HIPS really can lie. In 1888, H. G. 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.
鈥淢aybe we shouldn鈥檛 just blindly accept this 130-year-old idea,鈥� says Matthew Baron 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 鈥渞eptile-hipped鈥� ones, including carnivores like T. rex and long-necked herbivores like Apatosaurus.
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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. Based on these inherited features, his 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 (Nature, ).
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, actually chickens are mammals, not birds,鈥� says Mike Benton at the University of Bristol, UK. 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�, he says.
This article appeared in print under the headline 鈥淏iggest change to dinosaur tree in 130 years鈥�