Fossils are known from the Early Triassic Lystrosaurus Assemblage Zone of the Beaufort Group in the Karoo Basin of present-day South Africa, a region that had been an enclave of Gondwana.

Its presence in the Early Triassic indicates that rhinesuchids survived the Permo-Triassic Mass Extinction about 252 million years ago.

However, compared to the diversity of rhinesuchids that existed in the Permian Period, Broomistega is a very rare component of the Early Triassic Karoo fauna.

The skeletons do not show evidence of stiffening due to rigor mortis after death, but are pressed against the sides of the burrow as the animals would have been when alive.

The animal was still alive when it entered the burrow because the rib fractures show evidence of healing, but the injury probably impacted its ability to breathe and to move about.

During the Early Triassic the Karoo Basin was seasonally arid, so the Thrinaxodon may have been aestivating to conserve energy during a time when resource availability was low and the normally aquatic Broomistega may have entered to burrow to escape the hot and dry conditions of its environment.