DD19: What’s going on in dinosaur heads?

Garret (0:06)

Hello, and welcome to I Know Dino. I'm Garret.

Sabrina (0:10)

And I'm Sabrina.

Garret (0:11)

And today in our 19th Dino Download.

Sabrina (0:13)

We're talking about what's going on in dinosaur heads.

Garret (0:17)

In their heads?

Sabrina (0:20)

Yeah, like the brain case and stuff.

Garret (0:21)

Okay, yeah, that's in the head.

Sabrina (0:22)

We've got an update on the sharp-toothed Carcharodontosaur Siamraptor and the probably burrowing dinosaur Phona.

Garret (0:31)

I like a probably burrowing dinosaur.

Sabrina (0:33)

Mm-hmm. But I'm going to start with the Carcharodontosaur.

Garret (0:36)

Okay.

Sabrina (0:37)

So, Paleontologists found the quote-unquote missing brain case of Siamraptor. This was published in PLOS One. It's open access. So, you can check out the link in the notes here.

It was published by Soki Hattori and others. And Siamraptor, again, Carcharodontosaur, it lived in the early Cretaceous in what is now Thailand.

Garret (0:58)

That's the Siam.

Sabrina (1:00)

Like, that always reminds me of the king and I.

Garret (1:03)

The king of Siam.

Sabrina (1:04)

Yeah. Anyway, weird reference. I would say it dates me, but it predates me.

So, Carcharodontosaurs are the shark toothed lizards. They're carnivorous theropods that were fairly large. They were apex predators that lived in the late Jurassic to late Cretaceous, and they've been found everywhere except Antarctica.

Garret (1:26)

Yeah. When you say shark-toothed, some people might think that means they had rows and rows of teeth in their mouth, which they kind of did. They replaced their teeth very quickly like most reptiles do.

But really with Carcharodontosaurus, it was because of the serrations and some of the shape of the tooth that reminded the paleontologist who found them of a great white shark. So, Carcharodon is the genus name for the great white shark. So, Carcharodontosaurus is like the great white shark dinosaur.

Sabrina (2:02)

So we talked about Siamraptor back in episode 255 shortly after it was named. That episode was titled Brand New Allosaurus and a Tyrannosaurus that's still being excavated if you want to check it out.

Garret (2:14)

This was the brand new Allosaurus for those keeping track at home.

Sabrina (2:20)

255, that was many years ago now.

Garret (2:22)

Yeah, but it was new at the time.

Sabrina (2:24)

And at the time, they found isolated pieces of, they had found skull and lower jaw fragments, part of the hand, three neck bones, part of the hips, a tailbone, parts of backbones, parts of a leg and left foot.

Garret (2:40)

Pretty good.

Sabrina (2:40)

Yeah.

22 skeletal remains have been found. But this paper is about that quote unquote missing brain case.

Garret (2:48)

Oh, you did say skull fragments, but I guess that didn't include brain case.

Sabrina (2:54)

Yes.

So they found two partial brain cases from the same area where Siamraptor was found. And based on details of the bones, it seems to belong to a Carcharodontosaur, so that's promising. And Siamraptor is the only one around, the only Carcharodontosaur, so it seems that the brain cases belong to Siamraptor. Although the author said there's a possibility that there's a closely related species in the area, but you would need more fossils to know either way.

Garret (3:21)

It's highly probable that there were other close relatives nearby.

Sabrina (3:25)

Oh, I thought you were going to say that it's Siamraptor.

Garret (3:28)

Yeah, I mean both are likely, but you really just can't say.

Sabrina (3:32)

Well, based on the skull bones, it seems that an area on the front of the skull, the frontal, with a shallow depression, also known as Fossa, that may have housed blood vessels and helped with thermoregulation, moderating eye and or brain temperatures.

There's some fusions in the skull roof too that made it more robust, and the angles of the bones may mean that Siamraptor, if it does belong to Siamraptor, I suppose, that it kept its head relatively upturned, at least compared to relatives. It also had a tall nuchal crest. It's an anchor point for large neck and back muscles, which may have been to support a heavy head.

Garret (4:10)

Oh, cool.

Sabrina (4:10)

Yeah. Then based on this new finding, Siamraptor is the earliest branching carcharodontosaur.

Garret (4:17)

Okay. Sometimes when they find that something's the earliest branching, it's because it doesn't actually belong in that group, or there are bones from multiple species making things look weird and putting it outside of any sort of grouping obvious group with other members within, say, Allosauroidia or Carcharodontosaurs.

But depending on exactly where this was found, if it's found really close to the original find, in the same sediment, all that kind of stuff, yeah, it would make sense if it's Siamraptor. And you have to call it something. So referring it to Siamraptor until you know better is not a big deal. It's not like when they find a single bone and they name a holotype and give it a name and they're like, look, this is definitely a new thing and look how important this fossil is. In this case, it's more refining something that's already been named and described. So it seems like a good move.