[dinosaur] Baru from Australia + Bystrowiella from Triassic of Germany + squamate cranial sesamoids + end-Triassic volcanism

Ben Creisler

Some recent non-dino papers:

Adam M. Yates (2017)

The biochronology and palaeobiogeography of Baru (Crocodylia: Mekosuchinae) based on new specimens from the Northern Territory and Queensland, Australia.

PeerJ 5:e3458

https://doi.org/10.7717/peerj.3458

https://peerj.com/articles/3458/

New records of the Oligo–Miocene mekosuchine crocodylian, Baru, from Queensland and the Northern Territory are described. Baru wickeni and Baru darrowi are accepted as valid species in the genus and their diagnoses are revised. Both species are present in Queensland and the Northern Territory but are restricted in time, with B. wickeni known from the late Oligocene and B. darrowi from the middle Miocene. The broad geographic distributions and restricted time spans of these species indicate that this genus is useful for biochronology. The record of B. wickeni from the Pwerte Marnte Marnte Local Fauna in the Northern Territory establishes that the species inhabited the north-western margin of the Lake Eyre Basin (LEB) drainage system. More southerly Oligo–Miocene sites in the LEB contain only one crocodylian species, Australosuchus clarkae. The Pwerte Marnte Marnte occurrence of B. wickeni indicates that the separation of Baru and Australosuchus did not correspond with the boundaries of drainage basins and that palaeolatitude was a more likely segregating factor.

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Florian Witzmann & Rainer R. Schoch (2017)

Skull and postcranium of the bystrowianid Bystrowiella schumanni from the Middle Triassic of Germany, and the position of chroniosuchians within Tetrapoda.

Journal of Systematic Palaeontology (advance online publication)

http://www.tandfonline.com/doi/ref/10.1080/14772019.2017.1336579

Chroniosuchians form a mainly terrestrial or semi-terrestrial clade of Permian and Triassic crocodile- or varanid-like tetrapods, usually considered stem amniotes, but with disputed affinities within that grade. Two groups can be distinguished, the chroniosuchids and bystrowianids. Whereas the chroniosuchid skull and postcranium are well known, our knowledge of bystrowianids is restricted mainly to isolated vertebrae and osteoderms. The Middle Triassic bystrowianid Bystrowiella schumanni from south-western Germany was identified as the first taxon of this clade outside Russia and China, based on the morphology of its vertebrae and osteoderms. Here we expand on a full description of cranial and postcranial remains from this taxon, based on a partially articulated specimen and further isolated material. The material comprises large parts of the dermal skull roof, the pectoral girdle, ribs and limbs, and sheds light on many anatomical regions formerly unknown in bystrowianids. Among the autapomorphic features of Bystrowiella are the premaxilla with an edentulous crest lateral to the choana, the premaxillary teeth with conspicuous size differences, the jugal with an extremely long, narrow anterior process, and the enlarged postparietals and tabulars forming facets for articulation with the anteriormost osteoderm. As in chroniosuchids, the pre- and postfrontal are not in contact, but unlike in chroniosuchids, the internarial fontanelle and the antorbital fenestra are absent. In the amniote-like postcranium, the interclavicle is slender and has a conspicuous parasternal process, the humerus is waisted and bears a short supinator process, and the long, curved trunk ribs have widely separated rib heads and a slender shaft without blades or processes. Phylogenetic analysis, particularly based on numerous new postcranial features, supports the monophyly of chroniosuchians, even when the constituent synapomorphies (osteoderm and vertebral characters) are excluded from the matrix. Chroniosuchians nest at the base of the amniote stem, forming an unresolved polytomy with Silvanerpeton, embolomeres and more advanced stem amniotes.

Ricardo Montero, Juan D. Daza, Aaron M. Bauer & Virginia Abdala (2017)

How common are cranial sesamoids among squamates?

Journal of Morphology (advance online publication)

DOI: 10.1002/jmor.20719

http://onlinelibrary.wiley.com/doi/10.1002/jmor.20719/full

Sesamoids are elements that originate as intratendinous structures due to genetic and epigenetic factors. These elements have been reported frequently in vertebrates, although cranial sesamoids have been recorded almost exclusively in non-tetrapod Osteichthyes. The only tetrapod cranial sesamoids reported until now have been the transiliens cartilage (of crocodiles and turtles), and another one located in the quadrate-mandibular joint of birds. Here, we examined seven squamate species using histological sections, dissections of preserved specimens, dry skeletons, cleared and stained specimens, computed tomographies (CT), and report the presence of other cranial sesamoids. One is attached to the cephalic condyle of the quadrate, embedded in the bodenaponeurosis and jaw adductor muscles of Ophiodes intermedius (Anguidae). The other sesamoid is found at the base of the basicranium of several squamates, capping the sphenoccipital tubercle, on the lateral side of the basioccipital–basisphenoid suture. This bone has previously been reported as “element X.” We reinterpret it as a basicranial sesamoid, as it is associated with tendons of the cranio-cervical muscles. This bone seems to have the function of resisting tension-compression forces generated by the muscle during flexion the head. This element was previously known in several squamates, and we confirmed its presence in three additional squamate families: Gymnophthalmidae, Gekkonidae, and Pygopodidae. The evidence suggests that cranial sesamoids are a widespread character in squamates, and it is possible that this feature has been present since the origin of the group.

Lawrence M. E. Percival, Micha Ruhl, Stephen P. Hesselbo, Hugh C. Jenkyns, Tamsin A. Mather, and Jessica H. Whiteside (2017)

Mercury evidence for pulsed volcanism during the end-Triassic mass extinction

Proceedings of the National Academy of Sciences (advance online publication)

doi: 10.1073/pnas.1705378114

http://www.pnas.org/content/early/2017/06/13/1705378114

Significance

The end of the Triassic Period (∼201.5 million years ago) witnessed one of the largest mass extinctions of animal life known from Earth history. This extinction is suggested to have coincided with and been caused by one of the largest known episodes of volcanic activity in Earth’s history. This study examines mercury concentrations of sediments from around the world that record this extinction. Mercury is emitted in gaseous form during volcanism, and subsequently deposited in sediments. We find numerous pulsed elevations of mercury concentrations in end-Triassic sediments. These peaks show that the mass extinction coincided with large-scale, episodic, volcanism. Such episodic volcanism likely perturbed the global environment over a long period of time and strongly delayed ecological recovery.

Abstract

The Central Atlantic Magmatic Province (CAMP) has long been proposed as having a causal relationship with the end-Triassic extinction event (∼201.5 Ma). In North America and northern Africa, CAMP is preserved as multiple basaltic units interbedded with uppermost Triassic to lowermost Jurassic sediments. However, it has been unclear whether this apparent pulsing was a local feature, or if pulses in the intensity of CAMP volcanism characterized the emplacement of the province as a whole. Here, six geographically widespread Triassic–Jurassic records, representing varied paleoenvironments, are analyzed for mercury (Hg) concentrations and Hg/total organic carbon (Hg/TOC) ratios. Volcanism is a major source of mercury to the modern environment. Clear increases in Hg and Hg/TOC are observed at the end-Triassic extinction horizon, confirming that a volcanically induced global Hg cycle perturbation occurred at that time. The established correlation between the extinction horizon and lowest CAMP basalts allows this sedimentary Hg excursion to be stratigraphically tied to a specific flood basalt unit, strengthening the case for volcanic Hg as the driver of sedimentary Hg/TOC spikes. Additional Hg/TOC peaks are also documented between the extinction horizon and the Triassic–Jurassic boundary (separated by ∼200 ky), supporting pulsatory intensity of CAMP volcanism across the entire province and providing direct evidence for episodic volatile release during the initial stages of CAMP emplacement. Pulsatory volcanism, and associated perturbations in the ocean–atmosphere system, likely had profound implications for the rate and magnitude of the end-Triassic mass extinction and subsequent biotic recovery.

News:

http://www.ox.ac.uk/news/2017-06-19-volcanic-eruptions-triggered-dawn-dinosaurs