MESOZOIC

RESEARCH _Vertebrate and invertebrate palaeontology

First record of a non-pterodactyloid pterosaur from Switzerland

The remains of pterosaurs, the flying reptiles of the Mesozoic Era, are usually rare in vertebrate deposits, except in the few pterosaur Lagerstätten (Wellnhofer, 1991; Kellner, 1994, Buffetaut, 1995). The Late Jurassic carbonate deposits of the Swiss Jura mountains well illustrate this rarity, with only one pterosaur remain reported until now, a wing phalanx (from the fourth digit, bearer of the flight membrane) from the Solothurn Turtle Limestone (Late Kimmeridgian, Canton Solothurn), assigned to a Pterodactyloidea (Meyer & Hunt, 1999).

The shaft fragment of a wing phalanx (Photo 1) from the “Sur Roche de Mars” locality near Porrentruy (Fig. 1) is the second occurrence of a pterosaur from Switzerland. Moreover, this bone is the first record of a Swiss non-pterodactyloid pterosaur. It is assigned to a large-sized Rhamphorhynchinae indet. (Rhamphorhynchidae). A comparison with tetrapod assemblages from other Late Jurassic coastal environments of western Europe underlines the peculiar aspect of this discovery (Billon-Bruyat, 2005b).

Photo 1: Fragment of the shaft of a wing phalanx in dorsal (A), ventral (B), caudal (C), and cranial (D) views; sketch of the tranverse cross section (E). Scale bar: 1 cm. Abbreviation: lg, longitudinal groove.

Fig. 1: Stratigraphic position of the pterosaur specimen (MJSN RDM000-7) within the simplified section of the “Sur Roche de Mars” locality (Porrentruy; Swiss coordinates: 574300 / 252000). The bone has been found on the road cut during geological prospecting, the matrix surrounding the bone attributes it to the 200–250 bed interval, dated by ammonites (Orthaspidoceras schilleri) to the early Late Kimmeridgian.

Biogeochemistry

The study of oxygen isotope compositions of phosphate (δ18Op) from apatite of vertebrates (Photo 2+3) can be used to reconstruct the palaeoenvironmental conditions in which they lived, and thereby give an indication of their ecology. This has been done for coastal marine faunas from Tithonian lithographic limestones of western Europe (Billon-Bruyat et al., 2005). Our project will apply it to new and historical faunal assemblages of the Kimmeridgian, such as those from the Porrentruy area and the famous Solothurn Turtle Limestone (Switzerland). Turtle and crocodilian remains will help to estimate the water compositions, by using the oxygen isotope fractionation between their phosphate and ambient water (Barrick et al., 1999; Amiot et al., 2007). It will be possible to estimate the temperature in which the fishes, turtles and crocodilians lived in the Porrentruy area, notably in the Marnes à virgula.

Photo 2+3: Analyses of oxygen isotopes (CO2 trapped iin liquid nitrogen) at the Laboratory UMR 5125 CNRS “PEPS” (University Lyon 1). © Patrick Dumas

Within the Ajoie region, the Marnes à virgula of the Reuchenette Formation (early Late Kimmeridgian) may locally be developed as a claystone which is extremely rich in Nanogyra nana. These marls were depositied on the Jura carbonate platform, in a shallow, subtidal, protected marine environment in quiet water below the fair-weather wave base (Jank et al., 2005).

Currently, large-scale excavations (ca. 4200 m²) are carried out in the about 90 cm to 1 m thick Marnes à virgula. So far, our field crew has collected nearly 1360 vertebrate specimens. The use of a shovel excavator allows to uncover such important surfaces. It removes cm by cm and as soon as bone fragments are detected the excavator moves on to another excavation area, and the vertebrate remains are uncovered using light manual tools.

This facies contains many vertebrate remains found associated and sometimes even partially articulated (e.g., turtle carapaces). The taxa are typical of a coastal marine assemblage. It comprises mainly turtles (Billon-Bruyat, 2005a), including hitherto more than thirteen carapaces (more or less complete) and many isolated bones, assigned to the Plesiochelyidae sensu lato (Plesiochelyidae and “Thalassemydidae”). Reptile remains also include teeth and bones of teleosaurid crocodilians (Steneosaurus, Machimosaurus) and rare pterosaur bones. The fauna also includes chondrichthyes, osteichthyes, and invertebrates. No continental forms have so far been identified among the faunal assemblage, but many wood remains have been unearthed, being the only terrestrial indicators so far.

Photo 4: Mandibule of a marine crocodilian Steneosaurus (Teleosauridae).

Photo 5: Carapace of a plesiochelyid turtle.

Excavations in the Banné Member

The Banné member was defined by Gygi (2000a, b). Originally this member was called “Marnes à Ptérocères” (Ptérocère=Harpagodes oceani), and it was initially described by Jules Thurmann - a famous local palaeontologist - as “Marnes du Banné” (Banné marls), because they crop out at the Banné hill in the south of Porrentruy (Thurmann & Etallon, 1864), and wherefrom many of the specimens of the classical Thurmann collection derive from.

The Banné Member is a sequence of highly fossiliferous calcareous marls and marly limestones deposited in a shallow water lagoon, which are so rich in marine invertebrates (Bivalvia, Gastropoda, Brachiopoda, etc.) that they can be described as shell beds (lumachelles). Ammonites date the Banné Member to the late Early Kimmeridgian (152 ma).

Fig. 2: Reconstitution of the biodiversity of the Banné Member.

Between 2001 and 2007, the Palaeontology A16 accomplished systematic excavations in the Banné Member at the Courtedoux—Vâ Tche Tchâ site (Fig. 3). During the excavation, bulk sampling was carried out by two master students of the University of Würzburg (Hicks, 2006; Richardt, 2006). Further, very detailed surface documentations were realised on several bedding planes on one square meter each. Once the fossils are determined, these surface documentations help – together with the bulk sampling data – to estimate the frequency of a given species, and to define and characterize the associations and their vertical evolution (Fig. 4). In order to find the less frequent remains of vertebrates and rare invertebrates (e.g., echinoids, ammonites), larger surfaces were excavated with a shovel excavator.

Photo 6: Surface documentation of an excavated bedding plane during the excavation of the Courtedoux—Vâ Tche Tchâ site.