Edmontosaurus

[Barry the Baryonyx]

Edmontosaurus

_{(C) 1997 M.Shiraishi}

Edmontosaurus (ed-MON-toh-sawr-us) meaning 'Edmonton lizard' (after where it was found, in Edmonton, Alberta, Canada and Greek sauros meaning lizard) was a hadrosaurid dinosaur genus from the Maastrichtian, the last stage of the Cretaceous Period, 71-65 million years ago. A fully-grown adult could have been up to 9 metres (30 feet) long and some of the larger species reached 13 metres (43 feet). Its weight was in the region of 3.5 tonnes, making it one of the largest hadrosaurids.


Species

Edmontosaurus was erected by Lawrence Morris Lambe in 1917 from a find in the Edmonton Rock Formation, Alberta, using E. regalis as type species. Marsh named Claosaurus annectens in 1892, but this has now been reclassified as E. annectens. Likewise, Charles Mortram Sternberg named Thespesius in 1926, but this is also a species of Edmontosaurus, namely E. saskatchewanensis.

The well-known hadrosaurid genus Anatosaurus has been synonymized with Edmontosaurus. Anatosaurus, meaning "duck lizard", because of its wide, duck-like bill (Latin anato = duck + Greek sauros = lizard). The type species of Anatosaurus, A. annectens, was re-named Edmontosaurus annectens, forcing the name Anatosaurus to be abandoned as a junior synonym. Similarly, Anatosaurus saskatchewanensis was sunk into Edmontosaurus as E. saskatchewanensis. Two other species of Anatosaurus, A. longiceps (originally Trachodon) and A. copei (the famous mount at the American Museum of Natural History), were found to differ from Edmontosaurus were placed in a separate genus, Anatotitan.

Characteristics

Edmontosaurus could pass the toughest food back and forth across the teeth with its muscular cheek pouches. To fit so many teeth into its mouth, they were packed into tight "banks" of up to sixty rows, and new teeth constantly grew to replace lost teeth — analogous to a modern shark. The bones of the upper jaw would flex outwards as lower jaw came up, so the mandible could grind against it. Typical food would have included conifer needles, seeds and twigs, and these have been found in the body cavities of fossilized edmontosaurs. It was evidently a tree-browser.

The 1908 discovery in Wyoming was especially remarkable in that paleontologists actually recovered fossilized imprints of Edmontosaurus' skin. The impression must have been left by the skin drying very quickly and fixing its shape into the mud. It is from these impressions that we know the skin was scaly and leathery, and the thigh muscle was under the skin of the body. This would have given the impression that the leg left its body at the knee, and the whole thigh was under the skin. This only contributes to its resemblance to a duck. It also had a number of tubercles (bumps) along its neck and down its back and tail.

Edmontosaurus was bipedal but could certainly have walked on four legs. The forelimbs are shorter than the hinds but not sufficiently that four-legged motivation was unfeasible. The front feet also had hooves on two fingers, and weight-bearing pads like those of Camarasaurus. The rear feet had three funtional toes and all were hoofed. The bone structure in the lower limbs suggests that both the legs and feet were attached to very powerful muscles. The spine curved downwards at the shoulders, so Edmontosaurus would have had a low posture and would have browsed close to the ground. Despite the power of the limbs, Edmontosaurus would only have been slow-moving and had few defensive features. To survive, it must have had keen eyesight, hearing and smell to get early warning of predators.
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