Abstract
A charophyte assemblage including Latochara tenuicostata (PECK 1937) and Mesochara gr. voluta (PECK 1937) was found in the Lower Tithonian bone-bed 148 of the stratigraphic section at the Pointe de Chassiron, Oléron Island (Charente-Maritime, Southwestern France). This bed, which is well known for its rich and diverse fauna of tetrapods, was deposited in a margino-littoral environment of Purbeckian facies in the Late Jurassic Charente palaeogulf. The occurrence of Latochara at Oléron Island is the most southern location known in the distribution of this genus during the Late Jurassic. This suggests that the boundary between the charophyte Boreal and Tethyan provinces, defined on the basis of this distribution, is not solely determined by latitudinal (i.e. thermal) factors. Ecological factors such as salinity and competition with other charophyte families are hypothesized as alternative explanations.
Highlights
Palaeobiogeography of Late Jurassic and Early Cretaceous charophytes is a relatively new and poorly understood subject in charophyte research
Two main groups of fossils were found associated with the charophytes studied: ostracods and vertebrates
Whilst Latochara from the Lower Jurassic is known from southern France, (FEIST and CUBAYNES, 1984), in the Upper Jurassic and Lower Cretaceous, the genus was exclusively known from the Boreal domain, i.e. regions north of the Tethyan Sea
Summary
Palaeobiogeography of Late Jurassic and Early Cretaceous charophytes is a relatively new and poorly understood subject in charophyte research. Late Jurassic charophyte biogeography of the Northern Hemisphere, (Europe and North America), was characterized by SCHUDACK (1996) and SCHUDACK et al (1998) These studies were significant in showing that floras from North America and Northern Europe were much more like each other than like floras of the Tethyan domain. Later studies showed that even in the Northern part of the Iberian palaeoisland, Tithonian charophyte assemblages lacked this genus and were instead dominated by clavatoracean genera such as Globator and Clavator (HERNÁNDEZ et al, 1999; MARTÍN-CLOSAS, 2000). This suggested that the 20°C isotherm could be a real Late Jurassic bioprovincial boundary. The occurrence of the marker of the northern province, (the genus Latochara), south of the boundary, raises the question of whether factors other than thermal boundaries should be taken into account if we are to understand charophyte palaeobiogeography
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