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

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus of early Carboniferous

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

, 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 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 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 dorsorum'') comes from ...

(an arm muscle) attachment on the

humerus The humerus (; ) 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 and ulna, and consists of three sections. The humeral upper extremity consists of a r ...

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

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...

Ichthyostegalia Ichthyostegalia is an order of extinct 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 not all, ...

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 country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to ...

and classified as a

lobe-finned fish Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includ ...

. Its fossils were found in the Ballagan Formation. The

type specimen In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...

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 Jennifer Alice Clack, (''née'' Agnew; 3 November 1947 – 26 March 2020) was an English palaeontologist and evolutionary biologist. She specialised in the early evolution of tetrapods, specifically studying the "fish to tetrapod" transition: ...

named and reclassified the fossil as a primitive tetrapod. ''Pederpes'' is placed in the family

Whatcheeriidae Whatcheeriidae is an extinct family of tetrapods which lived in the Mississippian sub-period, a subdivision of the Carboniferous period. It contains the genera ''Pederpes'', '' Whatcheeria'', and possibly ''Ossinodus''. Fossils of a possible w ...

, 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 four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbo ...

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

class Class 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 differently ...

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 t ...

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

Romer's gap Romer's gap is an example of an apparent gap in the tetrapod fossil record used in the study of evolutionary biology. Such gaps represent periods from which excavators have not yet found relevant fossils. Romer's gap is named after paleontologist ...

and provides biologists with rare information about the development of tetrapods in a time where 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 humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either si ...

with a throat pouch the way many modern

amphibians Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbo ...

do.

References

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