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Re: [dinosaur] Fossorial Origin of the Turtle Shell
Dann Pigdon <email@example.com> wrote:
> River banks may be ideal places for basal burrowers to cut their teeth on (or
> claws, as the case may be).
> Soft damp soil that can be dug into horizontally may not require much in the
> way of burrowing ability,
> unlike drier environments that may require vertical digging into much harder
> sediments. River banks are
> also highly productive environments.
The semi-aquatic docodont _Castorocauda_ has both swimming and
burrowing skeletal adaptations. (Although large by Jurassic
mammaliaform standards, it was only <800g.) Interestingly,
_Castorocauda_ also has expanded (plated) thoracolumbar ribs.
Little _Haldanodon_, another docodont, also has both semi-aquatic and
fossorial adaptations (but no evidence of expanded ribs). Combined
swimming/burrowing habits appear to have been around for a long time