Triassic vertebrates from Villány
Study of Triassic sauropterygians from the Villány Mountains
Sauropterygians were one of the most successful and diverse marine reptile groups of the Mesozoic. Though their scientific study started already at the time of the birth of vertebrate paleontology (the beginning of the 19th century), their phylogenetic relationships are still not completely clear.
According to the most accepted hypotheses, the clade Sauropterygia includes the Placodontia and the Eosauropterygia (Pachypleurosauria, Nothosauroidea, Pistosauroidea). Early sauropterygians (placodonts, pachyoleurosaurs, nothosaurs, Figure 1) lived in nearshore environments, intraplatform basins and shallow epicontinental seas (the Tethys and its peripheral seas, Figure 2). Following their fast radiation (after the mass extinction at the end of the Permian) their diversity started to drop during the Middle and Late Triassic, they went extinct by the end of the Triassic (at the same time as the disappearence of warmer epicontinental seas). In contrast, the survival of pistosaurs can be attributed to their ability to adapt to pelagic mode of live. Plesiosaurs were distributed worldwide and became one of the most diverse groups of marine reptiles, until finally they died out at the end of the Cretaceous. Remains of sauropterygians were found in Europe, North Africa, West Asia, Southern China, and the western part of North America.
The study of marine reptiles, thus that of sauropterygians, can provide great help for the understanding of some evolutionary patterns (e.g. mass extinctions and the following recovery of life, or secondary aquatic adaptations). The study of their metabolic and thermoregulatory mechanisms can shed light on their ecological and evolutionary features. Sauropterygians are excellent examples of secondary aquatic adaptation thus their study can help the better understanding of the evolution of other vertebrate groups similarly adapted to marine life.
There were some researchers studying sauropterygians also within the Carpathian Basin. Nopcsa worked on nothosaurs in 1928. The vertebrate paleontological studies in Bihor, Romania, started in 1969, lead by Tibor Jurcsák. A specimen assigned to the genus Nothosaurus (Figure 3) was found in Middle Triassic rocks near Aleşd (Élesd).
At the end of the 19th and the beginning of the 20th century, the first documented sauropterygian remains were found also in present Hungary. Besides, Placochelys placodonta (Figure 4), found by Dezső Laczkó in 1889, and subsequently studied by Otto Jaekel (1902, 1907) and Olivier Rieppel (2001), belongs to the most important paleontological heritages of Hungary. For science, it is one of the best preserved placodontian ever found and regarding the evolution of the group an especially important representative of placodonts.
Lőrenthey (1907) and a few years later Lóczy Jr. (1912) both mention remains assigned to Nothosaurus, found in the quarry just opposite to the Villány train station. Fortunately, the study of sauropterygians have more and more relevances in Hungary. A few isolated nothosaur teeth have been found in various strata in the Mecsek Mts. The Middle Triassic limestones of Felsőörs yielded a nothosaur mandible fragment. In 2012, the Villány Mts again got to the focus of interest: as a result of a construction, started in 2011 on the Somsich Hill, Triassic formations, already known at the nearby classic outcrop in the road cut at Templom Hill, were exposed. Emília Pozsgai, a geologist exploring also the construction site, noticed some teeth, vertebrae and limb elements. In the spring of 2012, Attila Ősi and his research team joined the work, which resulted in several hundreds of Triassic vertebrate fossils. After the now well-known Late Cretaceous Iharkút locality, the Villány site provides the second, systematically collectible Mesozoic vertebrate fossil assemblage in Hungary. At the area of the construction from the Middle Triassic Templomhegy Dolomite Formation numerous, mostly nothosaurian teeth and bones, a fragmentary mandible assigned to the genus Nothosaurus, several placodontian teeth and tooth fragments, as well as a large number of unidentified bone fragments had been found. The strata of the Middle Triassic Mészhegy Sandstone Formation and the Lower Jurassic Somsicshegy Limestone Formation of the classical outcrop at the road cut, yielded, among others, reworked nothosaur teeth and bones, as well as placodont tooth fragments. Thus the study of sauropterygians can hardly be regarded as completed and certainly promises results in the future, perhaps in which the newly discovered Villány occurrence can also take part.
The eosauropterygian marine reptile fossils from Villány are investigated by Martin Segesdi. Research of Martin Segesdi is subsidized by the Human Capacities Grant Management Office (EMET) of the Hungarian Ministry of Human Capacities (NTP-NFTÖ-16-0257; National Talent Support Program Scholarship).
The eosauropterygian assemblage from Villány mostly contains isolated cranial and postcranial elements, but a partial skeleton of a small-sized specimen is also known. Among the nothosaurian remains are a three dimensionally preserved posterior part of the skull, nearly complete mandibles with teeth, and various humeri. While the mandibles probably belong to Nothosaurus giganteus, the fragmentary skull represents another Nothosaurus species. In addition one fragmentary humerus suggests the presence of another eosauropterygian marine reptile group besides nothosaurs.