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.

Upside down: ‘Cryobatrachus’ and the lydekkerinid record from Antarctica

“…Amphibamiforms are only confidently represented in the Lower Triassic by Micropholis stowi , which was recently documented from the lower Fremouw Formation (Gee and Sidor, 2021). FMNH PR 5020 is clearly not M .…”

“…Amphibamiforms are a relict clade that, unlike dvinosaurs, is documented from the lower Fremouw Formation in the form of Micropholis stowi (Gee and Sidor, 2021; Fig. 9.4), a taxon primarily known from two morphs from South Africa (Boy, 1985; Schoch and Rubidge, 2005).…”

“…This collective convoluted history only underscores the need for continued taxonomic work and the essentiality of revisiting historic specimens as taxonomic frameworks shift over time. The recent report of Micropholis stowi , representing the first occurrence of Amphibamiformes in Antarctica, based on recently collected material (Gee and Sidor, 2021) is both the most substantial and the most robust temnospondyl record from the entire lower Fremouw Formation. It is hoped that further collection and study of new material may provide a richer context through which to interpret the historic material.…”

“…Finally, recent collecting in the lower and middle Fremouw recovered substantial amounts of well-preserved, smallbodied temnospondyl material. Gee and Sidor (2021) recently identified some of the material from the lower Fremouw as belonging to Micropholis stowi Huxley, 1859, a taxon long known from the Lystrosaurus declivis Assemblage Zone (LAZ) in South Africa (Schoch and Rubidge, 2005), but other specimens undoubtedly belong to other clades. It would be similarly intuitive for a lydekkerinid, if not L. huxleyi specifically (which also occurs in Australia; Warren et al, 2006), to occur in the lower Fremouw, even if not in the form of 'C.…”

A new lapillopsid from Antarctica and a reappraisal of the phylogenetic relationships of early diverging stereospondyls

“…1). Such diminutive taxa belong to a variety of clades, including lapillopsids (Warren and Hutchinson, 1990; Yates, 1999; Yates and Sengupta, 2002); lydekkerinids (e.g., Hewison, 1996, 2007; Jeannot et al, 2006), rhinesuchids (e.g., Shishkin and Rubidge, 2000), rhytidosteids (e.g., Yates, 2000), and late surviving non-stereospondyls (e.g., Gee and Sidor, 2021; Schoch and Rubidge, 2005; Warren, 1998a).…”