Julien Benoit, Kenneth D. Angielczyk, Juri A. Miyamae, Paul Manger, Vincent Fernandez and Bruce Rubidge (2018)
Evolution of facial innervation in anomodont therapsids (Synapsida): Insights from X-ray computerized microtomography.
Journal of Morphology (advance online publication)
Sarah Werning (2018)
Medullary bone is phylogenetically widespread and its skeletal distribution varies by taxon.
Journal of Ornithology (advance online publication)
Female birds produce medullary bone to offset heightened calcium demand during egg shelling. The ephemeral nature of medullary bone hampers its observation in wild birds; thus, its phylogenetic distribution and ecophysiological correlates remain controversial. To address this, I candled a phylogenetically broad sample of bird skeletons spanning a large range of body sizes. I hypothesized that the presence of medullary bone would reduce or eliminate light penetrance through long bones. Candling suggested medullary bone was present in many adult female specimens, which was confirmed visually or with digital X-rays. This survey yielded the first unambiguous evidence of medullary bone in several taxa, including hummingbirds, tinamous, megapodes, and kiwi. The phylogenetic distribution of these new occurrences confirms that medullary bone is phylogenetically widespread among birds, including palaeognaths and passerines. The rapid assessment of complete skeletons supports a relationship between medullary bone and hematopoietic marrow, and establishes that the skeletal distribution of medullary bone varies taxonomically. Because the presence of medullary bone confirms sex, maturity, and reproductive status, its detection in specimens of known collection date can improve our understanding of life history and reproductive timing in wild birds, even decades later.
Caitlin E. Leslie,Â Daniel J. Peppe,Â Thomas E. Williamson,Â Matthew Heizler,Â Mike Jackson, Stacy C. Atchley,Â Lee Nordt &Â Barbara Standhardt (2018)
Revised age constraints for Late Cretaceous to early Paleocene terrestrial strata from the Dawson Creek section, Big Bend National Park, west Texas.
Geological ÂSocietyÂ Bulletin (advance online publication)
We analyzed samples for paleomagnetism, 40Ar/39Ar detrital sanidine ages, and mammalian fauna to produce a precise chronostratigraphic framework for the Upper Cretaceous to Lower Paleocene Dawson Creek section of Big Bend National Park, west Texas. Prior to this work, the absolute ages and durations of the Upper Cretaceous Aguja and Javelina Formations and Paleocene Black Peaks Formation were relatively poorly constrained. The documented polarity zones can be correlated to C32n-C31n, C29r, and C27r of the geomagnetic polarity time scale, with three hiatuses spanning more than 1.5 m.y. each. Rock magnetic analyses indicate that the dominant magnetic carrier in the Aguja and Black Peaks Formations is titanomagnetite, while the Javelina Formation has varying magnetic carriers, including hematite, magnetite, and maghemite. An overprint interval surrounding the Cretaceous-Paleogene boundary suggests the primary magnetic carrier, titanohematite, was likely reset by burial and/or overlying basaltic flows. These are the first independent age constraints for the CretaceousâPaleocene strata at the Dawson Creek section that determine the age and duration of deposition of each formation in the section, as well as the age and duration of multiple unconformities through the succession. As a result, these age constraints can be used to reassess biostratigraphic and isotopic correlations between the Big Bend area and other CretaceousâPaleogene basins across North America. Based on this new data set, we reassign the age of the mammalian fauna found in the Black Peaks Formation from the Puercan to the Torrejonian North American Land Mammal age. Our age constraints show that the dinosaur fauna in the Javelina Formation in the Dawson Creek area is latest Maastrichtian and restricted to chron C29r. Thus, the Javelina dinosaur fauna is correlative to the Hell Creek Formation dinosaur fauna from the Northern Great Plains, indicating differences between the faunas are not due to differences in age, and providing support for the hypothesis of provinciality and endemism in dinosaur communities in the late Maastrichtian. Further, the age constraints indicate that the previously documented mid-Maastrichtian and late Maastrichtian greenhouse events were rapid (<200 k.y.) and correlate closely with climate events documented in the marine record.
Eric Tohver,Â Martin Schmieder,Â Cris Lana,Â Pedro S.T. Mendes,Â Fred Jourdan,Â Lucas Warren &Claudio Riccomini (2018)
End-Permian impactogenic earthquake and tsunami deposits in the intracratonic ParanÃ Basin of Brazil.
GeologicalÂÂSocietyÂÂBulletin Â(advance online publication)
We investigate the stratigraphic record of the Permian-Triassic intracratonic ParanÃ Basin of South America for evidence of the Araguainha impact event. Soft-sediment deformation features are widespread at distances 50â1000 km from the impact site in the Lopingian (latest Permian) strata of the uppermost Passa Dois Group. Evidence of seismicity includes recumbent folds and slumps, clastic dikes, thixotropic wedges, and autoclastic breccias that resulted from sediment liquefaction. The vertical compaction of clastic dikes indicates their formation prior to sediment lithification, and dike formation is generally confined to stratigraphic intervals with heterolithic beds of varying density and viscosity, i.e., interbedded sandstone and siltstone. These seismogenic features are generally closer to the impact site (<1000 km) versus the distance (>2500 km) to the nearest active plate boundary. Seismites are limited in occurrence to the uppermost 100 m of the paleosurface at the time of impact, and the depth of seismite occurrence decreases with distance from the impact site. Above the seismite interval, the surface is extensively scoured and commonly overlain by a â4.5-m-thick debritic event bed. This sedimentary unit, the Porangaba bed, is a matrix-supported, unsorted conglomeratic breccia of variable thickness with an irregular, scoured base and tractional structures, including chaotically oriented to loosely imbricated clasts. Angular to subrounded clasts 10â400 cm in size are composed of altered chert, siltstone, and fine-grained sandstone that were derived from the underlying beds and are arrayed in a fining-upward pattern. In some localities, a second, clast-rich horizon is also observed with similar grading, but it has a smaller average clast size. This debrite bed has been identified in localities across the ParanÃ Basin at distances 50â1200 km from the impact site. The identification of zircon crystals with likely shock metamorphic planar microstructures in multiple samples obtained from this debritic layer links this stratigraphic horizon to the Araguainha impact event, and we interpret this bed as an ejecta-bearing tsunami deposit. The youngest population (n = 12) of unshocked, idiomorphic detrital zircon crystals provides a maximum depositional age of 253.0 Â 3.0 Ma for this event horizon, contemporaneous, within analytical error, with current geochronologic constraints on the impact event. These findings demonstrate that a catastrophic event around the Permian-Triassic boundary in Brazil created one of the worldâs most extensive seismite-tsunamite couplets.