Primitive fish had more sense than we thought

CT scans of vertebrate fish fossils have found early signs of sophisticated electroreception systems, which paved the way for the amazing detection ability of sharks, lungfish and other living species.

The research, led by Flinders University palaeontologists Ben King and Professor John Long, found evidence of electroreception in the fossils of Devonian lungfish – one of the earliest vertebrate sensory systems to appear.

“Electroreception is difficult to study in fossils, but synchrotron and micro-CT scans allow us to look inside the fossils and reveal 400 million-year-old sensory systems in stunning detail,” says lead author Benedict King, a PhD student at Flinders University.

“The discovery of electroreception in fossils of this age suggests that this sensory system played an important role in the early evolution of vertebrates, and allowed them to adapt to specialised ecological roles,” he says.

The new research paper, ‘Electroreception in Early Vertebrates: Survey, Evidence and New Information,’ by Benedict King, Yuzhi Hu (ANU) and Professor John Long, is published in the journal Palaeontology, and can be read online

Segment of a 400-year-old lungfish skull fossil.

The researchers applied CT scanning to some of the earliest vertebrate fossils, revealing that early members of the bony fish group already had sophisticated electroreception systems, enabling them to detect electric fields in their surroundings.

Electroceptors have been lost and gained by fish and amphibious species over epochs, but sharks and several other living primitive fish such as lungfish, which hail from the Devonian period, have this characteristic that is thought to be one of the earliest vertebrate sensory systems to appear, although its origins are mysterious.

“To date, we do not know the origin of electroreception, which is a major sensory system in living vertebrates, but this paper represents a ground-breaking study giving the first detailed overview of electrosensory systems in ancient fish,” says Professor Long.

“We now know that early ancestors to modern sharks and bony fish – the armoured placoderm fish – had more complex sensory systems with new organs present we never knew about before this paper.

“Jawless fish like lampreys have complex electrosensory buds and sharks have complex electrosensory apparatus that are highly sensitive to detecting electric field in water, but nothing exists in between these conditions.”

A new kind of organ found on some placoderms is a large sensory pit on the cheek, demonstrating that much change and development went on at the origin of these complex sensory systems.

The studies continues, as the researchers cannot yet confirm the actual function of this newly discovered ampullae – but they can verify that it was not part of the regular lateral line sensory system.

  • Read the paper
  • Read more in The Conversation article by Ben King and Professor Long
  • IFLScience! also covered the discovery here
Head of a Latimeria chalumnae showing two posterior openings for the rostral organ. Image courtesy Digital Fish Library
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