Monday, 28 September 2015

The Oldest African Coelacanth

The modern day coelacanth, Latimeria
The coelacanth is an iconic fish. Represented today by just one genus, Latimeria, the coelacanth family has a rich evolutionary history which includes close relatives of the first fish to develop lungs and limbs, and make the move onto dry land.

Today the coelacanths are well known and are prized by fishermen and scientists, but their fossils are equally valuable.

In the 1990s a series of fossils were collected from black shales at the late Devonian Waterloo Farm locality in South Africa's Eastern Cape. They were exposed during roadworks and 70 tonnes of excavated shale offered palaeontologists rich pickings. Over 30 specimens were collected, but they were in no condition to offer easy identification. Subsequent preparation allowed Dr Robert Gess from the University of the Witwatersrand to assign them to a new genus and species, Serenichthys kowiensis. What makes the species important, however, is the age.

Previously, only five other Devonian coelacanth species had been described, all from fragmentary material and none from Africa, from North America, Europe, China and Australia. The specimens, some of which are in excellent condition, throw light on the anatomy, and in turn, the early evolutionary history of the coelacanth family. The anatomy of the new species suggests that it lies on the line leading towards modern day coelacanths. Indeed it is quite neat that the first specimen of Latimeria itself came from South Africa.

One of the fossils of Serenichthys kowiensis
The fossils reveal the environment and lifestyle of Serenichthys. 'Remarkably, all of the delicate whole fish impressions represent juveniles. This suggests that Serenichthys was using a shallow, waterweed-filled embayment of the estuary as a nursery, as many fish do today,' said Gess. 'This earliest known record of a coelacanth nursery foreshadows a much younger counterpart, known from the 300 million year old Mazon Creek beds of Illinois in the United States.' The modern day coelacanth, Latimeria, is known to bear live young, but whether the young mature in nurseries remains unknown.

While coelacanths are living fossils by virtue of anatomy, it is important to understand whether the behaviours and lifestyles of living fossils are representative of their ancient counterparts. Ecological interactions are vital components of ecosystems, but often fail to be preserved in the fossil record. Living fossils will allow us to say whether we can match a behaviour over geological time and incorporate it into our reconstructions of ancient ecosystems, thus making them more accurate. Equally, this works in reverse.