Fossil link to oldest fish, and life on earth

Flinders University fossil hunters have unearthed a new evolutionary link to the first bony fishes in another step forward to more accurately understand our distant origins.

The palaeontology team used modern scanning techniques to uncover the origins of a 400 million-year-old fossil fish called Ligulalepis, revealing a 3D model of its ancient brain and confirming the ancestry of all modern bony fish.

Researchers from Flinders University, along with colleagues in the UK, Australia and Sweden, have also uncovered the fossil’s distant link with the bone structure of human skeletons, providing anatomical evidence about human evolution from fish which can today be found within the make-up of our own vertebrate bodies.

Flinders University Palaeontology Laboratory Research Associate, Dr Alice Clement, says the discovery of two 3D-preserved fossils in Australia allowed the team to scan hidden features inside the skull and lead to the reconstruction of an ancient brain cavity.

“Our research reveals previously unknown details about the pattern of dermal skull bones, the shape of the brain and other soft tissue features,” says Dr Clement.

“It resolves the big question about what the ancestor of all modern bony fish looked like.

“Understanding the structure is important because Ligulalepis is in a crucial position on the evolutionary tree.

“This discovery identified this fish as being the ancestor of all bony fish right before two major groups split and evolved different bodies,” she says.

Flinders University Strategic Professor in Palaeontology John Long says bony fish are an important group because land animals such as mammals, reptiles and amphibians evolved from them.

“Not many people would think humans evolved parts of their bone structure from a fish. We are all just highly advanced fishes, that’s the point of our story, ” Professor Long says.

The position of Ligulalepis in the evolutionary family tree at the base of the osteichthyan radiation. Image by Brian Choo.

“About 400 million years ago, some of these advanced fishes were starting to develop fins at the front that had bones that would eventually become the humerus, ulna and radius that forms our arm and these fish started to develop that in their fins,” Professor Long says.

Flinders researchers prepared the tiny fossil specimen, less than 2cm in length, out of the rock using weak acetic acid to expose the bone, than employed modern technology to visualise the skeletal anatomy of two fossils.

“CT scanning restored the anatomy of the two speciments and powerful X-rays were used to reveal hidden features inside the skulls,” Dr Clement says.

“The scans illustrate the changes early fish went through to achieve their current body plan. This includes fish we most like to eat like salmon, tuna and trout as well as those we keep as pets like goldfish.”

The first discovery of the fish called Ligulalepis was a tiny fossil found in limestone in Wee Jasper, New South Wales about 20 years ago. Then about two years ago, a second skull was discovered by Flinders University PhD student Benedict King at the same location.

“This fuelled debate around osteichthyan evolution ever since without any clear resolution as to where this enigmatic fish sits in the family tree,” Dr Clement says.

“But after the second skull was discovered by Flinders University, we also reconstructed the brain cavity which allowed us to digitally restore the brain shape for the first time.”

‘Neurocranial anatomy of an enigmatic Early Devonian fish sheds light on early osteichthyan evolution’ by Clement A, King B, Giles S, Choo B, Ahlberg PE, Young GC and Long JA has been published in eLife 

Read more in The Conversation.

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