Mesozoic

A presentation of the current data on the exceptionally diverse non-tyrannosaurid eutyrannosaur and tyrannosaurini genera and species of western North America during the end cretaceous North American interchange

GREGORY S. PAUL — 2025-06-30

Differences in proportions, anatomy, and species display features between specimens of all sizes from the latest Maastrichtian formations of the North American upper plains, greatly exceed those observed in other eutyrannosaur species, genera and subfamilies. The question is not whether more than one taxon was extant, but how many and at what ranks. Among the large Tyrannosaurus, early T. imperator retains the robust proportions, two lower functional incisors and postorbital boss features derived from earlier tyrannosaurids—the boss that includes highly atypical, large, long spindles not present in stratigraphically higher species. Among the latter, about half are robust T. rex specimens with single lower incisors, and are adorned by unique, very prominent “Mickey Mouse” postorbital display discs not previously observed in Tyrannosaurus. Contemporary T. regina skulls and skeletons are markedly more gracile, and lack either the postorbital spindles or discs. About half a dozen small remains are from juvenile specimens of Tyrannosaurus with the same tooth counts and lack of a prominent lateral dentary groove as the adults. Twice as many cannot be juveniles because their preserved hands are absolutely as large or larger than those of large adults—appendages do not atrophy with maturity in amniotes, and the feature excludes them from being tyrannosaurids. Furthermore, they have more teeth than adult specimens of Tyrannosaurus—tooth count reduction being abnormal or absent among growing reptiles. Growth arcs preserved in bone sections show these non-tyrannosaurids were growth slowing or ceasing subadults or adults, not rapidly increasing mass expansion expected in early ontogeny giants. The large-handed basal eutyrannosaurs are diverse, some but not necessarily all being Nanotyrannus or Stygivenator. Probably having evolved in Appalachia, the basal eutyrannosaurs were invading western North America (over the recently emerged land bridge), where they continued to evolve as they successfully competed with juvenile Tyrannosaurus. The result was an exceptionally diverse assemblage of tyrannosaurs at that end Cretaceous locality—caused by the rare ancient geographical event.

**On the supposed presence of Prognathodon solvayi in the Demopolis Chalk**

TREVOR H. REMPERT — 2025-06-30

While reporting on the mosasaurid fauna of the upper Demopolis Chalk of western Alabama and northeastern Mississippi, Derstler (1988) noted the presence of numerous remains of Plioplatecarpus sp. and Mosasaurus conodon, and a single isolated tooth of Prognathodon cf. Prognathodon solvayi. These remains are of Late Campanian age, originating from within a few meters of the lower boundary of the Bluffport Marl Member.

New insight into the paleobiology and systematics of the Mesozoic turtles of central europe (Chelonipus triunguis Karl & Tichy, 2000; Priscochelys hegnabrunnensis Karl, 2005) and their morphological relationship with the toothed turtle (Odontochelys semitestacea Li et al., 2008) of china

HANS-VOLKER KARL — 2025-06-30

The origin of the turtle body plan remains one of the great mysteries of reptile evolution. To establish the relationships between turtles of different clades in palaeobiological aspects is highly difficult. Here we describe a review of the oldest Mesozoic turtles of Central Europe (Chelyopsis triunguis; Priscochelys hegnabrunnensis) and their morphological relationship with the toothed turtle (Odontochelys semitestacea) of China. P. hegnabrunnensis is a fossil turtle from the Middle Triassic (lower Ladinian) of Hegnabrunn, Germany. It is known from a single, fragmentary shell plate and is considered a very early turtle, potentially the oldest known stem turtle. The fossil provides insights into the early evolution of turtle shells and their transition from a more primitive state. The habitat preferences of Priscochelys hegnabrunnensis remain uncertain. However, given the informative nature of the material available and, since that it was found mixed with marine and terrestrial faunas, it was probably allochthonous. The other older known turtle record is a trackway from the Bunter Sandstone of Thuringia (Germany) and represents the autochthonous ichno-taxon Chelonipus triunguis. Odontochelys semitestacea was a 220-million-year-old specimen excavated in Triassic deposits in Guizhou, China. Odontochelys only possessed the bottom portion of a turtle‘s armour, the plastron. It did not yet have a solid carapace as most other turtles do. Instead of a solid carapace, Odontochelys possessed broadened ribs like those of modern turtle embryos that still have not started developing the ossified plates of a carapace.

Dating of the volcanic rocks from the Shuzhugang Hill, Guangzhou: age constraints on the Late Cretaceous strata in the Sanshui and Zhujiangkou basins

HAI-LONG GAO — 2025-06-30

Well-developed Cretaceous-Paleogene strata are exposed in the Guangzhou-Foshan area. Owing to limited volcanic activity, isotopically datable material is scarce, and the chronology of these strata relies primarily on biostratigraphic correlations. The Baihedong Formation has been generally regarded as a sedimentary sequence deposited during the late Early Cretaceous, although robust chronological constraints are lacking. In the Shuzhugang Hill area, located south of Guangzhou, a suite of volcanic rocks is exposed and is generally assigned to the upper part of the Baihedong Formation, though some scholars attribute it to the Paleogene. Zircon U-Pb dating conducted in this study yielded an absolute age of 83.5 ± 0.7 Ma for these volcanic rocks, thereby constraining the deposition of the Baihedong Formation to the Late Cretaceous. This study provides a crucial chronological reference for defining the Cretaceous-Paleogene stratigraphic chronology framework across the Sanshui and Zhujiangkou basins.

On two rare wasps (Hymenoptera: Ohlhoffiidae; Panguidae) from mid-Cretaceous Kachin amber

CORENTIN JOUAULT — 2025-06-30

The Kachin amber biota is one of the most extensively studied and well-documented ecosystems of the Cretaceous, with over 2,000 arthropod species described to date. Among these are the Ohlhoffiidae, a family of stephanoid wasps currently known from four species, two from Kachin amber and two from the La Pedrera de Rúbies Formation in Spain. Despite their distinctiveness, little is known about their true diversity, biology, or intraspecific morphological variation. Here, we describe a new species of Ohlhoffia Jouault et al. 2020, as Ohlhoffia minuta sp. nov. which offers new insights into morphological variability within the family. We also report and illustrate a panguid wasp specimen identified as Pangu yuangu Li et al. 2019. Members of the Panguidae are known from both Wealden and Kachin ambers, yet like the Ohlhoffiidae, they remain poorly understood, with limited data available on their diversity and morphological variation at the species level.

**Erratum to: redescription of the Upper Jurassic Aeshna antiqua Vander Linden, 1827 in the anisopteran family Protolindeniidae (odonata)**

ANDRÉ NEL — 2025-06-30

The authors of the paper found some mistakes in the publication ‘Redescription of the Upper Jurassic Aeshna antiqua Vander Linden, 1827 in the Anisopteran family Protolindeniidae (Odonata)’.