New Evidence for That Huge Dinosaur Family Tree Rewrite

Artist's digest of Chilesaurus diegosuarezi, a dinosaur during a heart of a argumentative dinosaur family tree rewrite. (Credit Gabriel Lío)

Chilesaurus diegosuarezi, a Jurassic herbivore during a heart of a argumentative dinosaur family tree rewrite. (Credit Gabriel Lío)

Remember that paper that forsaken a few months ago totally rewriting a dinosaur family tree? Well, a researchers are back, this time regulating one of a odder dinos out there as justification for their bomb claim. Is it legit or only hype?

Back in March, researchers argued for a sum takedown of a long-established dinosaur family tree.

Today, Matthew Baron and Paul Barrett, dual of a 3 authors of that prior Nature paper, try to accelerate their case with a new demeanour during Chilesaurus diegosaurezi, a South American herbivore with a singular mash-up of features.


First described in 2015, Chilesaurus was found in 2004 by Diego Suarez, a immature boy traipsing around a southern Chilean furious with his geologist parents. It’s a honeyed story about a immature citizen scientist incidentally distinguished bullion (the seven-year-old suspicion he was collecting cow bones), yet a animal itself was also some-more engaging than a normal dino find.

Chilesaurus, that roamed a world about 145-150 million years ago, was creatively grouped with a theropods, those bipedal carnivores that include, many famously, T. rex and velociraptors (as good as a origin that eventually led to complicated birds).

There was only one problem: a tiny distance of a head, a leaf-shaped teeth, and a keratin-covered, beak-like underline called a rhamphotheca at a finish of a snout, all screamed “plant-eater.”

Like that sole vegan relations during a family Thanksgiving table, Chilesaurus was a peculiar one out among flesh-ripping, bone-gnawing theropods.

And… okay. There were a integrate other problems in terms of Chilesaurus being a convincing theropod.

Its feet were wider and had some-more toes — 4 to a standard theropod’s 3 — that are some-more obsolete traits harkening behind to a beginning dinosaurs. To tip it off, Chilesaurus had a pelvic corset of an ornithischian.

More on a nitty-gritty of dinosaur pelvic girdles in a moment. What matters right now is that Chilesaurus seemed to have a series of ornithischian traits.

The ornithischians enclosed all from four-legged armored ankylosaurs to duck-billed hadrosaurs. And Ornithischia is a totally apart bend on a dinosaur family tree from Theropoda.

Or is it?

Shaking The Family Tree

Back in March, Baron and Barrett (along with co-author David Norman) due in Nature that a normal dinosaur family tree was all wrong.

For some-more than a century, paleontologists divvied dinos adult into dual vital branches, Ornithischia and Saurischia, a separate that they believed occurred really early in a dinosaur story, during slightest 230 million years ago.

Saurischia then later split into Sauropoda (mostly big, infrequently huge and wholly herbivorous four-legged dinosaurs such as Brontosaurus and a titanosaurs) and Theropoda (the aforementioned bitey types).

Baron and association done a case, however, for a many opposite story. According to their model, Sauropoda was off doing a possess thing, presumably associated to a really early dinosaurs famous as Herrerasauridae. Meanwhile, a categorical bend of a dinosaur family tree, that they named Ornithoscelida, consisted of both Ornithischia and Theropoda.

Whoa. Months after that investigate came out, it still blows my mind. Here’s a nifty striking outline to demeanour during while we collect myself.

The dinosaur family tree, before and after new investigate formula published currently in Nature. The rider upsets one of a longest-held notions about how class can be classified. (Credit Nature)

The dinosaur family tree, before and after new investigate formula published in Nature. The rider upsets one of a longest-held notions about how class can be classified. (Credit Baron et al, doi:10.1038/nature21700)

The large dinosaur family tree rewrite was a outcome of a new dataset they gathered that compared traits of early dinosaurs and dinosauromorphs, a even progressing archosaurs that were not utterly dinos yet.

One critique of a Mar bombshell paper was that they focused on comparing animals from a emergence of a dinosaur age. So Chilesaurus, from roughly a center of a duration When Dinosaurs Ruled The Earth and with a patchwork of traits, done arguably a ideal class to spin their courtesy to next.

Oddball or Early Adapter?

Other researchers had formerly placed Chilesaurus in Theropoda by comparing it to a opposite collection of dinosaurs, one that a authors of today’s investigate advise was a small light on ornithischians. Even then, a group that initial described Chilesaurus concurred Theropoda wasn’t a good fit, yet it was a many expected formed on their dataset.

It turns out, according to today’s study, that when Baron and Barrett combined Chilesaurus to their dataset of early dinosaurs and dinosauromorphs, a animal fit rather good as a really early ornithischian, or even a probable “transitional” class withdrawal a theropod case to bend off into Ornithischia.

One of a large tip-offs to fixation Chilesaurus during a bottom of Ornithischia was, yep, that pelvic girdle.

Let’s get all adult into a whole dinosaur pelvic corset issue. Indulge me.

Ornithischians, possibly they resemble tanks or some-more gracile semi-bipedal sorts, have a pelvic corset with both a ischium and pubis indicating backwards. They were all herbivores (hey! You know who else is an herbivore…Chilesaurus!), and a figure of their pelvic corset left some-more room for a large tummy to routine all that vegetative matter. Yum.

Ornithischian pelvis (Credit Wikimedia Commons)

Typical ornithischian pelvic girdle (Credit Wikimedia Commons)

Saurischians, on a other palm (and, according to a normal dinosaur family tree, on a other branch), have an ischium that points retrograde and a pubis that points brazen which, many researchers believe, authorised some lineages to rise into quite fit bipeds. You don’t need room for a large swell when all you’re eating is meat. Consider a cow contra a cat.

Saurischian pelvis (Credit Wikimedia Commons)

Typical saurischian pelvic corset (Credit Wikimedia Commons)

Back to Chilesaurus. The animal — which, by a way, is famous from several specimens — had a pelvic corset with rear-pointing pubis and ischium, like a ornithischians. Originally, researchers suspicion it was an instance of meeting evolution: birds, for example, also have a backwards-pointing pubis and ischium, even yet they developed from one of a theropod lineages.

(Convergent expansion is not odd in a hoary record: separate class occupying identical ecological niches can tarry and flower by identical adaptations.)

The pelvic corset of Chilesaurus as shown in a 2015 Nature paper describing it for a initial time. (Credit Novas et al, doi:10.1038/nature14307)

The pelvic corset of Chilesaurus as shown in a 2015 Nature paper describing it for a initial time. (Credit Novas et al, doi:10.1038/nature14307)

Reclassifying Chilesaurus as an ornithischian — that is still being debated — fits if, and this is a large if, a field accepts a dinosaur family tree rewrite initial due in March.

Personally, I’m peaceful to trust that a textbooks may need rewriting one day — yet it is not this day. Chilesaurus is still a bizarre animal no matter where we place it in possibly a normal dinosaur family tree or a remix.

Accepting it as an early ornithischian, right during a ornithischian-theropod separate within Ornithoscelida, means that paleontologists still have to determine what it was doing using around some-more than 90 million years after a separate indeed occurred.

It means that there had to have been an as-yet-unknown “ghost lineage” of Chilesaurus-like fundamental ornithischians, a ancestors, holding onto many of their some-more obsolete traits for tens of millions of years while a rest of Dinosauria exploded with adaptations.

Sure, foreigner things have happened, yet I’m not persuaded. Yet.

Today’s second demeanour during Chilesaurus appears in Biology Letters.

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Posted by on Aug 16 2017. Filed under Living World. You can follow any responses to this entry through the RSS 2.0. You can leave a response or trackback to this entry

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