Everyone who is a paleontology fan is familiar with the goofy formalities of official nomenclature. Fossil specimens can’t be officially recognized until published in obsessive detail. Whoever publishes the find assigns the remains to some family and species. In the absence of genetic material, classification is done based on features, i.e., visible traits of the remains. And if the specimen appears to be different than any recognized species, the first publication can assign a new name.
Everyone who was paying attention in psychology class will immediately see that classification by visible traits is iffy, and classification based on a single specimen or a handful is, well, basically nonsense. The DNA revolution has largely meant discarding centuries of these subjective classifications in light of actual genetic trees.
The result of this messy methodology is an inevitable chain of claims and revisions, as specimens are declared a unique ‘new’ species and then reclassified as a variant of another group, and perhaps re-reclassified yet more times.
So, I was neither surprised nor particularly ready to hear a study that proposed to split the fossil species known as Tyrannosaurus rex into three species [2]. Based on a whopping 38 specimens, the researchers find evidence for three variants. A key part of the evidence is from the size of the animals, and more important, the number of teeth. These groupings only make sense in the temporal context, i.e., what variations are found at the same time.
It is important to note that there already are a variety of T. rex relatives and lookalikes, so it’s not out of the question that there could have been closely related strains of T. rex roaring around. Notably, one of the putative new sub species is known only from earlier periods, which certainly could represent an early offshoot.
These findings also suggest that there were two similarly large strains of T. rex in North America at the same time, at the end of the Cretaceous. Given the time spans involved, diversion and migration of variants from Asia might have occurred. The researchers speculate that the classic ‘rex’ and the putative gracile (but still huge) ‘regina’ might have specialized in different prey.
Well sure. Mightta, Coulda, Maybe.
This study is pretty carefully done, and, as noted, it’s scarcely impossible that there might have been variant strains of rexies. I mean, they were around everywhere for a long time. So sure.
And, to be fair, they marshal multiple sources of information to the argument, so it’s not a trivial hypothesis.
“Creating the groups based on what would make nice graphs would not be a powerful justification for doing so. However, generating groups on the combined basis of femoral ratios, incisiform dentary tooth numbers, and stratigraphic layers, and then graphing to reveal stronger linear conformity does provide support for the groups.”
([2], p. 21)
Still, I find it hard to be convinced by a small sample of animals that we know so little about. We know a little about the life history of rexies, what young ones looked like, the apparent lack of sexual dimorphism, what they hunted. But we really don’t know much about how they lived or even what they looked like, or even where and when they lived. And, most of all, we don’t know how much variability there was in the population. Just how real are these three slices of the rexie cake?
At the moment, I think it’s very premature to be finding multiple ‘species’ of these animals. This is an interesting observation, but I wouldn’t lean to heavily on a sample size of 38. I’m especially leery since there isn’t much explanation of what these differences might have meant, assuming they are real.
- Asher Elbein, They Want to Break T. Rex Into 3 Species. Other Paleontologists Aren’t Pleased, in New York Tiomes. 2022: New York. https://www.nytimes.com/2022/02/28/science/tyrannosaurus-rex-species.html
- Gregory S. Paul, W. Scott Persons, and Jay Van Raalte, The Tyrant Lizard King, Queen and Emperor: Multiple Lines of Morphological and Stratigraphic Evidence Support Subtle Evolution and Probable Speciation Within the North American Genus Tyrannosaurus. Evolutionary Biology, 2022/03/01 2022. https://doi.org/10.1007/s11692-022-09561-5
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