Ancient Lungfish Fossils Reveal New Clues to Life on Land

New evidence from extremely ancient fish is giving scientists a clearer picture of one of the most significant events in Earth’s history of life.

Over 400 million years ago, certain fish started to undergo subtle yet important changes. In time, these developments made it possible for animals to emerge from the water and colonise land. That transition ultimately paved the way for frogs, dinosaurs and humans.

Two newly published studies bring further detail to this evolutionary account. Both investigate lungfish, an ancient fish lineage that persists today and lies close to the evolutionary branch that gave rise to land animals.

Through the study of lungfish fossils, researchers are reconstructing the gradual emergence of the features early vertebrates required to survive beyond the shoreline.

Untangling an unusual fish fossil

One of the studies revisits a fossil unearthed decades ago in Western Australia. Initially, the specimen seemed disordered – with some sections damaged and others proving hard to understand.

When it was first formally described in 2010, the fossil appeared so strange that scientists considered whether it might belong to an entirely unrecognised kind of fish.

It was recovered from a reef system that predated the modern Great Barrier Reef by a vast margin. This Devonian reef was once located beneath the sea in the present-day Kimberley region of northern Western Australia, an area then inhabited by early fish species.

Researchers have now reassessed the enigmatic specimen with modern imaging technology. Detailed CT scans enabled them to examine the inside of its skull without opening it, exposing intricate features that had previously remained concealed.

Dr Alice Clement of Flinders University, the study’s lead author, said the fossil had initially looked exceptionally unusual, explaining that the researchers who originally described it “considered that it could be a whole new type of fish never before seen in science.”

Fossil scans clarify lungfish evolution

Digital imaging established that the specimen is a lungfish, while also offering an unusually comprehensive view of its brain cavity and the skull’s internal anatomy.

“Using high-tech scanning, this time we were able to create comprehensive new digital images of the external and internal cranium, showcasing the complexity of the brain cavity of this fascinating lungfish,” said Dr. Clement.

Using museum collections and national research facilities, the team also compared the fossil’s surviving inner-ear structures with those of other specimens from the same location.

“We were able to compare its most preserved inner ear area with other Gogo lungfish,” said researcher Hannah Thiele, who worked on the project.

“It adds to the wider understanding of the evolution of these earliest lobe-finned fishes, both in Gondwana and across the world.”

A skull preserved from ancient seas

The second investigation focuses on a site on the other side of the world, in what is now southern China. Scientists there discovered an exceptionally preserved lungfish skull in rocks roughly 410 million years old. The species has been called Paleolophus yunnanensis.

The fossil dates from an especially important period. Lungfish had already emerged, but had not yet diversified into the broad array of forms that appeared later in the Devonian. This makes the skull particularly valuable.

“Paleolophus gives us an unprecedented look at a lungfish from a time between their earliest appearance and their great diversification a few million years later,” said Dr. Brian Choo, a researcher at Flinders University.

“It was a time when the group was just starting to develop the distinctive feeding adaptations that would serve them for the remainder of the Devonian and onwards to the present day.”

Its skull combines ancient and more recent characteristics. Certain features are similar to those of the earliest lungfish fossils from China, whereas others more closely resemble later species found in locations including Wyoming in the US and Australia. This blend helps to address a longstanding gap that has frustrated palaeontologists.

What lungfish fossils reveal

Lungfish are more than remnants of a distant past. Several species remain alive, among them one native to Australia. Their anatomy provides rare clues to the slow transformation of fins into limbs and the evolution of air breathing.

“Lungfish are an incredibly ancient lineage, including the still living Australian lungfish from Queenland, that have long fascinated researchers due to their close relationship to the tetrapods, or backboned animals with limbs, including humans,” said Dr. Choo.

“The exceptional lungfish skull unearthed in 410 million-year-old rocks in Yunnan gives us major insights into the rapid evolutionary diversification between the early-, mid- and late Devonian.”

The complete study appeared in the journal Canadian Journal of Zoology.