Something fishy ….!?

Colleague Greg Brett has an unusual identification to share – his story is listed below:

Supraoccipital Crests of the Spotted Grunter

I received these two unusual bone pieces for identification from Carl Vernon who documents everything on his forages. These were collected by him on Bonza Bay Beach in Dec 2012 although from their clean state, they had been deposited some time previously.  I immediately recognised them as the occipital processes (skull crests) from a Spotted Grunter. I particularly remembered these pieces because they are a very unusual and pronounced part of that fishes skull in relation to those sections on other species of fish. Also I recall a written report from the late Prof JLB Smith (in ‘Our Fishes’) on the finding of these sections in middens on the west coast and the ramifications of the find.

The spotted grunter is of tropical Indo pacific origin and they do not occur west of False Bay; certainly not in harvestable numbers west of the Breede River. He deduces that this is empirical evidence of a historical warm indo pacific extension round Cape Point when the people responsible (Khoisan) for harvesting the species, lived there.  We queried the reason for these appendages; they are so morphologically extreme there must be some vital function.  Spotted grunter do not head butt reefs for food they feed on sand burrowing creatures and especially in estuaries, on sand and mud prawns. These prey items take refuge in burrows and perhaps therein lies a clue. It is hypothesised that these pronounced crests are exaggerated tympanic organs for detecting the presence of burrowing invertebrates in turbid environments in estuaries where they like to feed.


Supraoccipital crests of the Spotted Grunter


Spotted Grunter
Natural History Gallery
East London Museum

About East London Museum Science

Conservation Biologist East London Museum South Africa
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