Australasian Science: Australia's authority on science since 1938

Scans Reveal Our Fishy Ancestry

By John Long

A synchrotron scan of a 400 million-year-old fish has revealed how far back our own facial structures evolved, and a 28 million-year-old toothed whale fossil has revealed the origins of echolocation in modern whales.

In this modern age of rapid technological breakthroughs, what real currency does palaeontology still have in our lives? Why should I bother reporting on old dead things that seemingly have no real meaning in today’s society?

Recently I addressed a gathering of about 100 members of a well-known museum in Sydney. My talk was about exciting new fossil discoveries that elucidate the deep origins of the human body plan, largely based on a slew of recent spectacular fossil finds of early fishes that made headlines around the world.

I reminded the audience that the ancient Greeks saw scientific discovery as a major component of philosophy, as significant new discoveries about nature helped them to live better lives and appreciate our place in the world. Similarly, the study of ancient life offers our own lives a unique perspective that is central to our understanding of where we have come from as a species, and where we, and the Earth’s ecosystems, might be heading in the future.

Knowledge of our evolutionary distant ancestry gives philosophical meaning to the fact that we are all interconnected to every other form of life, and that all species, whether animal, plant, fungi or bacteria, share some common DNA. We have evolved from common ancestry way back in time. Palaeontology holds real value in revealing how the past experiments in life and the causes of mass extinctions are really the baseline studies for understanding the future sustainability of our modern biodiversity.

The first discovery I’d like to discuss concerns synchrotron scans of the 400 million-year-old placoderm fish Romundina, which give us new insights into how the vertebrate face evolved (Nature, doi:10.1038/nature12980). We know from the study of placoderms and more primitive jawless armoured fish fossils that limbs, jaws, teeth and skulls all first evolved within the initial 100 million years of vertebrate history. The face we all have today, with fixed eyes, nose and mouth, really became locked into vertebrate skull patterning when nasal capsules developed forwards of the eyes, and jaw bones became fixed above and below the mouth. Even the face of Mona Lisa can be directly compared with the face of an advanced placoderm once this stage in evolution was completed. Romundina showed us how this happened.

From the far north of Canada, a small tyrannosaurid dinosaur of 5–6 metres in length called Nunuqsaurus was announced in PLOS One by Drs Tony Fiorillo and Ronald Tykoski of the Perot Museum in Texas (doi: 10.1371/journal.pone.0091287). It lived in a cold polar climate about 70 million years ago, and was most likely an active hunter rather than a scavenger. Interestingly, the paper makes no mention of the previously reported polar tyrannosaur from Victoria reported in 2010 by Dr Roger Benson and others in Science (doi:10.1126/science.1187456).

Australia’s iconic modern bandicoots and bilby now have older fossil ancestors from the Riversleigh fossil deposits of mid-Miocene age (c. 20 mya), pushing their roots back at least another 15 million years. Dr Kenny Travouillon, Prof Mike Archer and colleagues from the University of NSW named the new fossil bandicoot Crash bandicoot (after the video game) and the bilby Liyamayi dayi in a report in the Journal of Vertebrate Paleontology (doi:10.1080/02724634.2013.799071).

Finally, a 28 million-year-old toothed whale from South Carolina, USA, named Cotylocara has revealed the origins of echolocation in modern whales. It shows distinct cavities in the skull for echolocation organs, highlighting that their origin came immediately after the split with baleen whales about 30 million years ago (Nature, doi: 10.1038/nature13086).

“This discovery hints at a much more complex and indeed more ancient early history for biosonar in odontocetes [toothed whales],” said Dr Erich Fitzgerald, a fossil whale expert at Museum Victoria. It is intriguing that every ‘most archaic’ fossil odontocete that’s dug up, including Cotylocara, is unmistakably an odontocete. That tells us that this discovery is by no means the final word, and that the most exciting, much older, transitional fossils are out there waiting to be found.”

That’s all for now, next month it will be all about the fossils, I promise.

John Long is Strategic Professor in Palaeontology at Flinders University.