Fossil Friday: Allosaurus

Species: Allosaurus fragilis (ah-loe-sore-us frrah-gee-lees)

What it means: Strange reptile

Other Species: A. europaeus, A. jimmadseni

Where I live: Western U.S.A.- The Morrison Formation / Portugal – The Lourinha Formation

When to find me: The Late Jurassic period, about 155 million years ago.

My favorite food: Meat! I’m a carnivore.

My neighborhood: The Morrison Formation covers a huge expanse of land with a variety of different habitats teaming with life. Most of it was very much like the Serengeti of modern day Africa, only with prairies of drought-tolerant ferns and cycad relatives instead of grass. Dense woodlands of tall conifers like the modern araucaria, ginkgoes, and tree ferns would only lie in places of plentiful water such as the few permanent rivers. Other areas had far more sparse and shrubbier vegetation like the open woodlands of acacia trees in the Serengetti.

Life in this environment would’ve adapted to long months of harsh drought, followed by a few months of monsoon that flooded the rivers. Many of the larger herbivores may have migrated like the herds in Africa do today, while most carnivores stayed behind to feast on the dead and dying, or else become opportunistic hunters of less traditional diets for lean times, such as fish or turtles in the rivers.

A few of my neighbors: First let me share the walking buffet…

  • Long-necked sauropods like Brachiosaurus, Camarasaurus, Diplodocus, Barosaurus, Apatosaurus, Suuwassea, Supersaurus, Haplocanthosaurus, and Dystrophaeus.
  • Armored dinosaurs like Stegosaurus, Hesperosaurus, Mymoorapelta, and Gargoyleosaurus.
  • Two-legged ornithopods like Dryosaurus, Camptosaurus, and Nanosaurus

At the buffet I can meet all sorts of fellow carnivores, including dinosaurs like Torvosaurus, Ceratosaurus, Saurophaganax, Marshosaurus, Stokesosaurus, Ornitholestes, Coelurus, Tanycolagreus, Elaphrosaurus, and Koparion.

Not to mention the countless lizards, crocodile relatives on land and water, mammals, frogs, turtles, fish, and all the pterosaurs flying in the sky!

Fun Facts:

  • Allosaurus gets its name from allos (Greek for strange, or different) + sauros (Greek for lizard or reptile). The name for the type species is fragilis, the Latin word for fragile, because of the birdlike features in its vertebrae.
  • Allosaurus was the most numerous carnivore in the Morrison Formation. Out of 190 known specimens of theropod dinosaurs, Allosaurus accounts for nearly 75% of that number.
  • Allosaurus is one of the many dinosaurs from the Morrison Formation discovered during the “Bone Wars”, a period of competition between paleontologists Edward Drinker Cope and Othniel Charles Marsh in the late 19th century. Othniel Charles Marsh first described the bones of Allosaurus in 1877.
  • The first bones ever found where thought to be “petrified horse hooves” by the locals, before it was sent to paleontologist Joseph Leidy, who identified the fossil as half a tail vertebrae and named it Antrodemus.
  • During the “Bone Wars” many dinosaurs were named from bones of the same animals. Most of the time because of miscommunication with their own teams over fragmentary fossils, and partially to “one up” each other, though this rivalry wasn’t quite as vicious as many sources claim. (Aside from destroying quarries rather than risk the other finding fossils there). Allosaurus received several names at this time- Marsh’s Creosaurus and Labrosaurus, and Cope’s Epanterias.
  • For over 50 years all the Allosaurus remains were joined under the name of the first known fossil, Antrodemus. But a single tail vertebrae is not enough to identify a genus of dinosaur, plus no one knew where the original bone was found, and so it was officially reclassified as Allosaurus by James Madsen, who published on a huge bonebed of Allosaurus from the Cleveland-Lloyd Dinosaur Quarry. More famously known as Dinosaur National Monument.

Fossil Finds: Numerous remains from many individuals, ranging from fragmentary bones to almost complete and perfect skeletons. There may be more Allosaurus fossils than any other large theropod (two-legged, generally carnivorous dinosaur). Many fossils include pathologies, or signs of injury and illness the dinosaur suffered during its lifetime. More than almost any other large theropod, we can understand a lot about how it grew and lived in its environment.


Madsen, James H., Jr. (1993) [1976]. Allosaurus fragilis: A Revised Osteology. Utah Geological Survey Bulletin 109 (2nd ed.). Salt Lake City: Utah Geological Survey.

Foster, John. Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press, 2007

“Allosaurus.” Wikipedia,

3 thoughts on “Fossil Friday: Allosaurus

  1. Phenomenal debut Morrison Formation post, but since when was Elaphrosaurus from this formation? I only know it from Tanzania.


    1. Hi Angel! Thank you, I’m glad you like it!

      I had never heard of Elaphrosaurus before, I just jotted down the list of dinosaurs from a book specializing on the Morrison Formation, “Jurassic West”. Most of my information on future Morrison Formation creatures will come from this very well-written and studious book.

      According to the author, Elaphrosaurus is indeed mostly known from Tanzania, but there were some isolated bones from several locations in the Morrison determined to be Elaphrosaurus. There is not enough material to determine if it is a new species or not. In any case, it seems that Elaphrosaurus was extremely rare in this area, but did actually make an appearance, so I will include it in the Morrison menagerie. 🙂

      I did not end up including Scelidosaurus in the Kayenta Formation because recent research has determined the scutes once thought to be from scelidosaurus was from something else entirely. If I come across something similar for any of the other creatures on the list here, then I will edit them accordingly. But I will not know until I get to them and research them individually.

      Paleontology is an ever growing and shifting field, that’s a big part of what makes it fun!


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