by Veronika Meduna Veronika.Meduna@radionz.co.nz
There was a whole diversity of of tyrannosaurs, and T. rex was just the end product of a hundred million years of evolution. _ Alan Tennyson
Tyrannosaurus rex is undoubtedly the most famous member of a group of carnivorous theropod, or "beast"-footed, dinosaurs. But the evolutionary origins of the tyrannosaur family began some 160 million years ago, spanned several continents and included many small, feathered creatures that look only vaguely related to the finely-tuned killing machine Steven Spielberg portrayed in Jurassic Park.
Tyrannosaurs: Meet the Family, an exhibition that opens at Te Papa Tongarewa this weekend, traces the evolutionary development from smaller, feathered varieties discovered in China to the mighty T. rex, which disappeared along with all large dinosaurs about 65 millions years ago.
The earliest tyrannosaurs were tiny, such as the cat-sized Dilong paradoxus with its unusual skull crest or the oldest tyrannosaur Guanlong wucaii. Some recently discovered specimens were found covered in proto feathers, providing evidence that at least some tyrannosaurs had a fluffy coat of down.
Te Papa curator Alan Tennyson says the feathers were useless for flying but have strengthened the evolutionary link between dinosaurs and birds. "“When I was a little kid, noone realised that dinosaurs had feathers at all. There was a link made between Archaeopteryx, the earliest bird, and dinosaurs. But then about 20 years or so ago a lot of dinosaurs with feathers started to be discovered and the link between dinosaurs and birds became even more obvious. Now we know that a lot of dinosaurs had feathers."
The use of feathers for flight was a mere byproduct of evolution, he says, and the primary function was most likley to provide warmth, suggesting that the smaller tyrannosaurs were active and warm-blooded, rather than cold-blooded like modern reptiles. One of the groups of theropods, the microraptors, are now thought to be the ancestors of modern birds.
‘Today we refer to birds as avian dinosaurs, and all the other ones that we traditionally think of as dinosaurs, as non-avian dinosaurs.'
Another feature of early tyrannosaurs is that they had much longer and stronger arms with three fingers. Alan Tennyson says the reason for T. rex's puny arms had a lot to do with balance. "There is one theory, and that is that because of the size of the large tyrannosaurs ... they couldn’t have too much weight at the front of their body, especially with their large heads."
Tyrannosaurs are known only from the Northern Hemisphere, with T. rex in north America and its similarly large cousin Tarbosaurus bataar in central Asia. This exhibition, which was originally designed by the Australian Museum, has been adjusted to include the discoveries, mostly by "dinosaur lady" Joan Wiffen, of large terrestrial dinosaurs in New Zealand.
Here you can listen to our earlier stories about Joan Wiffen's legacy and my own dinosaur hunt with a team of palaeontologists from GNS Science.
Science writer and editor of the Australian Geographic John Pickrell has delved into the latest discoveries of feathered dinosaurs in his book Flying Dinosaurs: how fearsome reptiles became birds, in which he asks just how closely T. rex is related to a chicken. You can listen to his interview with Nine to Noon.