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Re: [dinosaur] Fossorial Origin of the Turtle Shell
On Mon, Jul 18th, 2016 at 12:30 PM, Tim Williams <email@example.com> wrote:
> This is a fascinating idea - that digging behavior can lead to
> swimming behavior. In both activities the forelimbs are used to
> propel the body forward by the displacement of the surrounding media
> (soil vs water), as Lyson &c put it. So the osteological adaptations
> associated with one behavior (digging) were exapted toward the other
> behavior (swimming) in the line leading to turtles.
> The same transition, in the opposite direction, was previously
> proposed for another group of oddball tetrapods: the monotreme
> mammals. The echidnas (or spiny anteaters), which are fossorial and
> terrestrial, are hypothesized to have evolved from aquatic
> platypus-like ancestors, thereby making echidnas secondarily
> terrestrial (Phillips et al., 2009; www. pnas.org cgi doi 10.1073
The echidna's weekly developed electroceptors certainly suggest an aquatic
origin. However the platypus is also an
accomplished digger, which raises the possibility that the theoretical aquatic
platypus/echidna ancestor may have
itself arisen from burrowers, making the echidna secondarily fossorial as wll.
> I don't mean to imply that stem turtles were arboreal(!).
Stranger things have happened. The closest living relative of the highly
arboreal koala is the entirely non-arboreal
wombat, a burrower with all the climbing adaptations of a lubricated cannon
ball. Which lineage evolved from which
(climber from burrower, or burrower from climber) isn't entirely certain.
Spatial Data Analyst Australian Dinosaurs