Jaxtasuchus

Jaxtasuchus Temporal range: Middle Triassic
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Family:	†Doswelliidae
Genus:	†Jaxtasuchus Schoch & Sues, 2013
Type species
†Jaxtasuchus salomoni Schoch & Sues, 2013

Jaxtasuchus is an extinct genus of armoured doswelliid archosauriform reptile known from the Middle Triassic (Ladinian stage) of the Erfurt Formation, Germany. The type species Jaxtasuchus salomoni was named in 2013 on the basis of several skeletons and partial remains. Like other doswelliids, it is heavily armored with many rows of bony plates called osteoderms covering its body. Jaxtasuchus is the first doswelliid known from Europe and is most closely related to Doswellia from the Late Triassic of the eastern United States. Fossils have been found in aquatic mudstones alongside fossils of temnospondyl amphibians, crustaceans, and mollusks, suggesting that Jaxtasuchus was semiaquatic like modern crocodilians.

Discovery

Fossils of Jaxtasuchus have been found in the Lower Keuper of southern Germany, which dates back to the end of the Middle Triassic. The osteoderms of Jaxtasuchus were originally interpreted as the dermal bones of temnospondyl amphibians and later as the plates of aetosaur reptiles. The only other archosauriforms currently known from the Lower Keuper are Zanclodon laevis, which is known from a jaw fragment and several teeth, and Batrachotomus kupferzellensis, a large pseudosuchian archosaur that is known from several skeletons. Jaxtasuchus is the most abundant archosauriform reptile in the Lower Keuper. Its remains have been uncovered in five fossil localities: Kupferzell, Rielingshausen, Vellberg, Wolpertshausen, and Zwingelhausen. The holotype specimen is a mostly complete skeleton from Vellberg missing the head and neck. Also from Vellberg is a specimen preserving bones of the skull. Other more fragmentary specimens include limb bones and osteoderms. At some sites Jaxtasuchus is known only by its osteoderms.

Jaxtasuchus is named after Jagst, a tributary of the Neckar river in the region where fossils were found. The type species J. salomoni is named after Hans Michael Salomon, who discovered the holotype specimen and donated it to the Staatliches Museum für Naturkunde Stuttgart where it is now housed.

Phylogeny

Cladogram after Schoch & Sues, 2013:

Archosauromorpha	Mesosuchus Prolacerta Archosauriformes Proterosuchus Erythrosuchus Euparkeria Archosauria Turfanosuchus Avemetatarsalia Pseudosuchia Chanaresuchus Doswelliidae Vancleavea Tarjadia Archeopelta Doswellia Jaxtasuchus

Paleobiology

Fossils of Jaxtasuchus in Vellberg come from mudstones that were most likely deposited in brackish-water lakes or marshes. Because its fossils are common, they were probably not swept into aquatic environments from terrestrial areas. Jaxtasuchus was probably semiaquatic like modern crocodilians and resembled them in having heavy armor, short limbs, and a long tail. Sharp teeth suggest that Jaxtasuchus was most likely carnivorous. Aquatic temnospondyl amphibians such as Callistomordax, Kupferzellia, and Mastodonsaurus are common components of the fossil assemblage. Fossils of bivalves and ostracode crustaceans in these deposits provide evidence of fluctuating salinity levels over time, with most fossil vertebrates are found in layers corresponding to low salinity.