The tetrapod Caerorhachis bairdi Holmes and Carroll from the Lower Carboniferous of Scotland

Ruta, Marcello and Milner, Andrew R. and Coates, Michael I. (2001) The tetrapod Caerorhachis bairdi Holmes and Carroll from the Lower Carboniferous of Scotland. Transactions of the Royal Societ y of Edinburgh: Earth Sciences, 92 (3). pp. 229-261. ISSN 1755-6910

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Abstract

The tetrapod Caerorhachis bairdi, probably from the Pendleian Limestone Coal
Group in the Scottish Midland Valley, is redi agnosed and redescribed, and its affinities are
discussed. Caerorachis was originally interpreted as a temnospondyl amphibian, based on
characters that are now regarded as primitive for tetrapods, or of uncertain polarity. Several
features of Caerorhachis (e.g. gastrocentrous vertebrae, curved trunk ribs, reduced dorsal iliac
blade, L-shaped tarsal intermedium) are observed in certain primitive amniotes. In particular,
Caerorhachis resembles ‘anthracosaurs’, generally considered to be among the most primitive of
stem-group amniotes.
The phylogenetic position of Caerorhachis is considered in the light of recently published cladistic
analyses of Palaeozoic tetrapods. Most analyses place Caerorhachis at the base of, or within, ‘anthra-
cosaurs’. When multiple, equally parsimonious solutions are found, its ‘anthracosaur’ affinities are
shown in at least some trees, and are supported by several informative and, generally, highly
consistent characters. Alternative phylogenetic placements (e.g. sister taxon to temnospondyls) are
usually less well corroborated.
If the fundamental evolutionary split of most early tetrapods into stem-group lissamphibians (e.g.
temnospondyl s) and stem-group amniotes (e.g. ‘anthracosaurs’) is accepted, then the revised
interpretation of Caerorhachi s sheds light on near-ancestral conditions for Amniota.

Keywords:amniotes, 'anthracosaurs', characters, lower jaw, palate, relationships, skull
Subjects:C Biological Sciences > C300 Zoology
C Biological Sciences > C182 Evolution
F Physical Sciences > F641 Palaeontology
C Biological Sciences > C181 Biodiversity
Divisions:College of Science > School of Life Sciences
ID Code:11961
Deposited On:22 Sep 2013 19:55

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