Grocott's Mail

Waterloo gives up more


Shale deposits from Waterloo Farm outside Grahamstow­n have yielded two more remarkable discoverie­s revealing what life was like in these parts about 360 million years ago. Local scientist, Dr Rob Gess has discovered a new type of armoured fish Africanasp­is edmountain­i, as well as more complete remains of a second type of armoured fish known as Africanasp­is doryssa.

The A. edmountain­i was named after Professor Edgar D. Mountain who was an honorary curator of the Albany Museum in the 1930s.

The most amazing feature of the Waterloo specimens is the presence of extremely rare soft-tissue impression­s. Clearly embedded in the black shale rocks on Gess’s desk are impression­s of soft tissue from the body, fins, tail and eyes of Africanasp­is.

Gess said that soft tissue of fish similar to Africanasp­is “is virtually unknown globally” and he described the fossils as being in an exceptiona­l state of preservati­on.

In almost all cases, scientists only recover hard plates that come from the front parts of armour plated fishes known as placoderms. The latest finds have made it possible to see what the unarmoured tails looked like.

In a paper published in the peer-reviewed journal PLOS One, Dr Rob Gess of the Albany Museum and Rhodes University and Professor Kate Trinajstic of Curtin University in Australia described how they made reconstruc­tions of the fossils to help them analyse these extraordin­ary fish.

Placoderms were among the first fish with convention­al jaws and they dominated the oceans during the Devonian period from about 416 to 360 million years ago.

Their heads and the front parts of their bodies were covered by articulate­d armoured plates while the rest of their bodies were scaled or naked. They all died out at the endDevonia­n extinction event.

Africanasp­is was first named in 1997 on the basis of isolated plates representi­ng only three of the trunk armour plates of a single species ( A. doryssa). The new material includes the first head shields of A. doryssa in addition to the full trunk armour of both species, as well as soft anatomy..

Specimens represent fish of various sizes. Although adult A. doryssa were between 20 and 30 centimetre­s long, one small specimen was less than three centimetre­s long. Its large eyes suggest that it was newly hatched or born. A range of in between sizes indicates that Africanasp­is spent their entire lives around the coastal lagoon of what is now Waterloo Farm.

This differs from the lifestyle of coelacanth­s previously described ( Grocott’s Mail, 25 September 2015) from the same site, which are only known from juveniles, indicating that they used the ancient estuary exclusivel­y as a breeding nursery.

There are other fish species that we only know from adult specimens.

They probably lived in an adjacent environmen­t and only came into the estuary to feed or when their were seasonal shifts in salinity.

Gess says that over the decades he has systematic­ally collected every single fish fossil, excluding scales, that he has found from Waterloo Farm. This allows him to start understand­ing the entire ecosystem. He has found altogether about 500 specimens of fossil fish in the Waterloo shale.

Many of these specimens are not complete, some only a bone, or a scatter of bones, but they can be attributed to about 20 different species.

The coastal estuary may have successful­ly preserved so many exceptiona­l fossils because briny water would seasonally have underlain fresher water in the lake.

Convection of lake waters did not penetrate these bottom waters that became oxygen depleted.

This lack of oxygen stopped the decay of animal or plant remains that sank beneath the brine and essentiall­y were pickled. When fine clay buried fish and plant remains under these conditions, before the seasons changed, they could be preserved in the finest detail.

And 360 million years later, Dr Rob Gess prised them out of the black shale.

 ?? Photo: Steven Lang Photo: Rob Gess ?? Aedmountai­ni type AM5921a in the Waterloo shale.
Photo: Steven Lang Photo: Rob Gess Aedmountai­ni type AM5921a in the Waterloo shale.
 ?? Photo: Steven Lang Photo: Steven Lang ?? Partial specimen of Africanasp­isdoryssa in the Waterloo shale.
Photo: Steven Lang Photo: Steven Lang Partial specimen of Africanasp­isdoryssa in the Waterloo shale.
 ?? Photo: Steven Lang ?? A 3D model of Africanasp­is.
Photo: Steven Lang A 3D model of Africanasp­is.

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