First record of the amphibamiform Micropholis stowi from the lower Fremouw Formation (Lower Triassic) of Antarctica

ABSTRACT

The fossil record of temnospondyl amphibians in the immediate wake of the Permo-Triassic mass extinction captures extensive taxic and ecological diversity, with most records known from high paleolatitudinal settings. In southern Pangea, the most substantial records come from South Africa and Australia, with a total of over 20 taxa presently recognized. Temnospondyls have also been known from correlated horizons in the lower Fremouw Formation of Antarctica since the late 1960s, but these records are mostly fragmentary, thereby limiting taxonomic resolution to the family level and subsequent biostratigraphic correlations and comparisons between high-latitude basins. Here we report substantial new material of the amphibamiform Micropholis stowi, a relic dissorophoid previously known only from the Katberg Formation (Lystrosaurus declivis Assemblage Zone) of South Africa, from the lower Fremouw Formation. The exceptional preservation of the recently recovered material permits not only confident taxonomic referral but also tentative association of several individuals to the broad-headed morph of the taxon. The recognition of M. stowi in Antarctica represents only the fourth geographic occurrence of a dissorophoid from southern Pangea and supports the hypothesis that high-latitude environments served as refugia for temnospondyls during the mass extinction. In the case of M. stowi, such refugia permitted the persistence of a predominantly Permo-Carboniferous clade, and the Antarctic records discussed here further hint at a poorly sampled cryptic distribution, both of amphibamiforms in southern Pangea and of small-bodied temnospondyls in early Mesozoic deposits.

ACKNOWLEDGMENTS

Fieldwork resulting in the recovery of the specimen described here was supported by NSF ANT-1341304, with additional research and analysis supported by NSF ANT-1947094. We thank R. Masek for his excellent preparation and C. Shin for her illustration in Figure 2C. Logistical support in Antarctica was provided by the National Science Foundation through the U.S. Antarctic Program. We acknowledge the 2017–18 Shackleton Glacier team (P. Braddock, P. Makovicky, J. McIntosh, A. Shinya, N. Smith, R. Smith, N. Tabor, M. Whitney, and C. Wooley) and field camp support staff for their assistance and contributions. Thanks to the two reviewers, the technical editor (J. Harris), and the handling editor (J. Fröbisch) for constructive comments that improved this manuscript.