Palæos:		Unit 230: Rhynchocephalia
The Vertebrates		Page 000: Overview

Rhynchocephalia: Overview

A Rhynchocephalian Cladogram LEPIDOSAUROMORPHA |--SQUAMATA Rhynchocephalia |--Pleurosauridae `--Sphenodontidae |--Clevosaurs `--Sphenodontinae

Contents 230.000 Overview 230.100 Rhynchocephalia References

Introduction

Dethe confrounteth Everyman (and Sphenodon).   From Everyman

Anatomically, Sphenodon is rather plain vanilla; and, paradoxically, therein lies its interest. It lies just downstream in phylospace from the split between archosauromorphs and lepidosauromorphs.  It is rather unspecialized and, consequently, is about as close to the basic reptile morphotype as one might hope to find.  When Romer (1956) wrote his incomparable Osteology of the Reptiles, his constant anatomical point of reference was Sphenodon.  Carroll's (1988) Vertebrate Paleontology and Evolution continued this tradition; and, when the next landmark text on vertebrate paleontology is produced, it will doubtless carry on the tradition. There really is no alternative.  No reptile more basal than Sphenodon survives.  Its closest relatives are the iguanid lizards -- products of the Cretaceous squamate radiation.  Iguanids are fairly basic, but have the loose, specialized squamate skull: the very feature which has permitted the squamates to radiate into thousands of separate specialized forms.  Sphenodon has a classic, solid skull construction which doesn't permit a great deal of variation.  Think, for example, of  crocodylomorphs, temnospondyls or Mesozoic mammals.  That we are here proves that a solid, akinetic skull doesn't necessarily doom a taxon to morphological stagnation.  However, it is certainly a consideration.  

So, while we wait patiently for some scholar to pen the successor to Williston, Romer and Carroll, we may as well take a brief look at the phylogenetic neighborhood of paleontology's Everyman. ATW020406.

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