Ancient lungfish fossils discovered by scientists in Australia and China have revealed new insights into the evolution of Earth's earliest fish, which lived more than 400 million years ago. Two independent studies, by teams in Australia and China, provide new evidence for ancient lungfish, the closest living relatives of the tetrapods that eventually landed on land. The findings continue decades of field work at the fossil-rich Gogo site in northern western Australia, conducted by scientists in collaboration with the Chinese Academy of Sciences.
By studying living and fossil lungfish, researchers have gained important anatomical information about how tetrapods evolved. Tetrapods are vertebrates with four limbs, including humans, that completed the transition from aquatic to terrestrial life during the Devonian period. A particularly puzzling fossil from the Late Devonian strata of the Gogo Formation in Western Australia has now been reanalyzed using advanced imaging tools such as CT scans and computed tomography, with the results published in the Canadian Journal of Zoology.
Lead author Dr Alice Clement, from Flinders University's Palaeontology Laboratory, said each new study adds to scientists' understanding of the extraordinary diversity of lungfish preserved at the Gogo site, including specimens previously thought to be too poorly preserved to provide meaningful detail. The damaged fossil provides important new information from what is often described as Australia's first "Great Barrier Reef", a Devonian-age reef system in the Kimberley region of northern Western Australia.
Dr Clement, from the School of Science and Engineering, explained: "This unusual specimen is so mysterious that the authors who first described it in 2010 thought it might be an entirely new type of fish, never seen before by science. Using high-tech scanning this time, we were able to create comprehensive new digital images of the external and internal skull, illustrating the complexity of the brain cavity of this fascinating lungfish. In fact, we were also able to confirm that previous impressions may have been of looking backwards, with the front and back reversed."
Co-author Hannah Tiller, with support from multiple museums and institutions including the Australian Nuclear Science and Technology Organization, was able to use advanced techniques to shed new light on this most mysterious of specimens. "The fact that we were able to compare its best-preserved inner ear region with that of other barramundi fishes is an additional data point in an amazing collection of lungfish and early vertebrates," she said. "It adds to the broader understanding of the evolution of these earliest lobe-finned fishes, both in Gondwana and around the world."
Meanwhile, another study reconstructing the skulls of early fish, published in an academic journal, describes a species called Archaeus — a lungfish that swam in the waters off southern China 410 million years ago. Flinders University researcher Dr Brian Zhou and his colleagues at the Chinese Academy of Sciences, led by the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, named the new fossil Yunnan Paleophysis, meaning "ancient ridge from Yunnan".
Dr Zhou, from Flinders University's School of Science and Engineering, said: "The ancient spine fish gives us an unprecedented look at what the lungfish looked like in the period between their earliest appearance and their massive diversification millions of years later. This was a period when the group was just beginning to develop unique feeding adaptations that were characteristic of "The lungfish are an extremely ancient lineage that includes the living Australian lungfish in Queensland and have long fascinated researchers because of their close relationship to tetrapods, or vertebrates with limbs, including humans," he said.
This unique lungfish skull, unearthed from 410-million-year-old rocks in Yunnan, provides important insights into the rapid evolutionary diversification between the Early, Middle and Late Devonian. Dr. Zhou added that this new specimen has both similar and different characteristics when compared to the earliest and most primitive ghost fish fossils from southern China, as well as other forms such as the Skyloback fish in Wyoming and the Bismilla fish in Australia. The Chinese study was supported by the National Natural Science Foundation of China and the Australian Research Council Discovery Program, while the Gogo study was funded by the Australian Research Council. The researchers are grateful to the Gunyandi community and region for allowing access to their land, fossils and knowledge.