Articulated Krommaster spinosusCredit: Caitlin Reddy
Studies of a preserved rock imprint have revealed the oldest-known brittle star from the southern hemisphere. The newly defined Krommaster spinosus, which lived in the Early Devonian, some 410 million years ago was a starfish-like creature adorned with thorn-like spikes, etching a defining chapter in its species history, a study in PLOS One has shown.
A silicone cast made of its three-dimensionally preserved impressions showed it was covered in sharp, thorn-like spikes, hence the name, spinosus, while Krommaster refers to the Kromme River valley where it was collected. The chunk of rock which held brittle stars intertwined with fossil lamp shells was collected by palaeontologist Rob Gess, lead researcher of the Devonian Ecosystem Project lab at the Albany Museum in Makhanda, South Africa. He was scouting the Kromme River Valley in 2015 for an environmental impact assessment study for a planned power cable route when he spotted an unusual orange piece of rock standing out in a newly graded road.
“Although the site where the fossils were found is only about 10 km from the current coastline one must remember that the Indian Ocean did not exist 410 million years ago, and that the entire Eastern Cape is in fact made up of folded rocks that were once sand and mud on the floor of another sea, the Agulhas Sea. These ancient sea floor sediments even make up the mountains of the Eastern and southern Cape,” adds Gess.
Caitlin Reddy creating a silicon castCredit: Caitlin Reddy
The Krommaster spinosus find adds to what paleontologists know about such species from the ancient polar regions in the southern parts of Gondwana, from a time when what is now known as southern Africa still lay within the Antarctic circle. Most early brittle star fossils so far collected come from rocks that formed near the equator, in what was once the northern supercontinent of Laurasia.
The lead author Caitlin Reddy, from Rhodes University, South Africa, said the level of detail revealed when she opened the lens of rock is very rare, as the calcite bodies of brittle stars, unlike other sea creatures, disintegrate soon after death. “The detail left us speechless—from the thin plates on its body to the tiny, bristly spines. This degree of preservation is astounding,” she said.
Brittle stars are represented by more than 2,000 species today, 137 of which are found in South African waters. They occur in tones of greens, greys, oranges, beiges and reds.
