Placoderms have been called the \u2018dinosaurs of the seas\u2019 and, because the head and thorax is covered with bony plates, they’re also known as \u2018the armoured fish\u2019. But their best feature is their jaws. This is because, prior to placoderms, our vertebrate ancestors were like lampreys, with a pliable mouth that moseyed around sucking up food. So while we\u2019re captivated by the historic tragedy of the dinosaurs, and the evolution of opposable thumbs, jaws are the bigger deal.<\/p>\n\n\n\n
Vertebrate palaeontologists and long-time collaborators Professor Kate Trinajstic and Professor John Long know placoderms, and the arthrodira<\/a> in particular, probably better than anyone. Trinajstic explains that the arthrodire group of placoderms also had a neck joint that let the head rise and the jaws drop \u2013 which allowed feeding \u2013 and they ranged from moochers of the ocean floor to six-metre apex predators.<\/p>\n\n\n\n Hammer in hand, Trinajstic began exploring the Devonian reefs in Australia\u2019s northwest about 25 years ago. After being discovered in the 1940s, investigations at the Gogo Formation have been ongoing since the late 1960s, with great discoveries made by Long and others striving to further understand vertebrate evolution. According to Trinajstic, unlike the portrayals of palaeontologists feathering away at rocks with little brushes, the only way to capture a placoderm is to thwack open the limestone concretion, or \u2018nodules\u2019 that contain marine fossils. And they\u2019re quite common in the Gogo.<\/p>\n\n\n\n \u201cAfter perishing, placoderms living on the reef would have floated out and sunk into deeper water where oxygen is absent, which gives more chance of preservation,\u201d she explains.<\/p>\n\n\n\n \u201cAnd the nodules are fairly easy to find. We pick them up, hit them with a hammer so that they break along the fossil line, which is the weakest line in the rock.”<\/p>\n\n\n\n But if these fossil nodules are scattered randomly over the landscape, like shells on a beach, there for the picking, or thwacking, why isn\u2019t the Gogo swarming with bounty hunters?<\/p>\n\n\n\n Trinajstic says that while the Gogo is one of the world\u2019s best-preserved ancient reef complexes, and the limestone concretions are common, the location is kept fairly quiet. \u201cAnd most of the time we only find fossil \u2018ghosts\u2019, which are just a smear.\u201d<\/p>\n\n\n\n But every so often they find more than a smear. Over the past 10 years Trinajstic has contributed several important research discoveries from the Gogo, and this year she struck gold \u2013 a nodule containing a placoderm heart that thumped 380 million years ago. The discovery has caused palpitations in the scientific body of vertebrate palaeontology, because the heart is somewhat older than the previous vertebrate heart<\/a> discovered\u2026 by 250 million years.<\/p>\n\n\n\n But it wasn\u2019t a case of cracking open the nodule to reveal a tiny stone heart and yelling Eureka! Long found the nodule on a field trip years ago, but Trinajstic discovered the preserved heart only recently, from scans obtained by a combination of modern imaging techniques known as synchrotron radiation (SR) microtomography and neutron imaging.<\/p>\n\n\n\n It\u2019s rare for palaeontologists to find fossils of animal tissue like organs and muscles. Soft tissue usually decays before it can be fossilised, but under rare perfect conditions, fossilised soft tissue can occur. The second challenge is that prior to SR microtomography, palaeontologists needed to apply a weak acid solution to the rock surrounding a fossil. And, along with the rock, any fossilised soft tissue \u2013 muscle, for example, that may have clung to the bones, also dissolved away. An earlier method to study the fossil\u2019s soft anatomy involved the sectioning of the fossil, which of course destroyed the original version.<\/p>\n\n\n\n But now, scanning technologies, coupled with enormous computing power, enables palaeontologists to reveal and study fossil non-destructively, and will likely uncover more soft tissue fossils for the record.<\/p>\n\n\n\n Trinajstic joined Curtin as a research fellow in 2009, and since then has been using scanning techniques on Gogo fossils discovered during the past 22 years, and revealing previously unknown musculature<\/a> of the placoderms. In 2011 she received an esteemed fellowship from the Australian Research Council for the project \u2018Fleshing out the fossil record\u2019, to further investigate the development of the skeleton and specialised musculature in early vertebrates. The results have been astounding, a specimen of the genus Compagopiscis<\/em> revealing when the first teeth<\/a> evolved and studies on an Incisoscutum<\/em> specimen revealing the evolutionary origins of<\/a> internal fertilisation and live birth!<\/p>\n\n\n\n![\"\"](\"https:\/\/www.curtin.edu.au\/news\/wp-content\/uploads\/2022\/11\/Journal-image.jpeg\")
Old fossils are new again<\/strong><\/h3>\n\n\n\n
The heart of the matter… is actually the liver<\/strong><\/h3>\n\n\n\n
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