Why did fish decide to move out of the water and onto land 370 million years ago? New research from Flinders University reveals it was a brainy decision.
In a study, published in PeerJ, researchers used CT scanning to investigate the internal bones of an ancient Cladarosymblema narrienense fossil – a 330 million-year-old fish from the Carboniferous Period found in Queensland, and ancestor of the four-limbed vertebrate tetrapods – and found that it had a really smart brain, for a fish.
Interestingly, the investigation showed that Cladarosymblema had a brain much more similar to its eventual terrestrial ancestors than other fish friends that never made the move, suggesting its brain was part of the decision to relocate.
Cladarosymblema was a huge, predatory freshwater fish, and an extremely well-preserved fossil from Queensland was first described in 1995 by John Long, strategic professor in palaeontology at Flinders University.
“This fish from Queensland is one of the best preserved of its kind in the entire world, in perfect 3D shape, which is why we chose to work on it,” says Long.
This made it the ideal candidate to investigate, so the team used Australia’s largest CT scanner, located at Flinders University’s Tonsley campus, and the Australian Synchrotron in Melbourne to have a peek inside its skull.
This revealed previously unseen internal bones – particularly in the gill arch skeleton, the shoulder girdle and the palate bones (the upper mouth roof area).
“This helps us to understand the functional morphology and relationships of Cladarosymblema,” says Dr Alice Clement, lead author of the new paper and part of the Flinders Palaeontology Group.
“Additionally, a cranial endocast (mould of the internal cavity of this fish’s unusually large skull) gives clues as to the shape of the brain of this animal. The area for the pituitary gland – the so-called ‘master gland’ – is relatively large, suggesting a significant role in regulating various important endocrine glands.”
This larger part of the brain could have allowed the pituitary gland – which secretes hormones that control metabolism, growth, sexual maturation and blood pressure – to do its work and help the fish adjust to terrestrial life.
Thankfully, that old fish’s big brain moment led to life on land as we know it. Smart thinking, fishy friend!
Deborah Devis is a science journalist at Cosmos. She has a Bachelor of Liberal Arts and Science (Honours) in biology and philosophy from the University of Sydney, and a PhD in plant molecular genetics from the University of Adelaide.
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