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Palaeogeographic significance of dinosaur occurrences on the isolated Adriatic carbonate platform (w Croatia, ne Italy, sw Slovenia) from the tithonian to campanian/maastrichtian

The Adriatic Carbonate Platform (AdCP) is one of the largest Mesozoic carbonate platforms of the Perimediterranean region, and its deposits crop out in Italy, Slovenia, Croatia, Bosnia and Herzegovina, Serbia and Montenegro, and Albania. These deposits comprise the major part of the entire carbonate sequence of the Croatian Karst (External) Dinarides, which is very thick (in places more than 8, 000 m), ranging from Middle Permian (or even Middle Carboniferous) to Eocene age. Towards the NW and SE the platform width is reduced, but it can be traced to NE Italy, and to Greece and Turkey, forming a shallow marine carbonate belt more than 3000 km long, surrounded by the Tethyan Ocean. Dinosaurs represent especially interesting features when found on the isolated carbonate platforms, since the shallow-marine environments where their traces are preserved surrounded their habitats - they were mostly transient through the shallow-marine areas during their search for large quantities of food (both vegetation and prey, depending on their type) and fresh water necessary for their survival. All previous known occurrences of dinosaur activities on the Adriatic Carbonate Platform have been recorded in its northwesternmost part, i.e. the wider region of Istria. This area is characterized by a much thinner succession of Late Jurassic and Cretaceous deposits as a consequence of numerous short-lasting emersions and some long-lasting hiatuses (latest Oxfordian- late Tithonian, late Aptian- late Albian, Cenomanian/Santonian- Eocene) and important lateral and vertical facies variability. The most important deposits are represented by frequent shallowing-upward cycles with common black-pebble breccias indicating the reworking of coastal swamp deposits, LLH stromatolites, desiccation cracks, vadose features and palaeosols. Terrestrial conditions existed in part practically throughout the entire period of the existence of the AdCP. The occurrences of dinosaur bones and footprints in Istria (Croatia), and neighbouring NE Italy and SW Slovenia, from the Late Tithonian (Mezga et al., 2003) to the Late Campanian/Early Maastrichtian (Debeljak et al., 2002) document the existence of long-lasting continental environments in the NW part of the platform. The fact that dinosaurs inhabited this part of the AdCP over a period of 70 MY indicates the continuous existence of specific conditions. Therefore, this area could have represented a continuous habitat even during the highest relative sea-levels, probably as a spacious island in the central and western part of present Istria, which would, accompanied by data indicating an even longer hiatus in the neighbouring offshore area (from Late Tithonian to Pliocene - Veseli, 1999) provide a relatively large emerged area. However, the numerous and varied occurrences of dinosaur footprints and fossil remains in the NW part of the platform definitely indicate the possibility of the existence of a palaeogeographical "bridge" during the Cretaceous (Dalla Vecchia, 2002), at least during the lowest relative sea-levels. This interpretation would favour the palaeogeographical map proposed by Stampfli and Moser (1999), where the area of a huge Mesozoic carbonate platform was suggested as being located relatively close to Gondwana. Their proposed location of the palaeogeographic "bridge" in the northern part of the huge platform can be supported by the fact that, at present, no occurrences of dinosaur activity have been found south of NE Italy, SW Slovenia and Istria (W Croatia). Some recent indications of dinosaur footprints of Middle Cenomanian age in S Croatia probably represents the consequences of migration of individual animals across temporary emerged areas of the platform.

Adriatic Carbonate Platform; dinosaur footprints; terrestrial conditions; palaeogeographical

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