Turtles from Upper Cretaceous of Texas + Late Triassic vertebrates from Greenland + East Kirkton Quarry tetrapods redated to Mississippian Romer's Gap

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

Recent tetrapod papers:

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Thomas M. Lehman, Susan L. Tomlinson, Thomas A. Shiller & Steven L. Wick (2025)
Turtles of the Aguja and Javelina Formations, Upper Cretaceous (Campanian – Maastrichtian), West Texas
Cretaceous Research 106145
doi: https://doi.org/10.1016/j.cretres.2025.106145
https://www.sciencedirect.com/science/article/abs/pii/S0195667125000680

Highlights

Neurankylus baueri, Denazinemys nodosa, Thescelus rapiens occur in Aguja Formation
Denazinemys survived into late Maastrichtian time in Texas
distinct southern Campanian turtle assemblage in Mexico, Texas, New Mexico, and Utah
low diversity southern Maastrichtian turtle assemblage reflects dry inland habitat

Abstract

Freshwater turtles of the Aguja and Javelina formations include Basilemys, Adocus, Compsemys, and Aspideretoides which are widely distributed and have long ranges throughout Campanian-Maastrichtian strata in the Western Interior of North America. Several species with restricted ranges are however documented for the first time, including Neurankylus baueri, Denazinemys nodosa, and Thescelus rapiens. Fragmentary specimens also record an unidentified baenid, likely kinosternoids and chelydrids, and three trionychids other than cf. Aspideretoides spp. Specimens attributed to Neurankylus baueri are among the largest known. A Neurankylus specimen from the Javelina Formation likely represents a distinct unnamed late Maastrichtian species. Thescelus rapiens is reported for the first time outside of New Mexico. Denazinemys occurs throughout the Upper Cretaceous section, with the most complete specimens attributed to D. nodosa. The Denazinemys lineage was restricted to the southern part of the Western Interior throughout its history, and survived into late Maastrichtian time only in Texas. The Campanian turtle fauna is allied with those of northern Mexico, New Mexico, and Utah in the presence of bothremydids along with the baenids N. baueri, D. nodosa, and T. rapiens; together these comprise a distinct ‘southern’ Campanian assemblage. Maastrichtian turtles comprise a lower diversity fauna of mostly cosmopolitan taxa, as is also the case in correlative strata in New Mexico and Utah. This may reflect drier inland habitats represented in these ‘southern’ deposits, compared to coastal habitats that hosted a diverse endemic turtle fauna at northern sites bordering the remnant interior seaway at the end of Cretaceous time.

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Free pdf:

Valerian J.P. Jésus, Octávio Mateus, Jesper Milàn, and Lars B. Clemmensen (2025)
Late Triassic small and medium-sized vertebrates from the Fleming Fjord Group of the Jameson Land Basin, central East Greenland
Palaeontologia Electronica, 28(1):a18.
doi: https://doi.org/10.26879/1423
https://palaeo-electronica.org/content/2025/5520-triassic-greenland-vertebrates

Free pdf:
https://palaeo-electronica.org/content/pdfs/1423.pdf


The Late Triassic deposits in the Jameson Land Basin, central East Greenland, stand as a crucial fossil area, yielding a diverse Norian vertebrate fauna. This basin, situated at a palaeolatitude of 41° N on the northern rim of Pangea and bordered in the North by the Boreal Sea, was a hub of activity during the Late Triassic. A large ephemeral to perennial lake system developed in the central and eastern parts of the basin, with rivers transporting sediment from the uplands northwest of the basin. Our research focused on the microvertebrate remains recovered from an expedition to Jameson Land in 1991 which yielded significant findings. These specimens, meticulously photographed and listed in a catalogue, comprise 950 vertebrate remains. Notably, we have identified new taxa never described from the Late Triassic sediments of Greenland, including sharks (Lissodus, Rhomphaiodon), bony fish (Gyrolepis), and reptiles (Doswelliidae and Rhynchocephalia). The revision of two sphenodontians jaw fragments as Clevosauridae, in association with Lissodus lepagei, Lissodus cf. Lissodus minimus, Rhomphaiodon sp., Saurichthys sp., and Gyrolepis sp., which are taxa that are highly documented in Europe and Asia, confirms a relationship between faunas of Greenland and Eurasia during the Late Triassic, a statement previously based on macro vertebrate studies.

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Free pdf:

Hector K. Garza, Elizabeth J. Catlos, Thomas J. Lapen, Julia A. Clarke & Michael E. Brookfield(2025)
New U-Pb constraints and geochemistry of the East Kirkton Quarry, Scotland: Implications for early tetrapod evolution in the Carboniferous.
PLoS ONE 20(4): e0321714.
doi: https://doi.org/10.1371/journal.pone.0321714
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0321714

The transition of vertebrates from aquatic to terrestrial environments during the late Devonian to early Carboniferous marks a crucial evolutionary milestone. However, this transition remains poorly understood due to a scarcity of early tetrapod fossils during the late Devonian to early Mississippian, creating a gap in the fossil record known as Romer’s Gap (~360–345 Ma). Recent discoveries have narrowed this gap, providing critical insights into early tetrapod evolution. The East Kirkton Quarry in Scotland’s Midland Valley, has yielded tetrapod fossils considered early stem amphibians and amniotes. They have been proposed to be Mississippian (early Carboniferous) in age, yet data to inform their precise ages remain limited. Here, zircon grains from two tuffaceous clastic limestones and shales were dated using Laser Ablation-Inductively Couple Plasma-Mass Spectrometry (LA-ICP-MS). The study presents detrital zircon U-Pb dates, which refine the current biostratigraphy ages assigned to Westlothiana lizziae, Silvanerpeton miripedes, Balanerpeton woodi, Ophiderpeton kirktonense, Eucritta melanolimnetes, and Kirktonecta milnerae to a maximum depositional age (MDA) of 341 ± 3 Ma (±2σ, n= 7 dates), placing them in the middle-lower Visean (Holkerian-Arundian) rather than the previous assigned upper Visean (Brigantian). This revised maximum depositional age places the East Kirkton Quarry fossils within the older, critical interval of Romer’s Gap, bridging a significant evolutionary time interval in the Mississippian fossil record, and allows for refining future tetrapod time trees. X-ray Fluorescence and X-ray Diffraction analyses reveal heterogeneity in the lower East Kirkton Limestone of the East Kirkton Quarry, with variations in elemental and mineralogical compositions, reflecting episodic volcanic and detrital inputs and hydrothermal activity.

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