Using advanced neutron imaging technology, scientists examined the skull and braincase of Koharalepis jarviki, a large predatory fish that lived during the Devonian Period, often called the "Age of Fishes." The fossil was discovered in Antarctica's Lashly Mountains region and represents the only known specimen of its kind.

High-Tech Imaging Unlocks Ancient Anatomy

The research team used non-destructive scanning methods to peer inside the fossil and study structures that had remained hidden for hundreds of millions of years.

"This precious fossil belongs to a group called the Canowindridae which highlights the ancient links between Australia and Antarctica," says Flinders University Research Fellow Dr. Alice Clement, coauthor of a new article in Frontiers in Ecology and Evolution.

"It is important to study such specimens from the Devonian Age of Fishes when the waters teemed with predatory lobe-finned fish like this that are closely related to land animals (tetrapods)," says Dr. Clement, from the College of Science and Engineering.

Koharalepis belonged to the Canowindrid family, a group of fish that once lived across East Gondwana, with fossils now found in both Antarctica and Australia. Scientists consider these fish to be close relatives of the earliest four-limbed vertebrates that later evolved into land animals.

Clues to the Water-to-Land Transition

Lead author Corinne Mensforth, a PhD candidate from the Flinders Palaeontology Lab, says the fossil is especially valuable because it preserves the internal bones of the skull.

"We chose to focus on Koharalepis as it is the only fossil in the entire family to preserve the internal bones of the skull, which gives us valuable insights into its braincase and neuroanatomy."

The scans revealed that the fish's brain shared similarities with species associated with the evolutionary transition from aquatic to terrestrial life.

"We found evidence that the brain of Koharalepis was similar to those of the fishes that straddle the vertebrate water-to-land transition.

"We also found adaptations to life near the surface of the water, including openings in the top of the skull for additional air intake and an organ within the brain that detects light and circadian rhythms."

The researchers believe these features may have helped the animal survive in shallow environments where access to oxygen near the water's surface was important.

Ancient Predator Relied on More Than Vision

The study also sheds light on how Koharalepis may have behaved in its environment. Growing to around 1 meter in length, the fish was likely an ambush predator that hunted smaller animals in freshwater systems.

"Koharalepis which grew to about 1 meter was an ambush predator that preyed on other smaller animals in their environment, and with relatively small eyes it must have relied heavily on its other senses to capture its prey."

Flinders University Emeritus Professor John Long, who participated in earlier research that first described Koharalepis in 1992, says modern imaging technology made it possible to study internal structures without damaging the fossil.

"This has enabled us to understand some of the behavior, adaptations and relationships of Koharalepis to its environment and to the other tetrapod-like fishes -- and how fish first left the water to live on land approximately 385 million years ago," he says.

The new findings provide another important piece in the story of how vertebrates evolved from aquatic creatures into animals capable of living on land.

The study, "New data on the sarcopterygian Koharalepis jarviki (Tetrapodomorpha; Canowindridae) from the Late Devonian of Antarctica, revealed via synchrotron and neutron tomography" (2026), by Corinne L Mensforth, John A Long, Joseph J Bevitt (Australian Centre for Neutron Scattering, ANSTO) and Alice M Clement, was published in Frontiers in Ecology and Evolution.

The research was supported by the Australian Research Council (DP 200103398), with additional assistance from Dr. Matthew McCurry (Australian Museum) and Anton Maksimenko from the Australian Nuclear Science and Technology Organisation.