High-latitude Chondrichthyans from the Late Devonian (Famennian) Witpoort formation of South Africa

Abstract

New material from the Late Devonian Witpoort Formation (Witteberg Group, Cape Supergroup) of Waterloo Farm (Grahamstown, South Africa) includes teeth, spines, and rare endoskeletal remains of early chondrichthyans. Plesioselachus, formerly described from Waterloo Farm, is redescribed and reinterpreted on the basis of new specimens. A new species of Antarctilamna is reported and described for the first time, adding significantly to the range of skeletal anatomy covered by fossils attributed to this genus. Notably, it reveals new details of the jaws and braincase. Juvenile chondrichthyan material is also reported; although this provides only limited anatomical detail; it might be attributed to Antarctilamna. The record of Devonian chondrichthyans is poor compared with that of early osteichthyans, and these fossils are a significant addition to the data set. Thus far, the Waterloo Farm locality preserves a unique, high latitude, shallow marine (estuarine) biota dated to the latest part of the Devonian. The Waterloo Farm vertebrate assemblage thus provides a biogeographically outstanding comparison with better-known, contemporary vertebrate assemblages from much lower latitudes. Faunal lists from these localities have already been used to estimate the magnitude of an acute turnover of vertebrate diversity across the Devonian-Mississippian boundary. Waterloo Farm chondrichthyan diversity, albeit limited, is, at least, consistent with hypotheses of an End Devonian biotic crisis. Rather than providing an early glimpse of the increasingly well documented post-Devonian evolutionary radiation of modern gnathostome clades, it seems that Waterloo Farm vertebrates are mostly related to groups that flourished earlier within the Devonian record.