Trackways found in South Australia Hint at Polar Ornithomimids
The Ornithomimidae (Ostrich mimics), so called as their skeletons superficially resemble modern, ground living birds are known from extensive fossil material from the northern hemisphere. However, the discovery of a set of dinosaur tracks, in South Australia indicates that Theropods such as members of the Ornithomimidae may have roamed Gondwanaland too. These trackways support body fossil evidence that suggest that these dinosaurs were indeed common in the southern hemisphere. Indeed, the tracks made during the Cretaceous Period provide evidence of such dinosaurs living in polar regions in the southern hemisphere. Scientists have speculated that with these trace fossils, plus evidence from dig sites in northern latitudes, the “Ostrich mimics” may have been warm-blooded.
As the dinosaurs roamed the southern polar regions, they left a series of distinctive three-toed prints in the wet, sandy soil as they crossed a flood plain. Over time, these trace fossils became compacted into cliffs and it was Anthony Martin (Emory University) who discovered them in what is now Victoria, (Australia).
All together he found twenty-four complete prints, their different sizes perhaps representing different species or may be juveniles and adults of a single type of dinosaur.
A Close up of one of the Polar Tracks
Picture Credit: Anthony Martin
A single three-toed print can be made out in the picture, the ruler helps to provide scale.
The tracks are all of three-toed animals (that is, three toes to walk on – digitgrade stance). The narrow toes and their overall size indicate the bird-like prints of a type of bipedal dinosaur belonging to the Theropod group – Ornithomimids. These light, cursorial dinosaurs had compact bodies, long tails, long necks and very long legs. They were swift runners and palaeontologists believe that some of the larger species such as the four metre long Struthiomimus (Struthiomimus sedens), that lived in North America during the Late Cretaceous (Campanian faunal stage), could have reached speeds in excess of sixty kilometres an hour.
The tracks indicated that the Theropods were of three different sizes, ranging from the size of a chicken to around the size of a crane. Their size and fossil bones found at other locations in Victoria, suggest to the researchers that these tracks represent evidence of “Ostrich mimics”.
The slabs of sandstone were found along the rocky and remote Milanesia Beach in Otways National Park, west of Melbourne. The rough surf pounds the coastal cliffs, frequently fracturing slabs and breaking them away from the cliff face. When the tracks were made, Australia was connected to Antarctica and was located much closer to the South Pole, as a part of the ancient continent of Gondwanaland. It is thanks to amazing fossil sites such as the famous Dinosaur Cove and East Gippsland locations (Victoria, Australia) that scientists have learnt about the incredible fauna and flora of the Cretaceous polar regions.
Martin set off on the trail toward the footprints among the ragged slabs scattering the shore after he noticed ripple marks and trace fossils of insect burrows.
He commented: “The ripples and burrows indicate a floodplain, which is the most likely area to find polar dinosaur tracks.”
Researchers cannot determine the species of the Theropods from the tracks. It’s possible they were all of the same species (possibly even a Theropod family), or they could have been different species travelling in the same area at roughly the same time. Ichnologists (scientists who study trace fossils including tracks and prints), are always reluctant to name a specific species based on the trackway evidence, however, a recent, remarkable examination of a fossil of a Protoceratops unearthed in 1965 provided ichnologists with a “holy grail” of dinosaur fossils – a body fossil of a dinosaur adjacent to a footprint from the same dinosaur species (Protoceratops).
To read more about this remarkable discovery: Stopping a Dinosaur Dead in its Tracks
When the tracks were laid down between 115 million to 105 million years ago, (Late Aptian and Albian faunal stages) the Earth was experiencing global warming, with the average temperature of the area at 68 degrees Fahrenheit (20 degrees Celsius) — about 10 F (6 C) higher than current temperatures recorded in Victoria. The Cretaceous is one of the warmest periods in the Earth’s recent history. However, although the area would not have been as cold as polar regions today, dinosaurs would have had to have been tough to survive the low temperatures (it would have been cold enough to permit water to freeze at certain times of the year) and the prolonged period of darkness when the sun dipped below the horizon and the region was plunged into darkness for several months.
These harsh conditions would have dramatically affected the planet’s biology and ecology.
Martin went on to add: “These tracks provide us with a direct indicator of how these dinosaurs were interacting with the polar ecosystems during an important time in geological history.”
The discovery of potential Ornithomimid tracks in what would have been a polar environment adds credence to the study carried out by researchers at Canada’s Royal Tyrrell Museum (Alberta, Canada) who proposed that pits and marks preserved in fossilised Ornithomimidae arm bones suggest these dinosaurs may have been covered in proto-feathers.
A spokesperson for Everything Dinosaur commented about these tracks that hint at dinosaurs from polar regions:
“‘These trackways are certainly an exciting discovery and indicate that fleet-footed Theropods were living in the polar regions. However, it is impossible to tell whether these animals were residents or seasonal migrants. Finding such trace fossils so far south adds support to the theory that these Theropods may have been feathered to help insulate them and keep them warm. This in turn suggests that these dinosaurs may have been warm-blooded.”
The report of the footprints was published on line in the journal of Australian palaeontology “Alcheringa”.