The first complete skeleton of a tetrapod from the earliest
Carboniferous to be described.
This specimen shows the earliest example of a foot adapted for walking on land.
It fits in the middle of the temporal, morphological and phylogenetic gap that separates
the aquatic Devonian tetrapods from the terrestrial ones of the mid-Carboniferous.
See
Nature 418.
My student Jon Jeffery made a collecting trip to the basement of the Hunterian Museum
in 1996 to look for rhizodonts in furtherance of his PhD on that group of Carboniferous
fishes. Among other specimens, he brought to the lab a largish nodule of something that
'looked interesting', allegedly a rhizodont, but he wasn't sure. We looked at it for a
few moments, and then I noticed comma-shaped scales across the base of some of the
sections. Then some larger plates and cross-sections of bone at the far end of the animal.
This was no fish, but a tetrapod, and there were its hind legs and pelvis! The label said
'Calciferous Sandstone Series', which I knew to be Lower Carboniferous, though I wasn't
sure how low.
I sent a sample to John Richardson at the Natural History Museum and he
confirmed it as Late Tournaisian. What we had was - at that time - the only articulated tetrapod specimen
from the Tournaisian yet discovered - the next earliest tetrapod after the Late Devonian,
and the only tetrapod specimen from the Lower Carboniferous of Western Scotland.
The specimen was discovered in 1970 by Peder Aspen, after whom it is named.
Labelled as a rhizodont, it had escaped detection by me and all of my early tetrapod
colleagues who had trawled through the Hunterian's collections, and also by Stan Wood,
who had worked in the Hunterian in the early 1970's.
After four years, the specimen was more or less completely prepared, and turned
out to be similar in some ways to the primitive tetrapod
Whatcheeria from the
Viséan of
Iowa, described by Lombard and Bolt in 1995. But it is not the same animal, and has some
key differences. They have been placed into the clade called Whatcheeriida, which
appears to have had a wide distribution in time and space, and may even cross the
Devonian/Carboniferous boundary (see
Daeschler
et al. 2009 in the publications list.)