Edmontosaurus

Edmontosaurus was a large herbivorous hadrosaurid from western North America. It lived during the final 6.5 million years of the Late Cretaceous Period, roughly 72.5–66 million years ago. Fossils extend from Alberta and Saskatchewan into Montana, the Dakotas and Wyoming, with less specific material also known from Alaska.

Adults commonly reached 9–12 metres and an estimated 4–6 tonnes. Numerous skulls, skeletons, bonebeds and specimens preserving skin reveal far more than the flattened “duck-billed” stereotype suggests.

Quick facts

Discovery, naming and old genera

Othniel Charles Marsh named a skeleton from the Lance Formation Claosaurus annectens in 1892. Lawrence Lambe established Edmontosaurus in 1917 for E. regalis, based on Alberta skeletons collected by members of the Sternberg family. The name refers to the old Edmonton geological formation, not a fossil found inside the modern city.

Later researchers placed some specimens in Thespesius, Anatosaurus or Anatotitan. Revised comparisons of skull growth and anatomy brought the well-supported material into Edmontosaurus. Anatosaurus is therefore not an additional contemporary animal in most current classifications.

Two recognised species

E. regalis comes mainly from the Horseshoe Canyon Formation and is late Campanian to early Maastrichtian in age. Its skull was comparatively robust. E. annectens occurs in younger units including the Hell Creek and Lance formations and lived alongside Tyrannosaurus rex near the end of the Cretaceous.

The long, low skull of mature E. annectens develops gradually. Juveniles once received separate names because they looked shorter-faced. Growth series show why age, deformation and geological position must be assessed together. The method is explained in the classification guide.

Skull, beak and dental batteries

The broad front of the snout supported a keratinous beak that extended beyond the bone. Behind it, each jaw held columns of continually replacing teeth. Only part of the battery formed the active surface at one time, so claims of thousands of simultaneously working teeth are misleading.

Complex wear facets show that the jaws processed vegetation through combined movements. This was effective oral breakdown, although it did not copy mammalian chewing. Plant fragments associated with some specimens are difficult to interpret because sediment, decay and gut contents can become mixed.

Body, posture and size

A deep torso, long muscular tail and powerful hind limbs formed the main body plan. The forelimbs were strong enough to bear weight, and soft-tissue impressions show a padded, mitten-like hand rather than separate hoofed fingers spreading widely on the ground. The tail was held off the ground in normal movement.

Large adults were about 9–12 metres long. Reports of considerably larger animals rely on incomplete remains and uncertain scaling. Mass estimates of 4–6 tonnes depend on restored body volume. Compare this range with other dinosaurs in the interactive size guide.

Skin, soft crest and appearance

Several celebrated specimens preserve scale patterns across parts of the neck, body, limbs and tail. They reveal regional variation in scale size and arrangement but not a complete colour map. One fossil preserves a fleshy comb above the skull, showing that a hadrosaur without a hollow bony crest could still carry a conspicuous soft structure.

The complete distribution and variation of that comb are unknown. It may have served display or recognition, but sex differences have not been demonstrated. Fossilised skin also contracts and shifts after death, so a “mummy” is an exceptional sedimentary replica rather than an untouched carcass. See the wider limits in dinosaur skin and colour.

Habitat, bonebeds and behaviour

Edmontosaurus occupied river floodplains, coastal lowlands and northern seasonal environments. Different species and populations lived across millions of years, so a single habitat painting cannot represent the entire genus.

Bonebeds demonstrate that many individuals sometimes died or accumulated together, making aggregation plausible. They do not by themselves establish permanent herds, annual continental migrations or a fixed social hierarchy. Bite traces and damaged bones show that large tyrannosaurids fed on carcasses, but each trace must be evaluated before predation is distinguished from scavenging.

Evidence, inference and reconstruction