Heterodontosaurus had belly ribs

[Halichoeres]

A new specimen of Heterodontosaurus has been analyzed using CT scanning, and has both gastralia (belly ribs), and paddle-shaped sternal ribs. Sternal ribs are common in ornithischians, although usually of a different shape, but gastralia have not been described in any ornithischan before, despite being widespread in saurischians and many other tetrapod groups. The overall arrangement probably produced a breathing apparatus like that of crocodiles, where muscles originating on the pelvic girdle pull the lung peritoneum downward, expanding their volume to draw in air by negative pressure.

Here the authors reconstruct what belly ribs might have meant for breathing:

A. Silesaurus
B. Heterodontosaurus
C. Thescelosaurus
D. Corythosaurus (seems to reflect recent work on nuchal ligaments in hadrosaurs)

Appears to be open-access: https://elifesciences.org/articles/66036

[Faelrin]

Huh that's quite the revolutionary find here. Thanks for passing this along here. Also obligatory "when are they making (new) a figure of this?" question here.

[austrosaurus]

Love the lipstick on that Thescelosaurus! 

[ITdactyl]

Why is Heterodontosaurus so angry? Come to think of it, I don't remember any depiction of it that's not angry - the only calm one that comes to mind is that grooming statue I saw from a DK book.

[Halichoeres]

Huh that's quite the revolutionary find here. Thanks for passing this along here. Also obligatory "when are they making (new) a figure of this?" question here.

Yeah, I want one too! There have been three that I know of and they're all awful (the Inpro has a certain vintage charm, but I'm not personally that into vintage charm).

Love the lipstick on that Thescelosaurus! 

If you got it flaunt it.

Why is Heterodontosaurus so angry? Come to think of it, I don't remember any depiction of it that's not angry - the only calm one that comes to mind is that grooming statue I saw from a DK book.

I think it might be because of the palpebral bone, which meant there would be a flange above and in front of the eye. I think it really would make it look kind of angry, or at least fierce. Accipitriform birds have something similar and it makes 'em a little scowly.


On another note, it seems to me that the presence of gastralia, in the absence of well-behaved traits that resolve the base of the dinosaur tree, could easily nudge a phylogenetic analysis in the direction of the Ornithoscelida hypothesis.

[Patrx]

Fascinating! I guess it's about time for some company or other to make an updated Heterodontosaurus. Or, er, any heterodontosaurid toys at all.

[Faelrin]

@Halichoeres That's what I was starting to wonder about as well. Additionally other then how this may effect their positioning in the first place. Right now Heterodontosauridae are considered to be basal Ornithischians correct? I also wonder what this may mean for our friend Chilesaurus, if anything at all.

[ITdactyl]

Are gastralia diagnostic? Also, if the breathing apparatus is similar to crocodilians and tuatara, does that mean Heterdontosaurus is similarly sedate in its lifestyle? I mean, they're usually depicted as scowly mesozoic chicken porcupines hopping about - wouldn't this image need revision?

As for the toy version, I'm hoping for the fluffy chick look instead of the mesozoic Chupacabra...

[Gothmog the Baryonyx]

I wouldn't mind both looks, so long as they were small figures. But I doubt even one at this point.

[Halichoeres]

@Halichoeres That's what I was starting to wonder about as well. Additionally other then how this may effect their positioning in the first place. Right now Heterodontosauridae are considered to be basal Ornithischians correct? I also wonder what this may mean for our friend Chilesaurus, if anything at all.

Yeah, one analysis recently found heterodontosaurids to be close to Marginocephalia, but generally they show up as basal ornithischians. Chilesaurus doesn't seem to have gastralia, so that is an interesting question.

Are gastralia diagnostic? Also, if the breathing apparatus is similar to crocodilians and tuatara, does that mean Heterdontosaurus is similarly sedate in its lifestyle? I mean, they're usually depicted as scowly mesozoic chicken porcupines hopping about - wouldn't this image need revision?

They're present in a variety of tetrapod groups and seem to have been lost in ornithischians, so in that sense they are plesiomorphic and hence not diagnostic for a dinosaur clade. I can also imagine some fossilization scenarios where the gastralia simply aren't preserved despite the animal having them (see: previous heterodontosaur specimens), so tricky in that sense too.

On breathing, I don't know! Whereas pneumatized boned and flow-through lungs probably facilitated high metabolism and activity levels in dinosaurs, it doesn't seem to be the only way. Mammals have inefficient tidal breathing (albeit diaphragm instead of pelvic pump) and do just fine.