Stegoceras juvenile frontal bone from Texas + dinosaur tracks from Lower Cretaceous of Tibet

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

New papers:

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Steven L. Wick & Thomas M. Lehman (2024)
A rare ‘flat-headed’ pachycephalosaur (Dinosauria: Pachycephalosauridae) from West Texas, USA, with morphometric and heterochronic considerations
Geobios (advance online publication)
doi: https://doi.org/10.1016/j.geobios.2024.08.006
https://www.sciencedirect.com/science/article/abs/pii/S0016699524000767

Highlights

Describes a rare ‘flat-headed’ juvenile specimen of pachycephalosaurid dinosaur from the Late Cretaceous of West Texas, USA.
Adds critical new taxonomic comparative material representing a juvenile semaphoront within the pachycephalosaur ontogenetic continuum.
Helps resolve taxonomy and affinities among the pachycephalosaur record from North America.
Morphometric analysis supports the specimen as pertaining to a new ‘southern’ species of Stegoceras.
Describes an unusual heterochronic growth progression among pachycephalosaurs which seemingly represents a new taxonomic characteristic.
Represents a vital ‘southern’ dinosaur paleofaunal datum for North America.


Abstract

A juvenile pachycephalosaur frontal from the upper Aguja Formation (Late Cretaceous: middle Campanian) of West Texas, USA is unusually thin dorsoventrally, even compared to ‘flat’ frontals of young individuals pertaining to other pachycephalosaur taxa. The specimen is most comparable morphologically and morphometrically to Stegoceras validum. However, it is much thinner than any ‘juvenile’ example of that species, and also differs in the elongate form and radial arrangement of the surficial tubercles, as well as occurrence of radial grooves along the lateral margins of the bone. Such differences are unlikely a reflection of intraspecific variation. Instead, the Aguja specimen likely represents a previously unknown juvenile semaphoront from the southern Western Interior, referred herein to Stegoceras sp. and likely extends the distribution of this widespread Campanian genus. A morphometric evaluation suggests that the holotype specimen of Texacephale langstoni, also from the Aguja Formation, is probably an adult semaphoront of Stegoceras. However, both specimens represent different ontogenetic stages with dissimilar morphologies and so their potential conspecifity remains equivocal. The new Aguja specimen described herein likely represents a ‘paedomorphic’ Campanian pachycephalosaur – one where the onset of doming is displaced until well into ontogeny – a heterochronic attribute Stegoceras sp. shares with S. validum and Pachycephalosaurus wyomingensis. Where an adequate ontogenetic sample is available for comparison, other pachycephalosaur taxa do not seem to exhibit a similar growth progression, and so this appears to be a significant taxonomic characteristic. That some pachycephalosaurs delayed doming of the skull roof during growth is enigmatic, but it may have been an expression of sexual dimorphism, an aid in species recognition, or a response to harsh environmental conditions.

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Yangui Li, He Zhao, William J. Foster, Yue Yu, Lida Xing, Qiang Ye, Chuanshang Wang  & Huazhou Yao (2024)
First discovery of dinosaur tracks from the Lower Cretaceous Duoni Formation in eastern Tibet, China
Cretaceous Research 106009
doi: https://doi.org/10.1016/j.cretres.2024.106009
https://www.sciencedirect.com/science/article/abs/pii/S0195667124001824

Research highlights

The Lower Cretaceous dinosaur tracks in Tibet is report for the first time.
The tracks can indicate the potential Early Cretaceous dinosaurs.
The trackmaker’s gait and size of three trackways have been determined.
The chronostratigraphy is determined by sporopollen.
The paleoclimate, palaeobiogeography and paleoenvironment are discussed.


Abstract

Dinosaurs are known to have been abundant and diverse in eastern Tibet, and roamed the region from the Early Jurassic to the Late Cretaceous. Even though the evidence of dinosaurs is known throughout this interval, there are still many stratigraphic gaps that lack evidence, such as the Upper Jurassic and the Lower Cretaceous successions. Here, we report a new dinosaur tracksite from the Lower Cretaceous Duoni Formation of Basu County, where 28 track-bearing surfaces were discovered, which document a flourishing dinosaur community. Of these, three track layers with a high abundance of dinosaur tracks are described here, including sauropod, ornithopod and theropod trackways. These tracks suggest a possible exchange of trackmakers between this region and with adjacent areas of East Asia. The trackmakers’ size, gait, and speed were inferred. The paleoenvironment is interpreted as ephemeral lakes bordered by conifer dominated forests. Palynological analysis conducted along the Duola stratigraphic section suggests that the tracksite is Aptian-Albian (Lower Cretaceous) in age, and the paleoclimate of the Basu area was relatively warm and dry.

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