A Middle Triassic pachypleurosaur (Diapsida: Eosauropterygia) from a restricted carbonate ramp in the Western Carpathians (Gutenstein Formation, Fatric Unit): paleogeographic implications

Abstract

An eosauropterygian skeleton found in the Middle Triassic (upper Anisian) Gutenstein Formation of the Fatric Unit (Demänovská dolina Valley, Low Tatra Mountains, Slovakia) represents the earliest known occurrence of marine tetrapods in the Western Carpathians. The specimen represents a partly articulated portion of the postcranial skeleton (nine dorsal vertebrae, coracoid, ribs, gastral ribs, pelvic girdle, femur and one zeugopodial element). It is assigned to the Pachypleurosauria, more precisely to the Serpianosaurus-Neusticosaurus clade based on the following combination of features: (1) small body size; (2) morphology of vertebrae, ribs and femur; (3) tripartite gastral ribs; and (4) microanatomy of the femur as revealed by µCT. Members of this clade were described from the epicontinental Germanic Basin and the Alpine Triassic (now southern Germany, Switzerland, Italy), and possibly from Spain. This finding shows that pachypleurosaur reptiles attained a broader geographical distribution during the Middle Triassic, with their geographical range reaching to the Central Western Carpathians. Pachypleurosaurs are often found in sediments formed in shallow, hypersaline carbonate-platform environments. The specimen found here occurs in a succession with vermicular limestones in a shallow subtidal zone and stromatolitic limestones in a peritidal zone, indicating that pachypleurosaurs inhabited hypersaline, restricted carbonate ramps in the Western Carpathians.

The marine conservation deposits of Monte San Giorgio (Switzerland, Italy): the prototype of Triassic black shale Lagerstätten

“…dark sediment, complete skeletons, poor in benthos, rich in clay) have been recognized in many other places. Examples for such deposits have been documented from Europe (eastern Switzerland, Ducan: Furrer, 2004 ; western Austria: Zapfe & König, 1980 ; Wachtler & Perner, 2018 ; Italy: Stefani et al, 1991 ; Slovakia: Čerňanský et al, 2018 ; Slovenia: Hitij et al, 2010 ), Asia (Spiti, India: Romano et al, 2016 ; Myanmar: San et al, 2019 ), and North America (Idaho: Brayard et al, 2017 ; Nevada: Romano et al, 2019 ).…”

Depositional environment of the Middle Triassic Strelovec Formation on Mt. Raduha, Kamnik-Savinja Alps, northern Slovenia

“…8A), although due to the greater thickness of the Strelovec Formation in the Slatinski plaz section, sedimentation of this section probably occurred on more distal parts of the ramp environment, compared to the Raduha section. The diversified vertebrate fauna found in Strelovec Formation indicates shallow basin environment in close connection to carbonate platform with near-shore areas inhabitated with different fishes, pachypleurosaurs, ichtyosaurs, and horseshoe crabs (Hitij et al, 2010;Stockar, 2010;Čerňansky et al, 2018;Bicknell et al, 2019;Gale et al, 2022).…”

Conflicting evidence for the use of caudal autotomy in mesosaurs

“…The overall tail and limb morphology of nothosaurs is similar to what is observed for mesosaurs, which may suggest that mesosaurs may have also employed a type of locomotion similar to nothosaurs. Furthermore, it has been inferred that most nothosauroids would have been restricted to near-shore, shallow marine environments 39,40 , which is very similar to the environment mesosaurs are considered to have occupied 24,30 .…”