The suborder Diadectomorpha consists of three families. The Late Pennsylvanian-Early Permian Limnoscelidae and Early Permian Tseajaiidae have a strictly North American record, whereas members of the Late Pennsylvanian-Early Permian Diadectidae are found in both North America and central Europe. It is important to note here two taxonomic reassessments of reported limnoscelids. Initially, Martens (1989) reported the occurrence of a limnoscelid-like form from the Bromacker locality in the Lower Permian, Tambach Formation at the base of the Upper Rotliegend of central Germany. However, during the course of study of recently discovered, undescribed Diadectes specimens from the same locality, it became apparent that the limnoscelid-like specimen should instead be referred to that genus. Second, Romeriscus periallus, described as a limnoscelid from the Pennsylvanian of Nova Scotia by Baird and Carroll (1967), was restudied by Laurin and Reisz (1992), who reassessed the genus as a nomen dubium. It should also be noted here that our distribution survey does not include the North American diadectids Empedocles, Enpedias, Bolbodon, Chilonyx, Diadectoides, Nothodon, Helodectes, and Animasaurus, as they very likely represent junior synonyms of Diadectes (Olson, 1947; Berman and Sumida, 1995).
The taxa and their ages and localities, as well as the bibliographic sources of this data, used to plot the Late Carboniferous and Early Permian distributions of the diadectomorph families Limnoscelidae, Tseajaiidae, and Diadectidae in Figures 3 and 4 are as follows:
Late Carboniferous (Fig. 3)
Limnoscelis (New Mexico and Colorado) and Limnostegis (Nova Scotia); Williston (1911b), Carroll (1967), Fracasso (1980), Berman and Sumida (1990), and Berman (1993).
Desmatodon (Colorado, New Mexico, and Pennsylvania) and Diasparactus (New Mexico); Case (1908), Case and Williston (1913), Romer (1952), Vaughn (1969, 1972), Fracasso (1980), Berman (1993), Eberth and Berman (1993), and Berman and Sumida (1995).
Early Permian (Fig. 4)
Limnosceloides (New Mexico and West Virginia) Limnoscelops (Colorado), and limnoscelid (Utah); Romer (1952), Vaughn (1962), Lewis and Vaughn (1965), Langston (1966), and Berman (1993).
Tseajaia (New Mexico and Utah); Vaughn (1964), Moss (1972), and Berman (1993).
Diadectes (Colorado, Germany, New Mexico, Ohio, Oklahoma, Prince Edward Island, Texas, Utah, and West Virginia), Phanerosaurus (Germany), and Stephanospondylus (Germany); Meyer
Figure 3. Late Carboniferous distributions of the diadectomorph families Limnoscelidae (L) and Diadectidae (D). Localities, latitidue and longitude may be found in Appendix 1.
(1860), Geinitz and Deichmuller (1882), Olson (1947, 1967, 1975), Langston (1963), Lewis and Vaughn (1965), Berman (1971, 1993), and Berman and Martens (1993).
The diadectomorphs exhibit a distribution that is nearly restricted to North America. Of the three families only the diadectids are represented in Europe and then by only three genera from Germany. Two of these, Phanerosaurus (Meyer, 1860) and Stephanospondylus (Geinitz and Deichmuller, 1882), were described over a century ago on the basis of very fragmentary specimens from the Lower Rotliegend. No other materials have been found that can be referred to them, and Stephanosaurus may be a junior synonym of Phanerosaurus (Romer, 1925). A total of four specimens of Diadectes, a complete skeleton, an isolated skull, and the greater portions of two postcrania, have been recently recovered from the Lower Permian Tambach Formation of the Upper Rotliegend, Bromacker locality in central Germany. However, only the isolated skull has been briefly reported and was referred to the Diadectidae without description or generic assignment (Martens, 1993; Berman and Martens, 1993). A thorough examination of the three Bromacker specimens reveals, however, that they differs from the widely distributed Early Permian Diadectes species of North America in only very minor ways and, therefore, should be considered a new species of that genus. Our explanation of why Diadectes has remained undedected for so long in the Early Permian deposits of Europe is the same as that offered above to account for the similar, single European occurrence of Seymouria at the Bromacker locality.
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