MESOZOIC

PALAEONTOLOGY
   

Historical overview

Palaeontological research in the Jura Mountains started in the 19th century. Many important monographies have been published in the second half of the 19th century and at the beginning of the 20th century. Well-known classical works are those of Contejean (1859), Thurmann (1851), Thurmann & Etallon (1861-64), Gressly (1864), Greppin (1867, 1870, 1898-1900), Moesch (1874, 1875), Koby (1880-1889), Rollier (1888), De Loriol (1889-1892), Peyer (1946), and Bräm (1965), just to name a few. Many of these works still make reference today. The classical 19th century collection of Jules Thurmann (Thurmann & Etallon, 1861-1864) is housed in the Natural History Museum of Porrentruy, whereas the collection of Contejean is housed in Montbéliard in the “Musée du Château des ducs de Würtemberg”. Both collections are accessible for comparison.

Nevertheless, despite the palaeontological richness of the Canton Jura, comparatively few palaeontological studies have been carried out during the last few decades, even if several authors worked on the regional geology (including sedimentology and stratigraphy) of the Canton Jura (e.g., Laubscher, 1948; Schneider, 1960; Tschopp, 1960; Ziegler, 1956, 1962; Pümpin, 1965; Bolliger & Burri, 1967; Gygi & Persoz, 1986; Gygi et al., 1998, Gygi, 2000a, b).

The new discoveries of the Palaeontology A16

Since February 2000, the Palaeontology A16 excavates fossiliferous beds of Middle Oxfordian to Late Kimmeridgian age along the future course of the Transjurane highway of the Canton Jura (namely in the Ajoie district). This Late Jurassic sequence corresponds to coastal deposits of a shallow carbonate platform, at the threshold between the boreal and the tethyan realms.

To date, excavation activities have yielded numerous (>30’000 objects) and diverse fossils, including remains of marine, littoral and terrestrial organisms (plants, invertebrates and vertebrates). Invertebrates include ammonites, which give a precise biostratigraphic frame, and vertebrates include over 4200 dinosaur footprints, which testify at least three periods of large-scale emersion of the carbonate platform. The collection of the Palaeontology A16 is housed in Porrentruy at the “Office de la culture”.

Flora

Generally, macroremains of plants are rare and restricted to small coal remains. However, recently loads of wood macroremains have been excavated in the Marnes à virgula (Late Kimmeridgian). These remains are currently determined by Dr. M. Philippe (University of Lyon).

Besides, remains of dasycladacean algae (Goniolina sp.) bioimmurated by oysters are sometimes found (Photo 1). Plant microrests include charophytes (Porochara sp., Mesochara sp., Aclistochara sp.), which are determined by Dr. M. Schudack (Freie Universität Berlin). Palynological analyses are carried out by Dr. P. Hochuli (University of Zürich).
Photo 1: A dasycladacean seed head (Goniolina sp.) bioimmurated by Nanogyra nana.

For a detailed description of plant remains from the Vellerat Formation (Oxfordian) see also Van Konijnenburg-Van Cittert & Meyer (1996) and Gee et al. (2003).

Invertebrates

Marine invertebrates are very frequent on all excavation sites, but notably in the shell beds of the Banné Member (Kimmeridgian), which are almost entirely built up of invertebrates, mainly mollusc shells. Basically, the Oxfordian and Kimmeridgian invertebrate fauna are quite similar. Generally, the Late Kimmeridgian is the most fossiliferous and it yields also many ammonites, which allow to precisely date the excavated strata. The Late Oxfordian (Bure Member) reveals many crinoids (and other echinoderms) and corals, which are both scarcer in the Kimmeridgian. Trace fossils of invertebrates (burrows & borings) are common throughout the Oxfordian and Kimmeridgian.

Photo 2: Orthaspidoceras schilleri from the hardground at the base of the Marnes à virgula. Index ammonite for the Late Mutabilis zone (early Late Kimmeridgian).

Photo 3: Trichites sp. from the Banné Member. Incrusted by a terebratulid brachiopod (Sellithyris subsella), Nanogyra nana and serpulids. Note also the Gastrochaenolites borings.
Photo 4: Harpagodes sp. from the Banné Member. The typical gasteropod of the Kimmeridgian of Northwestern Switzerland.

Photo5: Hemicidaris mithra, a regular sea urchin from the Banné Member.

Vertebrates

Besides invertebrates it was so far the Kimmeridgian, which revealed many vertebrate remains as well. The vertebrate fauna is composed of fish and reptiles and it includes teeth, bones and footprints of saurischian dinosaurs.

Pisces
The fish fauna includes numerous isolated remains of chondrichthyans (cartilaginous fish, e.g., Asteracanthus, Hybodus, Ischyodus, Squatina, Spathobatis) and osteichthyans (bony fish, e.g., Caturus, Lepidotes, Macromesodon, Proscinetes). The fish fauna is studied in collaboration with Dr. Lionel Cavin of the Natural History Museum of Geneva.

Photo 6: Lower jaw of a pycnodontiform fish from the Marnes à virgula.

Photo 7: SEM photograph of a tooth of Hybodus sp. from the Marnes à virgula.

Reptilia
The reptile fauna includes numerous skeletal remains of crocodilians (e.g., Dakosaurus, Machimosaurus, Steneosaurus), pterosaurs, and chelonians, including many more or less articulated carapaces (e.g., “Thalassemydidae” indet., Plesiochelyidae indet.). Moreover, the presence of sauropod and theropod dinosaurs is attested by over 4200 footprints and 280 trackways, which have been discovered at three stratigraphic intervals at 7 different tracksites (Marty et al., 2007). The footprints have been left by juvenile to adult sauropods (narrow-gauge trackways of the ichnotaxon Parabrontopodus) and small- to large theropods (trackways of the ichnotaxa Megalosauripus and Carmelopodus). Both are represented by a variety of different size classes and trackway patterns and/or configurations (Marty et al., 2003, 2006, 2007).
Photo 8: Articulated plastron with parts of the dorsal carapace of a plesiochelyd turtle from the Marnes à virgula. Scale bar is 10 cm.

Photo 9: Tooth of the marine crocodilian Dakosaurus sp. from the Marnes à virgula.

Photo 10: Trackway (ichnotaxon Parabrontopodus) of a diplodocid sauropod from the main track level of the Courtedoux—Sur Combe Ronde tracksite (early Late Kimmeridgian). Pes length equals 40 cm, photo taken at night.

Photo 11: Chevenez—Combe Ronde tracksites, main track level. Crossroads of three trackways of small theropods. Footprints have been painted with water colour. Footprint length (lower left) is 15 cm.