Two types of large diameter burrows, recognized by non-overlapping size distributions, occur in high paleolatitude floodplain deposits of the Lower Triassic Fremouw Formation, Shackleton Glacier area, Antarctica. Type G (giant) burrows are gently dipping tunnels 8 to 19 cm in diameter. Type L (large) burrows are 2 to 6.5 cm in diameter, curved or subhorizontal tunnels that rarely branch; scratch markings on both burrow types generally are parallel or tangential to the long axis of the burrows.
Type G burrows are interpreted as produced by tetrapods based on similarity in size, architecture, and surface markings to Permian burrows from South Africa that contain complete skeletons of therapsids. These are the first tetrapod burrows described from Antarctica. Type L burrows have characteristics of both fossil tetrapod and crayfish burrows, precluding identification of an unique producer.
Triassic tetrapods, including therapsids, that lived in high southern latitudes probably burrowed to dampen the effects of seasonal environmental fluctuations, just as do many of their mammalian counterparts living today in high latitudes. The paleolatitudinal and paleooclimatic distributions of burrowing therapsids and their mammalian descendents can be assessed by focusing search efforts on very large burrows, and by identifying producers using criteria delineated herein; this will clarify the extent to which the burrowing habit originated and persisted in high latitudes.