A T-junction in a Trirachodon burrow complex. Source: Groenewald et al. 2001. Used with permission.
The earliest record of a colonial dwelling in tetrapods was described in 2001 from the lower Triassic of South Africa. It is a complex of interconnected burrows with a large number of entrances and multiple terminal chambers. A striking feature of these burrows is the central ridge. The researchers who discovered these fossils point out that the diameter of the burrow is much larger than the width of individual skeletons. Therefore, it is likely that the central ridge separated animal traffic going in opposite directions.
