Edmontosaurus annectens

Edmontosaurus annectens was one of the most abundant large herbivores on the river plains of latest Cretaceous western North America. It had a long, low skull, a broad toothless beak and immense dental batteries for processing vegetation. Numerous skulls and articulated skeletons document substantial changes in skull proportions as the animal grew; this evidence led researchers to fold the long-snouted Anatotitan copei into the adult growth series of E. annectens. Exceptionally preserved carcasses from Wyoming add a rare external view. A 2026 study found that their scales, a fleshy midline crest, interlocking tail spikes and hoof sheaths survive as a paper-thin clay template rather than original organic tissue.

Its fossils occur between approximately 68 and 66 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

The skull was elongate and low, widening into a toothless keratin-covered beak. Behind it, closely packed columns of replacement teeth formed dental batteries that maintained broad grinding surfaces as worn teeth were shed. The body was deep and muscular, balanced by a long tail reinforced with ossified tendons. Robust hind limbs and shorter forelimbs allowed quadrupedal walking, while the proportions remain compatible with bipedal movement in some circumstances. Clay-templated specimens show tiny pebble-like scales over much of the body, a tall fleshy crest along the neck and trunk, a single interlocking spike row over the hips and tail, and wedge-shaped hoof sheaths around all three hind toes.

• Long, low skull widening into a broad toothless beak
• Dense dental batteries with continuously replaced grinding teeth
• Deep torso and long tail reinforced by ossified tendons
• Powerful hind limbs combined with shorter weight-bearing forelimbs
• Pebble-like body scales documented by clay-templated integument
• Tall fleshy midline crest extending along the neck and trunk
• Interlocking spike row continuing over the hips and tail
• Three wedge-shaped hoof sheaths on each hind foot

John Bell Hatcher, William H. Sullins and Adam Hermann Utterback collected the exceptionally complete holotype USNM 2414 in Niobrara County, Wyoming, in September 1891. Othniel Charles Marsh named it Claosaurus annectens in 1892. The species later passed through Thespesius, Anatosaurus and Anatotitan before modern revision placed it in Edmontosaurus. Charles H. Sternberg found the famous AMNH 5060 ‘mummy’ in the Lance Formation near Lusk in 1908; Henry Fairfield Osborn described its skin impressions in 1912. Two newly studied Wyoming mummies, one juvenile and one early adult, were described in 2026 and revealed an almost continuous external body profile.

Discovery credit: John Bell Hatcher, William H. Sullins, A. H. Utterback.

Naming authors: Othniel Charles Marsh.

Edmontosaurus annectens occupied low coastal plains east of the young Rocky Mountains during the final part of the Maastrichtian. The Lance, Hell Creek and equivalent formations record broad rivers, shifting channels, ponds, swamps and seasonally wet floodplains draining toward the Western Interior. Conifers, flowering trees, shrubs, ferns and low ground cover formed a varied plant community. Triceratops, Thescelosaurus and Ankylosaurus shared parts of this landscape, while Tyrannosaurus was the largest predator.

Its beak could crop a broad swath of vegetation and the dental batteries repeatedly sliced and crushed food, but fossils do not identify one preferred plant. Limb proportions support efficient quadrupedal travel and permit bipedal movement, without revealing how often each posture was used. Bonebeds and sites with several individuals show that edmontosaurs sometimes died together and may have gathered, but they do not establish permanent herds or a particular migration route. Hoof sheaths and a padded hind foot refine how the animal contacted soft ground; they do not imply horse-like speed or behaviour.

• The holotype USNM 2414 preserves most of one skull and skeleton, an unusually informative name-bearing specimen for a dinosaur described in the 1890s.
• AMNH 5060 has been popularly called a mummy for more than a century, even though the surviving surface is fossilized rather than dried original skin.
• The 2026 mummies preserve the first confirmed hoof sheaths in a reptile and show three separate hooves on each hind foot.
• The long-snouted animal once called Anatotitan copei is now usually interpreted as a large adult Edmontosaurus annectens.
• Most preserved body scales are only a few millimetres wide despite the animal reaching roughly ten metres in length.

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1. 01
   The Paleobiology Database

   Open source
2. 02
   Fourth note on the Dinosauria of the Laramie

   Othniel Charles Marsh · American Journal of Science · 1892

   Open source
3. 03
   Cranial Growth and Variation in Edmontosaurs (Dinosauria: Hadrosauridae): Implications for Latest Cretaceous Megaherbivore Diversity in North America

   Nicolás E. Campione, David C. Evans · PLOS ONE · 2011

   Open source
4. 04
   Integument of the Iguanodont Dinosaur Trachodon

   Henry Fairfield Osborn · Memoirs of the American Museum of Natural History · 1912

   Open source
5. 05
   Duck-billed dinosaur fleshy midline and hooves reveal terrestrial clay-template ‘mummification’

   Paul C. Sereno, Evan T. Saitta, Daniel Vidal and 7 coauthors · Science · 2026

   Open source
6. 06
   Fossil ‘Mummy’ Shows Glimpse of Dinosaur Skin

   American Museum of Natural History · 2017

   Open source
7. 07
   Edmontosaurus annectens (Marsh, 1892), USNM 2414

   Smithsonian National Museum of Natural History

   Open source