The City of Ipswich, located about 40 km west of Brisbane, seems an unlikely place to find dinosaurs fossils. Driving through the area today gives neither little sense of its recent past, nor that of a much more distant time.
But Ipswich has produced the oldest evidence of dinosaurs in Australia. A fresh look at these fossils has revealed they are not what they first seemed, and it is causing us to reconsider how the story of Australia’s dinosaurs began.
In a new study lead by Dr Anthony Romilio, published in Historical Biology, we reanalyse a sequence of 220-million-year-old tracks from the Ipswich Coal Measures, thought to have belonged to a carnivorous dinosaur.
Our results show they actually belonged to an early sauropodomorph — a distant relative of the plant-eating sauropods that roamed the planet much later, during the Jurassic and Cretaceous periods. This is the first time fossil evidence of basal sauropodomorphs has been recognised in Australia.
Subterranean dinosaur tracks
The Ipswich area was once the principal source of coal for Brisbane and the state of Queensland. Suburbs such as Ebbw Vale, New Chum and Swanbank were dotted with underground mines during the late 1800s and first half of the twentieth century, before open cut operations took over in the 1980s. Expanding urban development and the expansion of mining in other parts of the state saw mining operations cease in this part of Ipswich in the 1990s.
Underground mining operations involved the creation of deep shafts and tunnels from which miners could access seams of coal sandwiched between other layers of rock. Some tunnels would descend hundreds of metres below the surface.
The coal would be removed from the seam by hand, and pillars were left in place to support the ceiling of the resulting underground ‘room’. It was hard, dangerous work.
In the mid 1960s, miners working at the Rhondda Colliery in New Chum made a startling discovery. As they removed the coal from a seam they were following 213 metres below the surface, it exposed a series of giant three-toed tracks in the overlying siltstone. A dinosaur walking across the swampy vegetation over 220 million years ago had made the tracks. The surface was buried with fine silt and mud, preserving the tracks as natural casts. For the miners, it was as if the dinosaur had just walked overhead .
Since their initial discovery, it has been assumed that some type of predatory dinosaur made these tracks. The only problem was, they were reportedly really big: an estimated 40–46 cm long, indicating a trackmaker that would have been just under 2 m high at the hips.
This isn’t necessarily very large for a theropod. Allosaurus fragillis, was about this size. Tyrannosaurus rex was even bigger, with a hip height of about 3.2m.
But the tracks found in Ipswich were created during the Late Triassic, about 220 million years ago — 65 million years before A. fragillis and 150 million years before T. rex.
Fossil evidence from around the world indicates that large theropods didn’t begin to appear until the start of the Jurassic, some 20 million years after the Ipswich tracks were made.
220 million years ago, during the Late Triassic, dinosaurs had yet to displace synapsids as the most dominant terrestrial tetrapods, and it was long assumed that their rise, both in stature and diversity, didn’t commence until the start of Jurassic.
Was something unusual afoot in Australia during the Late Triassic?
Dispelling the myth of the ‘Triassic terror’
As part of a broader review of Australian dinosaur tracks, we thought it would be a good idea to have a closer look at the tracks from the Rhondda Colliery. The mine has long been closed, so the original tracks are no longer accessible, but archival photographs and a plaster cast of one of the tracks are held in the Queensland Museum.
Utilising the photos and the cast we were able to create a 3D digital model of the track, allowing more detailed comparisons with other dinosaur tracks around the world. Our study revealed two important things.
First, that the tracks were not as big as initially reported; excluding drag marks and other unrelated surface features they are closer to 32–34 cm long as opposed to the initial estimate of 40–46 cm.
Second, the shape of the tracks and the sequence in which they were made is more consistent with early sauropodomorphs, the distant relatives of the lumbering sauropods of the Late Jurassic and Cretaceous.
The towering Triassic terror of the Ipswich Coal Measures was no more. In its place was peaceful plant-eater.
The remains of basal sauropodomorphs have been found in Upper Triassic rocks in continental Europe, Argentina, Brazil and South Africa. By the start of the Jurassic they had achieved a near global distribution, with fossils in North America, China and Antarctica. This is not surprising given that at that time the continents were still connected in a single landmass called Pangea.
Our new interpretation of the Rhondda Colliery tracks shows that basal sauropodomorphs also occurred in Australia. While we often like to think of Australia as a refuge for the weird and wonderful, it wasn’t necessarily that different to other parts of the world 220 million years ago, when dinosaurs were free to roam across the southern landmasses.
Romilio, A., Klien, H., Jannel, A. and Salisbury, S.W. 2021. Saurischian dinosaur tracks from the Upper Triassic of southern Queensland: possible evidence for Australia’s earliest sauropodomorph trackmakewr. Historical Biology. DOI: 10.1080/08912963.2021.1984447. PDF
Read the story in UQ News
Read an article on this story in The Conversation
