Aaron R. H. LeBlanc, Kirstin S. Brink, Megan R. Whitney, Fernando Abdala & Robert R. Reisz (2018)
Dental ontogeny in extinct synapsids reveals a complex evolutionary history of the mammalian tooth attachment system.
Proceedings of the Royal Society B 285 20181792Â
The mammalian dentition is uniquely characterized by a combination of precise occlusion, permanent adult teeth and a unique tooth attachment system. Unlike the ankylosed teeth in most reptiles, mammal teeth are supported by a ligamentous tissue that suspends each tooth in its socket, providing flexible and compliant tooth attachment that prolongs the life of each tooth and maintains occlusal relationships. Here we investigate dental ontogeny through histological examination of a wide range of extinct synapsid lineages to assess whether the ligamentous tooth attachment system is unique to mammals and to determine how it evolved. This study shows for the first time that the ligamentous tooth attachment system is not unique to crown mammals within Synapsida, having arisen in several non-mammalian therapsid clades as a result of neoteny and progenesis in dental ontogeny. Mammalian tooth attachment is here re-interpreted as a paedomorphic condition relative to the ancestral synapsid form of tooth attachment.
Not yet mentioned but may be of interest:
A.V. Lopatin & A.O. Averianov (2018)
Earliest Placentals: at the Dawn of Big Time.
Priroda 2018 (4):Â 34-40 (in Russian)Â
The analysis of the earliest placental mammals found in the Lower Cretaceous of Asia (110â130 Ma) suggests that the evolutionary success of placentals is based on the physiological advantages associated with the improvement of homeothermy, sensory and dental systems, and the special reproductive strategy that included fast juvenile growth, accelerated maturation, and well developed care of the offspring.
David A Tarailo (2018)
Taxonomic and ecomorphological diversity of temnospondyl amphibians across the PermianâTriassic boundary in the Karoo Basin (South Africa).
Journal of Morphology (advance online publication)
Temnospondyl amphibians experienced a geologically brief interval of success in the wake of the endâPermian mass extinction. This study examines the relationship between taxonomic and ecological diversity of temnospondyls across the PermianâTriassic boundary in the Karoo Basin of South Africa. Ecomorphological diversity, as implied by differences in cranial shape, was incorporated into the study by the use of a landmarkâbased geometric morphometric analysis. Both taxonomic diversity and cranial disparity are low during the Permian and increase across the PermianâTriassic boundary. Taxonomic diversity is stable through the Triassic, but disparity shows subsequent increases during the Olenekian and Anisian. Temnospondyls are restricted in size immediately following the extinction, but size range fully rebounds by the Olenekian. Cranial shape is heavily influenced by phylogenetic relatedness, and the observed increases in disparity may be partly the result of decreases in the net relatedness of coeval Karoo stereospondylomorph temnospondyls in younger faunas. The increase in community level taxonomic diversity for temnospondyls in the Karoo following the endâPermian mass extinction was likely facilitated by an influx of distantly related and ecologically distinct species.
Graciela Delvene, Rafael P. Lozano, Martin Munt, Rafael Royo-Torres, Alberto Cobos & Luis AlcalÃc (2018)
Bivalves and oncoids as palaeoenvironmental indicators at Late Jurassic and Early Cretaceous dinosaur sites from Spain.
Proceedings of the Geologists' Association (advance online publication)
Bivalves from the Late Jurassic and Early Cretaceous stratigraphic section at Las Zabacheras (Galve Sub-basin Teruel, northern Spain), are reviewed from both systematic and palaeoautoecological perspectives. For this study the Villar del Arzobispo Formation, well known for important dinosaur occurrences, was sampled from the boundary with the underlying Higueruelas Formation (Late Jurassic), to the first levels of the overlying El Castellar Formation (Early Cretaceous). The bivalve taxa have Late Jurassic affinity, pointing to a possible Jurassic-Cretaceous boundary towards the top of the Villar del Arzobispo Formation. We have sampled oncoids, whose nuclei are bivalves, through the section to study environment change in this lithostratigraphical formation. Geochemical trace elements and Î13C and Î18O stable isotope analysis of the oncoids enable us to determine the conditions in which the microbialites were formed and provide further palaeoenvironmental data from the deposits containing the bivalves. Bivalve taxa change from the lower part of the Villar del Arzobispo Formation, where Ceratomya excentrica and Unicardium cf. subregulare are characteristic of marine conditions, becoming more continental towards the top of the formation with the presence of Unionoidean bivalves, and in the 'Wealden' facies of the El Castellar Formation, where Teruella gautieri, has been found. Bivalves and oncoids allow us to recognize continental conditions where the first dinosaur of Spain, the sauropod Aragosaurus ischiatus was found, in an open water system, where there was limited evaporation, and with enough energy to produce well oxygenated water.
Rebecca C. Terry, Jesse A. Laney & Samuel H. Hay-Roe (2018)
Quantifying the digestive fingerprints of predators on the bones of their prey using scanning electron microscopy.
PALAIOSÂ 33 (11): 487-497
Paleoecological reconstruction relies on accurately determining the taphonomic origin of fossil deposits. Predation is a common mechanism by which skeletal remains become concentrated over time, leading to the formation of modern and fossil prey death assemblages. Skeletal element representation and breakage patterns within such death assemblages can be used to infer the identity of the responsible predator. However, assemblage-level metrics cannot be used to infer if a single fossil specimen is predator-derived. Microscopic digestive etching on individual bones can also indicate past predation events because acidic gastric fluids create distinctive micrometer-scale fissures in cortical bone. Here we establish a quantitative approach to predator identification from small mammal prey remains using microscopic digestive damage patterns. To do this, we collected mandibles from rodents digested by 13 predator species from local wildlife rehabilitation centers, and imaged them using an FEI Quanta 200 SEM. Results indicate that bones exposed to gastric fluids show clear digestive fissures, and that owl-digested specimens can be readily distinguished from specimens that were digested by diurnal raptors and mammalian carnivores. Specifically, owl-digested specimens are characterized by a high density of small and short digestive fissures. Within the owls, digestive fissure patterns appear to scale with owl body size. Finally, we used linear discriminant analysis to build a classification scheme from our modern data and applied it to Holocene mouse fossils from Two Ledges Chamber, Nevada. We found that the fossil specimens display the digestive fingerprints of owls. Quantification of microscopic digestive fissures thus offers a promising new approach for elucidating the taphonomic history of individual fossil specimens.