Javelina Formation tyrannosaurid maxilla likely Tyrannosaurus rex + sauropod tracks from Lower Cretaceous of China (free pdfs)

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

New dinosaur papers:

Free pdf:

Chan-Gyu Yun (2026)
Geometric and linear morphometric approaches to establish taxonomic identity of a controversial tyrannosaurid maxilla specimen
Lethaia 60(2): 1-10
doi: https://doi.org/10.18261/let.60.2.2
https://www.scup.com/doi/10.18261/let.60.2.2

Free pdf:
https://www.scup.com/doi/epdf/10.18261/let.60.2.2

An isolated maxilla of a tyrannosaurid theropod was reported from the Javelina Formation (Maastrichtian) of the Tornillo Group of Texas several decades ago. Since then, the taxonomic identity of the specimen has remained controversial: some regard it as a specimen of Tyrannosaurus rex, a common tyrannosauroid species in the late Maastrichtian of western North America, while others have raised a possibility that it might represent a distinct taxon, based on the small size, and proportions of the anterior body, maxillary fenestra and jugal ramus. In this work, the taxonomic identity of this controversial specimen is reassessed, using linear and geometric morphometric analyses. Both analyses find the Javelina maxilla specimen is indistinguishable from the hypodigm of Tyrannosaurus rex. Furthermore, results of the geometric analysis suggest the supposed unique morphology of the specimen may not be attributable to allometry or ontogeny, but may simply fall within the range of intraspecific variation. Thus, there seems to be no clear evidence that this specimen is distinct from Tyrannosaurus rex, and the hypothesis that a tyrannosaurid taxon from the Javelina Formation represents a different taxon, is tentatively rejected.

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Free pdf:

Lida Xing, Lin Liu, Brent H. Breithaupt, Shan Jiang, Yong Ye, Xin Shen and Qi Qi (2026)
Possible Sauropod Tracks from the Lower Cretaceous Penglaizhen Formation of the Sichuan Basin, China
Fossil Studies 4(2): 16
doi:  https://doi.org/10.3390/fossils4020016
https://www.mdpi.com/2813-6284/4/2/16


The Sichuan Basin is a pivotal region for understanding the transition and evolution of Jurassic–Cretaceous dinosaur faunas in China. Despite a rich skeletal record, the quadrupedal track record from the Penglaizhen Formation remains scarce. This study reports a new sauropod tracksite discovered near Zhoujiagou in the Shuangliu District of Chengdu, Sichuan Province. The tracks occur within the upper strata of the Lower Cretaceous Penglaizhen Formation. The tracksite preserves at least three tracks constituting a possible trackway. These medium-sized impressions are characterized by a sub-circular morphology, a weak heteropody, and a potential wide-gauge trackway pattern. Based on these morphological attributes, the tracks are preliminarily referred to the Brontopodus morphotype. This discovery fills a critical gap in the sauropod ichnological record of the Penglaizhen Formation and provides evidence suggesting that mamenchisaurid dinosaurs, or their functional equivalents, persisted in the Sichuan Basin into the Early Cretaceous.

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[Wade Thompson]

I honestly always suspected that at least south of the Tyrannosaurus/Tyrannnosaurid specimens from the south were T. rex. I mean, predators today can have huge ranges. For example, saltwater crocodiles range from Northern Australia to India if I remember correctly. So I don’t get why extinct and ancient predators would be any different.

[Thomas Richard Holtz]

Heck, pumas range from Alaska down into South America, and wolves all the way across the northern continents.

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[Tristan Stock]

And modern ranges are themselves fairly restricted compared to historic and Plesitocene ranges due to the effects of human activity. Tyrannosaurus could be throughout all of Laramidia during parts of the Maastrichtian, and maybe even into Asia given certain biogeographic models suggesting an origin over there. Though of course, hard to test with our limited fossil record. Need a bunch of formations of all the same age to be extensively sampled to get a proper sense of fossil taxon ranges.

What's more interesting to me is that the Javelina formation and other similar units like Ojo Alamo have a significantly different herbivorous dinosaur fauna from the coeval Hell Creek and Lance faunas up North. Completely different ceratopsians and hadrosaurs (with the single exception of Torosaurus overlapping) as well as the sauropod presence down south. Herbivores do tend to be much more specialized for their respective climate and floral zone, while for carnivores "meat is meat" so they often show less specialization, but even then bulk-feeding megaherbivores like sauropods are gonna cover huge home ranges to keep themselves fed. They also occur at roughly the same latitude as Hell Creek if not further North in Asia earlier in the Maastrictian. Seems a bit weird that not a single titanosaur tooth has shown up anywhere north of New Mexico.

[Wade Thompson]

I’ve heard that the reason why or at least one of the reasons why Alamosaurus hasn’t been found in places like hell creek is because Alamosaurus preferred warmer environments like semi arid environments and hell creek was too cold for Alamosaurus.

[Thomas Richard Holtz]

 As I mentioned on Facebook, this paper is interesting and shows thatthe Javelina maxilla falls within the known range of Tyrannosaurus rex maxillae (and that the "T. imperator" and "T. regina" specimens don't separate out as separate forms.)

But had I reviewed it, I would have said this study would have greater explanatory power if some definite NON-Tyrannosaurus rex specimens were also included (for instance, some Tarbosaurus and Daspletosaurus maxillae.) If there were broad overlap with the non-T. rex forms and T. rex, then this set of morphometrics couldn't actually be used to discriminate between these taxa. But if they did separate out in morphospace, but the Javelina specimen was nested among T. rex, that would lend even higher weight to it being a southern Tyrannosaurus.

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[Mickey Mortimer]

"Both analyses find the Javelina maxilla specimen is indistinguishable from the hypodigm of Tyrannosaurus rex."

Actually the geometric morphometric analysis found it outside the range of Tyrannosaurus rex. Nobody who reviewed the paper looked at Figure 3? 

Mickey Mortimer

[Sean McKelvey]

If it's an outlier in fig. 3 than so are several others.

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[Mickey Mortimer]

"If it's an outlier in fig. 3 than so are several others."

Not necessarily. No other specimen is as far lower left. It's POSSIBLE the species' variance covers that area, but if T. "vannus" was a different diverging species, a reasonable expectation would be that it's just outside the variance of T. rex, as Figure 3 shows. I'm not saying TMM 41436-1 isn't T. rex, and as a lumper I'd probably even support it being T. rex given no other information. But to have Figure 3 being one of your two pieces of information justifying an entire paper is... bad.

Mickey Mortimer

[Mickey Mortimer]

For anyone who cares, this is how Paul's supposed Tyrannosaurus species map out in Yun's Figure 3. imperator is red, regina is green, rex is purple, unknown is black. Despite Yun saying "the fact that in both linear morphometric analysis incorporating the dimensions of these parts and geometric morphometric analysis capturing their overall shape and proportions, the supposed specimens of Tyrannosaurus imperator (e.g. FMNH PR 2081, MB.R.91216, MOR 1125) and Tyrannosaurus regina (e.g. BHI 3033, TMP 81.6.1, USNM 550000) do not cluster with one another but overlap broadly with Tyrannosaurus rex (sensu Paul et al. 2022 and Paul 2025), indicates that the proposed differences are not statistically supported", the top graph (Figure 3C) has T. imperator with a higher Principal Component 2 than rex and regina. So again I have no personal opinion on the validity of T. imperator yet, but Yun's statement is wrong. Another thing the reviewers might have checked...


Mickey Mortimer

[Sean McKelvey]

I'm not a PhD, my thoughts on this matter are basically irrelevant, so don't take this too seriously. But, as a layman I feel like I have a decent perspective from that side of the fence. To the average person, this comes across as, essentially, a semantics argument. It's frustrating and just a bit annoying. There is a reason why many people are either distrustful of this science, or just find the constant media articles that go back and forth on things irritating. Every few months we get another announcement that T.rex is actually 3 species in a trench coat, but then another one that says it's not, and is one species and so forth. So, my main question is this

Is this actually a case of said maxilla being an outlier, or do we simply lack enough material to make a proper comparison? 

Unless I am mistaken we have just over a dozen good specimens of Tyrannosaurus. That really does not seem like a large enough sample size to be getting a solid grasp of the extent of variation at play here.

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[Mickey Mortimer]

The "just a dozen good Tyrannosaurus specimens" trope is just silly at this point. We have WAY more Tyrannosaurus specimens than all but maybe 20 other Mesozoic theropods. Maybe. 

"Is this actually a case of said maxilla being an outlier, or do we simply lack enough material to make a proper comparison?"

That's the thing. Apparently it IS an outlier in one way of looking at the data. Could that be individual variation? Sure. The sample size is still small and there will be actual outliers in any real species sample. My issue is just that the paper claimed evidence for an argument when it wasn't true. And there are so many other possibilities. Imagine UCMP 118742 wasn't known/analyzed. Then "vannus" would be outside the rex range in Figure 2 as well.  Or maybe UCMP 118742 is also "vannus", which would also make sense in Figure 3C. The former has never even been described in detail, so really who knows. 

"There is a reason why many people are either distrustful of this science, or just find the constant media articles that go back and forth on things irritating. Every few months we get another announcement that T.rex is actually 3 species in a trench coat, but then another one that says it's not, and is one species and so forth"

There are a lot of issues here.
- Press conferences are designed as if new paper X shows all previous ideas were wrong, because that's exciting.
- Authors make a unique claim that they are right and all others are wrong, which may be ultimately correct but is at the time a fringe view not supported by consensus.
- A claim is made which is based on bad data, like pretending we have a resolved enantiornithine topology and running some analysis on that, or any new topology that doesn't reflect on why it's different than previous ones and quantify how well supported the new one is.
- Papers like Yun's that claim things that actually aren't reflected by their own data.

It's almost like peer reviewers should be paid so they consistently give a ****.

Mickey Mortimer