Christophe Hendrickx, Fernando Abdala & Jonah N. Choiniere (2019)
A proposed terminology for the dentition of gomphodont cynodonts and dental morphology in Diademodontidae and Trirachodontidae.
Gomphodont cynodonts were close relatives of mammals and one of the Mesozoic lineages of cynodont therapsids that became extinct at the end of the Triassic. Gomphodonts were omnivorous to herbivorous animals characterized by labiolingually expanded postcanines, which allowed tooth-to-tooth occlusion. The morphology of the upper and lower postcanines presents important means of distinguishing among major lineages within Gomphodontia, that is, Diademodontidae, Trirachodontidae, and Traversodontidae, but the dentition of most Diademodontidae and Trirachodontidae remain poorly documented. Here, we present a comprehensive description of the dentition of each diademodontid and trirachodontid species, as well as detailed illustrations of each dental unit, after firsthand examination of material and 3D reconstructions of postcanine teeth. Based on dental morphology, Trirachodon berryi and "Trirachodon kannemeyeri," considered as separate taxa by some authors are here interpreted as representing different ontogenetic stages of the same species. Likewise, Sinognathus and Beishanodon, thought to belong to non-cynognathian cynodonts and traversodontids by some authors, are referred to Trirachodontidae and Gomphodontia based on dental characters, respectively. Finally, we propose a standardized list of terms and abbreviations for incisors, canines, and postcanines anatomical entities, with the goal of facilitating future descriptions and communication between researchers studying the gomphodont dentition.
Rachel H. Dunn, ÂCandice Cooper, ÂJoshua Lemert, ÂNatalie Mironov & Julie A. Meachen (2019)
Locomotor correlates of the scapholunar of living and extinct carnivorans.
Journal of Morphology (advance online publication)
The relationship of carpal morphology to ecology and habitat is under studied in carnivorans and more generally in mammals. Here, we use 3Dâscanning techniques to assess the usefulness of a carpal bone, the scapholunar, in carnivorans to reflect ecology and habitat, and to reconstruct the ecology of five extinct carnivorans from two fossil sites: Rancho La Brea and Natural Trap Cave. We 3Dâscanned scapholunars and measured articular surface areas and angles between articular facets using GeoMagic and Rhino 3Dâsoftware. We analyzed the difference in these metrics using multivariate analysis of variance and discriminant function analysis. Results show that the scapholunar reflects ecological signal, with clear groupings of cursorial carnivorans and grappling/climbing carnivorans; however, phylogenetic signal was also present in the results with hyaenids, canids, and large felids in distinct morphospaces. Extinct species Miracinonyx trumani (American cheetah) and Smilodon fatalis (sabertooth cat) showed surprising results with M. trumani grouping with pantherines instead of Acinonyx or Puma, suggesting it runs but still retains the ability to grapple prey. S. fatalis groups with pantherines, but also shows some unique adaptations, suggesting it had a different range of wrist motion than living cats. Overall, the scapholunar is a good indicator of ecology and functional morphology and can be another tool to use in modern and fossil carnivorans to reconstruct extinct ecologies and locomotor behaviors.
Ricardo S. De Mendoza (2019)
Phylogenetic relationships of the Early Miocene diving and flightless duck Cayaoa bruneti (Aves, Anatidae) from Patagonia: homology or convergence?
Papers in Palaeontology (advance online publication)
Cayaoa bruneti, from the early Miocene Gaiman Formation of Chubut, Argentina, provides the earliest evidence for diving behaviour and the earliest example of flight loss within Anseriformes. It is also the only known diving duck from South America. A new phylogenetic analysis using only morphological characters places Cayaoa bruneti as part of a single radiation of diving ducks within Anatinae, as sister group to the Erismaturinae. Partition analysis of subsets of characters shows that the humerus and femur have the strongest effect in generating this phylogeny, while the skull characters result in groupings closer to those seen in analyses with molecular data. When the analysis is constrained by enforcing the molecular tree as a backbone, Cayaoa bruneti emerges as a basal branch within the Erismaturinae. These results make Cayaoa bruneti an independent and early example of the recurring evolution of flightlessness in large marine Anatidae.
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Interdigital cell death (ICD) is correlated with life-history strategy in tetrapods
Atmospheric oxygen modulates local oxygen tension in the interdigital region
High oxygen levels can induce ICD in an amphibian that typically lacks it
Blood vessel density and Bmp signaling are critical for the appearance of ICD
Amphibians form fingers without webbing by differential growth between digital and interdigital regions. Amniotes, however, employ interdigital cell death (ICD), an additional mechanism that contributes to a greater variation of limb shapes. Here, we investigate the role of environmental oxygen in the evolution of ICD in tetrapods. While cell death is restricted to the limb margin in amphibians with aquatic tadpoles, Eleutherodactylus coqui, a frog with terrestrial-direct-developing eggs, has cell death in the interdigital region. Chicken requires sufficient oxygen and reactive oxygen species to induce cell death, with the oxygen tension profile itself being distinct between the limbs of chicken and Xenopus laevis frogs. Notably, increasing blood vessel density in X. laevis limbs, as well as incubating tadpoles under high oxygen levels, induces ICD. We propose that the oxygen available to terrestrial eggs was an ecological feature crucial for the evolution of ICD, made possible by conserved autopod-patterning mechanisms.