Microphon exiguus: an Aquatic Neotonic Kotlassiid Seymouriamorph (Reptiliomorph) From Permian Russia

New finds of Microphon exiguus (Seymouriamorpha, Kotlassiidae) in the Severodvinian beds of the Sukhona River Basin, Russia

Author:

Bulanov

Abstract:

New data on the morphology and ontogeny of the Permian kotlassiid Microphon exiguus Ivachnenko, 1983 (Tetrapoda, Seymouriamorpha), based on the collection from the Ust’e Strelny locality (Russia, Vologda Region; Severodvinian Regional Stage), are reported. At the definitive stage, M. exiguus retains the larval skull habitus (short preorbital region, a few marginal teeth, widely open posttemporal fenestra) and seismosensory grooves. These features, along with the reduced nasolacrimal duct, are indicative of an important role of pedomorphosis in the evolution of Severodvinian kotlassiids and, in particular, the genus Microphon, which should be regarded as a neotenic, permanently aquatic Permian amphibian.

Two New Bystrowianid Chroniosuchians From Olenekian Triassic Russia

New bystrowianid chroniosuchians (Amphibia, Anthracosauromorpha) from the Triassic of Russia and diversification of Bystrowianidae

Authors:

Shishkin et al

Abstract:

The first bystrowianids recorded in the Gamskian Horizon of the East European Platform, Vyushkoviana operta gen. et sp. nov. and Dromotectum abditum sp. nov. (Amphibia, Chroniosuchia), are described based on specimens from the Malaya Northern Dvina and Don river basins. The patterns of the dermal scute evolution observed in bystrowianids warrant the subdivision of the group into the subfamilies Bystrowianinae Vjuschkov 1957, Dromotectinae subfam. nov. and Axitectinae subfam. nov. The second and third show progressive reduction of the external (paraxial) zone of the interosteoderm articulation. New data supporting close proximity or phyletic succession of the chroniosuchid and bystrowianid types of the osteoderm design are revealed. The concept of the Chroniosuchidae as a paraphyletic group is rejected. Evolutionary significance of the key features distinguishing the bystrowianid subfamilies is analyzed.

Gephyrostegus: a Problematic Reptiliomorph From Asturian Carboniferious Czech Republic

Cranial anatomy, ontogeny, and relationships of the Late Carboniferous tetrapod Gephyrostegus bohemicus Jaekel, 1902

Authors:

Klembara et al

Abstract:

We review the cranial morphology of the Late Carboniferous terrestrial tetrapod Gephyrostegus bohemicus from the coal deposits of the Nýřany Basin in the Czech Republic. Gephyrostegus is known from several skulls ranging in length from about 25 mm to about 58 mm (holotype). The narrow skull is about twice as long as wide and shows a well-ossified quadrate and articular, but no evidence of braincase ossification. Autapomorphic features include a pustular ornamentation on some skull table bones, and a plate-like tabular process exhibiting a fine dorsal pitting. Gephyrostegus shares with Bruktererpeton fiebigi (Late Carboniferous, Germany) the presence of low, anteromedially to posterolaterally orientated sharp ridges on the posteroventral surface of the vomer. It shares with seymouriamorphs a rectangular, transverse pterygoid process and closely packed, radially arranged rows of small denticles on the palate. A phylogenetic analysis retrieves Gephyrostegidae (Gephyrostegus, Bruktererpeton) as sister group to Seymouriamorpha, although this wider clade receives low bootstrap support.