Brain space gives new insight into prehistoric lungfish

Evolution of the Brain and Nervous System in Animals Dating back more than 400 million years, examining the fossil remains of ancient lungfish provides a missing link to the rise of four-legged land animals on Earth.

An international study led by Australia’s Flinders University compared detailed 3D models of cranial endocasts with brain spaces from surviving bone groups of six Paleozoic lungfish (dipnoi) fossils to better understand cerebral lungfish evolution.

Lead author Dr Alice Clement of Flinders University said this could in turn help explain early tetrapods, which later moved from water to land on four legs.

The discovery was described in an international journal elife, presents the evolutionary history of these lobe-finned fishes (Sarcopterygii) and reveals how the olfactory region appears to be more plastic than the hindbrain and has undergone significant expansion in several taxa.

“Our findings show that lungfish brains have evolved continuously throughout their 400 million-year history, but it suggests that they probably rely on their sense of smell rather than sight to navigate their environment. This is quite different from other fishes that rely much more strongly on sight. using,” said Dr Clement of Flinders University’s Ecology and Evolution (Paleontology) Research Laboratory.

“He says that understanding how the lung brain has changed throughout evolutionary history helps us understand what the brains of early tetrapods (our terrestrial ancestors) might have looked like – it can give us an idea of ​​the senses that were more important than others (such as sight versus smell). »

For this study, Australian researchers, along with co-authors from the UK, Canada and Sweden, used powerful imaging methods to virtually reconstruct these brain models.

Lead author Dr Tom Challands, of the University of Edinburgh in Scotland, said the work being done is important to evolutionary and wider paleontological science.

“This paper effectively doubles the number of lung endocasts known, as their preservation quality is often compromised by crushing or disintegrating a fossil, and brains themselves have very low preservation potential, and no fossil lungs are currently known,” he says.

“Lipfish have survived for more than 400 million years from the Devonian period to the present day and provide unique insight into the condition of early tetrapods as well as their own evolutionary history. »

Using X-ray tomography as a paleontological tool, cranial endocasts of six Paleozoic lungfishes (Iowadipterus halli, Gogodipterus paddyensis, Pillararhynchus longi, Griphognathus whitei, Orlovichthys limnatis And Rhinodiptera ulrichi) can be studied non-destructively. Fossils come from Australia, USA, Russia and Germany.

A dataset of 12 taxa, six fossil and two extant taxa, was subjected to a multivariate morphometric analysis using 17 variables.

“Study of our ‘fish cousins’ helps us understand how fish left the water about 350 million years ago and began to evolve into land animals (tetrapods) and then humans. Maybe some features of their nervous systems still remain with us,” said Dr. Clement.

Thank you: This research was supported by grants DP160102460 and DP200103398 from the Australian Research Council, Flinders University, a Wallenberg Fellowship from the Knut and Alice Wallenberg Foundation, the Natural Sciences and Engineering Research Council of Canada, and a discovery grant from Calidus Services Ltd. UK.

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Materials provided by Flinders University. Note: Content may be edited for style and length.

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