Walter G. Joyce, Tyler R. Lyson & Scott Williams (2016)
New cranial material of Gilmoremys lancensis (Testudines, Trionychidae) from the Hell Creek Formation of southeastern Montana, U.S.A.
Journal of Vertebrate Paleontology e1225748 (advance online publication)
Plastomenidae is a speciose clade of soft-shelled turtles (Trionychidae) known from Campanian to Eocene deposits throughout western North America. We here describe two large skulls from the Upper Cretaceous (Maastrichtian) Hell Creek Formation of Carter County, Montana, that document the adult morphology of the plastomenid Gilmoremys lancensis. Whereas juveniles of this species, as previously documented by five subadult skulls, have narrow skulls, a narrow processus trochlearis oticum, a deep and narrow median palatal groove, low accessory ridges, and a secondary palate fully formed by the maxilla, skeletally mature individuals have notably broad skulls, a broad processus trochlearis oticum, a shallow but broad median palatal groove, high accessory ridges, and a substantial contribution of the vomer to the secondary palate. An expanded phylogenetic analysis reveals that the Campanian Aspideretoides foveatus and the Paleocene Aspideretoides superstes, nov. comb., are situated within Plastomenidae as sister to all previously identified plastomenid turtles, despite their general resemblance to trionychine soft-shelled turtles. The name Aspideretoides should therefore not be used as a taxonomic wastebasket for fossil trionychids with unclear phylogenetic relationships.
SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP
Masakazu Asahara, Masahiro Koizumi, Thomas E. Macrini, Suzanne J. Hand and Michael Archer (2016)
Comparative cranial morphology in living and extinct platypuses: Feeding behavior, electroreception, and loss of teeth.
Science Advances 2(10): e1601329
The modern platypus, Ornithorhynchus anatinus, has an eye structure similar to aquatic mammals; however, platypuses also have a “sixth sense” associated with the bill electro- and mechanoreception that they use without opening their eyes underwater. We hypothesize that Ornithorhynchus and the Miocene taxon Obdurodon have different sensory capacities, which may have resulted from differences in foraging behavior. To estimate differences in foraging, sensory systems, and anatomical divergence between these monotremes, we compared their skull morphologies. Results indicate that the bill of Obdurodon is more dorsally deflected than that of Ornithorhynchus, suggesting a pelagic foraging behavior in Obdurodon compared to the bottom-feeding behavior in Ornithorhynchus. The infraorbital foramen of Obdurodon, through which the maxillary nerve passes sensory data from the bill to the brain, is relatively less developed than that of Ornithorhynchus. Whereas bill-focused sensory perception was likely shared among Mesozoic monotremes, the highly developed electrosensory system of Ornithorhynchus may represent an adaptation to foraging in cloudy water. Computed tomography imagery indicates that the enlarged infraorbital canal of Ornithorhynchus restricts the space available for maxillary tooth roots. Hence, loss of functional teeth in Ornithorhynchus may possibly have resulted from a shift in foraging behavior and coordinate elaboration of the electroreceptive sensory system. Well-developed electroreceptivity in monotremes is known at least as far back as the early Cretaceous; however, there are differences in the extent of elaboration of the feature among members of the ornithorhynchid lineage.
Morgan F. Schaller, Megan K. Fung, James D. Wright, Miriam E. Katz & Dennis V. Kent (2016)
Impact ejecta at the Paleocene-Eocene boundary.
Science 354(6309): 225-229
Extraterrestrial impacts have left a substantial imprint on the climate and evolutionary history of Earth. A rapid carbon cycle perturbation and global warming event about 56 million years ago at the Paleocene-Eocene (P-E) boundary (the Paleocene-Eocene Thermal Maximum) was accompanied by rapid expansions of mammals and terrestrial plants and extinctions of deep-sea benthic organisms. Here, we report the discovery of silicate glass spherules in a discrete stratigraphic layer from three marine P-E boundary sections on the Atlantic margin. Distinct characteristics identify the spherules as microtektites and microkrystites, indicating that an extraterrestrial impact occurred during the carbon isotope excursion at the P-E boundary.
Sean M. Harrington, Dean H. Leavitt, and Tod W. Reeder (2016)
Squamate Phylogenetics, Molecular Branch Lengths, and Molecular Apomorphies: A Response to McMahan et al.
Copeia 104(3):702-707. 2016
Morphology-based studies of squamate phylogenetics recover very different topologies from studies that use molecular or combined molecular and morphological data. This has led to some stimulating dialogue regarding the respective merits of the alternative hypotheses, with the primary point of disagreement being the placement of Iguania. Molecular phylogenetic studies place Iguania in a highly nested position as a member of the clade Toxicofera, additionally containing Anguimorpha and Serpentes, whereas morphology-only studies have traditionally placed Iguania as sister to all remaining squamates. McMahan and colleagues recently posited that the molecular phylogenetic hypothesis of the placement of Iguania is a result of incorrect root placement. These authors mapped molecular data (i.e., DNA sequence data) onto phylogenetic hypotheses and identified more molecular apomorphies on the basal branches of the morphology-based phylogeny. They concluded from this result that the molecular data support the morphological phylogenetic hypothesis of Iguania being sister to all remaining squamates. Here, we map molecular data onto additional phylogenetic hypotheses and show that the conclusions of McMahan and colleagues are flawed for three key reasons: 1) they misinterpreted a measure of branch length as a measure of branch support; 2) they considered only two phylogenetic hypotheses; and 3) their counts of molecular apomorphies are severely biased by their decision to collapse clades into large polytomies. We demonstrate that counting the molecular apomorphies along a given branch is a poor measure of support for a clade and that the molecular data do not provide support for the morphology-based squamate phylogeny as the optimal topology.
Referenced paper is available free here:
McMahan, C. D., L. R. Freeborn, W. C. Wheeler, and B. I. Crother. 2015. Forked tongues revisited: molecular apomorphies support morphological hypotheses of squamate evolution. Copeia 103:525–529.