Re: Whales and Hippos

["Tim Williams" <tijawi@hotmail.com>]

Eric Lurio wrote:

> > Well, the simple fact is that the artiodactyl/whale connection was 
> > confirmed
> > by DNA analysis, and NOBODY has ever found Mesonychid DNA...EVER!!!! The 
> > last
> > of them died out during the early Oligocene. The tooth analysis shows 
> > clear
> > whale/mesonychid releationship.

Then Thewissen et al.'s paper in _Nature_ might surprise you.  With new 
pakicetid material, there is strong evidence that the similarities between 
the teeth of mesonychids and proto-whales are due to convergence.


Chris Brochu wrote:

> > I don't necessarily disagree with what was written below (though I
> > didn't  think the Sys Bio paper by Naylor and Adams was all that
> > great); [snip]

> > > Yes the tooth data support whales as mesonychians but nothing else does.
> > > Not several independant molecular data sources (different genes, SINES
> > > etc.) nor postcranial anatomy. There was a good paper about this a few
> > > months ago in Systematic Biology. [snip]

The paper that Chris and Adam are referring to is:

Naylor, G.P. and Adams, D.C. (2001).  Are the fossil data really at odds 
with the molecular evidence?  Morphological Evidence for Cetartiodactyla 
phylogeny reexamined.  Syst. Biol. 50(3): 444-453.

The take-home message of the paper is (as Adam Yates mentions) beware of 
non-independence of characters.  A great many dental characters of mammals, 
hitherto scored as independent characters, are developmentally or 
functionally correlated.

Many months ago, I remember having a friendly argument with one of the 
co-authors of this paper (in MS form) over the value of dental characters.  
In particular, whether the homoplasy of tooth characters  implied that *all* 
dental characters should be discarded in future analyses.  I said no way.  
Also, the molecular data has been cited in support of a common transition 
for both hippopotamids and whales to the aquatic realm ("return to water").  
The cladogram of Naylor and Adams (2001) - which includes all morphological 
characters except dental characters - does indeed place the Cetacea close to 
the hippotamids and far from the base of the Artodactyla (and the 
Mesonychia).  However, this cladogram actually places the whales closest to 
the entelodonts, with the Cetacea as sister taxon to _Archaeotherium_.



Tim


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