A guest post from the Sedgwick Museum’s Douglas Palmer
Whilst Jerry Lee Lewis was certainly not thinking of dinosaurs when he recorded his famous 1957 hit song, he was referring to hips. And, as all dinophiles know, dinosaurs can be divided into two fundamentally distinct groups based on the structure of their hips. Ever since 1887 when the Cambridge trained palaeontologist Harry Seeley (1839-1909)* first published his subdivision of the dinosaurs, there have been the reptile-hipped (saurischian) and the bird-hipped (ornithischian) dinosaurs and all new dinosaur finds have been allocated to one or other side of the divide.
But no longer: scientists from the University of Cambridge (Dave Norman and Matt Baron) and London’s Natural History Museum (Paul Barrett) have radically shaken and reconfigured the dinosaur family tree. Using modern computational methods, they have analysed and compared a vast data set, which includes the characteristics of many recently discovered early dinosaurs and related dinosaur-like fossils. As a result they have recognized important new relationships, which are at odds with Seeley’s scheme. And, they have resolved some of the outstanding problems with the old scheme. Tyrannosaurus rex, everyone’s favourite monster, is no longer lumped with the giant plant-eating sauropods as a saurischian but has moved, along with all its theropod relatives, closer to the ornithischians.
This regrouping of all the meat eating theropods, which are now known to include the birds (or avian dinosaurs), with the ornithischians brings them together as the Ornithoscelida. This resurrected name, which means ‘bird-legged’, was originally coined in 1870 by the famous evolutionary biologist Thomas Henry Huxley (1825-1895) nearly two decades before Seeley’s division of the dinosaurs.
One of the great advantages of the new scheme is that all the dinosaur groups which developed bird-like feathers are now in the ornithoscelidan grouping. The reptile-hipped saurischians are now reduced to include just the sauropod-like (sauropodomorph) plant eating dinosaurs plus a small group of Triassic age carnivores, the herrerasaurids, which appear to be early ‘experimental’ types of saurischian dinosaurs. Even so, the saurischians still include all the serious heavyweight dinosaurs, such as Diplodocus, Brontosaurus and Brachiosaurus.
Whilst the authors will go along with ‘We ain’t fakin’, a whole lotta shakin’ goin’ on’, it is unlikely that the status quo will be abandoned overnight, and only time will tell whether the new classification holds up for another hundred years and more.
- Journal reference: Baron, M. G., Norman, D. B. & Barrett, P. M. 2017. A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature doi:10.1038/nature21700
*Harry Seeley was employed in 1859 by the Rev. Professor Adam Sedgwick as his assistant in the University of Cambridge’s Woodwardian (now Sedgwick) Museum and matriculated from Sidney Sussex College in 1863. Seeley catalogued fossils for the Museum, arranged collections and published papers on the pterosaur fossils of the Cambridge Greensand. In 1872 Seeley married, moved to London and held a succession of academic posts at King’s College London. His geological hammer is part of the Museum’s current display of geological hammers.