RE: Unorthodoxies in Reptilian Phylogeny [Romer 1971]

[Michael Mortimer <mickey_mortimer111@msn.com>]

The paper was about two hypotheses Romer did not believe but felt should be 
considered since they were proposed by people whose opinions he respected.
 
One was that archosaurs were derived from varanopsid synapsids, which Reig 
proposed because he thought Varanodon had an antorbital fenestra.  Reig 
proposed other characters as well, but Romer showed all of them were 
plesiomorphies.  As for the antorbital fenestra in Varanodon, from what I can 
tell it seems to be a fenestra above the maxilla dorsal process and behind the 
septomaxilla, while the archosaurian equivalent is of course posteroventral to 
the maxilla dorsal process.  So non-homologous anyway.  Ironically, the two 
taxa listed as linking the captorhinomorphs and archosaurs by Romer 
(Mesenosaurus and Elliotsmithia) are now recognized as varanopid synapsids.  So 
his ideas were no better, merely deriving archosaurs from generalized 
"captorhinomorphs" like all other reptiles.  Molecular analyses disprove an 
archosaur-synapsid clade regardless.
 
The other hypothesis is Kuhn-Schnyder's that sauropterygians and at least six 
other reptile clades developed independently from amphibian-grade taxa.  This 
was based on the retained tabulars and postparietals of nothosaurs, which Romer 
noted are present in many basal reptiles.  Also Kuhn-Schnyder thought 
Simosaurus had an otic notch, but this was merely a non-homologous feature on 
the posterior surface of the skull, not a real otic notch on the dorsolateral 
surface.  He apparently had no good evidence for the other clades being derived 
separately and Romer noted the high degree of homoplasy that would entail.  He 
also thought placodonts and sauropterygians were distantly related because the 
former have a broad bone ventral to their temporal fenestra but the latter have 
a narrow bone.  This suggested to him that placodonts evolved from ancestors 
with one pair of temporal fenestrae while sauropterygians derived from diapsid 
ancestors.  Romer saw no particular similarity to lepidosaur or archosaur 
diapsids and kept the two together as euryapsids.  Of course we now know both 
came from diapsids, making Kuhn-Snyder partially correct.  Romer derived 
euryapsids from protorosaurs, in which he also included the basal diapsid 
Araeoscelis and the archosauromorph Trilophosaurus.  It seems he was incorrect.
 
Mickey Mortimer








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> Date: Mon, 21 Dec 2009 14:01:28 -0800
> From: davidpeters@att.net
> To: dinosaur@usc.edu
> Subject: Unorthodoxies in Reptilian Phylogeny [Romer 1971]
>
> Romer 1971 wrote a paper with an intriguing title: Unorthodoxies in Reptilian 
> Phylogeny. Evolution 25:103-112.
>
> How unorthodox was Romer in 1971? And what were some of his more interesting 
> pre-cladistic conclusions?
>
> Just curious.
>
> David Peters
> davidpeters@att.net