''Mesanerpeton'' 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 Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of four-limbed

stem-tetrapod The Stem Tetrapoda are a cladistically defined group, consisting of all animals more closely related to extant four-legged vertebrates than to their closest extant relatives (the lungfish), but excluding the crown group Tetrapoda. They are thus ...

from the

Mississippian Mississippian may refer to: * Mississippian (geology), a subperiod of the Carboniferous period in the geologic timescale, roughly 360 to 325 million years ago * Mississippian cultures, a network of precontact cultures across the midwest and Easte ...

(

Tournaisian The Tournaisian is in the ICS geologic timescale the lowest stage or oldest age of the Mississippian, the oldest subsystem of the Carboniferous. The Tournaisian age lasted from Ma to Ma. It is preceded by the Famennian (the uppermost st ...

) of

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 ...

. It contains a single species, ''Mesanerpeton woodi'', who based on a disarticulated specimen including a

clavicle The clavicle, collarbone, or keybone is a slender, S-shaped long bone approximately long that serves as a strut between the scapula, shoulder blade and the sternum (breastbone). There are two clavicles, one on each side of the body. The clavic ...

vertebrae Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

, and forelimb bones from the

Ballagan Formation The Ballagan Formation is a Formation (geology), geologic formation in Scotland and England. It preserves fossils dating back to the early part of the Carboniferous Period (geology), period (Tournaisian – early Visean). Its name comes from the ...

. The vertebrae are poorly-ossified and similar to ''

Crassigyrinus ''Crassigyrinus'' (from , 'thick' and , 'tadpole') is an extinct genus of carnivorous stem tetrapod from the Early Carboniferous Clackmannan Group of Scotland and possibly Greer, West Virginia. Discovery The type specimen was originally descri ...

'', but the forelimb was robust. The shape and level of torsion present in the humerus are intermediate between Devonian stem-tetrapods and later Carboniferous tetrapods. This transitional condition, and the associated rerouting of the

brachial artery The brachial artery is the major blood vessel of the (upper) arm. It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa ...

and

median nerve The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve originates from the lateral and medial cords of the brachial plexus, and has cont ...

, may indicate that ''Mesanerpeton'' had a higher stride length and more efficient locomotion on land compared to its predecessors.

References and notes

Notes

Stegocephali Tournaisian life Mississippian sarcopterygians of Europe Fossil taxa described in 2016 Taxa named by Jenny Clack {{Paleo-tetrapodomorph-stub