Tyrannosaur bones are relatively familiar finds on the northern continents of the globe, cropping up everywhere from modern-day Colorado to China. But until now, they appeared to be oddly missing from the southern half of the globe. The discovery of a distinctively tyrannosaur-like hipbone in Victoria, Australia, however, might change the way scientists think about the distribution—and evolution—of this infamous group of dinosaurs.
"The absence of tyrannosauroids from the southern continents was becoming more and more anomalous as representatives of other 'northern' dinosaur groups started to show up in the south," Paul Barrett, of the Department of Paleontology at the Natural History Museum in London and a coauthor of the new report, said in a prepared statement.
The hipbone fossil is 30 centimeters long. "The bone is unambiguously identifiable as a tyrannosaur because these dinosaurs have very distinctive hip bones," asserted lead study author Roger Benson, of the Department of Earth Sciences at the University of Cambridge, in a prepared statement.
Extrapolating from the size of the hipbone, the researchers estimate that the new tyrannosaur would have been about the size of a person, measuring some three meters long and weighing in at about 80 kilograms. The animal lived in the Early Cretaceous, when members of the family were still small compared to the towering, Late Cretaceous Tyrannosaurus rex.
This as-yet unnamed dinosaur lived about 110 million years ago—about 40 million years before its revered relative the T. rex. At this time, the southern continents (Australia, Africa, South America and Antarctica) were still connected to each other, providing the researchers with "hints at the possibilities that others remain to be discovered in Africa, South America and India," Barrett said. The fossil find was detailed online on March 25 in Science.
Why did this group of dinosaurs appear to be so small and scant in the southern hemisphere while some tyrannosaurs later on were massive, dominating predators in the northern hemisphere? "It is difficult to explain why different groups succeeded in the north and south if they originally existed in both places," Benson said. "We can only answer these questions with new discoveries."
Image of where the new tyrannosaur fossil was found, in a place known as Dinosaur Cove in Victoria, Australia during the period in which the animal lived, courtesy of Roger Benson/Cambridge