Tuesday, 11 April 2017

Surreal 360 million year old spiky armoured fishes reconstructed for the first time


Africanaspis is a genus of armour plated (placoderm) fish, only known from the Late Devonian (360 million year old) Waterloo Farm lagerst├Ątten of South Africa.  It was first named, in 1997, on the basis of isolated plates representing only three of the trunk armour plates, of a single species (Africanaspis doryssa).

Ongoing excavation of shale rescued from Waterloo Farm, by Dr Rob Gess, who found the original material, has since then produced far more complete material. In a paper published in PLOS One on 5th April 2017, by Dr Rob Gess of the Albany Museum and Rhodes University and Professor Kate Trinajstic of Curtin University, reconstructions of the entire head and body armour of this extraordinary fish are revealed. Incredibly though that’s not where it ends – in several specimens there are also compressions preserved of the unarmoured tails that protruded behind the armoured body. This soft unarmoured portion of the body is completely unknown in the vast majority of armour plated fish.

The authors furthermore reveal that a second, more robust species which they named Africanaspis edmountaini  also inhabited the Waterloo Farm lagerst├Ątten lagoon.
Specimens represent fish of a range of sizes. Although adult Africanaspis doryssa were between 20 and 30 centimetres long, one minute specimen was less than 3 centimetres long. Its large eyes suggest that it was newly hatched or born. This range of sizes indicate that Africanaspis  spent its entire life around the coastal lagoonal lake that is represented at Waterloo Farm. This differs from the lifestyle of coelacanths previously described from the same site, which are only known from juveniles, indicating that they used the ancient estuary exclusively as a breeding nursery.

Link to paper online:

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0173169

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