Tweaking the Dinosaur Family Tree
Since the late 1800s, dinosaurs have been grouped into two camps based on the shapes of their hips—the Saurischia (lizard-hipped) and the Ornithischia (bird-hipped). Late last week, researchers published a study in the journal Nature that would revise those groupings, changing the relationships between sauropods such as Diplodocus and theropods such as Tyrannosaurus. If they turn out to be correct, the reassignments would shift our understanding of when and where certain groups of dinosaurs evolved. Science writer Riley Black joins Ira to talk about the change, and the possible effects of restructuring dinosaur genealogy.
Science writer Riley Black writes the “Laelaps” blog at Scientific American. She is also the author of the books Skeleton Keys (Penguin Random House, 2019) and My Beloved Brontosaurus: On the Road with Old Bones, New Science, and Our Favorite Dinosaurs.
IRA FLATOW: Now it’s time to play Good Thing, Bad Thing. Because every story has a flip side, since the late 1800s, dinosaurs have been grouped into two camps based on the shapes of their hips. You have the Saurischia and the Ornithiscia. And one is lizard hipped and the other is bird hipped. And last week, researchers published a study in the journal Nature that would shake up those hip-based groupings. Joining me now to talk about the change and the possible effects of restructuring dinosaur genealogy is science writer Brian Switek. He writes the Laelaps blog at Scientific American, and he’s author of the book My Beloved Dinosaurs. He joins me by Skype. Welcome back.
BRIAN SWITEK: Thanks for having me back on.
IRA FLATOW: Are your beloved dinosaurs being upset?
BRIAN SWITEK: They seem OK with it. I mean, they’ve been dead for over 66 million years. But, you know, it’s a bit of a shake up. I think it’s more the paleontologists who might be a little bit more upset with this one.
IRA FLATOW: I misspoke, it’s my beloved Brontosaurus. Sorry.
BRIAN SWITEK: Thank you.
IRA FLATOW: So tell me, what is the shakeup actually happening? What’s going on here?
BRIAN SWITEK: This is a new family tree that was just published. And like you said in your intro, we’ve had the same organization for the two major branches of the dinosaur family tree since 1888. So now you have those two groupings sort of flipping a little bit. So you had, in the Saurischia dinosaurs, you had the Theropods, so things like Velociraptor and T-rex. And you had the Sauropods, things like Brontosaurus. And all the way on the other side of the family tree, in the Ornithiscians, you had things like Triceratops, and Stegosaurus, and all those guys.
Now, this new study says that the Theropods and the Ornithiscians are more closely related to each other than to the Sauropod dinosaurs. So basically you have Tyrannosaurus and Triceratops being close relatives of each other. And then the dinosaurs like Brontosaurus all the way out on the other side of the family tree. So it’s a bit of a switch in the arrangement that’s traditionally been held.
IRA FLATOW: Wow, so really how big a switch is it? I mean, small switch, big switch?
BRIAN SWITEK: It’s a pretty big switch, because it brings up some big questions. For example, in dinosaurs like Tyrannosaurus and Brontosaurus, you have an air sack system, what was called pneumatic vertebrae, these air sacks that invaded the bones and made them light while keeping them strong. If this new system is correct, that wasn’t something that was inherited from a common ancestor, that was something that had to evolve twice. Or there’s some other weird evolutionary arrangement. So this changes a little bit of what we think about how these animals evolved and how they acquired the traits that made them dinosaurs.
IRA FLATOW: I guess, as you’re saying, the good thing here is that it gives us a better picture, right, of how it really works, but what’s the bad thing about this then?
BRIAN SWITEK: The bad thing is we don’t really know whether to change the textbooks just yet. I mean, phylogenies come out almost every week. And this is an important one, it certainly seems to be a well-supported one. But it’s a hypothesis, like anything else. And there are some areas of dinosaur family history that we don’t know a lot about yet. Like, for example, the earliest Ornithiscian dinosaurs, there’s not really a good record of those.
So there’s the chance that someone’s going to find a complete skeleton somewhere, and it’s going to rearrange things all over again. It might go back to something traditional, it might support this new study, it might be something else. And that’s just the nature of science. It’s not like a paper is divine fiat, where it just becomes law and all the textbooks are changed. So it’s an interesting idea, but we don’t know yet whether it’s going to stick.
IRA FLATOW: One last question for you, why our hips the key feature?
BRIAN SWITEK: That’s becasue when Harry Govier Seeley who formed the system back in the late 1800s, the dinosaurs he had to work with were really these derived animals, these animals that had been dinosaurs, [INAUDIBLE] dinosaurs that had been around for a long time, that really had these hip shapes well established, and it was a really good way to tell a difference between the two. They had split so long ago that you could really tell which group was which on the basis of these hips.
But now, as we’re going further and further back, into the earliest days of the dinosaurs, it’s getting a little bit more confusing, or similarities are crossing boundaries that we didn’t think that they would cross. And that’s actually another good thing, is that we’re getting this better picture of the first days of the dinosaurs that we never really had until recently. So, yeah, there’s going to be a bit of turmoil and a bit of changing around, but it’s really a sign of how much we’re learning about that first 10 or so million years, when dinosaurs really became what they were.
IRA FLATOW: Fascinating, Brian, thank you for taking time to be with us today.
BRIAN SWITEK: Always a pleasure.
IRA FLATOW: Good luck on your book, My Beloved Brontosaurus. Brian Switek writes the Laelaps blog at Scientific American, and author of My Beloved Brontosaurus.