Edmontosaurus

Phylogeny: Dinosauria > Ornithischia > Genasauria > Neornithischia > Cerapoda > Ornithopoda > Iguanodontia > Ankylopollexia > Styracosterna > Hadrosauriformes > Hadrosauroidea > Hadrosauridae > Saurolophinae > Edmontosaurini

Overview: There are two accepted species of Edmontosaurus – the type species Edmontosaurus regalis and the geologically younger Edmontosaurus annectens. Getting to the point of one genus with two species has been complicated. Edmontosaurus regalis was first described in 1917 by the renowned Canadian paleontologist Lawrence M. Lambe, based on fossils found within the rocks of Alberta’s Horseshoe Canyon Formation. Said formation was previously known as the Edmonton, in honor of the nearby city, Edmontosaurus being named after both. Fossilized remains now referred to Edmontosaurus annectens were described by Othniel C. Marsh in the 1890’s, who assigned them to the genus Claosaurus as a new species (C. annectens). Later, fossils of this species would come to be associated with other genera, most prominently Trachodon. Edmontosaurus annectens fossil material would also be used to establish the genus Anatosaurus in the 1940’s, as well as Anatotitan in the 1990’s. Both supposed genera draw their name from a Latin root word meaning “duck”, as a reference to the wide, duck-like snout seen on E. annectens specifically.

Nowadays, the names Trachodon, Anatosaurus, and Anatotitan are all considered junior synonyms of Edmontosaurus. There are differences between the Edmontosaurus species. E. regalis tended to have a shorter, taller snout, as opposed to the more duck-like snout of E. annectens. Fossilized soft tissue traces on E. regalis reveals that some of them possessed fleshy, rooster-like head crests, but no such fossil evidence has yet been found on E. annectens. Said crest may’ve been present only on males, used for sexual display. Both species grew to be in excess of twelve meters long, making them among the largest known hadrosaurids, but E. annectens was often longer. Some studies find E. regalis to have been bulkier on average, however. Aside from these differences, the two had far more similarities. Both had the general hadrosaur body plan, being able to walk on their hind legs, but likely spent most of their time grazing down on all fours. Their bodies were sturdily built, set on strong limbs and the neural spines on the vertebrae were often quite tall along the tail. Both of the species were among the largest herbivores in their local environments.

Hadrosaurs are famous for their unique feeding adaptations. Like its kin, Edmontosaurus possessed a keratinous beak, well suited for snipping stems and snapping branches, but also columns of teeth towards the back of the mouth. These teeth were packed tightly together, creating a solid grinding surface, capable of processing even the toughest of plants. They would constantly be replaced as it grew, with no specimen ever being found with worn teeth or lacking them, which sets this creature apart from many herbivorous mammals (elephants famously starve to death in old age due to their teeth running out from wear). In the past, Edmontosaurus and its kin were thought to have mostly eaten soft water plants, living a semi-aquatic life. This was partly based on fossil mummies of the genus supposedly possessing traces of webbing on the hands. In reality, this turned out to be the remnants of padding on its front paws – Edmontosaurus was a land-dwelling animal. Fossils of the species E. annectens did live in a fairly wet, coastal environment, however. It lived alongside many famous Late Cretaceous dinosaurs like Triceratops, Ankylosaurus, and Tyrannosaurus.