Pederpes

QPederpes is an extinct genus of early Carboniferous tetrapod, dating from the lower Mississippian, 348-347.6 million years ago (mya). Pederpes contains one species, P. finneyae, 1 m long. A single fossil was found in East Kirton quarry, West Lothian, Scotland, in early Carboniferous rocks. It is the first (and only) known near-complete skeleton of a tetrapod from the earliest Carboniferous. It lacks only the tail and some digits.^[1]

Pederpes Temporal range: Lower Mississippian
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Superclass:	Tetrapoda
Family:	Whatcheeriidae
Genus:	Pederpes Clack, 2002
Species
P. finneyae Clack, 2002 (type)

Pederpes had a large, somewhat triangular head, similar to that of later American Whatcheeria. This specimen shows the earliest example of a foot adapted for walking on land. The feet look like the feet of later, more terrestrially adapted Carboniferous forms. Pederpes is therefore the earliest known tetrapod that walked on land.

It fits in the middle of the a gap in the fossil record which separates the aquatic Devonian tetrapods from the terrestrial ones of the mid-Carboniferous.

Discovery and classification

Pederpes was discovered in 1971 in central Scotland and classified as a lobe-finned fish. The type specimen was a nearly complete, articulated skeleton (bones still connected). Only the tail and some bones of the skull and limbs were missing. It was not until 2002 that Jennifer Clack named and reclassified the fossil as a primitive tetrapod.^[1]

Pederpes is of uncertain relationship to other tetrapod families. While undoubtedly amphibian in life mode, Pederpes is not considered an amphibian in the meaning of modern amphibians. It is a very basal (primitive) tetrapod.

Pederpes is an important fossil because it comes from the period of time known as Romer's gap, a 20 million year gap in the sequence of tetrapod fossils. It is therefore a transitional fossil, and gives biologists rare information about the development of tetrapods in a time when terrestrial life was scarce.^[2]

Anatomy and lifestyle

Pederpes was 1 metre long, estimating the tail as one-third of the body length. This is average-sized for an early tetrapod.

The shape of the skull and the fact that the feet face forward rather than outward. This shows that Pederpes was well adapted to life on land. It is the earliest known fully terrestrial animal, although the structure of the ear shows that its hearing was still much more functional underwater than on land. It may have spent much of its time in the water and could have hunted there.

The narrow skull suggests that Pederpes breathed by inhaling with a muscular action like most modern tetrapods, rather than by pumping air into the lungs with a throat pouch the way modern amphibians usually do.

References

1. Clack J.A. 2002. An early tetrapod from 'Romer's Gap'. Nature 418, 72–76
2. Clack J.A. 2012. Gaining ground: the origin and evolution of tetrapods. 2nd ed, Bloominton, Indiana: Indiana University Press. ISBN 978-0-253-35675-8, (Pederpes at Google Books)