Mcnamaraspis kaprios

Mcnamaraspis kaprios

Image copyright of John Long

The Napier Range in western Kimberly comprises a large barrier reef complex, dating from the later part of Devonian period 380 million years ago. The area is particularly well known for its excellently preserved, three-dimensional skeletons of various types of fish.

The unique state of preservation of the fish specimens has allowed scientists from the Western Australian Museum to extract a wealth of anatomical information.

A recently (2009) described placoderm fish (armoured prehistoric fish) demonstrates the oldest known examples of internal fertilisation organs and the earliest known example of an umbilical cord.

In this ancient barrier reef complex, fish fossils were encased in limestone nodules that are distributed within a shale unit. The hard nodules formed around the slowly decaying fish at a very early stage of rock formation, preventing their skeletons from being crushed flat by the weight of the overlying sediments.

During the late Devonian period oxygen levels were lower in the atmosphere (and consequently also in sea water) than they are today (about 17 vs 21 per cent) resulting in slower rates of decay.

In 1986, the former curator of vertebrate palaeontology at the Western Australian Museum, Dr John Long, found a placoderm fish while splitting open Gogo limestone nodules with his geo pick. About one in 1,000 nodules contain a fossil fish. Back at the laboratory in Perth, Dr Long slowly dissolved the limestone (using buffered acetic acid), revealing the skeleton of a immaculately preserved, undescribed species of placoderm fish.

The fish was formally described in 1995 and given the name Mcnamaraspis kaprios. The genus name Mcnamaraspis was given in honour of the former curator of invertebrate palaeontology at the museum, Dr Ken McNamara. Later in 1995, Mcnamaraspis kaprios was selected as the State Fossil Emblem for Western Australia.

