An ancient Australian air-breathing fish, dating back to 380 million years ago.

Alice Spring’s Finke (Larapinta) River, often cited as one of the oldest rivers in the world, was once home to waters teeming with bizarre animals, including a sleek, lobe-finned predatory fish with large fangs and bony scales.

The newly described fossil fish has been named Harajicadectes zhumini by an international team of researchers led by Flinders University palaeontologist Dr Brian Choo.

The fossil is named after the Harajica Sandstone Member where the fossils were found in the “Red Centre” of Australia and the Ancient Greek dēktēs (“biter”). It also pays tribute to Professor Min Zhu, currently at the Chinese Academy of Sciences in Beijing, who has made major contributions to early vertebrate research.

Part of the ancient lineage of Tetrapodomorphs, some of which became the ancestors of limbed tetrapods – and later humans – Harajicadectes are particularly distinguished by their large openings on the top of their skulls.

“These spiracular structures are thought to facilitate surface air breathing, with modern African bichir fish having similar structures for sucking air from the water surface,” says Dr Brian Choo, a paleontology researcher at Flinders, who studied the most complete specimen in water. Newly described Harajicadectes, which reached approximately 40 cm.

“This feature appears in several lineages of Tetrapomodorph at around the same time during the Middle and Late Devonian.

“In addition to the Harajicadectes of Central Australia, large spiracles also appeared in Gogonasus of Western Australia and in elpistostegalians like Tiktaalik (the closest relatives of tetrapod limbs). Additionally, they also appear in the Pickeringius, a fish ray-finned from Western Australia, first described in 2018.”

Professor John Long of Flinders, a leading Australian expert on fossil fish and co-author of the new discovery published in the Journal of Vertebrate Paleontologyargues that the synchronized onset of this adaptation to air breathing may have coincided with a period of decreasing atmospheric oxygen during the Middle Devonian.

“The ability to supplement gill respiration with aerial oxygen likely provides an adaptive advantage,” says Professor Long. “We found this new form of lobe-finned fish in one of the most remote fossil sites in all of Australia, the Harajica Sandstone Member in the Northern Territory, almost 200 km west of ‘Alice Springs, dating from the Middle-Late Devonian about 380 million years old.

“It is difficult to determine where Harajicadectes fits within this group of fishes, because it appears to have convergently acquired a mosaic of specialized features characteristic of largely distinct branches of the tetrapodomorph radiation.”

The publication is the culmination of 50 years of exploration and research.

Professor Gavin Young of the ANU first discovered fragmentary specimens in 1973 and many other fossils recovered in 1991 were studied by the Melbourne Museum and Geosciences Australia in Canberra.

Attempts to study these fossils proved difficult until the Flinders University expedition in 2016 found a nearly complete specimen.

“This fossil demonstrated that all the isolated pieces collected over the years belonged to a single new type of ancient fish,” says Dr Choo, from Flinders College of Science and Engineering.

The 2016 specimen was transferred to the Museum and Art Galleries of the Northern Territory in Darwin.