Professor Kate Trinajstic started her career as a cardiac nurse, but you won't find the heart she discovered in any medical textbooks.
Following her curiosity about our origins — and a mid-life transition to palaeontology — she has discovered a 380-million-year-old heart from some of our earliest ancestors, Gogo fish from Western Australia's Kimberley region.
The find marks a key evolutionary moment — and reveals humans may have evolved in larger leaps than first thought.
The research, published in the peer-reviewed academic Science journal, also shows how the head and neck began to change to accommodate jaws, a critical stage in the evolution of our own bodies.
"We tend to think of evolution as happening as a series of small steps," the Curtin University Professor said.
"But this discovery showed us that in our earliest ancestors the changes occurred as a big bang — all in one hit."
Professor Trinajstic and her colleagues didn't just find a heart, but also a stomach and liver almost perfectly preserved.
A few decades ago finding soft tissue like this would have been impossible, but thanks to modern scanning techniques scientists can peer into the fossils without having to dissolve them with acid.
"This is the most complete set of organs we've got in a jawed vertebrate … and these are some of our earliest ancestors," Professor Trinajstic said.
Hundreds of millions of years ago, well before dinosaurs roamed the earth, fish known as placoderms used to swim in an ancient sea called the Gogo reef.
We now know the area as Fitzroy Crossing in Western Australia's North West.
Placoderms are like the dinosaurs of the deep and Dr Zerina Johanson from the Natural History Museum in London said this discovery was "extremely important".
"In placoderms, [it is one of] the first times where we see a neck — so what we can see is that the head is movable from the trunk," she said.
"It's an important evolutionary event that was associated with the movement of the heart and creation of the muscle for the movement of the neck."
Stuff of scientists' dreams
Discoveries of Gogo fish and placoderms have led to some key breakthroughs in our evolutionary understanding.
"We see some of the first appearances of not only front fins but the fins at the back which eventually evolve in our arms and legs," Dr Zerina Johanson said.
"So there are many things going on in these placoderms that we see evolving into ourselves today."
Co-author Professor John Long from Flinders University, who has been involved in some of the biggest Gogo fossil discoveries in the region, said it was "the stuff of palaeontologists' dreams."
"Without doubt, these fossils are the best preserved in the world for this age… Gogo has given us world firsts — from the origins of sex to the oldest vertebrate heart.
"[This] is now one of the most significant fossil sites in the world."
He said it was time the site was seriously considered for world heritage status.
