Rare fossils 410 million years old
Rock on small farm road unearths newly described species
Makhanda-based researchers have described surprisingly well-preserved fossils of brittle stars discovered in the Eastern Cape. What makes this find extraordinary is that brittle stars (starfish cousins) almost always disintegrate soon after death so finding them intact is extremely rare.
The almost perfectly preserved fossils look like a cross between a starfish and a spider, not very different from any of the 137 species of brittle stars that inhabit the coastal waters of SA today.
If coming across one on a beach, we might easily think of it as some kind of prickly starfish.
Brittle stars have long, thin, almost parallelsided legs, while starfish tend to have thicker, often tapering legs. Brittle stars use their almost whip-like legs to move around in “a sort of spidery fashion” on the seafloor.
The previously unknown species of spiny sea creatures has been named Krommasterspinosus because their fossils were found in the Kromme River Valley near Humansdorp and because their five arms are lined with rows of spines.
Lead researcher of the study published in the PLOS ONE scientific journal, Caitlin Reddy, said she could not believe her eyes when the largest specimen was uncovered.
“The level of detail left us speechless – from the thin plates on its body to the tiny, bristly spines. This degree of preservation is astounding and very rare,” she said.
At 410 million years old, she said the fossil brittle stars were the oldest ever discovered in the Southern Hemisphere and entire ancient supercontinent of Gondwana.
They lived and died in the early Devonian period more than 170 million years before the first dinosaurs walked the earth.
Since Southern Africa lay within the Antarctic Circle at that time, the recently discovered fossils are especially significant for being among the very few known from polar regions.
On the last day of their lives, a population of juvenile and adult brittle stars, all belonging to the same species, were living among shells in a shallow marine environment.
Heavy rains feeding a nearby river suddenly washed a pulse of muddy waters downstream to engulf and smother them alive.
Many more layers of mud and sand covered the drift of shells and brittle stars over millions of years. The layers of sedimentation were eventually transformed into rock and folded into mountains hundreds of millions of years later.
The mountains weathered away till the cluster of fossil shells and brittle stars was disturbed by a grader on a small farm road.
Palaeontologist and principal researcher at the Albany Museum’s Devonian Ecosystems Project, Dr Rob Gess, happened to be conducting an environmental impact study in the Kromme River Valley in the Eastern Cape in 2015.
While he was walking down the small, recently graded farm track, he spotted an unusual orange lens of rock partly graded out of the bank of the road.
Looking closer, he realised it was almost entirely comprised of fossil lamp shells with brittle stars intertwined within them.
Realising this was something exciting and new, and not wanting to damage the delicate fossils, he removed some large chunks to archive in the Albany Museum collection for later research.
The right moment came when Reddy took on the project and broke open the stored blocks under laboratory conditions to reveal the threedimensionally preserved impressions of the ancient brittle stars.
These fossils are in fact moulds in the mud rock where the original brittle stars’ skeletons dissolved away hundreds of millions of years ago.
Brittle stars are made up of interlocking plates that are different in every species. To recover the exact shape of the plates, Reddy carefully cast the imprints with black silicone.
This revealed that the new species had been
covered in thorn-like spines. Reddy photographed the casts under a microscope so she could see minute details and compare them with other known species. Her observations revealed the unique shape of the brittle star’s plates, convincing her and Gess they had found a new species.
Gess supervised her work and arranged additional oversight from Mhairi Reid, who did her MSc on younger brittle stars from SA, and later from Dr Ben Thuy, an internationally renowned brittle star expert from the National History Museum in Luxembourg.
Thuy was impressed with Reddy’s “outstanding preparation and digitisation work” enabling him to “contribute to this exciting scientific study entirely by virtual means, working on highresolution photographs of the fossils. Thus, none of the valuable and fragile specimens had to be shipped. This is a prime example of how international scientific collaborations come to fruition in times of digital communication”.
This newly-described species is important as it is known to science only from a single lens of orange rock found on a small farm road. It is part of a larger family of brittle fish, or ophiuroids belonging to the Echinodermata phylum.
Ancient brittle stars have been completely replaced by modern counterparts found in oceans today. However, it appears both the archaic and modern forms of ophiuroids coexisted until at least the Triassic period (252-201 million years ago). Researchers believe brittle stars seen in the oceans today are a lot more mobile than their predecessors which had larger disks.
Today there are more than 2,000 species of brittle stars inhabiting all the oceans around the world. Link to journal article: