Coryphodon eocaenus was a large, heavy-bodied pantodont herbivore, part of an extinct radiation of placental mammals that produced some of the first genuinely large terrestrial herbivores after the end-Cretaceous extinction. More complete Coryphodon skeletons outside Britain show a robust, graviportal animal with sturdy limbs rather than a fast runner.

Its broad cheek teeth carried powerful transverse and oblique shearing crests, combining cutting and crushing during chewing. Tooth form and isotopic work on Coryphodon support a plant-based diet and have also been interpreted as evidence that at least some members of the genus spent substantial time around or in water. A semi-aquatic, wetland-associated lifestyle is therefore plausible for C. eocaenus, but it is an inference from the wider genus and is not demonstrated directly by the London Clay jaw.

The British type is a fragment of the right lower jaw with part of the second molar and a complete third molar. Consequently, the species is locally known from dental anatomy, while the familiar picture of its stocky body and limbs comes chiefly from more complete Coryphodon material elsewhere.