Re: Drinker and Oryctodromeus (was Re: Dinosaurs burrowed to keep warm)

[Tim Williams <twilliams_alpha@hotmail.com>]

Dann Pigdon wrote:

> Perhaps burrow-dwelling is primitive for hypsies, or even basal 
> ornithopods? I've read that Heterodontosaurids lacked stiffening tendons in 
> their tails.

Also, back in the 1970's, Thulborn proposed that heterodontosaurids 
hibernated (or aestivated) during the dry season.  But this was based on 
tooth wear patterns (ihe thought that heterodontosaurids replaced their 
teeth wholesale only once a year, and had to avoid feeding during this 
period).  AFAIK there was no taphonomic evidence to support this hibernating 
behavior.  The idea went over like a lead balloon (heterodontosaurids could 
in fact replace their teeth continuously).  Hopson even named a 
heterodontosaurid _Abrictosaurus_ ("awake lizard") to express his 
skepticism.

_Heterodontosaurus_ itself had powerful forelimbs, based on the prominent 
deltopectoral crest and olecranon process.  Weishampel and Witmer (1990) 
suggested that heterodontosaurids dug up tubers and roots with their 
forelimbs.

If burrowing is primitive for ornithopods, then it would make sense for this 
behavior to be retained in critters like _Atlascopcosaurus_ and 
_Leallynasaura_, which had to endure those long polar winters in SE 
Australia.

> Those 'eyelid bones' above the eyes would also have provided good 
> protection from collapsing burrow material (or just plain bumping their 
> head on the ceiling).

Hey maybe that's why the pachycephalosaurs evolved really thick skulls!  
After all, there is evidence that heterodontosaurids are closely related to 
pachycephalosaurs.  Those thick skull roofs served as 'hard hats'!  ;-)

Cheers

Tim

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