Strange Bedfellows: Odd Couple Fossils Discovered In The Same Burrow
June 23, 2013

Mammal, Amphibian Found Cohabitating In Fossilized Burrow

redOrbit Staff & Wire Reports - Your Universe Online

Sorry, Felix and Oscar, but an international team of researchers have found a real-life odd couple that puts Neil Simon’s famous duo to shame – a mammal forerunner and an ancient amphibian, which were discovered sharing a burrow during the Early Triassic period.

The discovery, which was detailed in Friday’s edition of the journal PLOS One, was made by scientists from South Africa, Australia and France while studying a 250 million year old fossilized burrow in the Karoo Basin of South Africa.

The burrow revealed an amphibian, which was suffering from broken ribs, nestled beside a sleeping mammal, believed to be the shelter’s original inhabitant. The researchers believe the amphibian was seeking protection, and that the two vertebrates wound up being trapped and eventually fossilized due to a flash flood.

The research team, which was led by Dr. Vincent Fernandez from Wits University in South Africa and the European Synchrotron Radiation Facility (ESRF), discovered the strange bedfellows using synchrotron imaging. They believe the cohabitation was the result of harsh conditions that followed the Permo-Triassic mass extinction.

“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 study authors wrote. “The discovery of this rare rhinesuchid represents the first occurrence in the fossil record of a temnospondyl in a burrow.

“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,” they added. “Among possible explanations for such unlikely cohabitation, Thrinaxodon aestivation is most plausible, an interpretation supported by the numerous Thrinaxodon specimens fossilized in curled-up postures.”

The fossil dates from 250 million years ago, which would place it at the beginning of the Triassic Period at a time when the planet was still recovering from the mass extinction event responsible for wiping out the majority of life on Earth.

One of the study authors, Dr. Della Collins Cook of Indiana University, believes the amphibian’s broken ribs were the result of “a single, massive trauma.” While it survived the injuries, it was “surely quite handicapped,” leading it to seek refuge in the mammal’s burrow – where it was apparently permitted to remain.

Additionally, Fernandez reports the Broomistega remains represent the first complete skeleton of the species that has ever been discovered. From studying the skeleton, he said the researchers have concluded it “was a juvenile and mostly aquatic at that time of its life.”

Other study authors include Professor Bruce Rubidge, Dr. Fernando Abdala and Dr. Kristian Carlson, all of Wits University, as well as Dr. Adam Yates of the Museum of Central Australia and Dr. Paul Tafforeau of the ESRF.