RE: Turtles and Crocodylians are not Reptiles - no? What are they?

[Tim Williams <twilliams_alpha@hotmail.com>]

Nick Pharris wrote:


>> Actually, no. Under Thewissen &c's phylogeny, there is a 3-way
>> polytomy (trichotomy) composed of Mesonychia, _Andrewsarchus_ and
>> the Cetacea+Artiodactyla clade. The hippopotamids are inside the
>> crown Artiodactyla, in the Suina clade. Because the whales are
>> recovered in a Cetacea-Raoellidae clade at the base of the
>> Artiodactyla, cetaceans are *not* closer to hippos than to
>> mesonychians. Not according to this phylogeny, anyway.
>
> Yes they are. The existence of a "Cetacea+Artiodactyla clade" that
> excludes Mesonychia means that cetaceans are closer to hippos (as
> artiodactyls) than they are to mesonychians. It's just that, under
> Thewissen et al.'s phylogeny, cetaceans are not any closer to hippos
> than they are to llamas, babirusas, chevrotains, mule deer, okapis,
> etc., etc.


Ummm... no, they're not, Nick.  While it is true that Thewissen &c's phylogeny 
found Cetacea to form a clade with Artiodactyla to the exclusion of Mesonychia, 
this does not automatically make cetaceans closer to hippos than to 
mesonychians.  Cetaceans (plus raoellids) are at the base of the Artiodactyla, 
and the Cetacea+Artiodactyla clade forms a trichotomy with Mesonychia and 
_Andrewsarchus_.  The Raoellidae+Cetacea clade is recovered as the sister taxon 
to the crown Artiodactyla clade (pigs, babirusas, hippos, llamas, chevrotains, 
mule deer, cows, gnus, okapis, etc etc).  So, as Mike Keesey pointed out, under 
Thewissen &c's phylogeny cetaceans are outside the crown Artiodactyla.   


BTW, I'm not actually saying that cetaceans are *closer* to mesonychians than 
to hippos.  All I'm saying is that, according to this phylogeny, cetaceans are 
*no closer* to hippos than to mesonychians.  Thus, when you say "cetaceans are 
not any closer to hippos than they are to llamas, babirusas, chevrotains, mule 
deer, okapis, etc., etc", I totally agree.  But this statement alone 
contradicts the Whippomorpha hypothesis.


As such, no matter how you look at it, Thewissen &c's topology finds absolutely 
no support for the Whippomorpha hypothesis.  Remember, the Whippomorpha 
hypothesis does more than just unite hippos and whales; it also breaks up the 
Suina (the pig-peccary-hippo clade), and puts the hippos (and whales) inside 
Ruminantia (which has led to the name 'Cetruminantia' as a result).  In 
contrast, Thewissen &c re-unites the Suina (pig-peccary-hippo) clade, which is 
outside the Ruminantia (chevrotains, mule deer, cows, gnus, okapis, etc etc - 
but not whales or hippos).  


Cheers

Tim



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