A foot-long (30 centimeter) piece of bone unearthed in Australia is the first evidence that ancestors of the mighty T. rex once lived in the Southern Hemisphere.
The remains are from an animal much smaller than the famed predator, but add to the knowledge of how this type of dinosaur evolved.
"The new discovery tells us that 110 million years ago, in the middle of their history, tyrannosaurs were everywhere. So the question is, why did they achieve giant size as apex predators in the north, but dwindle away in the south?" Benson said in an interview via e-mail.
Dinosaurs dominated the land for 170 million years, holding the place in the ecology that mammals do today, Benson explained. Learning about how species change and diversify, and about mass extinctions in the past, can help us understand modern threats, he said.
In addition, he said, learning about ancient creatures helps in understanding the evolution of modern animals.
"For instance, in recent history paleontologists established that dinosaurs gave rise to birds. Prior to this, birds were a mystery," Benson explained. "They have lots of distinctive features, feathers, warm-blood, air-filled bones, but there was no consensus on where they came from. Now we know, we can find out how they evolved.
"Tyrannosaurs are relatively close to birds so knowing about then gives us one piece of the puzzle," he said.
The newly reported bone was found by co-author Tom Rich of Museum Victoria in Melbourne, Australia. It was uncovered in Dinosaur Cove in southeast Australia, where occasional fossils were being found.
Although only one bone was found, "it shows that 110 million years ago small tyrannosaurs like ours might have been found worldwide. This find has major significance for our knowledge of how this group of dinosaurs evolved," Benson said. "The bone is unambiguously identifiable as a tyrannosaur because these dinosaurs have very distinctive hip bones."
Benson said the newly reported bone would have come from an animal between 9 and 10 feet (2.7-3 3.05 meters) long weighing 175 pounds (79 kilograms). By contrast T. rex, which flourished about 40 million years later, was about 40 feet (12 meters) long and weighed about 4 tons. (3.6 metric tons)
The newly identified dinosaur has been designated NMV P186069.
Benson thinks the main reason so few fossils have been uncovered in Australia is that the right rocks simply haven't been explored thoroughly yet.
"Serious dinosaur exploration in the Southern Hemisphere has only recently started. Most discoveries have been made in the past 10-20 years," he said. "So paleontologists are only just filling in the list of dinosaur groups that were in the South."