Pederpes
Encyclopedia
Pederpes is an extinct genus of early Carboniferous tetrapod
, dating from the Tournaisian age (lower Mississippian, 359 - 345 Ma). Pederpes contains one species, P. finneyae, 1 m long.
This most basal Carboniferous tetrapod had a large, somewhat triangular head, similar to that of later American sister-genus Whatcheeria
, from which it is distinguished by various skeletal features, such as a spike-like latissimus dorsi (an arm muscle) attachment on the humerus
and several minor skull features. The feet had characteristics that distinguished it from the paddle-like feet of the Devonian
Ichthyostegalia and resembled the feet of later, more terrestrially adapted Carboniferous forms. Pederpes is the earliest-known tetrapod to show the beginnings of terrestrial locomotion and despite the probable presence of a sixth digit on the forelimbs it was at least functionally pentadactyl.
and classified as a lobe-finned fish. Its fossils were found in the Ballagan Formation. The type specimen was a nearly complete, articulated skeleton. 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.
Pederpes is placed in the family Whatcheeriidae
, of uncertain relationships to other tetrapod families. While undoubtedly amphibian in life and reproductive mode, under cladistic taxonomy
, Pederpes is not considered an amphibian in the meaning of modern amphibians
. As a very basal (primitive) tetrapod, it falls under the traditional class
Amphibia in Linnaean taxonomy
.
Pederpes is an important fossil because it comes from the period of time known as Romer's Gap
and provides biologists with rare information about the development of tetrapods in a time where terrestrial life was rare.
The shape of the skull and the fact that the feet face forward rather than outward indicate that Pederpes was well adapted to land life. It is currently 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, and 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 many modern amphibians do.
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
, dating from the Tournaisian age (lower Mississippian, 359 - 345 Ma). Pederpes contains one species, P. finneyae, 1 m long.
This most basal Carboniferous tetrapod had a large, somewhat triangular head, similar to that of later American sister-genus Whatcheeria
Whatcheeria
Whatcheeria is an extinct genus of early tetrapod from the Early Carboniferous of Iowa. Fossils have been found in 340 million year old fissure fill deposits in the town of Delta. The type species W. deltae was named in 1995...
, from which it is distinguished by various skeletal features, such as a spike-like latissimus dorsi (an arm muscle) attachment on the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
and several minor skull features. The feet had characteristics that distinguished it from the paddle-like feet of the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
Ichthyostegalia and resembled the feet of later, more terrestrially adapted Carboniferous forms. Pederpes is the earliest-known tetrapod to show the beginnings of terrestrial locomotion and despite the probable presence of a sixth digit on the forelimbs it was at least functionally pentadactyl.
Discovery and Classification
Pederpes was discovered in 1971 in central ScotlandScotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
and classified as a lobe-finned fish. Its fossils were found in the Ballagan Formation. The type specimen was a nearly complete, articulated skeleton. 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.
Pederpes is placed in the family Whatcheeriidae
Whatcheeriidae
Whatcheeriidae was a family of tetrapods which lived in the Mississippian sub-period, a subdivision of the Carboniferous period. It contains the genera Pederpes and Whatcheeria...
, of uncertain relationships to other tetrapod families. While undoubtedly amphibian in life and reproductive mode, under cladistic taxonomy
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
, Pederpes is not considered an amphibian in the meaning of modern amphibians
Lissamphibia
The subclass Lissamphibia includes all recent amphibians and means smooth amphibia.Extant amphibians fall into one of three orders — the Anura , the Caudata or Urodela , and the Gymnophiona or Apoda .Although the ancestry of each group is still unclear, all share certain common characteristics,...
. As a very basal (primitive) tetrapod, it falls under the traditional class
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
Amphibia in Linnaean taxonomy
Linnaean taxonomy
Linnaean taxonomy can mean either of two related concepts:# the particular form of biological classification set up by Carl Linnaeus, as set forth in his Systema Naturæ and subsequent works...
.
Pederpes is an important fossil because it comes from the period of time known as Romer's Gap
Romer's gap
Romer's Gap is an example of a gap in the fossil record used in the study of evolution. Such gaps represent a period from which excavators have found no or very few fossils. Romer's gap is named after paleontologist Dr...
and provides biologists with rare information about the development of tetrapods in a time where terrestrial life was rare.
Anatomy and Lifestyle.
Pederpes was 1 m long, making it average-sized for an early tetrapod.The shape of the skull and the fact that the feet face forward rather than outward indicate that Pederpes was well adapted to land life. It is currently 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, and 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 many modern amphibians do.