Allosaurus species versus Tyrannosaurus species

[Gregory Paul]

As you may recall, when the Paul et al. Tyrannosaurus species paper came out it was treated like a crisis for western civilization comparable to the Russian invasion of Ukraine that happened about the same time -- I exaggerate but not by much. The paper did not have a sufficient sample size (actually is fairly comparable to the Scannella et al. Triceratops paper), there were not enough characters (never mind some sibling species are diagnosed by just one), the stratigraphy was not precise enough, the statistics were inadequate, no phylogenetics. There was an immediate counter paper signed by a multitude. Wikipedia still limits T. imperator and T. regina to the text discussion. 

Finishing up my new paper on the subject I took and look for the first time since 2020 at the Chure and Loewen paper describing the new species A. jimmadseni (great guy BTW) to check something out. I wish I had done that before the 2022 paper and cited its methods and criteria. You know, that one that has raised barely a peep if any opposition to the naming of a new species of venerable Allosaurus.That might have shut a lot of people up. 

Let's see here. No statistics. No phylogenetics. No detailed stratigraphy, just a quick mention that one species is from the Salt Wash member and the other from the Brushy Basin member (detailed lateral correlations are not possible across the vast Morrison Formation). Just 7 characters, all minor, and one problematic (the A. fragilis lectotype has a lacrimal hornlet about as big as the A. jimmadseni holotype, and bigger than Big Al, so there may not be a real diff), smaller sample size than Paul et al. A simple paper, nothing fancy smancy about it. The only place the species are distinguished is in the species diagnoses, which is of course entirely sufficient for distinguishing and naming intravenous sibling species. Everyone knows that, which is why the paper was published and accepted with no fuss and bother. Wikipedia posted the new species name immediately as they should have. 

So what the bloody el is going on here?

It is the Trex mafia, aka the Tyrannosaurus rex cult, also known as the Society for the Preservation and Protection of the Tyrant Lizard King. 

Everyone loves good ol Allosaurus, but it is a second tier dinosaur, no need to react like a volcano is about to wipe out the town just because a few characters and some casual stratigraphy are used to show that there is more than one species of that old genus. 

But T rex is THE KING, that demands special treatment if one dare to challenge its throne as the one and only Tyranno species. There is not science behind that contention, it's a desire. 

Because of their similar lacrimal horns there is little if any difference between the species identification displays of the Allosaurus species, which is typical of big theropods. There is little difference in visual displays of albertosaurs and daspletosaurs combined, and all Tarbosaurus specimens are much the same as one another. Because there is lots of variation between the postorbital bosses of Tyrannosaurus they are automatically multiple paleospecies, the technical question is how many. 

Had I cited and detailed the straightforward methods, data and analysis from the C&L paper in the 2022 study, there is a good possibility that would have aborted the hyper reaction. What could be said if the same people who were good with A. j. paper when the Tyranno paper was far more extensive in its analysis? I am not going to make that mistake again. This time round if anyone wishes to counter the new paper you need to show how it does not meet the standards of C&J which I cite in depth -- or show that that too is deficient. 

GSPaul

[Mickey Mortimer]

To be fair, I didn't accept A. jimmadseni or your Tyrannosaurus species, so at least I'm consistent.  And after reading Loewen's thesis on Allosaurus variation I'm underwhelmed regarding unpublished support for jimmadseni as well.

Mickey Mortimer

[Gregory Paul]

What is of interest is how the C&L Allo results were received with no fuss or bother, and no one has yet opposed them in the technical literature. While the P et al Tyranno species paper which had deeper analysis caused all the woe and discontent and an immediate technical reply -- while still ignoring the C&L paper. Such an extreme disparity was not science based, it was emotional. If the Tyranno study was really so defective as to receive such an intense reaction, then the same should have happened with the Allo paper. Or it the latter is OK, then the Tyranno paper should have been received as a useful contribution to the subject. 

If there are any who think A. j. is the same species as A. f. then they should publish on why that is. That includes those who continue to oppose T. imperator and T. regina. Or detail why the two Allosaurus species are valid while the three Tyrannosaurus are not. As stressed in the Paul et al. paper, there needs to be consistency in designating intragenus sibling species, and no special treatment for the tyrant lizard. 

The stepped down ventral jugal margin of A. fragilis distinguishes it from the straight margin of stratigraphically earlier A. jimmadseni, so they latter looks valid. 

GSPaul 

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[Mickey Mortimer]

The problem with the jugal margin character is that its distribution isn't so neat.  Supposed A. fragilis AMNH 600 has a straight ventral margin, and if you look at Figure 12C of the A. jimmadseni description, supposed A. jimmadseni BYU 5122 has as convex a ventral margin as A. fragilis.  Indeed, if you look at that figure, there's really no difference between supposed A. jimmadseni SMA 0005 and A. fragilis UMNH VP 8976.  It's really a gradual range of variation where the A. jimmadseni holotype's concave margin is on one extreme with the 35 degree bend of UMNH VP 8972 on the other. 

And that's really the problem with A. jimmadseni in a nutshell- you take only the fragilis and jimmadseni types and they look quite different and are from different levels, but try adding other specimens in and everything gets mixed up. Even the characters that made it to the official diagnosis of Chure and Loewen are largely absent in A. jimmadseni paratype MOR 683 they describe (row of foramina in maxillary antorbital fossa; straight posteroventral maxillary edge; rotated and flared axial intercentrum), present in A. fragilis neotype USNM 4734 (transversely concave posterodorsal nasal surface; tall lacrimal horn; lateral margin of jugal straight in dorsal view), or present in all Allosaurus (well developed antarticular).  Given the overlap in anatomical features for all characters except one that can be evaluated in more than one specimen in each stratigraphic layer, A. jimmadseni is considered a junior synonym of A. fragilis.  But it doesn't seem fair to publish a rebuttral until Loewen's thesis is published, even though as I said earlier I don't think the information in it strengthens his case.

Mickey Mortimer

[Gregory Paul]

Because intragenus sibling species are so similar there is going to be a lot of nonbimodal overlap within many of the characters. That is true of early Triceratops horridus relative to the unnamed species, and the latter relative to later T. prorsus in the Scannella et al. paper. When Carr et al. (2022) got after Paul et al. (2022) for having nonbimodal characters they were way off base, that being common in taxonomy. That A. jim. and A. frag. are separated in time reinforces their being distinct species. They might still be that if not stratigraphically separated, although sexes is also very possible in that case. 

AMNH 600 seems to have the jugal step-down. In any case that and 666 may be a distinct species, as I note in the new field guide. 

GSPaul

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[Mickey Mortimer]

The problem with that philosophy is in Allosaurus at least, the specimens are so seldomly well described (and it doesn't help that Madsen made idealized illustrations for the Cleveland-Lloyd population) that usually you'll have the C-L specimens having state A, the jimmadseni type having state B, then maybe three other specimens that can be evaluated from the lit of which at least one won't match stratigraphically.  These aren't characters where we can say 80% of fragilis have state A and 80% of jimmadseni have state B, they're 3-2 for fragilis and 1-1 for jimmadseni (assuming stratigraphic separation) or 2-0 fragilis and 0-1 jimmadseni, etc..  The numbers never reach anything close to statistical significance, which then means you're basically depending on stratigraphical separation of two species to be the initial assumption instead of having the morphology argue for the separation.  Which is exactly how you work in your Field Guides, so I'm not surprised you support it.  You see a stratigraphic separation, assume that means a taxonomic difference, and sometimes there's a character difference or two between at least two specimens.  It's very Hueneian- "hey, a theropod way out here! that's near certainly a new species, let's name it Walgettosuchus."  You're both quite possibly correct considering the longevity and range of dinosaur species, but I prefer to keep everything morphologically justified first, then supported by stratigraphy if that happens to be true.  In any case, if anything I'd say the case of jimmadseni-fragilis is anagenesis but would like more published testing before I committed to that.

Mickey Mortimer