麻豆传媒

Hips really can lie. In 1888, H.鈥匞. Seeley split the dinosaur family tree into two branches based on pelvic bones, but a new analysis suggests a complete rejig of early dinosaur types and challenges assumptions about where the first dinosaurs lived and what they ate.

鈥淢aybe we shouldn鈥檛 just blindly accept this 130-year-old idea,鈥� says at the University of Cambridge. 鈥淪eeley鈥檚 idea, while it was brilliant for his time, it鈥檚 arguably archaic. It鈥檚 based on very few specimens.鈥�

Seeley divided dinosaurs into 鈥渂ird-hipped鈥� animals, like the herbivorous Stegosaurus and Triceratops, and 鈥渞eptile-hipped鈥� ones, including carnivores like Tyrannosaurus rex and long-necked herbivores like Apatosaurus.

Instead of focusing on the pelvic bone, Baron and his team analysed 457 characteristics of 74 species
and found that 21 other anatomical features divide the dinosaurs differently. 聽Some of the common features shared between dinosaurs that were previously thought unrelated include straight thigh bones instead of the S-shaped ones found in some later dinosaurs, shoulder bones three times the length of the forelimb, and the first metatarsal 鈥� a long foot bone 鈥� not reaching the ankle joint.

鈥淚t sounds like trivial little features, very picayune things, but when you get that big a pile of bits of information just accumulating, you really do come up with a picture, a rearrangement,鈥� says , a palaeontologist at the University of California, Berkeley.

Based on these inherited features, the new tree puts T. rex and other theropods on one side with the old 鈥渂ird-hipped鈥� creatures, and leaves the sauropods like Apatosaurus grouped with those related to Herrerasaurus, a bipedal carnivore found in South America.

This tree structure hasn鈥檛 been suggested before, says , a palaeontologist at the University of Brighton, UK. However, people have long recognised that there are a striking number of similarities in how the different dinosaur lines evolved. 鈥淭hose have always been considered to be convergent evolution. Perhaps they鈥檙e not,鈥� she says.

Omnivorous ancestor

Because both new branches include carnivores and herbivores, Baron鈥檚 team concludes that the common ancestor of all dinosaurs may have been omnivorous.

The results also suggest that the cradle of dinosaur evolution may not have been South America, as has long been accepted. It could instead have been in the northern hemisphere since fossils of the oldest members of the new branches are found there.

鈥淚t鈥檚 as if somebody suddenly said, 鈥楢ctually chickens are mammals, not birds鈥�,鈥� says , a palaeontologist at the University of Bristol, UK. 鈥淏ut we have a lot of knowledge of chickens, so we can say that鈥檚 ridiculous. In this case, we don鈥檛 have complete specimens for them all, so we can鈥檛 say with certainty it鈥檚 ridiculous.鈥�

A few of the 21 features that link the new branches could be questioned, but if they hold up under scrutiny, the team鈥檚 case is 鈥渦ndeniable鈥�, says Benton.

Read more: Giant flying reptile was top predator like a winged T. rex