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.

======

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.

=====

[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.

--
You received this message because you are subscribed to the Google Groups "Dinosaur Mailing Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to DinosaurMailingG...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/a9382f92-810b-4f4e-9721-9cfd3771367en%40googlegroups.com.

--

Thomas R. Holtz, Jr.
Email: tho...@umd.edu         Phone: 301-405-4084
Principal Lecturer, Vertebrate Paleontology

Office: CHEM 1225B, 8051 Regents Dr., College Park MD 20742

Dept. of Geological, Environmental, and Planetary Sciences, University of Maryland
http://www.geol.umd.edu/~tholtz/

Phone: 301-405-6965
Fax: 301-314-9661              

Faculty Director, Science & Global Change Program, College Park Scholars

Office: Centreville 1216, 4243 Valley Dr., College Park MD 20742
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address: 

                        Thomas R. Holtz, Jr.
                        Department of Geological,

                            Environmental, and Planetary Sciences
                        Building 237, Room 1117

                        8000 Regents Drive
                        University of Maryland
                        College Park, MD 20742-4211 USA

[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.

--

You received this message because you are subscribed to the Google Groups "Dinosaur Mailing Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to DinosaurMailingG...@googlegroups.com.

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/bd6879b4-b674-4a59-b06e-e9736db6dc19n%40googlegroups.com.