Ancient Burrows found in Antarctica

A team of American scientists have discovered fossilised burrows in Antarctica, trace fossils of ancient land animals that pre-date the dinosaurs.  This is the first time trace fossils such as burrows have been found on this continent.  The burrows have been dated to the Early Triassic and were dug by land living, vertebrates approximately 245 million years ago.

Although, no remains of the excavators have been found, Christian Sidor of Washington University, who led the team has stated that these burrows were dug by Tetrapods and are not likely to have been dug out by invertebrates such as crayfish.  Tetrapod is the scientific name given to four-legged vertebrates and those two-legged and limbless vertebrates descended from them.  The term Tetrapod, literally means “four feet”.  The limbs of Tetrapods have distinct digits, they are believed to have evolved in the Devonian.  The oldest Tetrapod fossils, multi-digit animals such as Ichthyostega and Acanthostega have been found in late Devonian river and lake deposits (dated around 360 million years ago).  These first four-limbed vertebrates were mainly aquatic creatures but their muscular limbs, perhaps evolving first as an aid to clambering through weed clogged water or perhaps digging for shellfish, were a wonderful pre-adaptation for venturing onto land.

Though no animal remains were found inside the burrow casts, the hardened sediment in each burrow preserved a track made as the animals entered and exited, according to the American palaeontologists.

“In addition, scratch marks from the animals’ initial excavation were apparent in some places. We have got evidence that these burrows were made by land-dwelling animals rather than crayfish,” commented Christian, the expedition leader and assistant professor of biology at the University of Washington.

Despite the absence of fossil bones, the burrows’ relatively small size prompted the US team to speculate that their owners might have been small lizard-like reptiles called Procolophonids or an early mammal relative called Thrinaxodon.  Thrinaxodon was a Cynodont, a small carnivorous synapsid which like other Cynodonts and Dicynodonts are believed to have lived in burrows and fossils of this little animal, no more than 50 cm long have been found in Antarctica.

The fossils were created when fine sand from an overflowing river poured into the animals’ burrows and hardened into casts of the open spaces. The largest preserved burrow is about 35 cm long (14 inches), 15 cm wide (6 inches) and 8 cm deep (3 inches).

During this time in the Earth’s history Antarctica was joined to landmasses that were to eventually form South America, Africa, India and Australia, although Antarctica may not have been directly over the south pole as it is today, it was certainly a cold, harsh environment and the southerly latitude would have meant that this area would have been in darkness for part of the year.  Perhaps these little vertebrates dug burrows to escape the most extreme of the climatic conditions around at the time.

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