[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

MORE CRETACEOUS LIZARDY THINGS



Sorry everyone, still dealing with lizards here. Don't worry if you don't like
it, this is not a tripping tyrannosaur thread. Yet.

Adam Yates said..

> The interesting thing about Lee's phylogeny is that it turns all those 
> funny little burrowing snakes into a monophyletic group, rather than a 
> paraphyletic grade of basal snakes as in past hypotheses. This of course 
> suggests two things 1) a fossorial phase in early snake evolution is less 
> likely & 2) The characters shared between the fossorial snakes and 
> amphisbaenids are not necessarily primitive for snakes. Indeed I suspect 
> a fossorial existance places quite an evolutionary "straight jacket" on 
> lepidosaur groups creating quite an impressive set of convergences.

Rieppel's amphisbaenian-scolecophidian characters are generally to do with jaw
or tail base muscles, perhaps the complexes most applicable for arguments of
convergence in fossorial lepidosaurs. And very nice evidence that all their
similar features _are_ convergent is that there was actually *another*
lepidosaur clade (Sphenodontida (=Sphenodontia) and Lacertilia [incl.
Amphisbaenia and Serpentes] are the two major ones), unrelated to either
amphisbaenians or snakes, that parallelled both of them. These animals were
fossorial with chunky, amphisbaenian-like skulls: they lived and died in the
Cretaceous. A complete skull of one of these things - last I heard the group was
not named nor were its member taxa - was reported and described somewhere in _In
the Shadows of Dinosaurs_.

Amphisbaenians were already around in the Cretaceous: Currie et al. described
a Chinese proto-amphisbaenian in _Can. J. Earth Sci._ in the SinoAmerican Dino
volume I. It also seems that snakes were more diverse and abundant in the
Cretaceous than previously supposed (most sources tell you that there were a few
early python-type animals in S. America, but that was it). I've seen some
cladograms (I really ought to give names and refs when I say things like this)
where the viperid clade is shown as diverging in the Upper Cret (_Jour. Zool._
late in 1996). So you can now have a dinosaur suffering from snake-bite. As yet
though, no members of the python-boa clade in the Santana (an 'in' joke);-)

Personally, I think that amphisbaenians are related to cats (I'm kidding: this
was a suggestion made by some 19th century zoologists). Cool news: we now have
Cretaceous madtsoiids in Europe. They apparently swam from Africa across the
European archipelago in the Campanian or so, joining the late Cretaceous
'laurasian flavour' dinosaur fauna already there. Extant snakes can swim for
miles - a boa constrictors swam to Martinique from the S. American mainland
sometime around 1902 (anything to do with Mt. Pelee?), and reticulated pythons
do a lot of island-hopping in the Asian archipelagos. I imagine a 1 ton snake
the girth of an oil drum could do even better.

"We can't go in there!"
"Why not?"
"Are you kidding? _Orange_? In this suit??"

DARREN NAISH