Fossil millipedes associated with articulated tetrapod skeletons in the Early Triassic Karoo Basin, South Africa

Abstract

Millipede fossils of late Permian to Early Triassic age are exceptionally rare worldwide. Two specimens of Triassic millipedes, both associated with multitaxic tetrapod aggregations, have previously been reported from the South African Karoo Basin. Taxa associated with millipede fossils include the cynodont Galesaurus planiceps and the parareptile Saurodektes kitchingorum (previously Owenetta kitchingorum). Here we report and briefly describe three new millipede- tetrapod associations from the Early Triassic Lystrosaurus declivis Assemblage Zone. The first includes two millipedes associated with an articulated small therocephalian Scaloposaurus constrictus, the second comprises an articulated skeleton of the dicynodont Lystrosaurus murrayi with a single millipede, and the third contains an articulated Lystrosaurus sp. specimen, also with a single millipede. In all specimens the high degree of skeletal articulation which, coupled with in-situ preservation of delicate bones and millipede exoskeletons, suggest rapid burial soon after death, and likely that they died in a place protected from weathering and agents of dispersal. Possible hypotheses to explain the presence of millipedes closely associated with articulated tetrapod skeletons include: shelter sharing, predator-prey accumulations, and postmortem scavenging by the millipedes. Of these, our taphonomic interpretation favours the latter. Within the Karoo Supergroup, the appearance of millipede fossils in the uppermost Balfour and lower Katberg formations suggests that the scarcity of plant detritus on the Karoo floodplains in the aftermath of the end-Permian mass extinction event may have contributed to millipedes switching to a more scavenging feeding strategy.