Altenglanerpeton

''Altenglanerpeton'' is an extinct genus of microsaur amphibian from the Late Carboniferous or Early Permian of Germany. ''Altenglanerpeton'' was named in 2012 after the Altenglan Formation in which it was found. The type and only species is ''A. schroederi''.

Description

''Altenglanerpeton'' is known from a single partial skeleton from an outcrop of the Altenglan Formation, which is part of the Saar–Nahe Basin. The Altenglan Formation dates back to the Carboniferous-Permian transition, about 299 million years ago. The skeleton was discovered sometime in the 1870s in the village of Werschweiler, and was first described by German paleontologist Eckart Schröder in 1939. Schröder tentatively assigned the specimen to the microsaur ''Microbrachis'', although its classification as a microsaur was questioned in later years.

The holotype skeleton includes a crushed skull preserved in dorsal or top view, and a straight length of vertebrae and associated ribs that are poorly preserved. The forelimbs and parts of the pectoral girdle are also preserved. The hind limbs and tail are missing. ''Altenglanerpeton'' has a robust skull with small, widely spaced eye sockets. The skull appears triangular from above as well as from the side, since it has a narrow and pointed snout. One distinguishing feature of ''Altenglanerpeton'' is the extension of the jugal bones far in front of the eye sockets. Unlike many other microsaurs, ''Altenglanerpeton'' lacks a network of lateral line grooves across its skull. ''Altenglanerpeton'' has an elongated body with around 30 simple spool-shaped vertebrae and small, poorly developed limbs. It is similar in appearance to the ostodolepids ''Micraroter'' and ''Pelodosotis'', both of which have long bodies and tiny limbs.

Classification

''Altenglanerpeton'' belongs to a group of early amphibians called microsaurs, characterized by their small size and simple vertebrae. When ''Altenglanerpeton'' was first named in 2012, a phylogenetic analysis was conducted to determine its relationship with other lepospondyls. In support of Schröder's original assignment, ''Altenglanerpeton'' was placed as a microsaur. "Microsauria" is now considered to be a paraphyletic grouping, meaning that it does not form a true clade. ''Altenglanerpeton'' belongs to a similar group called Recumbirostra, which is a clade. ''Altenglanerpeton'' was found to be most closely related to ''Tambaroter'', named in 2011 from the Early Permian Tambach Formation of Germany. According to the analysis, ''Altenglanerpeton'' and ''Tambaroter'' form a clade that is the sister taxon to the family Brachystelechidae. ''Altenglanerpeton'' is most similar in appearance to ostodolepids, and although both are members of Recumbirostra, Ostodolepidae is only distantly related to ''Altenglanerpeton''. Below is a cladogram showing the phylogenetic position of ''Altenglanerpeton'' from Glienke (2012):

Paleoenvironment

The layer of the Altenglan Formation in which ''Altenglanerpeton'' was found is thought to have been deposited in a lake environment, specifically that of Hauptkalk Lake, a large, shallow body of water that covered much of the Saar–Nahe Basin at the Carboniferous-Permian transition. Sedimentation rates in the lake were low, meaning that few fossils were preserved. Besides the ''Altenglanerpeton'' skeleton, only three tetrapod fossils are known from Hauptkalk Lake deposits: two specimens of the temnospondyl '' Apateon pedestris'' and a skull of the temnospondyl ''Sclerocephalus bavaricus''. The microsaur ''Batropetes'' is also known from the Saar-Nahe Basin, but it comes from the younger Odernheim Subformation.

The presence of ''Altenglanerpeton'' in a lake deposit suggests that it was aquatic. The long body and reduced limbs would have facilitated lateral undulation as a form of swimming. Although it is not preserved in the holotype specimen, the tail may have had an elongated tadpole-like fin. In contrast, the robust skull and lack of lateral line grooves in ''Altenglanerpeton'' suggest that it was primarily terrestrial. While most aquatic amphibians have large, forward-facing eyes and three-dimensional vision for capturing prey underwater, ''Altenglanerpeton'' has small, laterally-directed eyes that would have been more suitable for burrowing, as in living caecilians. With its elongated body, ''Altenglanerpeton'' may have undulated through soil and leaf litter.

References

{{Taxonbar, from=Q4736247

Carboniferous amphibians of Europe
Permian amphibians of Europe
Recumbirostrans