A new species of Dimetrodon (Synapsida: Sphenacodontidae) from the Lower Permian of Germany records first occurrence of genus outside of North America

摘要

A new species of the sphenacodontid synapsid Dimetrodon, D. teutonis, is described on the basis of a single, adult specimen consisting of a large portion of the presacral vertebral column. The holotype was collected from the Lower Permian Tambach Formation, lowermost formational unit of the Upper Rotliegend, of the Bromacker quarry locality in the midregion of the Thuringian Forest near Gotha, central Germany. This is the first record of the genus outside of North America and, therefore, provides not only additional biological evidence of a continuous Euramerican landmass during the Early Permian, but also the absence of any major physical or biological barrier to faunal interchange of terrestrial vertebrates. An estimated weight of 14 kg for D. teutonis is half that of the smallest, previously recognized species, D. natalis. Sphenacodontid phylogeny indicates that the diminutive size of D. teutonis represents an autapomorphy and is in general accord with the absence of large-sized, basal synapsid predators at this truly terrestrial upland locality. It is speculated that the diminutive size of D. teutonis was probably an adaptation to a truly terrestrial, relatively uplands existence like that represented by the Bromacker locality. Here it subsisted on small vertebrates (and possibly large invertebrates) of the Bromacker assemblage, in which the dominant members in both size and abundance were herbivorous diadectids, and it was unlikely to encounter large predators.