Synchrotron Reveals Early Triassic Odd Couple: Injured Amphibian and Aestivating Therapsid Share Burrow

PLoS One. 2013 Jun 21;8(6):e64978. doi: 10.1371/journal.pone.0064978. Print 2013.

Abstract

Fossorialism is a beneficial adaptation for brooding, predator avoidance and protection from extreme climate. The abundance of fossilised burrow casts from the Early Triassic of southern Africa is viewed as a behavioural response by many tetrapods to the harsh conditions following the Permo-Triassic mass-extinction event. However, scarcity of vertebrate remains associated with these burrows leaves many ecological questions unanswered. Synchrotron scanning of a lithified burrow cast from the Early Triassic of the Karoo unveiled a unique mixed-species association: an injured temnospondyl amphibian (Broomistega) that sheltered in a burrow occupied by an aestivating therapsid (Thrinaxodon). The discovery of this rare rhinesuchid represents the first occurrence in the fossil record of a temnospondyl in a burrow. The amphibian skeleton shows signs of a crushing trauma with partially healed fractures on several consecutive ribs. The presence of a relatively large intruder in what is interpreted to be a Thrinaxodon burrow implies that the therapsid tolerated the amphibian's presence. Among possible explanations for such unlikely cohabitation, Thrinaxodon aestivation is most plausible, an interpretation supported by the numerous Thrinaxodon specimens fossilised in curled-up postures. Recent advances in synchrotron imaging have enabled visualization of the contents of burrow casts, thus providing a novel tool to elucidate not only anatomy but also ecology and biology of ancient tetrapods.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amphibians*
  • Animals
  • Fossils*
  • Mammals*
  • Nesting Behavior*
  • South Africa
  • Synchrotrons*

Grants and funding

This work was supported by the ESRF (proposal EC-847), the University Research Committee (URC) of Wits, and the Palaeontological Scientific Trust (PAST). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.