion very quickly, taking many bites in a smaller amount of time. Scientists hypothesize that Allosaurus may have used its jaws and teeth like a saw, to hack away mouthfuls of meat off of bones as it fed. Adding to this, there are numerous sauropod bones from the same habitat as Allosaurus that were found with scrape marks that match Allosaurus teeth on them. We may never know if Allosaurus actually killed these plant-eaters first or if it was simply scavenging an already dead animal, but either way we can agree Allosaurus' neck, skull, jaws, and teeth were a great butchering adaptation!
 |
| Image from Stephen Lautenschlager's 2015 study comparing the gapes, from left to right, of Allosaurus, Tyrannosaurus, and the therizinosaurid, Erlikosaurus. Note how Allosaurus was capable of the widest bite. |
Allosaurus' mouth wasn't its only weapon. This dinosaur is possibly most famous for its relatively long, strong arms, and three large, hook-shaped claws on each hand. The first finger of each hand possessed the largest claw, but all were more than capable of dealing substantial damage together and keeping struggling prey in place as the jaws did work on removing flesh from the bone.
Thanks to numerous well-preserved specimens of Allosaurus, scientists have been able to tell a bit about its lifestyle...and that its lifestyle was rough! Allosaurus specimens have been found with numerous stress fractures on both the front limbs and the hind limbs, that healed over. This tells us that Allosaurus was using its arms for something getting injured in the process sometimes. It is possible Allosaurus was attacking large prey, like sauropods, with its front limbs, holding on with its hook-like claws, and slashing with its teeth to inflict bleeding wounds until its prey was too weak to stand any longer. In addition to these injuries, Allosaurus have also been found with bite wounds from other Allosaurus on their skulls, which tells us that there was some intraspecies violence going on. Another Allosaurus specimen was discovered with a nasty puncture wound in its tail that had healed over. This wound matches the spike of a Stegosaurus, one of Allosaurus' contemporaries, suggesting that the two famous dinosaurs may have fought on occasion. Lastly, yet another Allosaurus was discovered with a puncture wound through its PELVIS, likely inflicted by yet another Stegosaurus tail spike which appears to have not healed fully and therefore was the death of the unlucky Allosaurus.
We also have juvenile specimens from Allosaurus, showing that this dinosaur was more slender, with proportionally longer legs when it was young, and bulked up as it matured into adulthood. Allosaurus also had two small bony crests, one in front of each eye. In life these crests likely had a layer of bony material, called keratin, making them even larger. These were probably display adaptations to communicate within the species who was mature and who wasn't. It is even possible that these crests were different sizes, or even colors between males and females. Some believe these crests may have also been weapons that Allosaurus would have used to shove each other with in life to establish dominance. We may never know for sure!
 |
| Drawing of Allosaurus jaw from Darren Tanke's 1998 paper, showing bite wounds that were proposed to have been from another Allosaurus. |
Lastly, paleontologists have discovered impressions of some of Allosaurus' skin! The skin would have been from the dinosaur's side, and had small, bumpy scales. It is unknown if this kind of skin would have covered the whole body, or if there were different kinds of scales or other kinds of body covering, like feathers, elsewhere.
References
Carpenter, Kenneth
(2002). "Forelimb biomechanics of nonavian theropod dinosaurs in
predation". Senckenbergiana Lethaea. 82 (1): 59–76.
Gilmore, Charles
W. (1920). "Osteology of the carnivorous dinosauria in the United States
National Museum, with special reference to the genera Antrodemus (Allosaurus)
and Ceratosaurus". Bulletin of the United States National Museum. 110:
1–159.
Holtz, Thomas R.,
Jr.; Molnar, Ralph E.; Currie, Philip J. (2004). "Basal Tetanurae".
In Weishampel David B.; Dodson, Peter; Osmólska, Halszka. The Dinosauria (2nd
ed.). Berkeley: University of California Press. pp. 71–110.
Lautenschlager,
Stephan (2015-11-04). "Estimating cranial musculoskeletal constraints in
theropod dinosaurs". The Royal Society. Archived from the original on
2016-03-19.
Madsen, James H.,
Jr. (1993) [1976]. Allosaurus fragilis: A Revised Osteology. Utah Geological
Survey Bulletin 109 (2nd ed.). Salt Lake City: Utah Geological Survey.
Rayfield, Emily
J.; Norman, DB; Horner, CC; Horner, JR; Smith, PM; Thomason, JJ; Upchurch, P
(2001). "Cranial design and function in a large theropod dinosaur".
Nature. 409 (6823): 1033–1037.
Snively, Eric.;
Cotton, John R.; Ridgely, Ryan; Witmer, Lawrence M. (2013). "Multibody
dynamics model of head and neck function in Allosaurus (Dinosauria,
Theropoda)". Palaeontologica Electronica. 16 (2).
Tanke, Darren H.
(1998). "Head-biting behavior in theropod dinosaurs: Paleopathological
evidence" (PDF). Gaia (15): 167–184.
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