PALEONTOLOGY IN JULY, 2025

ABSTRACT

Tyrannosaurus rex ranks among the most comprehensively studied extinct vertebrates1 and is a model system for dinosaur palaeobiology. As one of the last surviving non-avian dinosaurs, Tyrannosaurus is a crucial datum for assessing terrestrial biodiversity, ecosystem structure and biogeographic exchange immediately preceding the end-Cretaceous mass extinction—one of Earth’s greatest biological catastrophes. Palaeobiological studies of Tyrannosaurus, including ontogenetic niche partitioning, feeding, locomotor biomechanics and life history have drawn upon an expanding skeletal sample comprising multiple hypothesized growth stages—and yet the Tyrannosaurus hypodigm remains controversial. A key outstanding question relates to specimens considered to exemplify immature Tyrannosaurus, which have been argued to represent the distinct taxon Nanotyrannus. Here we describe an exceptionally well-preserved, near somatically mature tyrannosaur skeleton (NCSM 40000) from the Hell Creek Formation that shares autapomorphies with the holotype specimen of Nanotyrannus lancensis. We couple comparative anatomy, longitudinal growth models, observations on ontogenetic character invariance and a novel phylogenetic dataset to test the validity of Nanotyrannus, demonstrating conclusively that this taxon is distinguishable from Tyrannosaurus, sits outside Tyrannosauridae, and unexpectedly contains two species—N. lancensis and Nanotyrannus lethaeus sp. nov. Our results prompt a re-evaluation of dozens of existing hypotheses based on currently indefensible ontogenetic trajectories. Finally, we document at least two co-occurring, ecomorphologically distinct genera in the Maastrichtian of North America, demonstrating that tyrannosauroid alpha diversity was thriving within one million years of the end-Cretaceous extinction.

LINK(S)

https://www.nature.com/articles/s41586-025-09801-6

ABSTRACT

Squamates (lizards and snakes) comprise almost 12,000 living species, with wide ecological diversity and a crown group that originated around 190 million years ago1,2. Conflict between morphology and molecular phylogenies indicates a complex pattern of anatomical transformations during early squamate evolution, which remains poorly understood owing to the scarcity of early fossil taxa1,3. Here we present Breugnathair elgolensis gen. et sp. nov., based on a new skeleton from the Middle Jurassic epoch (167 million years ago) of Scotland, which is among the oldest relatively complete fossil squamates. Breugnathair is placed in a new family, Parviraptoridae, an enigmatic group with potential importance for snake origins, that was previously known from very incomplete remains. It displays a mosaic of anatomical traits that is not present in living groups, with head and body proportions similar to varanids (monitor lizards) and snake-like features of the teeth and jaws, alongside primitive traits shared with early-diverging groups such as gekkotans. Phylogenetic analyses of multiple datasets return conflicting results, with parviraptorids either as early toxicoferans (and potentially stem snakes) or as stem squamates that convergently evolved snake-like dental and mandibular traits related to feeding. These findings indicate high levels of homoplasy and experimentation during the initial radiation of squamates and highlight the potential importance of convergent morphological transformations during deep evolutionary divergences.

LINK(S)

https://www.nature.com/articles/s41586-025-09566-y

https://www.nature.com/articles/s41586-025-09566-y.pdf

ABSTRACT

One of the most widely cited objections to hypotheses that defend a central role for humans in late Pleistocene megafaunal extinctions in South America has been the assumption that extinct megafauna was a marginal resource in early human economies. On the basis of accurate chronological frames and faunal quantitative data, we demonstrate that extinct megafauna were the principal prey item of early foragers from ~13,000 to 11,600 calibrated years before the present, and this fact had likely been obscured by lumping together pre- and postextinction archaeological faunal assemblages within a single chronological window. We also show that the most exploited extinct taxa were at the apex of the ranking of the prey choice model. After the diversity and abundance of megafauna had already declined severely (~12,500 B.P.), and especially after they had virtually disappeared (~11,600 B.P.), the human diet was broadened. This strongly reinforces the idea that humans must be central to the debate on Quaternary extinctions in South America.

LINK(S)

https://www.science.org/doi/10.1126/sciadv.adx2615

https://www.science.org/doi/epdf/10.1126/sciadv.adx2615

ABSTRACT

A new saurolophine hadrosaurid dinosaur, Ahshislesaurus wimani gen et sp. nov., from the lower Hunter Wash Member of the lower Kirtland Formation (~75.02 Ma) of New Mexico is described. The specimen was briefly described before and referred to the stratigraphically younger Kritosaurus navajovius, which is known from the De-na-zin Member (~73.83–73.49 Ma) of the uppermost Kirtland Formation. The holotype of A. wimani consists of an incomplete diagnostic skull, several isolated cranial elements including the right jugal, quadrate, dentary, and surangular, and a series of articulated cervical vertebrae. In addition to the holotype of A. wimani, several specimens from the same strata may also belong to this newly identified species, including a well-preserved left dentary and a partial skeleton, as well as two humeri, one belonging to a large adult and the other to a juvenile. The skull of A. wimani preserves several taxonomically informative characters that show close affinities with the stratigraphically younger Naashoibitosaurus ostromi from the De-na-zin Member. Together with Naashoibitosaurus, Ahshislesaurus forms a potentially novel clade of flat-headed saurolophine hadrosaurids. This clade suggests the saurolophines were a taxonomically diverse group, which, during the last 20 million years of the Cretaceous, were among the dominant herbivorous dinosaurs in southern Laramidia. Recognition of a new hadrosaurid species from New Mexico also provides further evidence for latitudinal variation in the hadrosaurid fauna during the Late Cretaceous in Laramidia.

LINK(S)

https://www.krqe.com/wp-content/uploads/sites/12/2025/09/Enormous-new-duck-billed-dinosaur-species-identified-in-northwest-New-Mexico-Journal.pdf