Brain compartment provides new insight into prehistoric lungfish

The development of the brain and nervous system in animals goes back more than 400 million years, with the study of the fossil remains of ancient lungfish constituting a missing link in the emergence of four-legged land animals on Earth.

An international study, led by Flinders University in Australia, compared detailed 3D models of cranial endocasts of six Paleozoic lungfish (Dipnoi) fossils with the brain chambers of the surviving sister group of terrestrial vertebrates to better understand the evolution of cerebral lungfish.

This in turn may help with the interpretation of early tetrapods, which then moved from water to land on four legs, says lead author Dr. Alice Clement of Flinders University.

The discovery, described in the 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 undergoes significant elongation in several taxa.

“Our findings show that lungfish brains evolved continuously throughout their 400-million-year history, but this suggests that they probably always relied on their sense of smell rather than sight to navigate their environment. This is quite different from other fish, that use vision much more powerfully,” says Dr Clement of Flinders University’s Ecology and Evolution (Paleontology) Research Laboratory.

“She says that understanding how the brains of lungfish changed throughout their evolutionary history helps to 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, the Australian researchers, along with co-authors in the UK, Canada and Sweden, used powerful imaging methods to virtually reconstruct these brain models.

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

“This paper effectively doubles the number of lung endocasts known, as their preservational quality is often damaged by crushing or breaking a fossil, and the brain itself has very low preservation potential and is not currently known from any fossil lungfish,” he says.

“The wrasse has persisted for over 400 million years from the Devonian period to the present day and provides 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) could be studied non-destructively. The fossils come from Australia, the USA, Russia and Germany.

The six fossils and the two extant taxa were subjected to a dataset of 12 taxa for a multivariate morphometric analysis using 17 variables.

“The study of our ‘fish cousins’ continues to help us understand how fish left the water about 350 million years ago and began to evolve into land animals (tetrapods) and then into humans. Perhaps some of their nervous system traits still remain with us ,” says Dr. Clement.

Thanks: 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, a Discovery Grant from the Natural Sciences and Engineering Research Council of Canada and Callidus Services Ltd UK.

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

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