FISH FINGERS TELL A WHOLE NEW EVOLUTIONARY STORY

Article published on 13 November 2020

A 375-million-year-old fish fossil is casting new light on our own evolution, and on the complex history of the earliest vertebrates.

Professor John Long always thought he was simply examining fish when he looked at fossils. Now, thanks to his latest discovery that has radically changed evolutionary knowledge, he realises that he has spent 40 years investigating the genesis of human evolution – and it’s all down to finding evidence of an ancient fish with fingers.

The startling discovery underlines Professor Long’s belief that evolution is quite different from what he calls the “Hollywood version” that is fixated on the transition from monkey to man. Professor Long takes a much longer view – that all of us are connected with all living things, and that bony fish, the earliest vertebrates from 400 million years ago, represent a great unexplored mine of information about the longer evolutionary process.

“In science, knowledge is not written in stone. It is subject to change in the light of fresh evidence,” says Professor Long. “This is a remarkable fossil because it reveals that the digits in our hands evolved before vertebrates left the water to colonise land.

“The big question is what does a fossil tell us about the overall narrative of evolution. To shine a light on that and to challenge existing knowledge changes the model of how we look at evolution.”

As Strategic Professor in Palaeontology at Flinders University, Professor Long has been working with an international team over five years to examine an extraordinary 1.57 metre long Elpistostege fish fossil found in Miguasha, Canada: the perfect example of a complete skeleton from the Devonian period, 375 million years ago. It has revealed startling new insights into how the human hand evolved from fish fins. This has required slow, methodical and careful analysis before results were published in the prestigious Nature (journal) in early 2020, but its influence on evolutionary thinking has been profound.

New analysis of fossils that were discovered many years ago can rewrite evolution thanks to the advances of technologically advanced analysis tools available in the modern laboratory. Flinders University’s Palaeontology laboratory has a glowing international reputation, having an experienced team and the most modern apparatus to tease out new information – which is exactly why Professor Richard Cloutier from Universite du Quebec a Rimouski in Canada started a conversation with Professor Long over a beer at an international conference, mentioning that more scanning and investigation needed to be done on his exceptional Elpistostege fossil.

Professor John Long

It began as a fishing expedition by the palaeontologists for new answers, and after five years of collaborative work, their published results signify a new definite marker in the evolutionary tree. “We knew we had the world’s best fossil specimen of its type, but we didn’t know what the story was,” says Professor Long.

Elpistostege has slowly revealed many secrets since a small part of its skull roof was first found in Quebec in 1938, then another part of the skull found and described in 1985, demonstrating it was an advanced lobe-finned fish. The remarkable new complete specimen was discovered in 2010, but it took collaboration with Professor Long and the Flinders University team from 2014 to take its analysis a step further. The first paper was completed in 2019 when Professor Cloutier spent six months working with Professor Long at the Bedford Park laboratory as a Flinders University Visiting International Fellow.

CT scan data examined by Flinders Palaeontology Group colleague Dr Alice Clement revealed the hidden mystery, that this fish had digits in its fin. From this astonishing realisation, work progressed quickly. Sifting through 17,000 possible decisions in a data matrix, she was able to identify where this fish sits in the evolutionary timescale.

Professor Mike Lee analysed phylogenetic data to demonstrate that Elpistostege is now the most evolutionary advanced fish known, and that its unexpected pattern of skeletal development places it one node down on the evolutionary tree to all tetrapods – adding a missing link in evolutionary history.

“This has led us to propose a different theory of how fingers evolved and gave rise to the vertebrate hand structure that persists in the more than 33,800 species of tetrapods alive today, including humans,” says Professor Long.

Great patience is needed in the laboratory to tease out all the relevant information concealed in a fossil, and what it means in the broader evolutionary discussion. Indeed, Professor Long is currently grafting at many fossil analysis projects, in some instances waiting for an advanced technological application to reveal the whole story.

Where to next? More 390-million-year-old tetrapod trackways of the Devonian age are being studied, with significant sites in Ireland and rural Victoria showing the earliest evidence of tetrapods walking on the world. More secrets in unfound fossils abound. More evolutionary answers beckon.