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Early tetrapod Pederpes in new Nature issue



From: Ben Creisler bh480@scn.org
Early tetrapod Pederpes in new Nature issue

Here are the citations, abstracts, and key passages from 
two articles on a newly identified early tetrapod.

CLACK, J.A. 2002. An early tetrapod from 'Romer's Gap.'  
Nature 418, 72 - 76 (2002)
The fossil record of early tetrapods has been increased 
recently by new finds from the Devonian period and mid-
late Early Carboniferous period. Despite this, 
understanding of tetrapod evolution has been hampered by a 
20-million-year gap ('Romer's Gap') that covers the 
crucial, early period when many key features of 
terrestrial tetrapods were acquired. Here I describe the 
only articulated skeleton of a tetrapod, Pederpes, yet 
found from the Tournaisian epoch (354-344 million years 
ago (Myr)). The new taxon includes a pes with five robust 
digits, but a very small, possibly supernumerary digit 
preserved on the manus suggests the presence of 
polydactyly. Polydactylous early tetrapods may have 
survived beyond the end of the Devonian and pentadactyly 
cannot be assumed for the pes. However, the pes has 
characteristics that distinguish it from the paddle-like 
feet of the Devonian forms and resembles the feet of 
later, more terrestrially adapted Carboniferous forms. 
Pederpes is the earliest-known tetrapod to show the 
beginnings of terrestrial locomotion and was at least 
functionally pentadactyl. With its later American sister-
genus, Whatcheeria, , it represents the next most 
primitive tetrapod clade after those of the Late Devonian, 
bridging the temporal, morphological and phylogenetic gaps 
that have hitherto separated Late Devonian and mid-
Carboniferous tetrapod faunas.
Misidentified as a rhizodont fish on its discovery in 
1971, recent preparation has revealed the specimen to be a 
tetrapod of about 650 mm in presacral length, lacking only 
a few parts of the skull, the tail, and some limb 
elements .......
Tetrapodomorpha Ahlberg, 1991
Whatcheeriidae fam. nov.
Pederpes finneyae gen. et sp. nov.
Etymology. Pederpes, Peder after Peder Aspen, its 
discoverer (Peder is the Norwegian form of Peter, which is 
Greek for rock), and erpes (Greek for crawler), that 
is, 'rock crawler' (Pederpes can also be split into Peder 
and pes (foot), that is, 'rock foot'). finneyae, after S. 
M. Finney, who prepared the specimen.
Commentary:
CARROLL, R. 2002. Palaeontology: Early land vertebrates. 
Nature 418, 35 - 36 (2002)
A 350-million-year-old fossil provides evidence of an 
almost unknown stage in the origin of land vertebrates. It 
is also a reminder of how little is known of the 
relationships between the main lineages of amphibians and 
reptiles.... 
Although the full length of the tail of Pederpes is not 
known, the animal was probably nearly a metre in length. 
It was a short-limbed, large-skulled predator, resembling 
an especially ungainly crocodile. But it almost certainly 
reproduced in the water, somewhat like modern aquatic 
salamanders. Grooves in the skull for lateral-line canals -
 a characteristic of fish - suggest that it lived partly 
in the water. The foot structure, however, indicates it 
could walk on land. Pederpes is advanced over its Devonian 
antecedents in having only five toes on the foot, yet has 
a relict of a tiny finger on the forelimb reminiscent of 
the supernumerary digits of the best-known amphibians - 
Ichthyostega and Acanthostega - from the Upper 
Devonian......
The absence of fossils of early members of most Palaeozoic 
lineages also precludes the possibility of establishing a 
reliable classification of the main groups of living 
tetrapods. Without knowledge of the earliest recognizable 
ancestors of the groups leading to amniotes and the three 
orders of modern amphibians (frogs, salamanders and 
caecilians), we cannot determine whether the modern 
amphibians had an immediate common ancestry or which of 
the Palaeozoic lineages is the closest relative of 
amniotes. Clack's discovery raises hopes that further 
searches in Lower Carboniferous deposits, especially in 
Scotland, may finally provide an answer to these questions.