''Pederpes'' ("Peter's Foot") is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus of early Carboniferous stegocephalian, dating from 348 to 347.6 Ma in the Tournaisian age (lower Mississippian). ''Pederpes'' contains one species, ''P. finneyae'', 1 m long. This most basal Carboniferous stegocephalian 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 The latissimus dorsi () is a large, flat muscle on the back that stretches to the sides, behind the arm, and is partly covered by the trapezius on the back near the midline. The word latissimus dorsi (plural: ''latissimi dorsi'') comes from L ...

(an arm muscle) attachment on the

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

and several minor skull features. The feet had characteristics that distinguished it from the paddle-like feet of the

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

Ichthyostegalia Ichthyostegalia is an obsolete order of early amphibians, representing the earliest landliving vertebrates. The group is thus an evolutionary grade rather than a clade. While the group are recognized as having feet rather than fins, most, if ...

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

Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

and classified as a

lobe-finned fish Sarcopterygii (; )—sometimes considered synonymous with Crossopterygii ()—is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates ar ...

. Its fossils were found in the Ballagan Formation. The

type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

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 an amphibian in the broad sense, under cladistic taxonomy, ''Pederpes'' is not a member of the

crown group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor ...

amphibia Amphibians are ectothermic, anamniotic, four-limbed vertebrate animals that constitute the class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all tetrapods, but excluding the amniotes (tetrapods with an amniotic ...

n in the meaning of modern amphibians. As a very basal (primitive) tetrapod, it falls under the traditional

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

Amphibia in

Linnaean taxonomy Linnaean taxonomy can mean either of two related concepts: # The particular form of biological classification (taxonomy) set up by Carl Linnaeus, as set forth in his ''Systema Naturae'' (1735) and subsequent works. In the taxonomy of Linnaeus th ...

. ''Pederpes'' is an important fossil because it comes from the period known as

Romer's gap Romer's gap is an apparent gap in the Paleozoic tetrapod fossil record noted in the studies of paleontology and evolutionary biology, which represent periods in the Early Carboniferous from which excavators have not yet found relevant transition ...

and provides biologists with rare information about the development of tetrapods in a time when terrestrial life was rare. The fossil was discovered in the Ballagan Formation, Inverclyde Group, claviger-macra (CM) palynozone (348 to 347.6 mya), Tournaisain Tn3c, Courceyan, Dinantian, Lower Carboniferous.

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 The lungs are the primary organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the backbone on either side of the heart. Their function in the respiratory syste ...

with a throat pouch the way many modern

amphibians Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

do.

References

External links

Taxonomicon entry for Pederpes

Taxonomicon entry for P. finneyae

Abstract of description

* Dixon, Dougal.The World Encyclopedia of Dinosaurs and Prehistoric Creatures. Anness Publishing Ltd. London, UK: 2007. {{Taxonbar, from1=Q134953, from2=Q20719025 Carboniferous tetrapods Fossil taxa described in 2002 Carboniferous tetrapods of Europe