RE: [dinosaur] Fossorial Origin of the Turtle Shell

[Dann Pigdon <dannj@alphalink.com.au>]

On Mon, Jul 18th, 2016 at 9:23 PM, "Thomas R. Holtz, Jr." <tholtz@umd.edu> 
wrote:

> > From: dinosaur-l-request@usc.edu [mailto:dinosaur-l-request@usc.edu] On 
> > Behalf Of Tim Williams
>>
> > Interesting.  I guess, for small tetrapods, swimming and digging/burrowing 
> > go together quite well - 
> > which makes the transition quite easy in either direction.
> > 
> Even animals larger like this--muskrats, beavers--are both burrowers and 
> swimmers.

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 ability to swim to some degree would be useful to a burrower in such an 
environment, to survive the 
occasional flood. A body form that has both burrowing and swimming abilities 
(neither being very competent) 
could easily lead to specialisation in either one or the other. Being highly 
specialised in one may reduce 
the efficiency of the other, but won't always rule it out completely. Even 
marine turtles with their highly
specialised aquatic limbs still manage to dig decent sized holes to bury their 
eggs in the sand, although it's
a laboured process. 

And echidnas are still surprisingly good swimmers (that snout makes a good 
snorkel):
https://urldefense.proofpoint.com/v2/url?u=http-3A__www.abc.net.au_news_2015-2D12-2D02_echidna-2Dplucked-2Dfrom-2Dtasmanias-2Dlake-2Decho-2Dby-2Dworried-2Dfisherman_6990760&d=DQIDAw&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=I4cgExnZySC8ukk-bX5lrl3j8mFjdZkYp_yDt4Hg7Ek&s=lrV0ehLmUjEVkhaXPAHWnQXy7hdHEV1iIi4CYzFSCXs&e=
   

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Dann Pigdon
Spatial Data Analyst               Australian Dinosaurs
Melbourne, Australia               
https://urldefense.proofpoint.com/v2/url?u=http-3A__home.alphalink.com.au_-7Edannj&d=DQIDAw&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=I4cgExnZySC8ukk-bX5lrl3j8mFjdZkYp_yDt4Hg7Ek&s=1E0JdHg8koQlq7sGIbq_GvqV4vNdITBAKQ46-wDtJsc&e=
 
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