T. rex, regina and imperator

This news is about a month old, but I'm just getting around to hearing it myself. That's what comes from mostly ignoring the news. Greg Paul and a couple of other guys I don't know just submitted a paper that proposes splitting T. rex into three species, T. rex, T. regina and T. imperator. Phil Currie also contributed, but withdrew his name from the paper, because while he thinks the analysis is helpful and interesting, he's not on board with the proposal of new species at this point. As Paul himself said, if it were any other prehistoric animal, everyone would shrug and not make a big deal out of it. He's already done so himself with other animals, including the splitting of Brachiosaurus and Giraffatitan and the splitting of Dakotadon from Iguanodon. The former has wide acceptance across the paleontological community, while the latter does (so far) not. But because it's T. rex, it's going to be controversial.

Curiously, I always thought of him as more of a lumper than a splitter, because of his Predatory Dinosaurs of the World book way back in 1988, where he proposed that both Tarbosaurus and Daspletosaurus should be lumped into the Tyrannosaurus genera as Tyrannosaurus bataar and torosus respectively. Those proposals didn't stick either.

Anyhoo, the crux of the argument is that its long been known that there are at least two "morphs" of skeletons among the known T. rex skeletons, a gracile and robust morph. The paper suggests that there is also a difference in the number and shape of the predentary teeth. It also makes the point that you can time-bound these differences, or at least find clusters, and that the length of time that T. rex lived (up to 3.6 million years) is long enough that most of its surrounding animals had at least anagenic species replacement. So, T. imperator would be the earlier part of the Maastrichtian and would represent an earlier robust animal, which later split into T. rex, a later robust animal with a different dentition, and T. regina, a gracile animal with the same different dentition. In general, the most positive response I've seen among the paleontological community is from Thomas Holtz who says that it's an interesting idea and a testable hypothesis, wherein we can see if new specimens, as they're uncovered, fit into these categories or not. Although he points out that T. lancensis would have priority over T. imperator. More's the pity; if this proposal does stand the test of time, which I think is unlikely, T. imperator is a way cooler name. 

Most, however, think that the groupings are too arbitrary, lack distinct diagnostic lines, and that the whole thing just describes normal variation within the species. But still; it's an interesting proposal, and going to the work of refuting the proposal will probably increase our knowledge of the T. rexes anyway.