Re: Mammal - Like - Reptiles

[Pieter.Depuydt@rug.ac.be]

Paul wrote:
> I am trying to find some information about
> the mammal-like-reptiles such as:
> 
> Lystrosaurus  Thrinaxodon  and  Cynognathus.

As a matter of fact, the name "mammal-like reptiles" should be 
discarded and replaced by "synapsids" (or non-mammalian synapsids in 
a strict  The concept "Reptile" in the old 'natural history' meaning 
and in its new cladistic definition has nothing to do with synapsids. 
In the history of amniotes, the two lineages (Synapsida and Reptilia, 
or Theropsida and  Sauropsida) diverged very early from a common 
amniote ancestor and evolved independently. Features that are 
considered typically reptilian, such as presence of scales and 
uricotely (excretion of nitrogen mainly as uric acid) are probably 
unique apomorphies of Reptilia and were not present in synapsids. The 
"reptilian"-like appearance of synapsids is in fact the retainment 
of a  primitive basal amniote "Bauplan", which together with 
the cumulative acquisition of more mammal-like characters gave 
rise to the mosaic of "reptilian" and "mammal-like" features which 
has given synapsids their familiar nickname.

Pieter Depuydt