Field of Science

The Dicynodon-Lystrosaurus Assemblage Zone Boundary May Not Approximate the Marine-Defined Permo-Triassic Extinction Event

Wow, well this should definitely generate some discussion and a bit of research.... 

Gastaldo, R. A., Kamo, S. L., Neveling, J., Geissman, J. W., Bamford, M., and C. V. Looy. 2015 Is the vertebrate-defined Permian-Triassic boundary in the Karoo Basin, South Africa, the terrestrial expression of the end-Permian marine event? Geology (Advanced Online). doi: 10.1130/G37040.1

Abstract: The end-Permian extinction records the greatest ecological catastrophe in Earth history. The vertebrate fossil record in the Karoo Basin, South Africa, has been used for more than a century as the standard for understanding turnover in terrestrial ecosystems, recently claimed to be in synchrony with the marine crisis. Workers assumed that systematic turnover at the Dicynodon assemblage zone boundary, followed by the appearance of new taxa directly above the base of the Lystrosaurus assemblage zone, is the continental expression of the end-Permian event and recovery. To test this hypothesis, we present the first highprecision age on strata close to the inferred Permian-Triassic boundary. A U-Pb isotope dilution–thermal ionization mass spectrometry zircon age of 253.48 ± 0.15 Ma (early Changhsingian) is from a silicified ash layer ~60 m below the current vertebrate-defined boundary at Old Lootsberg Pass (southern South Africa). This section yields newly discovered plants and vertebrates, and is dominated by a normal polarity signature. Our collective data suggest that the Dicynodon-Lystrosaurus assemblage zone boundary is stratigraphically higher than currently reported, and older than the marine extinction event. Therefore, the turnover in vertebrate taxa at this biozone boundary probably does not represent the biological expression of the terrestrial end-Permian mass extinction. The actual Permian-Triassic boundary in the Karoo Basin is either higher in the Katberg Formation or is not preserved. The currently accepted model of the terrestrial ecosystem response to the crisis, both in this basin and its extension globally, requires reevaluation.

So Long Paleorhinus and Pseudopalatinae

Long needed redescription of the type material of the phytosaur Parasuchus hislopi from India and a revision of the non-mystriosuchin parasuchid phytosaurs. It will take me awhile to abandon the name Pseudopalatinae. 

Kammerer, C. F., Butler, R. J., Bandyopadhyay, S., and M. R. Stocker. 2015. Relationships of the Indian phytosaur Parasuchus hislopi Lydekker, 1885. Papers in Paleontology (early online). 

The neotype skull of the Indian phytosaur Parasuchus hislopi Lydekker, 1885 (ISI R42) is re-evaluated and compared with the type material of other basal phytosaurs. Parasuchus hislopi is extremely similar to species previously placed in Paleorhinus (P. bransoni and P. angustifrons), sharing with them such characters as a series of nodes on the lateral surface of the jugal, paired ridges on the squamosal and a frontal depression. Parasuchus hislopi represents a valid species: it can be distinguished from P. bransoni by a relatively low narial eminence and P. angustifrons by the absence of paired nasal depressions. Inclusion of Parasuchus hislopi in a phylogenetic analysis of phytosaurs recovers it in a well-supported clade with P. bransoni and P. angustifrons. Parasuchus is considered the senior synonym of Paleorhinus and Arganarhinus. Parasuchus (here considered to include P. hislopi, P. angustifrons, P. bransoni and P. magnoculus) has a broad circum-Pangaean distribution, with species occurring in the south-western United States, Morocco, central Europe and India. Phytosaur higher-level taxonomy is also revised: Parasuchidae is redefined to include ‘Paleorhinus-grade’ phytosaurs and the later-diverging Mystriosuchinae (the group formerly known as Phytosauridae), and Pseudopalatinae is renamed Mystriosuchini for reason of priority.

A New Lagerpetid Dinosauromorph from the Late Triassic of Argentina

Martínez, R. N., Apaldetti, C., Correa, G. A., and D. Abelín. 2015. A Norian lagerpetid dinosauromorph from the Quebrada del Barro Formation, northwestern Argentina. Ameghiniana (future issue) doi:10.5710/AMGH.21.06.2015.2894

The early evolution of Ornithodira, the clade that includes pterosaurs and dinosaurs, is poorly known. Until a decade ago, the basal radiation of Dinosauromorpha, the clade including dinosaurs and birds, was poorly understood because of a scarce of fossil record, which was restricted to specimens known of the Ladinian Chañares Formation from Argentina. In the last years the discovery of several non-dinosaurian dinosauromorphs dramatically expanded this record and also demonstrated that this group—previously restricted to the Middle Triassic—persisted at least well into the Norian. Although Norian non-dinosaurian dinosauromorphs have been reported from several places around the world, the only known Norian non-dinosauriform dinosauromorphs—Dromomeron romeri and Dromomeron gregorii—come from North America. We report here the first record from the Southern Hemisphere of a non-dinosauriform dinosauromorph, Dromomeron gigas sp. nov., from the Norian Quebrada del Barro Formation, northwestern Argentina. A phylogenetic analysis recovers Dromomeron gigas nested into the monophyletic group Lagerpetidae, and as the sister taxon to Dromomeron romeri. The inclusion of D. gigas within Lagerpetidae suggests that body size increased in this lineage over time, as was previously demonstrated for Dinosauriformes as a whole, and that lagerpetids reached a larger size than previously thought. Finally, the new finding provides novel information on the basal radiation of Dinosauromorpha constituting the first record of a Norian association of dinosaurs with non-dinosauriform dinosauromorphs outside North America.