Pea-brained South African leaves scientists fishing for more answers
Experts have discovered clues as to why coelacanth brains are much smaller than they sho be
Big heads don’t necessarily mean big brains – at least not for coelacanths, the “living fossil” fish.
Using X-ray and imaging technology, researchers have moved a step closer to understanding why the coelacanth brain only fills 1% of the cavity that houses it.
The fish’s skull is hinged, or split in half by an “intercranial joint”, making it much bigger than what is necessary to hold the brain.
“Coelacanths (Latimeria chalumnae) are iconic animals thought to be on the line to the first land animals or tetrapods, because of their strange hinged head,” said researcher John Long, of Flinders University in Adelaide, Australia.
This separation of the skull is probably explained by the coelacanth notochord, a tube that extends below the brain and spinal cord in the early phases of life. In other species, it degenerates into a small rod.
“The notochord for the coelacanth expands dramatically to become 50 times bigger than the brain in the adult fish,” said Long.
When researchers examined the X-ray of a 5cm-long foetus, the earliest available developmental stage, they found the huge growth of the notochord prevented the coelacanth skull from forming one unit.
“These are very unique observations, but they represent only a tiny step forward,” said lead study author Hugo Dutel. “Latimeria still holds many clues for our understanding of vertebrate evolution, and it is important to protect this threatened species and its environment.”
The coelacanth was widely thought to have gone extinct for 70 million years, until its accidental discovery off the coast of the Eastern Cape in 1938.