Torridorefugium eskridgensis (new ichnogenus and ichnospecies): Amphibian aestivation burrows from the lower Permian Speiser Shale of Kansas

摘要

Burrows of the lysorophid amphibian Brachydectes elongatus occur in deposits interpreted as ephemeral ponds within the Lower Permian Speiser Shale of eastern Kansas. The burrows of B. elongatus have been previously recorded in the Lower Permian strata of Texas, Oklahoma, and Kansas, but have not been described in detail and an ichnotaxonomic designation has not been provided. Torridorefugium eskridgensis new ichnogenus and ichnospecies show two types of burrow architecture distinguished by width-to-length ratios. Type I burrows are elongate, elliptical tubes 4-32 cm long and 2-7 cm wide. Type 11 burrows are short, elliptical tubes 1.5-3.5 cm long and 2.5-5 cm wide. Both Type I and 11 burrows may contain coiled skeletons of B. elongatus. Torridorefugium eskridgensis occur in clusters of up to 45 burrows with maximum concentrations of 20/m(2).The type specimens of Torridorefugium eskridgensis occur in a 40-cm-thick lens of calcareous mudstone that fills a 100-m-long paleodepression within a well-developed paleosol. The burrow clusters are capped by surfaces with evidence of subaerial exposure, and overlain by nonburrowed, massive mudstone containing the fossils of the charophyte Stomachara, the ostracodes Carbonita and Paraparchites, fish, amphibians, and reptiles. This succession suggests that lysorophids burrowed in response to episodic, perhaps seasonal, droughts on the Permian midcontinental coastal plain. Permian lysorophid burrowing behavior is analogous to that of the extant aestivating amphibians Amphiuma sp. and Siren intermedia that inhabit ephemeral rivers and ponds of the southeastern United States.