Allosaurus — The Jurassic Predator with an Overbite

When and where

Allosaurus lived from 155 to 145 million years ago during the Late Jurassic. Most of its remains come from the Morrison Formation in North America, a sequence of sedimentary rock that stretches across Colorado, Utah, Wyoming, and New Mexico. Smaller finds have turned up in Portugal, in the Alcobaça and Lourinhã formations. The climate was warm and seasonal, with floodplains and river channels supporting forests of conifers, ferns, and cycads. Allosaurus shared this landscape with Stegosaurus, Apatosaurus, Diplodocus, and Camarasaurus. It was the top predator in an ecosystem packed with enormous herbivores.

How we know

The first identifiable Allosaurus fossils were described in 1877 by Othniel C. Marsh, the same paleontologist who named Apatosaurus and Stegosaurus. Marsh chose the name "Allosaurus", meaning "different lizard", because he thought the vertebrae looked unlike those of other dinosaurs he had seen. For much of the 20th century the genus was buried under the name Antrodemus, but a 1976 review of material from the Cleveland-Lloyd Dinosaur Quarry in Utah restored Allosaurus. That quarry has produced thousands of bones from at least 46 individuals, making it one of the richest dinosaur sites in the world. The taxonomy is still messy. Paleontologists recognize at least three valid species, with Allosaurus fragilis as the best known. The Wikipedia article on Allosaurus tracks the ongoing work to sort out which specimens belong where.

What set it apart

Allosaurus reached about 8.5 metres in length and weighed roughly 1 to 2 tonnes. Its skull was large and narrow, lined with 14 to 17 serrated teeth in each side of the upper jaw. The teeth curved backward and had sharp edges suited for slicing flesh. The forelimbs were short but muscular, with three clawed fingers that could grip prey. The neck was strong and the vertebrae had hollow spaces, which kept the skeleton light without sacrificing strength. Some researchers have argued that Allosaurus hunted in packs based on bonebeds that preserve multiple individuals together. Others think these groups were scavengers drawn to carcasses, or simply animals that died in the same place by chance. Most evidence points to an active predator that also scavenged when carcasses were available.

For collectors and classrooms

A hand-painted Allosaurus figurine gives a solid sense of how this predator looked in life. Good models show the oversized skull, the muscular neck, and the three-fingered forelimbs accurately. In classrooms they give students something solid to hold while learning about theropod anatomy and Jurassic ecosystems. If you are putting together a collection, an Allosaurus model pairs naturally with a Stegosaurus or Diplodocus from the same formation. You can find a hand-painted figurine here.