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High latitudes Gondwanan Devonian Tetrapods

Tutusius umlambo and Umzantsia amazana

Tutusius umlambo and Umzantsia amazana are extinct tetrapods that lived 360 million years ago. The two tetrapods are described from the same site, which is the Late Devonian (late Famennian) Gondwana locality of Waterloo Farm in South Africa, then located within the Antarctic Circle. This provides the first evidence that Devonian tetrapods were not restricted to the tropics (30 degrees north and south of the equator) as was formerly believed (Clack ) and suggests that they may have been global in distribution. Waterloo Farm fossils have been metamorphosed and intensely flattened, with the bone tissue replaced by secondary metamorphic mica that is partially altered to kaolinite and chlorite during uplift. They also provide the first evidence of Devonian tetrapods from the continent of Africa, and only the second and third taxa from Gondwana[A tetrapod fauna from within the Devonian Antarctic Circle.

File:Artists reconstruction by Maggie Newman showing Umzantsia (left) and Tutusius (right).jpg

Artists reconstruction by Maggie Newman showing Umzantsia (left) and Tutusius (right)

Tutusius umlambo

Description

Tutusius umlambo has a generic name in honour of Archbishop Desmond Tutu, in recognition of his outstanding contribution to the political and social development of South Africa. The specific name from isiXhosa “umlambo”, meaning “river”, referring to the depositional environment.

Waterloo Farm tetrapod(Tutusius umlambo)

Tutusius is represented by a single bone from the shoulder girdle, the cleithrum. It tapers to a point anteroventrally and carries a single attachment scar for the scapulocoracoid, which extends along the anteroventral process, forms a v-shaped dorsal peak, and ends posteriorly in a projecting buttress. The cleithrum lacks ornament and has a distinct flexure point demarcating the obliquely sloping ventral half of the bone from the more vertical dorsal half. The blade of the cleithrum is broad and thin. It differs from all other tetrapod cleithra in the presence of a projecting posterior flange, with striated texture and a jagged margin, on the middle part of the blade.

Umzantsia amazana

Description

Umzantsia amazana is derived from isiXhosa “uMzantsi”, meaning “south” (also “South Africa”), referring to its place of origin, and “amazana” meaning “water ripples”, referring to its distinctive dermal ornament.

Waterloo Farm tetrapod(Umzantsia amazana)

Dermal bones of Umzantsia carry a distinctive ornament consisting of fine parallel ridges reminiscent of water ripples. This allows identification of a number of cranial bones and a cleithrum from one bedding plane which are probably derived from a single individual. The dermal ornament covers about 80% of the cleithrum of Umzantsia; this fishlike characteristic contrasts with the un-ornamented cleithra of most other Devonian tetrapods, suggesting a phylogenetic position between those tetrapods and their sister group, the Elpistostegalians. The only other tetrapod with dermal ornaments on the cleithrum is Parmastega though it covers far less of the cleithrum. The cleithrum tapers to a point anteroventrally and carries a single attachment scar for the scapulocoracoid, which extends along the anteroventral process, forms a v-shaped dorsal peak, and ends posteriorly in a projecting buttress. The blade of the cleithrum carries a semicircular posterodorsal extension. The jugal (cheek bone beneath the eye) extends anterior to the orbit and contacts the prefrontal. The jugal has a very short orbital margin and lacks a distinct dorsal postorbital process. A decayed lower jaw from a different individual of the same species was also described.