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Palacrodon, a near-crown stem reptile, is known from several Triassic sites across the globe, and is easily recognized by its dentition characterized by labiolingually expanded molariform teeth coupled with acrodont tooth implantation. Here we explore the nature of tooth implantation and attachment in specimens of Palacrodon from South Africa and Arizona, U.S.A. using µCT. We note the presence of unusual ridges located underneath the tooth crowns in Palacrodon browni. Such ridges are not present in specimens from Arizona, which warrants the naming of a new species P. parkeri. We conducted a broad survey of internal tooth morphology across extant and extinct pan-reptiles (n = 212), and we conclude that homologous ridges like those we observe in P. browni are not present in any other species of reptile. As such, our ability to determine the function of the ridges is limited, though we hypothesize it is related to tooth attachment via unmineralized soft tissues. [ABSTRACT FROM AUTHOR]

As practitioners of a historical science, paleontologists and geoscientists are well versed in the idea that the ability to understand and to anticipate the future relies upon our collective knowledge of the past. Despite this understanding, the fundamental role that the history of paleontology and the geosciences plays in shaping the structure and culture of our disciplines is seldom recognized and therefore not acted upon sufficiently. Here, we present a brief review of the history of paleontology and geology in Western countries, with a particular focus on North America since the 1800s. Western paleontology and geology are intertwined with systematic practices of exclusion, oppression, and erasure that arose from their direct participation in the extraction of geological and biological resources at the expense of Black, Indigenous, and People of Color (BIPOC). Our collective failure to acknowledge this history hinders our ability to address these issues meaningfully and systemically in present-day educational, academic, and professional settings. By discussing these issues and suggesting some ways forward, we intend to promote a deeper reflection upon our collective history and a broader conversation surrounding racism, colonialism, and exclusion within our scientific communities. Ultimately, it is necessary to listen to members of the communities most impacted by these issues to create actionable steps forward while holding ourselves accountable for the past. [ABSTRACT FROM AUTHOR]

Resolving the phylogenetic relationships of early amniotes, in particular stem reptiles, remains a difficult problem. Three-dimensional morphological analysis of well-preserved stem-reptile specimens can reveal important anatomical data and clarify regions of phylogeny. Here, we present the first thorough description of the unusual early Permian stem reptile Bolosaurus major, including the first comprehensive description of a bolosaurid braincase. We describe previously obscured details of the palate, allowing for insight into bolosaurid feeding mechanics. Aspects of the rostrum, palate, mandible, and neurocranium suggest that B. major had a particularly strong bite. We additionally found B. major has a surprisingly slender stapes, similar to that of the middle Permian stem reptile Macroleter poezicus, which may suggest enhanced hearing abilities compared to other Paleozoic amniotes (e.g., captorhinids). We incorporated our new anatomical information into a large phylogenetic matrix (150 OTUs, 590 characters) to explore the relationship of Bolosauridae among stem reptiles. Our analyses generally recovered a paraphyletic "Parareptilia," and found Bolosauridae to diverge after Captorhinidae + Araeoscelidia. We also included B. major within a smaller matrix (10 OTUs, 27 characters) designed to explore the interrelationships of Bolosauridae and found all species of Bolosaurus to be monophyletic. While reptile relationships still require further investigation, our phylogeny suggests repeated evolution of impedance-matching ears in Paleozoic stem reptiles., (© 2024 American Association for Anatomy.)

Geckos are a speciose and globally distributed clade of Squamata (lizards, including snakes and amphisbaenians) that are characterized by a host of modifications for nocturnal, scansorial and insectivorous ecologies. They are among the oldest divergences in the lizard crown, so understanding the origin of geckoes ( Gekkota ) is essential to understanding the origin of Squamata , the most species-rich extant tetrapod clade. However, the poor fossil record of gekkotans has obscured the sequence and timing of the assembly of their distinctive morphology. Here, we describe the first North American stem gekkotan based on a three-dimensionally preserved skull from the Morrison Formation of western North America. Despite its Late Jurassic age, the new species already possesses several key characteristics of the gekkotan skull along with retained ancestral features. We show that this new stem gekkotan, and several previously named species of uncertain phylogenetic relationships, comprise a widespread clade of early crown lizards, substantiating faunal homogeneity in Laurasia during the Late Jurassic that extended across disparate ecological, body-size and physiological classes.

True crabs (Brachyura) are one of the few groups of arthropods to evolve several types of compound eye, the origins and early evolution of which are obscure. Here, we describe details of the eyes of the Cretaceous brachyuran Callichimaera perplexa , which possessed remarkably large eyes and a highly disparate body form among brachyurans. The eyes of C. perplexa preserve internal optic neuropils and external corneal elements, and it is the first known post-Paleozoic arthropod to preserve both. Additionally, a series of specimens of C. perplexa preserve both the eyes and carapace, allowing for the calculation of the optical growth rate. C. perplexa shows the fastest optical growth rate compared with a sample of 14 species of extant brachyurans. The growth series of C. perplexa , in combination with the calculation of the interommatidial angle and eye parameter, demonstrates that it was a highly visual predator that inhabited well-lit environments., Competing Interests: The authors declare no competing interests., (© 2021 The Authors.)