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BEAK EVOLUTION IN TETRAPODS
Yet again the thread has died and I never had the time to send this
message in when it was alive. Too much work, too little time.
Those of you wondering about the evolution of beaks in reptiles might
want to consult:
LEE, M.S.Y. 1997. The evolution of beaks in reptiles: a proposed
evolutionary constraint. _Evolutionary Theory_ August 1997: 249-254
(I don't seem to have the volume number, sorry).
Mike notes that tetrapod beaks only occur in taxa that exhibit a
caruncle (egg tooth) when hatching. Apparently, the caruncle is an
amniote synapomorphy that has been lost in therian mammals and
squamates and it's suggested that beaks evolve via modification of
this structure. This explains the evolution of beaks in all
groups bar therians, squamates, lissamphibians and basal tetrapods.
Little known is that monotremes have a caruncle (with a bony core,
the os carunculae) as do marsupials. Maybe it's possible, therefore,
for marsupials to evolve beaks (!).
Interesting in another context is Mike's contention that
huphesuchians are ichthyosaurs AND that they are beaked. He cites 'M.
Caldwell, unpublished data 1996' for this. Has Dr. Caldwell published
this does anyone know? I haven't seen any huphesuchian fossils, but I
am familiar with Carroll and Dong's monograph on _Huphesuchus_. No
hint of a beak there: I would really like to see confirmation.
Are turtles neodiapsids, or parareptiles? I have an opinion on this,
but regardless, one new piece of data should be mentioned: recently
identified procolophonoid scutes have sculpturing and morphology more
like that of turtles than of any other group of armoured tetrapods.
This is consistent with the placement of turtles within parareptilia.
Lingham-Soliare has a new paper in _Lethaia_ on a _Mosasaurus_ brain
endocast that supposedly reveals a fatal injury. Shards of bone
preserved within the endocast indicate that the mosasaur was rammed,
its braincase was invaded, and it died of a cerebral trauma! Other
mosasaur specimens reveal injuries related to ramming behaviour (Dale
Russell has mentioned a tylosaur with a squashed rostral prow).
Tom Rich and colleagues assert in the same issue that
_Ausktribosphenos_ is a tribosphenid, and not a symmetrodont or
monotreme, as a number of other early mammals workers have argued in
"In the words of a famous rabbit, this means war: total and