Tuesday, 9 December 2014

A new species of Salamander from the Early Cretaceous of Western Siberia.

Salamanders, Caudata, are one of the three extant groups of Lisamphibians, along with Frogs, Anura, and Caecilians, Gymnophiona. The earliest fossil Salamanders known date from the Middle Jurassic, and include both crown group Salamanders (all living Salamanders, their most recent common ancestor, and everything descended from that ancestor) and stem group Salamanders (Salamanders which lived before the most recent common ancestor of all living Salamanders, or which are descended from such Salamanders but not the most recent common ancestor), suggesting that more-or-less modern forms appeared very early in the history of the group. The crown group Salamanders quickly become dominant in the fossil record, with only one report of Cretaceous stem group Salamanders, based upon isolated vertebrae from the Cloverly Formation of Wyoming.

In a forthcoming paper in the journal Acta Palaeontologica Polonica available online from 28 November 2014, Pavel Skutschas of the Vertebrate Zoology Department at Saint Petersburg State University and the Laboratory of Mesozoic and Cenozoic Continental Ecosystems at Tomsk State University describes a possible stem group Salamander from the Ilek Formation of Western Siberia.

The specimen comprises a single fragmentary trunk vertebra, which Skutschas does not name, but which he feels is likely to represent a stem group Salamander as it has a notochordal centrum  (a common feature to all Lisamphibians), is longer than it is wide (seen in all Salamanders and no Frogs), lacks the extra muscle attachments seen in Caecilians, is far larger than any known Mesozoic crown group Salamander (all of which were quite small, the modern Giant Salamanders having appeared later) is heavily ossified (again not seen in Mesozoic crown group Salamanders) and has scattered pits on its ventral and lateral surfaces (a feature seen in some other stem group Salamanders but not in any known crown group Salamander).

Fragmentary trunk vertebral centrum of stem salamander Caudata, from the Shestakovo locality, Lower Cretaceous (Aptian–Albian) Ilek Formation, Western Siberia, Russia; in right lateral (A), left lateral (B), ventral (C, anterior towards top), posterior (D), anterior (E), and dorsal (F, anterior towards top) views. Photographs (A1–C1, D–F) and interpretive drawings (A2–C2). All images at same scale. Skutschas (2014).

The Ilek Formation of Western Siberia has yielded a variety of other relict vertebrates with Jurassic affinities, including Choristoderes, Paramacellodid Lizards, Tritylodonts, Docodont Cynodonts and Protosuchian and Shartegosuchid Crocodyliforms. Skutschas suggests that environmental conditions in Western Siberia remained constant and stable across the Jurassic-Cretaceous boundary, and that the area therefore provided a refugia for vertebrate groups that went extinct elsewhere.

See also…

Paedomorphisis is a pattern of developmental change in which an organism evolves to retain juvenile traits into its adult, sexually mature stage. This is a recurring evolutionary pattern in some groups of animals, with different but related lineages often separately developing the same traits in this way. One such group is the Lungless Salamanders (Plethodontidae), a group...

Newts, Pleurodelinae, are small members of the...

The Daohugou Beds are a fossil Lagarstätte from Ningcheng County in Inner Mongolia, which have produced a large number of well preserved Middle Jurassic Vertebrates, Insects, Plants and other fossils...

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