Through the Early Cretaceous interval, 110 million to 107 million years in the past, Australia was a lot additional south than it’s right this moment. But fossils from a number of websites on the Otway Coast in Victoria present dinosaurs have been widespread within the area.
Probably the most considerable have been ornithopods — small plant-eaters with beaks and cheeks filled with enamel. However till just lately, it was unclear precisely what number of species coexisted on the identical time.
Thus far, 5 ornithopod species have been named from the Cretaceous of Victoria. There are three from the Otway Coast: Atlascopcosaurus loadsi, Diluvicursor pickeringi and Leaellynasaura amicagraphica; and two from the Bass Coast: Qantassaurus intrepidus and Galleonosaurus dorisae.
The rocks uncovered on the Bass Coast (and the fossils they comprise) are round 15 million to twenty million years older than these on the Otway Coast. Throughout this interval, Australia’s local weather warmed dramatically.
There’s substantial proof of glaciation in South Australia about 125 million years in the past, however by 110 million years in the past, heat weather-loving crocodile family members have been roaming fortunately in Victoria.
As such, it was presumed the Bass Coast’s Qantassaurus and Galleonosaurus — which lived in older, colder circumstances — most likely by no means crossed paths with the Otway Coast’s Leaellynasaura, Atlascopcosaurus and Diluvicursor. However is that true?
Wendy White/Dinosaur Dreaming
Eric The Purple West
Because of analysis led by my former pupil Ruairidh Duncan, we’re now in a greater place to reply this query. For his Honours venture, Ruairidh studied fossils from a website on Cape Otway known as Eric the Purple West (ETRW).
In 2005, a partial ornithopod skeleton was found at ETRW. This skeleton was named Diluvicursor pickeringi in 2018 and comprised solely a tail, a partial shin, ankle, and a hind foot.
Stephen Poropat/Museums Victoria
A number of extra digs by a bunch of volunteers known as Dinosaur Dreaming noticed the location produce many extra ornithopod bones, together with some jawbones. Till Ruairidh studied these jawbones, we had no concept whether or not they belonged to current species or new ones.
Slightly assist from know-how
Many of the ornithopod jawbones from ETRW have been damaged in half after they have been found. This isn’t uncommon, because the bones are softer than the rock by which they’re encased.
Nonetheless, relying on how they have been damaged, one half of a jawbone may need had rock eliminated solely from the tongue facet, and its matching half may need had rock eliminated solely from the cheek facet.
Though this allowed the 2 halves of the jaw to click on collectively properly, it meant Ruairidh couldn’t observe most of his specimens as full bones from both the tongue or cheek facet. Properly, not with out some assist from know-how.
Monash College’s Alistair Evans micro-CT scanned a number of ornithopod specimens retrieved from the ETRW website. Similar to medical CT scanners, micro-CT scanners generate a sequence of 2D cross-sectional photos by a 3D object (however on a smaller scale).
The scans allowed Ruairidh to digitally take away the rock from his specimens — which have been all lower than ten centimetres lengthy — and reconstruct each in 3D.
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Ruairidh analysed the ornithopod jawbones from the ETRW website and in contrast them with the opposite Victorian ornithopod species. (Three of the 5 ornithopods identified from Victoria have been already named and described on the idea of higher jawbones, which enabled a direct comparability).
He discovered one higher jawbone was attributable to Atlascopcosaurus (probably the most full specimen identified of this species) and one other to Leaellynasaura (the primary grownup specimen identified of this species).
We had anticipated the ultimate two bones may belong to a Diluvicursor. As a substitute, we have been stunned to find they have been intently comparable with Galleonosaurus — the species beforehand solely identified from the Bass Coast, with rocks that have been roughly 15-20 million years older than these uncovered at ETRW.
In different phrases, we’d discovered proof of an ornithopod species that had remained nearly unchanged for not less than 15 million years!
The presence of an ornithopod so just like Galleonosaurus at ETRW implies that little or no change in tooth and jaw anatomy (and presumably food plan) occurred in these dinosaurs in nearly 20 million years, regardless of marked climatic change.
This may imply their favorite crops modified little in abundance all through this time, by which case they’d have confronted little strain to vary the form or construction of their enamel and jaws.
It stays unimaginable to check the jawbones from ETRW with the one specimen of Diluvicursor pickeringi — as no jawbones have been discovered with it.
However maybe the absence of a novel jawbone kind for Diluvicursor may imply this species is definitely the identical as one of many different species that are represented by jawbones. In that case, it’s almost definitely Atlascopcosaurus or the Galleonosaurus-like species; a really completely different tail and foot have been tentatively assigned to Leaellynasaura.
Sadly, figuring out this can hinge on discovering an ornithopod skeleton matching that of Diluvicursor, related to a cranium matching the jaws of Atlascopcosaurus or Galleonosaurus.
And provided that greater than 40 years of digging for dinosaurs in Victoria has revealed solely 4 partial ornithopod skeletons, we is perhaps ready some time.
Nonetheless, Ruairidh’s analysis has demonstrated three completely different ornithopod species have been fortunately residing in southeast Australia, throughout the Antarctic Circle about 110 million to 107 million years in the past — when the world was typically a lot hotter than it’s right this moment.
Thus far, the ETRW website has produced an abundance of fossil proof, together with crops (principally conifers, ferns and early flowering crops), bony fish, lungfish, plesiosaurs, pterosaurs, huge-clawed megaraptorid theropods, Australia’s solely toothless and long-necked elaphrosaurine theropod, and even historic mammals.
It has solely produced one ornithopod skeleton: the aforementioned Diluvicursor. However who is aware of what we would discover subsequent?
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