The Gogo Fish - Mcnamaraspis kaprios - is an extinct placoderm of the Late Devonian period ( ~ 380 mya). It inhabited the ancient reef systems of north Western Australia and grew up to 50 cm in length.
With large eyes, articulated jaw and razored dentition plates the Gogo Fish would have been a formidable predator. It has a distinctive cartilaginous snout and is a member of the order Arthrodira, meaning ‘jointed neck’, and like other placoderms in that order it was able to increase the size of its bite by rapidly levering up its head shield as well as dropping down its jaw. This anatomical feature would have enabled it to attack and swallow creatures that were not very much smaller than itself.
Remarkably intact fossil specimens of the Gogo Fish, along with other placoderms, have been discovered in the Gogo formation of Western Australia - an ancient inland sea during the Late Devonian period. Internal organs have even been detected in these well preserved specimens and most recently the oldest heart in the fossil record (Trinajstic et al, 2022)
Most fossil remains are typically flattened in form - due to geological pressure over time - but Gogo Fish remains have been discovered that are uniquely encased within limestone nodules (Long et al. 2006) After careful dissolving of the surrounding limestone fully intact specimens have emerged. This has allowed for a much greater understanding of the anatomical structure of placoderms and a re-evaluation of their relative position in the phylogenic tree of vertebrate evolution.
It has been speculated that the armoured bite of the more predatory placoderms evolved as an effective means of cracking through the shelled defenses of the plentiful arthropods. It has been noted that at around the same period trilobites began to appear with a profusion of spines, possibly as a counter defense to the predatory placoderms.
The Gogo Fish became the state fossil of Western Australia in 1995.
With thanks to Prof John Long for assistance with anatomical detail.