Unearthed in from 50-million-year-old Eocene deposties of Wyoming, 10 meter-long Eohadrus excelsius is one of the best-preserved specimens of hadrosaurid diversity during the Cenozoic.  The skull morphology of this species is quite similar to that of its Cretaceous ansestors such as Kritosaurus and Bactrosaurus, with a blunt, toothless beak and layers of small, diamond-shaped teeth in the back of its mouth.  The limbs of Eohadrus, however, are quite distinct from those of its ansestors, the forelimbs being roughly the same lenghth as the hindlimbs.  Eohadrus, then, was a fully quadripedal galloper, like modern hadrosaurids, and unlike the still partially bipedal basal hadrosaurids of the Mesozoic.  Eohadrus's neck was long and flexible, and its tail, no longer nessisary for balance, but still the anchor for the muscles of the legs, was deep and blunt.

    Unlike its plains-dwelling descendents, Eohadrus was most likely a forest-living animal, browsing from the ground and from low-growing trees.