Jane B Rees

Niels Bonde

Academic paper

Secondary Adaption to Life in Water; University of Copenhagen, Geologisk Museum, 13-17 IX 1999

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Plesiosaur material from the Hasle Formation includes 24 teeth, 10 vertebrae, three humeri/femora (one very small juvenile), several gastralia, one phalanx and some undetermined fragments (ribs ?). Most teeth have a morphology similar to that of Attenborosaurus conybeari (Sollas, 1881) from the lower Lias of Charmouth, southern England. In addition, there is a single, much more elongated tooth, probably of another species, and one 40 mm tooth-crown is more stout, perhaps belonging to yet another species. The postcranial remains have not been studied in detail, however, some vertebral centra are so short, that they might be "pliosaurian" (one "pliosaurian like" tooth has been found - lost during preparation). Early Jurassic plesiosaurs are primarily known from the lower Lias deposits of the Lyme Regis area in southern England. Here, more than one hundred specimens, many of them associated remains, have been collected. Originally, most species found here were assigned to the genus Plesiosaurus but recent studies by Bakker (1993) and Storrs (1997) have shown that this genus only contains a single English species and possibly one or two continental species from the Toarcian. Thus, Plesiosaurus is limited to the Lias. In contrast to the other, non-marine Early Jurassic deposits on Bornholm, the sandstones and siltstones of the Hasle Formation were deposited in a marine environment, at a depth of 10-40 meters, one or two kilometres from the coast line (Surlyk and Noe-Nygaard 1986). The age of the formation is early Pliensbachian (ammonite zones of Uptonia jamesoni to Prodactylioceras davoeC). The sandstone yields a fauna of molluscs, especially gastropods and bivalves, all in a very poor state of preservation. Shark teeth are quite common (Rees 1998). All vertebrate material has been collected from the Hasle Sandstone in the cliff section south of Hasle harbour on the westcoast, apart from one humerus/femur, which was found at the exposures of the Hasle Sandstone on the southcoast somewhat west of Sose Odde. This bone, the largest vertebrate fossil found on the island of Bornholm, was declared a danekrse (Bonde 1993).

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