Sunday, May 12, 2019

[Paleontology • 2019] Mystriosuchus steinbergeri Description and Phylogenetic Placement of A New Marine Species of Phytosaur (Archosauriformes: Phytosauria) from the Late Triassic of Austria

Mystriosuchus steinbergeri 
Butler, Jones, Buffetaut, Mandl, Scheyer & Schultz, 2019

Phytosaurs are a group of carnivorous, semi-aquatic archosaurian reptiles that attained an almost global distribution during the Late Triassic. We here describe a new species of the phytosaur genus Mystriosuchus from the Norian Dachstein Limestone of Austria, from a marine lagoonal depositional environment. The new Austrian material comprises remains of at least four individuals of similar size (c. 4 m in total length) found in association but disarticulated, and includes one complete and two partial skulls and postcrania. All of these specimens apparently represent a single taxon, which is distinguished by numerous anatomical features from the two previously named Mystriosuchus species. Maximum parsimony analysis of a comprehensive morphological dataset provides strong statistical support for the phylogenetic position of the new Austrian taxon in Mystriosuchus, as the sister taxon to a clade comprising M. planirostris and M. westphali. Histological analysis suggests that the Austrian phytosaur specimens represent individuals that were at least eight years old at time of death, but which had not yet reached skeletal maturity. Taphonomic and palaeoenvironmental data suggest that these phytosaurs were living in the marine lagoon in which they were preserved, providing the strongest evidence to date of marine adaptations in phytosaurs.

Keywords: bone histology, fossils, marine adaptations, morphology, phylogeny, reptiles

Figure 5. Holotype skull of Mystriosuchus steinbergeri sp. nov. (NHMW 1986/0024/0001)
 in right lateral (A), posterior (B), medial cross-sectional (C), dorsal (D) and ventral (E) views.

Figure 1. Photographs taken in 1982 during the collection of the type and referred material of Mystriosuchus steinbergeri sp. nov. A, the type locality. The five figures in the centre of the photograph are clustered around the excavation site. B, the excavation team, including from left-to-right, Johann Segl, Sepp Steinberger, Georg Sverak and Walter Prenner. Georg Sverak is using the pneumatic hammer to drill a hole for a wedge used to split the blocks of limestone for removal. C, Georg Sverak and Walter Prenner in front of their tent. D, photograph of the block, as originally excavated, including the holotype skull (NHMW 1986/0024/0001; bottom right of photograph) and paratype mandible (NHMW 1986/0024/0002; top middle of photograph) in close association.

Life reconstruction of Mystriosuchus steinbergeri sp. nov. in the Dachstein Limestone depositional environment.
Illustration: Mark Witton.


Archosauriformes Gauthier, 1986 
Phytosauria Jaeger, 1828
Parasuchidae Lydekker, 1885 sensu Kammerer et al., 2015 
Mystriosuchinae Huene, 1915 sensu Kammerer et al., 2015 
Leptosuchomorpha Stocker, 2010 sensu Jones & Butler, 2018 
Mystriosuchini Huene, 1915 sensu Jones & Butler, 2018 

Mystriosuchus Fraas, 1896

Mystriosuchus steinbergeri sp. nov.

Etymology: The species is named for Sepp Steinberger, who discovered and helped collect the holotype and referred specimens.

Richard J. Butler, Andrew S. Jones, Eric Buffetaut, Gerhard W. Mandl, Torsten M. Scheyer and Ortwin Schultz. 2019. Description and Phylogenetic Placement of A New Marine Species of Phytosaur (Archosauriformes: Phytosauria) from the Late Triassic of Austria. Zoological Journal of the Linnean Society. zlz014. DOI:  10.1093/zoolinnean/zlz014