|Posted by Mark Cantrell on July 21, 2017 at 3:50 PM|
Dinosaur family tree is just plain wrong, say scientists
We think we know dinosaurs, right? Well think again, writes Mark Cantrell. According to scientists at the University of Cambridge, we've got the family tree all wrong
FOR 130 years, palaeontologists had it all figured. But now scientists at the University of Cambridge, working with their peers at the Natural History Museum in London, have come to a startling conclusion – we’ve messed up the dinosaur family tree.
Cue red faces – of embarrassment or bluster – from a string of dead palaeontologists. On the other hand, anyone can make a mistake, especially when dealing with the ongoing work in process that is assembling the fossil record. So, hold that shame and get ready for some science-speak.
The crew from Cambridge and the Natural History Museum have come to the conclusion that the family groupings used to categorise dinosaurs needs to be rearranged, re-defined and re-named. Naturally, that's exactly what they've done.
Up to now, palaeontologists have used a classification system that has placed dinosaur species in one of two distinct categories: Ornithischia and Saurischia. But after analysing dozens of fossil skeletons and tens of thousands of anatomical characteristics, the researchers concluded that this is inaccurate.
“This study radically redraws the dinosaur family tree, providing a new framework for unravelling the evolution of their key features, biology and distribution through time,” said Professor Paul Barrett, of the Natural History Museum, who co-wrote the research paper. “If we're correct, it explains away many prior inconsistencies in our knowledge of dinosaur anatomy and relationships and it also highlights several new questions relating to the pace and geographical setting of dinosaur origins.”
The classification system used to construct dinosaurs' family tree dates back to Victorian times. Dinosaurs were first recognised as a unique group of fossil reptiles in 1842 as a result of the work of the anatomist, Professor Richard Owen (who later went on to found the Natural History Museum in London).
Over subsequent decades, various species were named as more and more fossils were found and identified. During the latter half of the 19th century it was realised that dinosaurs were anatomically diverse and attempts were made to classify them into groups that shared particular features.
It was Harry Govier Seeley, a palaeontologist trained in Cambridge under the geologist Adam Sedgwick, who determined that dinosaurs fell quite neatly into two distinct groupings: Saurischia or Ornithischia. This classification was based on the arrangement of the creatures’ hip bones and in particular whether they displayed a lizard-like pattern (Saurischia) or a bird-like one (Ornithischia).
As more dinosaurs were discovered and analysed it became clear that they belonged to three distinct lineages: Ornithischia, Sauropodomorpha and Theropoda. In 1887 Seeley placed the sauropodomorphs (which included the huge ‘classic’ dinosaurs such as Diplodocus and Brontosaurus) together with the theropods (which included Tyrannosaurus Rex), in the Saurischia.
The ornithischians and saurischians were at first thought to be unrelated, each having a different set of ancestors, but later study showed that they all evolved from a single common ancestor.
This new analysis of dinosaurs and their near relatives, published in the journal Nature (March 2017), concluded that the ornithischians need to be grouped with the theropods, to the exclusion of the sauropodomorphs. It has long been known that birds (with their obviously ‘bird-like’ hips) evolved from theropod dinosaurs (with their lizard-like hips).
However, according to the researchers the re-grouping of dinosaurs as proposed in their study shows that both ornithischians AND theropods had the potential to evolve a bird-like hip arrangement – they just did so at different times in their history.
“When we started our analysis, we puzzled as to why some ancient ornithischians appeared anatomically similar to theropods. Our fresh study suggested that these two groups were indeed part of the same [group]. This conclusion came as quite a shock since it ran counter to everything we’d learned,” said Matthew Baron, lead author of the research paper.
“The carnivorous theropods were more closely related to the herbivorous ornithischians and, what’s more, some animals, such as Diplodocus, would fall outside the traditional grouping that we called dinosaurs. This meant we would have to change the definition of the ‘dinosaur’ to make sure that, in the future, Diplodocus and its near relatives could still be classed as dinosaurs.”
The revised grouping of Ornithischia and Theropoda has been named the Ornithoscelida which revives a name originally coined by the evolutionary biologist, Thomas Henry Huxley in 1870.
“The repercussions of this research are both surprising and profound. The bird-hipped dinosaurs, so often considered paradoxically named because they appeared to have nothing to do with bird origins, are now firmly attached to the ancestry of living birds,” said co-author Dr David Norman, of the University of Cambridge.
“For 130 years palaeontologists have considered the phylogeny of the dinosaurs in a certain way. Our research indicates they need to look again at the creatures’ evolutionary history. This is simply science in action. You draw conclusions from one body of evidence and then new data or theories present themselves and you have to suddenly reconsider and adapt your thinking. All the major textbooks covering the topic of the evolution of the vertebrates will need to be re-written if our suggestion survives academic scrutiny.”
One might say there's nothing quite like evolution for ruffling feathers – even among palaeontologists, it seems.
Kulindadromeus, a small bipedal ornithischian dinosaur that is now part of the new grouping Ornithoscelida and identified as more obviously sharing an ancestry with living birds. Courtesy of the University of Cambridge. Credit: Pascal Godefroid