The ancestor of all bony fish has a surprising link to humans

Flinders University palaeontologists have used modern scanning techniques to discover the secrets of a 400-million-year-old fossil fish called Ligulalepis — the ancestor of all modern bony fish.

Collaborating with colleagues from the UK and Sweden, the researchers also uncovered the fossil’s 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 bodies. Their work has been published in the journal eLife.

The first discovery of Ligulalepis was a tiny fossil found in limestone in Wee Jasper, NSW, 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 [bony fish] evolution ever since, without any clear resolution as to where this enigmatic fish sits in the family tree,” said Flinders University Research Associate Dr Alice Clement.

“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.”

Dr Clement said the discovery of the second fossil allowed the team to scan hidden features inside the skull and led to the reconstruction of an ancient brain cavity. The researchers prepared the tiny specimen, less than 2 cm in length, out of the rock using weak acetic acid to expose the bone, then employed modern technology to visualise the skeletal anatomy of the two fossils.

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

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

Flinders University Strategic Professor in Palaeontology John Long noted that 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,” said Professor Long, before revealing that “we are all just highly advanced fishes”.

“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 form our arm and these fish started to develop that in their fins,” he said.

Ligulalepis illustration by Brian Choo, Flinders University Palaeontology.