Edmontonia was an armoured dinosaur, a part of the nodosaur family from the Late Cretaceous Period. It is named after the Edmonton Formation (now the Horseshoe Canyon Formation), the unit of rock it was found in. Edmontonia fossils have never been found in Alberta, Canada.

Description

Edmontonia was bulky and tank-like at roughly 6.6m (22 ft) long and 2m (6 ft) high. It had small, ridged bony plates on its back and head and many sharp spikes along its back and tail. The four largest spikes jutted out from the shoulders on each side, two of which were split into subspines in some specimens. Its skull had a pear-like shape when viewed from above.

Discovery and species

The type species of Edmontonia, E. longiceps was discovered in 1924 by George Paterson. It wasn't named until 1928 by C. M. Sternberg. E. rugosidens, formally named by Gilmore in 1930, is reported from the Aguja formation in Texas. Edmontonia species include:

• E. longiceps (type);
• E. rugosidens, which is sometimes given its own genus, Chassternbergia, first coined as a subgenus by Dr. Robert T. Bakker in 1988 (Edmontonia (Chassternbergia) rugosidens) and based on differences in skull proportion from E. longiceps. This subgenus or genus is not generally accepted;[Etymology of Chassternbergia: In honor of Charles Mortram Sternberg (1885-1981), a Canadian paleontologist who, in 1928, named and described Edmontonia longiceps, a nodosaurid ankylosaur which Robert Bakker would later use as the basis for proposing the new nodosaurid family Edmontoniidae, which would include a new subgenus, Chassternbergia as well as the new genus Denversaurus schlessmani. Sternberg, honored for his earlier work on Edmontonia longiceps.]
• And E. australis, which is known from cervical scutes only, and is considered to be a dubious name.

Usually included in this genus is Denversaurus schlessmani ("Schlessman's Denver lizard"). This taxon was erected by Bakker in 1988 for a skull from the Late Maastrichtian Upper Cretaceous Lance Formation of South Dakota, but considered by later workers to belong to Edmontonia rugosidens. The type specimen of Denversaurus is in the collections of the Denver Museum of Natural History (now the Denver Museum of Nature and Science), Denver, Colorado (for which the genus was named).

Paleobiology

The large spikes were probably used between males in contests of strength to defend territory or gain mates. The spikes would also have been useful for intimidating predators or rival males, protection, or for self-defense. To protect itself from predators, an Edmontonia might have crouched down on the ground to minimize the possibility of attack to its defenseless underbelly.

Rings in the petrified wood of trees contemporary with Edmontonia show evidence of strong seasonal changes in precipitation and temperature,; this may hold an explanation for why so many specimens have been found with their armor plating and spikes in the same position they were in life. The Edmontonia could have died due to drought, dried up, and then rapidly become covered in sediment when the rainy season began.

References