Broomistega: an injured amphibian in a Thrinaxodon burrow

Broomistega putterilli was a rhinesuchid temnospondyl from Early Triassic South Africa. One nearly complete skeleton was discovered by synchrotron scanning inside a burrow cast, close to the skeleton of the cynodont Thrinaxodon. The amphibian had several partially healed rib fractures, showing that it survived a serious injury for some time before burial. The unusual association is one of the most revealing cases in the ancient amphibian catalogue, though it does not prove the two animals behaved as companions.

Quick facts

From an old name to a rare Triassic survivor

Robert Broom described the species Lydekkerina putterilli in 1930 from Early Triassic rocks of South Africa. In 2000, Mikhail Shishkin and Bruce Rubidge reassessed the material and established the genus Broomistega. Its anatomy identifies it as a rhinesuchid temnospondyl, part of a family whose better-known record is largely Permian. The South African material places this lineage among animals living after the end-Permian mass extinction.

The name-bearing specimen TM 184 is incomplete, preserving the back of the skull and part of the jaw. Additional skulls and partial skeletons provide more information about the animal. The genus is commonly interpreted as paedomorphic, retaining juvenile-like features as it matured, but the exact developmental history is inferred from anatomy rather than from a complete growth series.

A hidden skeleton inside a burrow cast

Specimen BP/1/5558 is a lithified cast of a burrow from the Karoo Basin. It had long been known as a burrow fill. Synchrotron X-ray scanning revealed an almost complete skeleton of Thrinaxodon (BP/1/7199) and, beside it, the temnospondyl skeleton BP/1/7200. The amphibian lay belly-up. The two skeletons remained articulated and were not mixed together, preserving their positions within the same confined space.

The scan also showed seven consecutive ribs of Broomistega with partially healed fractures. The pattern is consistent with a single crushing injury that had begun healing weeks before death. This is direct evidence that the trauma was not immediately fatal. Researchers infer that it likely impaired movement and breathing, but those effects cannot be measured directly from the fossil.

The body proportions and weak adaptation for digging suggest that Broomistega did not excavate the burrow itself. Its presence inside a narrow tunnel is therefore consistent with entering an existing refuge. The skeletons show close association, not an attack: they are not disarticulated or intermixed, and no compelling feeding traces establish predation.

What happened in the burrow?

The 2013 synchrotron study proposed that Thrinaxodon was aestivating, a dormant state associated with hot or dry conditions, when the injured amphibian entered the burrow. The cynodont may have tolerated its presence, and a later pulse of sediment could have filled the tunnel and buried both animals. The curled posture of other Thrinaxodon fossils and the regional environmental context make the scenario plausible.

None of those steps is directly recorded as behaviour. The fossil gives a snapshot of two animals in one burrow, their body positions and the healing injury. It does not show how long they shared the space, whether Thrinaxodon was physiologically dormant, or whether one animal was aware of the other. “Shared shelter” describes the preserved association; “peaceful coexistence” would go beyond it.

Burrow casts are valuable because soft-bodied or small animals can be preserved in place with the tunnel architecture around them. Here, the cast links vertebrate anatomy to a refuge-making behaviour. It also shows why non-destructive imaging can change a specimen’s scientific meaning: the internal skeletons were not visible from the exterior surface.

Life, injury and limits of reconstruction

Broomistega had a broad temnospondyl skull and a body plan consistent with a water-associated animal. It may have taken small aquatic prey, but no stomach contents establish a menu. A damaged individual capable of moving to a burrow also suggests some mobility on land, although it was not anatomically specialized for digging.

The cover depicts the two animals in the burrow without an attack. Their relative positions are based on the scan; the living posture, soft tissues, skin and colour are reconstructed. The fossil cannot tell us whether Thrinaxodon deliberately tolerated the amphibian or whether the animals arrived at different times. The strongest account holds to what is visible: an injured temnospondyl survived long enough for fractures to heal and was later buried in a burrow alongside a cynodont.

That evidence makes Broomistega more than a name on a species list. It records injury and recovery in an individual, and a rare association between unrelated tetrapods during a difficult interval in Triassic ecosystems. The uncertainty around the final scene is part of the story rather than a reason to dismiss it.