Speculative Biology Sunday: Pachyodoben

6 Feb

A lone Pachyodoben sleeps on a riverbank. Person to scale.

Pachyodoben (meaning thick walrus-face) was the largest genus of the herbivorous amphibians from the Mid-Triassic. They were semi-aquatic, inhabiting rivers, swamps and estuaries. They foraged for browse and roots during dawn and dusk, keeping cool in the water during the heat of the day and sleeping by the riverbank at night. Easily recognisable by their armoured backs, short tusks, stubby tail. For its time it was the largest herbivore ever, weighing in at two to three and a half tonnes.

There ancestry seems to come from the big headed, squat bodied Dissorophidae of the early Permian, but where in their evolution they switched to herbivory is unclear. One of their key adaptations for herbivory is their stunning ability to fake heterodonty, having both tusks and grinding ‘molars’ made from bone. Their only teeth as small and peg-like, used for stripping foliage.
The ‘molars’ seem to have been a key adaptation for switching to herbivory, as only the larger species otherwise use gastroliths to facilitated the breakdown of vegetable material.

Most of the larger species of Pachyodoben fed more on roots than low browse, and dug for them with their tusks. There is even evidence of them using their bulk to topple trees to unearth the fossial fare.

Adults were too large to be bothered by predators, even the young were well armoured enough to keep terrestrial carnivores at bay, but there is evidence of the young being preyed upon by Xenacanthidan sharks, tearing at their vunerable underbellies from beneath the surface; Mothers always putting themselves between their young and the deeper water, with red spots on their belly warning of violent retaliation should the sharks be willing to try anything.

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One Response to “Speculative Biology Sunday: Pachyodoben”

  1. Leechman February 6, 2011 at 12:32 pm #

    You’re a thick walrus face.

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