Late Cretaceous tetrapod vertebrates from Maastrichtian type area stratigraphic ranges + turtle fossils from Upper Cretaceous of Mexico + caseid synapsid cloacal opening (free pdfs)

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

Recent papers:

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Free pdf:

Lars P.J. Barten, John W.M. Jagt & Eric W.A. Mulder (2026)
Updated stratigraphical ranges of Late Cretaceous tetrapod vertebrates from the Maastrichtian type area and the impact of megabiases on their record
Deinsea 24: 33 - 54
DOI: 10.5281/zenodo.21248985

Free pdf:  
https://www.researchgate.net/publication/408733403_Updated_stratigraphical_ranges_of_Late_Cretaceous_tetrapod_vertebrates_from_the_Maastrichtian_type_area_and_the_impact_of_megabiases_on_their_record


Upper Cretaceous strata in the type area of the Maastrichtian Stage (Late Cretaceous) in the south-east Netherlands and north-east Belgium are renowned for their marine and terrestrial tetrapod remains. Here we provide an update of the stratigraphical distribution of all currently known tetrapod taxa in this area, as based predominantly on numerous recent discoveries during the last two decades. This yields further insights into mosasaur community compositions over time, as illustrated by the first record of Plioplatecarpus sp. from the upper lower Maastrichtian (Gulpen Formation, Vijlen Member, interval 6). In addition, new records of a small marine turtle, provisionally assigned to Ctenochelys, extend the stratigraphical distribution for the genus in the type Maastrichtian. An apparent paucity in tetrapod diversity during deposition of the Lixhe 1, 2 and 3 members (Gulpen Formation) and a significant increase in the number of taxa recorded from the overlying Lanaye Member (Gulpen Formation), presumably reflect either a collecting or taphonomic bias or (temporary) absence of tetrapods in the basin during deposition of this portion of the Gulpen Formation and a probable link to the Mid-Maastrichtian Event (MME), recently documented for the Lixhe 2 and 3 members. The various mosasaur taxa occur relatively continuously throughout the Lanaye Member and all members of the overlying Maastricht Formation and, with some exceptions, range up to the Cretaceous-Paleogene (K/Pg) boundary in the study area.

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Free pdf:

Oliver A. López-Conde, Gerardo Carbot-Chanona & María L. Chavarría-Arellano (2026)
Restos de tortuga en el Cretácico Superior (Maastrichtiano) de Chiapas amplían el registro geológico y geográfico de este taxón en México
Turtle remains in the Upper Cretaceous (Maastrichtian) of Chiapas expand the geological and geographical record of this taxon in Mexico
Paleontología Mexicana 15(2): 335-347 (in Spanish)
DOI: https://doi.org/10.22201/igl.05437652e.2026.15.2.441
https://paleontologiamexicana.geologia.unam.mx/index.php/paleontologia/article/view/441

Free pdf:
https://paleontologiamexicana.geologia.unam.mx/index.php/paleontologia/article/view/441/695


Turtles are important members of Upper Cretaceous vertebrate assemblages throughout North America and are considered an useful tool for defining biogeographic patterns. In Mexico, fragments of fossil turtle shells are known from several Upper Cretaceous formations, including El Gallo, Baja California; Corral de Enmedio and Packard Shale, Sonora; Aguja and San Carlos, Chihuahua; and Aguja, Cañón del Tule, and Cerro del Pueblo, Coahuila. In this study, we formally describe turtle remains from the Ocozocoautla Formation (Maastrichtian, Upper Cretaceous) in the State of Chiapas, southern Mexico. The turtle specimens are referred to as Testudine indeterminate and Pleurodira indeterminate. These specimens represent the southernmost record of turtles within the Upper Cretaceous of Mexico. Knowledge of Cretaceous turtle richness in Mexico has increased with new remains from Chiapas. These specimens are important because they constitute the second formal report of turtle remains in the Maastrichtian of Mexico.

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Free pdf:

Lorenzo Marchetti, Antoine Logghe, Arnaud Rebillard, Mark J. MacDougall & Jörg Fröbisch (2026)
The evolutionary significance of the earliest cloacal opening in Synapsida
iScience 29(8): 116752
doi: https://doi.org/10.1016/j.isci.2026.116752
https://www.sciencedirect.com/science/article/pii/S2589004226021309


Highlights

A 294 Ma tail impression with epidermal scales and cloacal opening is described
This impression is associated with Dimetropus and attributed to caseid synapsids
The cloacal opening (vent) is sub-vertical as in modern amphibians and crocodiles
The orientation of the vent changed at least three times during tetrapod evolution

Summary

The cloaca is a fundamental structure of modern terrestrial vertebrates, including the terminal parts of the urogenital and digestive systems that converge in a single channel and opening (vent). Although it is widespread in amphibians and reptiles (including birds) and occurs in mammals, the fossil record of this structure is scarce. Here we present an exceptional specimen from the early Permian Bromacker locality (294 Ma), which includes a tail impression with two rows of elevated scales separated by a vertical slit, that we interpret as cloacal lips and vent. Because of its morphology and association with the footprint Dimetropus, we attribute this impression to caseid synapsids. This represents the first occurrence of a cloaca in the fossil record of stem mammals. The comparison with modern and fossil specimens allows us to hypothesize a vertical vent orientation for early crown tetrapods, that subsequently changed orientation at least three times during tetrapod evolution.

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