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sphenodonts, etc.



DANGER!  SPECULATION COMING UP! 


Several days ago I asked:

> Does anybody have any 
> suggestions as to why sphendonts seem to have been so completely 
> outcompeted by lizards?  Is there anything besides skull kinesis that 
> seems likely?  Is my premise right--i.e., have they indeed been 
> outcompeted by LIZARDS?  How would we know?

Darren Naish replied that sphenodonts did well against lizards into the 
Triassic, then something happened that might not have been related to 
competition from lizards.

It turns out the modern tuatara--the only surviving sphenodont--lives 
much of its life at a low temperature.  They are nocturnal, and frequent 
burrows during the day, with the result that their core body temperature 
is typically well below 80 degrees F--even in the 60's.  (This 
information courtesy Ted Grannon, herpetology curator at the Evansville 
Zoo; he informs me that in the U.S., Ron Goellner of the St. Louis Zoo is 
the foremost authority on the tuatara, but I haven't talked to him.)

Of course, much may have changed since the Triassic--lifestyles may well 
have been different for small sphenodonts at that time.  But diurnal 
lizards (were they diurnal then???) and nocturnal sphenodonts could 
possibly have coexisted indefinitely.  Maybe it wasn't competition by 
lizards at all.  Perhaps it was competition by ictidosaur therapsids 
(such as _Diarthrognathus_) or the earliest mammals, which many people 
believe have a high likelihood of having been endothermic and nocturnal, 
that did in nocturnal insectivorous sphenodonts.  Perhaps also, the 
latter were preyed upon by the "fabulous fur-balls."

Just speculation.  Like I said before, how would we know?  

It seems to me, though, that we ought to be able to speculate once in a 
while about some of this stuff, especially when it comes to behavior and 
inter-species and intra-species interactions.  Aren't those topics worth 
discussing?  I can see, however, that protracted debates on speculative 
matters, after people have initially expressed their thoughts, serve no 
purpose (at least, not for me).  There should be a medium ground for 
discussions here.  In fact, all we really KNOW about dinosaurs is their 
bones, and their condition, orientation, etc. when discovered (I know we 
could have an epistemological debate about that, but skip it, please!).  
The dialogue on this list can't be expected to have the rigor of a 
refereed journal.  OTOH, we don't want debate for the sake of debate.  
That's what really gets to me.



P.S. Thanks to those (GO, Tom, and Nick) who responded to my questions 
about _Protoavis_, etc. and the dino-bird connection.  I think my head is 
clearing. I'll have a few follow-up comments later.

*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu