Limnoiketes

''Lydekkerina'' is an extinct genus of stereospondyl temnospondyl. It is the type genus of the family Lydekkerinidae. Fossils have been collected from Early Triassic deposits in South Africa and Australia. The type species is '' L. huxleyi'', first described in 1889. While most other stereospondyls were semiaquatic, ''Lydekkerina'' was exclusively terrestrial.

Description

''Lydekkerina'' was a relatively small temnospondyl, growing up to around in length. Skulls range in length from in the smallest known individual to up to in larger individuals. The skull is wedge-shaped and has a parabolic outline with convex lateral margins. Shallow pits cover the surface of the skull. Teeth line the palate as well as the jaws, and some skulls even bear large ectopterygoid tusks on the underside of the skull.

''Lydekkerina'' can be distinguished from other lydekkerinids on the basis of several skull characteristics. One such feature is the presence of vomerine shagreen, tiny bumps covering the bones of the palate. An opening at the tip of the palate called the anterior palatal vacuity is divided by two projections of the skull roof, a second distinctive feature of the genus. Moreover, distinctive ridges are present on the underside of the skull roof around the eye sockets, probably to provide structural support.

History and classification

''Lydekkerina huxleyi'' was first briefly described as a species of ''Bothriceps'' by Richard Lydekker in 1889. The specific name honors Thomas Henry Huxley, an English biologist who named the genus ''Bothriceps'' in 1859 from material in Australia. Robert Broom, a South African paleontologist, provided a more accurate description of the species in 1915 and reassigned it to the new genus ''Lydekkerina'', named after Lydekker. The type specimen and a paratype specimen were described in much greater detail, particularly the lower jaw, in 2007 by R. Hewison, and a detailed account of its sacral region, pelvic girdle and hind limb.

''Lydekkerina'' is one of the most common temnospondyls found from the Permo-Triassic Karoo Basin of South Africa. Many fossils have been found from the ''Lystrosaurus'' Assemblage Zone of the Beaufort Group. Many, however, are poorly preserved, being crushed or deformed. The variable conditions of specimens has resulted in confusion in identification. Some paleontologists have proposed that variations in skull shape among specimens represent deformities rather than true morphologies. Therefore, characteristics that distinguish different lydekkerinids from one another may be the results of preservation, not taxonomic distinctness. In 2006, it was proposed that the South African lydekkerinids '' Limnoiketes'' and '' Broomulus'' were synonymous with ''Lydekkerina'' for this reason.

A second species of ''Lydekkerina'', ''L. putterilli'', was named by Broom in 1930. Its description was based on a small partial skull from the Permian ''Dicynodon'' Assemblage Zone. It was later considered to be a juvenile rhinesuchid related to ''Uranocentrodon''. In 2000, ''L. putterilli'' was assigned to its own genus, ''Broomistega''.

Broom described a third species, ''L. kitchingi'', from the ''Dicynodon'' Assemblage Zone in 1950. In 1996 it was reassigned as a juvenile form of the rhinesuchid '' Muchocephalus''. In 2003, both ''L. kitchingi'' and ''Muchocephalus'' were synonymized with ''Laccosaurus''.

Temnospondyl remains from the Early Triassic Rewan Formation of Queensland, Australia, were described in 2006 and assigned to ''Lydekkerina huxleyi''. These remains possess characters diagnostic of ''Lydekkerina'' such as the ridges underneath the skull roof and the vomerine shagreen.

Paleobiology

Because the bones of ''Lydekkerina'' are more heavily ossified than other stereospondyls, it is thought to have been terrestrial. Large bony projections on the skeleton likely served as attachments for strong muscles. Joints between bones were well-developed, enabling effective locomotion on land. The sensory system of pressure-sensitive sulci across the skull is poorly developed, suggesting that ''Lydekkerina'' had little use for these organs in a land environment. The skeleton of ''Lydekkerina'' is similar to those of early stereospondyl relatives such as the archegosauroids, but bears little resemblance to those of the exclusively terrestrial Permian temnospondyls.

References

{{Taxonbar, from=Q2634677

Stereospondyls
Prehistoric amphibian genera
Prehistoric amphibians of Australia
Triassic temnospondyls of Australia
Early Triassic amphibians of Africa
Triassic temnospondyls of Africa
Taxa named by Robert Broom
Fossil taxa described in 1915