̽��ֱ�� of Cambridge - Matthew Baron

Shaking the dinosaur family tree: how did ‘bird-hipped’ dinosaurs evolve?

sc604 — Wed, 21 Sep 2022 14:57:37 +0000

Researchers have conducted a new analysis of the origins of ‘bird-hipped’ dinosaurs – the group which includes iconic species such as Triceratops – and found that they likely evolved from a group of animals known as silesaurs, which were first identified two decades ago.

Study identifies dinosaur ‘missing link’

sc604 — Tue, 15 Aug 2017 23:01:26 +0000

A bizarre dinosaur which looked like a raptor but was in fact a vegetarian may be the missing link between plant-eating dinosaurs and theropods, the group that includes carnivores such as Tyrannosaurus rex and Velociraptor.

Researchers from the ̽��ֱ�� of Cambridge and the Natural History Museum used a comprehensive dataset to analyse more than 450 anatomical characteristics of early dinosaurs and correctly place the creature, known as Chilesaurus, in the dinosaur family tree. Their results, reported in the journal Biology Letters, suggest that Chilesaurus effectively fills a large gap between two of the major dinosaur groups, and shows how the divide between them may have happened.

Chilesaurus, which was discovered in southern Chile, was first described in 2015. It lived during the Late Jurassic period, about 150 million years ago, and has an odd collection of physical characteristics, which made it difficult to classify. For example, its head resembles that of a carnivore, but it has flat teeth for grinding up plant matter.

“Chilesaurus almost looks like it was stitched together from different animals, which is why it baffled everybody,” said Matthew Baron, a PhD student in Cambridge’s Department of Earth Sciences and the paper’s joint first author.

Earlier research suggested that this peculiar dinosaur belonging to the group Theropoda, the ‘lizard-hipped’ group of dinosaurs that includes Tyrannosaurus, but the new study suggests that it was probably a very early member of a completely different group, called Ornithischia. This shuffling of the dinosaur family tree has major implications for understanding the origins of Ornithischia, the ‘bird-hipped’ group of dinosaurs that includes Stegosaurus, Triceratops and Iguanodon.

̽��ֱ��bird-hipped dinosaurs have several common physical traits: the two most notable of these are an inverted, bird-like hip structure and a beak-like structure for eating. ̽��ֱ��inverted hips allowed for bigger, more complex digestive systems, which in turn allowed larger plant-eaters to evolve.

While Chilesaurus has a bird-like hip structure, and has flat teeth for grinding up plants, it does not possess the distinctive ‘beak’ of many other bird-hipped dinosaurs, which is what makes it such an important find.

“Before this, there were no transitional specimens – we didn’t know what order these characteristics evolved in,” said Baron. “This shows that in bird-hipped dinosaurs, the gut evolved first, and the jaws evolved later – it fills the gap quite nicely.”

“Chilesaurus is one of the most puzzling and intriguing dinosaurs ever discovered,” said co-author Professor Paul Barrett of the Natural History Museum. “Its weird mix of features places it in a key position in dinosaur evolution and helps to show how some of the really big splits between the major groups might have come about.”

“There was a split in the dinosaur family tree, and the two branches took different evolutionary directions,” said Baron. “This seems to have happened because of change in diet for Chilesaurus. It seems it became more advantageous for some of the meat eating dinosaurs to start eating plants, possibly even out of necessity.”

Earlier this year, the same group of researchers argued that dinosaur family groupings need to be rearranged, re-defined and re-named. In a study published in Nature, the researchers suggested that bird-hipped dinosaurs and lizard-hipped dinosaurs such as Tyrannosaurus evolved from a common ancestor, potentially overturning more than a century of theory about the evolutionary history of dinosaurs.

Although their dataset has already thrown up some surprising results, the researchers say that as it currently analyses only early dinosaurs, there are probably many more surprises about dinosaur evolution to be found, once characteristics of later dinosaurs are added.

̽��ֱ��research was funded by the Natural Environment Research Council (NERC).

Reference:
Matthew G. Baron and Paul M. Barrett. ‘A dinosaur missing-link? Chilesaurus and the early evolution of ornithischian dinosaurs.’ Biology Letters (2017). DOI: 10.1098/rsbl.2017.0220

A ‘Frankenstein’s monster’ dinosaur may be the missing link between two major dinosaur groups, plugging what was previously a big gap between them.

Chilesaurus almost looks like it was stitched together from different animals, which is why it baffled everybody.

Matthew Baron

Nobu Tamura

Life reconstruction of Chilesaurus diegosuarezi

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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New study shakes the roots of the dinosaur family tree

ps748 — Wed, 22 Mar 2017 17:16:55 +0000

For 130 years palaeontologists have been working with a classification system in which dinosaur species have been placed in to two distinct categories: Ornithischia and Saurischia. But now, after careful analysis of dozens of fossil skeletons and tens of thousands of anatomical characters, the researchers have concluded that these long-accepted familial groupings may, in fact, be wrong and that the traditional names need to be completely altered.

̽��ֱ��classification of dinosaurs 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 renowned geologist Adam Sedgwick, who determined that dinosaurs fell quite neatly into two distinct groupings, or clades; 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 described 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 T. rex), in the Saurischia. ̽��ֱ��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 today in the journal Nature, concludes 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, the re-grouping of dinosaurs proposed in this 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.

Lead author, Matthew Baron, says:

“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 clade. This conclusion came as quite a shock since it ran counter to everything we’d learned.”

“ ̽��ֱ��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.”

̽��ֱ��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.

Co-author, Dr David Norman, of the ̽��ֱ�� of Cambridge, says:

“ ̽��ֱ��repercussions of this research are both surprising and profound. ̽��ֱ��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.”

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.”

While analysing the dinosaur family trees the team arrived at another unexpected conclusion. For many years, it was thought that dinosaurs originated in the southern hemisphere on the ancient continent known as Gondwana. ̽��ֱ��oldest dinosaur fossils have been recovered from South America suggesting the earliest dinosaurs originated there. But as a result of a re-examination of key taxa it’s now thought they could just as easily have originated on the northern landmass known as Laurasia, though it must be remembered that the continents were much closer together at this time.

Co-author, Prof Paul Barrett, of the Natural History Museum, says:

"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. 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".

̽��ֱ��research was funded through a Natural Environment Research Council (NERC) CASE studentship.

Matthew Baron et al: 'A new hypothesis of dinosaur relationships and early dinosaur evolution' Nature, 23 March 2017

10.1038/nature21700

A short video guide has been prepared by the Natural History Museum to accompany this paper.

More than a century of theory about the evolutionary history of dinosaurs has been turned on its head following the publication of new research from scientists at the ̽��ֱ�� of Cambridge and Natural History Museum in London. Their work suggests that the family groupings need to be rearranged, re-defined and re-named and also that dinosaurs may have originated in the northern hemisphere rather than the southern, as current thinking goes.

This conclusion came as quite a shock since it ran counter to everything we'd learned

Matthew Baron

Pascal Godefroid

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

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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