Tetrapods of the Pennsylvanian nodules from Mazon Creek, Illinois

Abstract

ABSTRACT. A revision of the Pennsylvanian amphibians and reptiles from Mazon Creek, Illinois, reveals that Amphibamus (including Mio- batrachus and Mazonerpeton) belongs to the rhachitomous labyrinthodont family Dissorophidae. Micrerpeton (including Eumicrerpeton) is the larva of a labyrinthodont possibly different from Amphibamus. Sauropleura, a nectridian, is recorded for the first time from this locality. Spondylerpeton, an embolomere, the aistopod Phlegethontia, and the captorhinomorph rep- tile C'ephalerpeton conclude the list of determinable genera. “Mazonerpeton” costatum is probably not a tetrapod- and “Amphibamus” thoracatus is non-vertebrate. The close similarity between Paleozoic vertebrate faunas of North America and Europe is attributed to rapid initial dispersal of newly evolved animals and cannot be regarded as evidence of a closer migration route than the Bering Strait land-bridge. Comparison with the diverse present-day amphibian and reptilian faunas of Europe and North America is misleading as these are composed, with few exceptions, of ancient fami- lies whose range was formerly far more extensive than at present. On the other hand, none of the faunal evidence opposes some more intimate con- nection; it is quite indeterminate as to the position of the migration route.