Melissa Harris-Perry: I'm Melissa Harris-Perry, and this is The Takeaway. The year 1993, a team of genetic scientists led by an eccentric businessman have brought dinosaurs back to life and opened a wildlife park.

Thomas Carr: Life finds a way.

Melissa Harris-Perry: Yes, I know. It's just fiction, the world of Jurassic Park.

Speaker: Boy, no I hate being right all the time.

Melissa Harris-Perry: In this iconic scene, the king of dinosaurs, Tyrannosaurus Rex escapes his paddock after the facility loses its power. According to some experts, the life-sized animatronic dinosaur is the best film portrayal of a T-Rex to date. Now almost 30 years after the films debut, the T-Rex is causing an up row thanks to a new study.

Thomas Carr: The central claim is what we thought of as Tyrannosaurus Rex is really three species, including T-Rex and two others.

Melissa Harris-Perry: That's Thomas Carr.

Thomas Carr: Paleontologist at Carthage College in Kenosha, Wisconsin.

Melissa Harris-Perry: The other two proposed species are called Tyrannosaurus imperator or the emperor and Tyrannosaurus Regina, the queen. I asked Thomas what difference this proposed reclassification would actually make.

Thomas Carr: Well, depending on how you look at it, either it makes a lot of difference or no difference at all. If we accept the claim at face value, then this means that the evolution of Tyrannosaurus is a little bit more complicated than we originally thought. If you consider it skeptically and really take a closer look at the evidence that's offered in support of three species, it really doesn't hold up. For some of us, it really doesn't change anything. At the end of the day, it just looks like there really is one species and that's Rex.

Melissa Harris-Perry: I'm going to need you to walk me through this just a little bit. First of all, tell me that your skepticism is not just about trying to protect your Twitter handle @TyrannosaurusCarr. This is an actual scientific skepticism that you have.

Thomas Carr: Yes, it is. Species are very important in terms of biology. Species are our point of reference for understanding how evolution works, and we have to make sure that as best we can that we really have got it right. Up until that recent paper, basically, all the available evidence has been pointing toward the notion that there's only one species of Tyrannosaurus in the American West at the end of the age of dinosaurs and that's Tyrannosaurus Rex.

The authors of the paper do rightly point out that there is variation. This is something that Darwin demonstrated back in 1859 that variation differences between individuals is just a fact of life and that kind of makes species fuzzy things. At the end of the day, each member of a species shares species-specific features, identifying features. Our job as paleontologists, as biologists is to sort out the difference between the variation and also the species identifying features.

In the paper, some species identifying features have been suggested but previous work has shown that those features really have different and better support explanations such as individual variation or growth variation, not species features.

Melissa Harris-Perry: Maybe bring it a little closer to home, to an animal that we would have in our household. I have, goodness, help me. I have three dogs. One of my dogs is a little tiny seven-pound Yorky mix, and one of the other dogs is a fairly enormous who knows what kind of mix, but definitely in the 70-pound range, but they're both dogs. They're both not just like dogs, but they're both domesticated dogs. Is that what you mean by variation within a species?

Thomas Carr: No, not exactly. Dogs are a special case. Dog breeds are the product of artificial selection. That selection that's been imposed by people selecting for favorable traits. I think maybe if we backed up to the ancestral dog that is wolves. Believe it or not every single dog all around the world are actually highly modified wolves modified by people, but let's consider wolves. If we take a population of wolves and we just say, look at pelt color and some are gray, some are dark gray and some wolves are black.

There's variation in say pelt color. It might be variation in size, but that's also affected by diet to a certain degree. The same thing we see in T.Rex. In the paper, it was hypothesized or suggested that there's robust that is very heavily built individuals versus brassle or very slender individuals. That's a variation that the study focused in on. The problem is this, is that the authors didn't demonstrate that those extremes of variation robust and brassle are actually real categories.

If you look at their measurements that they use to justify robust and brassle, the measurements actually form a continuum. They seamlessly grade into each other. If you look at the actual measurements of T.Rex with five bones of the same length. One feature that the article focused in on was the circumference of the femur relative to the length of the bone, and that gave a ratio, which was a measure of robust versus brassle. In terms of real measurements, the difference between a brassle and a robust Tyrannosaurus is only a difference of less than two and a half inches of circumference of the thigh bone.

For animals that are 40 feet long, I think a two-and-a-half-inch difference in femur circumference is a thing that we should expect to see in a natural population. We're talking about really small differences. Overall, in terms of these sorts of differences, the total range for femur circumference is only six inches that's the height of a coffee cup. We're not talking about real extremes in proportions here. These are, it just looks like shades of gray to me.

Melissa Harris-Perry: I'm wondering then why this study sparked such intense debate?

Thomas Carr: The reason for that is that the evidence is really quite weak. There's three lines of evidence. The first is the femoral circumference to length ratio and as I mentioned, those grade into each other, and the range is small and a difference between purported robust and brassle is also really small. It just looks like normal variation that we'd expect in any population of wild animals living in extinct. The other line of evidence is the form of the first two teeth in a lower jaw.

The problem with that is that the teeth are pretty variable upfront. That's not just in T-Rex, but also its closest relatives. We have difference in the number of teeth in the lower jaw, and that presents problems of whether or not we're actually comparing apples to apples, not apples to oranges. Also, if you dig into their actual data they provide tooth measurements for fossils that don't have teeth. They've measured the tooth sockets, and it's not clear exactly what measurements are being compared.

Finally, they also set their three species into a stratigraphic framework. What that means is a time framework based on the main unit of rock the T-Rex is found in. In Montana and adjacent states like the Dakota and elsewhere, there's a deposit of rock called a Hell Creek formation. It's about a million years old. It spans that amount of time right up to the extinction of the age of dinosaurs. They've blocked that out into thirds, a lower third, a middle third, and an upper third.

Those are really general spans of time. We're talking about blocks of 300,000 years, and the claim is that specimens occur in each third and say specimens and the first third are, different from the ones later on. The problem with that approach is that it's too low resolution. A picture of what's really happening with the individual T-Rex skeletons. We really don't know if say the early ones are really all early we don't know if the later ones are really all that late in the rock sequence. There's a certain amount of ground truth thing of the position of the individual skeletons in the rocks that we just don't yet know. Dividing them up into time blocks of thirds is just really vague.

It's not much really to hang the hypothesis on noticed ad that in terms of doing meter by meter positioning of skeletons in the Hell Creek Formation has been done for another dinosaur and that's Triceratops. Where a team of researchers actually went out into the Badlands and made sure that they knew exactly where the fossils came from. That's a rigorous approach to this question and thus the study of Triceratops uncovered the pattern that we have one species of Triceratops early on in the Hell Creek and a different one later and we'd very much like to do that for T-Rex but we just don't yet have the precise information

Melissa Harris-Perry: As you talk about the triceratops changes and I'm thinking also, in addition to my three dogs, I also have 25 chickens. I recall learning that the dinosaurs I'd grow up loving might. In fact, I look a bit more like my backyard chickens than I had ever imagined as a school child. I'm wondering about our emotional effective, deeply personal attachment to dinosaurs and to our childhood received wisdom about them. How those emotional attachments might even affect the ways that scientists receive new information.

Thomas Carr: They shouldn't. Scientists are trained to view data objectively to have a certain detachment from new information, detachment from their own latest stupid ideas. I know that I've had certain notions that I've had to let go of in the face of new data. For scientists, that's a fairly easy move to make because we're trained that way. We're trained not to be emotionally invested in our hypotheses.

We're trained to roll the punch of the data. When we see something come across the desk that isn't as rigorous as it should be and makes fairly extraordinary claims. We are obligated to be detached and skeptical and honest in our appraisal of the idea that's being offered. Not everyone's trained that way admittedly the scientific frame of mind takes quite a bit of work in terms of detaching from emotion. It's absolutely essential to really get at the heart of things and to figure out nature of what it really is not out what we wish it to be.

Melissa Harris-Perry: Despite your scientific detachment, do you have a favorite dinosaur?

Thomas Carr: [laughs] My favorite dinosaur is always the one that I'm currently working on. In fact, I have a couple of projects on the go on T-Rex in particular. T-Rex is right now my favorite dinosaur. I'm sure that'll change as soon as the next project comes along.

Melissa Harris-Perry: Thomas Carr paleontologist at Carthage College in Kenosha, Wisconsin. Thanks so much for joining us.

Thomas Carr: Thanks so much for having me. It's been a pleasure.

[00:14:30] [END OF AUDIO]

Copyright © 2022 New York Public Radio. All rights reserved. Visit our website terms of use at www.wnyc.org for further information.

New York Public Radio transcripts are created on a rush deadline, often by contractors. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of New York Public Radio’s programming is the audio record.