F Rosa Rubicondior: Just Another (Not) Missing Link!

Saturday 19 August 2017

Just Another (Not) Missing Link!

Chilesaurus diegosuarezi, from the Late Jurassic period.

Artist's impression. Photograph: Gabriel L O/AFP/Getty Images
Chilesaurus and Ornithischia | Biology Letters

One of the mysteries of dinosaur evolution has been explained. It's another of those 'missing' links! It's a transitional species between two major groups of dinosaur - the herbivorous species like stegosaurus and the carnivores like T. rex.

Publishing in Biology Letter Matthew G. Baron of the Department of Earth Science, Cambridge University, UK and Paul M. Barrett of the Natural History Museum, have shown that a dinosaur from the Late Jurassic, found in Chile, formerly believed to be a theropod dinosaur turned vegetarian, is actually the stem species that was the progenitor of two quite different groups - the saurischians and the ornithischians.

These two groups were formerly thought to be only distantly related with no clear connection between them. This new examination of Chilesaurus diegosuarezi shows that this genus was the 'missing link' between the two groups. It wasn't a case of a carnivorous theropod reverting to vegetarianism but the vegetarian group from which the carnivores had evolved.

A close examination showed that Chilesaurus diegosuarezi had a mixture of both groups, just as you would expect as 'transitional' species to have.

The enigmatic dinosaur taxon Chilesaurus diegosuarezi was originally described as a tetanuran theropod, but this species possesses a highly unusual combination of features that could provide evidence of alternative phylogenetic positions within the clade. In order to test the relationships of Chilesaurus, we added it to a new dataset of early dinosaurs and other dinosauromorphs. Our analyses recover Chilesaurus in a novel position, as the earliest diverging member of Ornithischia, rather than a tetanuran theropod. The basal position of Chilesaurus within the clade and its suite of anatomical characters suggest that it might represent a ‘transitional’ taxon, bridging the morphological gap between Theropoda and Ornithischia, thereby offering potential insights into the earliest stages of ornithischian evolution, which were previously obscure. For example, our results suggest that pubic retroversion occurred prior to some of the craniodental and postcranial modifications that previously diagnosed the clade (e.g. the presence of a predentary bone and ossified tendons).

The scientific importance of this discovery is not exactly earth-shattering to science, despite the news media sensationalising it with stories about how the textbooks will have to be re-written. Of course they'll have to be rewritten. They're always having to be rewritten to keep up with the latest discoveries and developments. For science, it simply clarifies something that wasn't fully understood or explained. It merely confirms what was predicted by evolutionary theory anyway - that related groups of dinosaur shared a common ancestor in their evolutionary history.

For creationism, although this discovery will make not one iota of difference to their insistence that these 'transitional' species never existed, it should make a difference if creationism was really based on evidence. Evidence like this, if they applied the same standards they demand science adhere to in terms of evidence, should destroy a fundamental claim of creationism and render the entire notion redundant.

Which is why those who make their living selling creationism will never acknowledge these sorts of facts. The truth is simply too toxic for them.

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