Evrim Yazgin
Cosmos science journalist
About 400 million years ago, some intrepid fish became the first vertebrate animals to walk on land. Now a fossil jawbone found in northern Australia might help explain what these pioneering fish ate.
Lobe-finned fish such as coelacanths are closely related to modern lungfish. Lungfish got their name because these “living fossils” from Africa, South America and Australia can breathe air.
Fossil jawbones from ancient lungfish that lived 380 million years ago (mya) have been re-examined using new techniques to reveal insights into their diets. The findings are presented in a paper published in the iScience journal.
The fossils were found in northwestern Australia’s Gogo Formation.
Rocks in the formation date to the late Devonian period. The Devonian – also known as the “Age of Fishes” – lasted from 419 to 359 mya. During this time, the Gogo region was a shallow reef in a tropical climate.
3D finite element model (FEM) analysis was performed on jawbones of 5 of the 11 species of ancient lungfish found in the Gogo Formation. CT scans were done on an expanded group of 7 species. You can view the virtual 3D models online at Morphosource.
The techniques allowed the palaeontologists to measure the strength and features of the fossilised mandibles to see how the different species coexisted.
Understanding ancient lungfish diets may shed light on the evolution of the first tetrapods – vertebrates that walk on land.
“We’re slowly teasing apart the details of how the bodies and lifestyles of these animals changed as they moved from being fish that lived in water, to becoming tetrapods that moved about on land,” says corresponding author Alice Clement from Flinders University in South Australia.
“Our comprehensive dataset offers the most detailed quantification of biting performance in any fossil fish thus far, providing biomechanical evidence for diverse feeding adaptations and niche partitioning within Gogo lungfishes,” says co-author Olga Panagiotopoulou from Touro University in the US.
“We were then able to model the stress and strain experienced by these lower jaws during biting,” she says.
The findings challenge earlier conceptions based on the size and shape of the fossil mandibles.
“The results were somewhat surprising, with some ‘robust’-looking lower jaws appearing to not be all that well suited to biting stress, and some of the more gracile or slender jaws appeared to be able to withstand stress and strain very well,” says co-author John Long who is also at Flinders.
Pillararhynchus had the most robust mandibles, suggesting that it was the most likely of the Late Devonian Gogo lungfish to feed on hard-shelled prey. Griphognathus had a unique “duckbill-shaped” jaw similar to a modern platypus which could have been used to sift through sediment for meals. Rhinodipterus had a slender jawbone with a surprisingly high resistance to stress.
Long says predatory lungfish evolving to fill specific environmental niches was likely the source of their remarkable diversification in the Late Devonian.
“The Late Devonian reefs of the Gogo Formation were a truly unique lungfish community with species possessing a whole host of different behaviours and abilities,” says lead author Joshua Bland, also from Flinders.
“To capture parts of that story, hidden in the bone, was extremely rewarding. It felt like we lifted the veil on some real functions behind the form. It was impressive to see the more complex morphology perform better in our tests.”