Dulai Alfréd: A Bakony természettudományi kutatásának eredményei 26. - A Dunántúli-középhegység hettangi és kora-szinemuri (kora-jura) brachiopoda faunája I. Diverzitás, rétegtani elterjedés, paleoökológia, paleobiogeográfia, faunafejlődés (Zirc, 2002)

Summary

marine horst. The ratio of the brachiopod orders at the different Hungarian localities suggests that Early Jurassic basins in the Bakony Mts were deeper than those in the Gerecse Mts. The presence of characteristic Sinemurian taxa (VÖRÖS, 1980, 1984a) refers to the Mediterranean fauna province both in the Bakony and Gerecse Mountains. Some genera appearing already in the Hettangian at some localities (Caicirhynchia, Liospiriferina, Zeilleria, Cuneirhynchia) are present at all localities in the Early Sinemurian. Some brachiopod genera show local distribution: for example, Rhynchonellina and Securina occur only at Lókút Hill and Som Hill, the two sides of Hajag-Papod horst. On the basis of the earlier papers, the three significant brachiopod orders (rhynchonellids, spiriferinids, terebratulids) show very similar changes in the Early Jurassic: after a gradual increase from the Hettangian to the Pliensbachian, the maximum diversity was reached in the Pliensbachian, followed by a drastic decrease in the Early Toarcian, related to the Toarcian anoxic event. However, in the light of the newly-investigated material from the Transdanubian Central Range, the diversity of the brachiopod fauna did not increased as evenly and gradually from the Hettangian to the Pliensbachian as was previously thought. A relatively diverse fauna (9 genera) had already appeared in the Hettangian and a very diverse brachiopod fauna (22 genera) occurred in the Early Sinemurian Bucklandi Zone. There are no new genera in the Semicostatum and Obtusum Zones and only a few new taxa appeared during the Late Sinemurian (e. g. Lokutella, Papodina). Early Sinemurian diversity is nearly as high as in the Late Sinemurian. Complementing the Sinemurian faunal list with the new results, 100 brachiopod species are now known from the Sinemurian of the Transdanubian Central Range. Study of the Pliensbachian brachiopods, documenting 101 species is more or less complete, while important Late Sinemurian faunas will be examined in the near future, so the number of Sinemurian species will probably increase. It means that the maximum diversity of the Early Jurassic brachiopod fauna was probably reached by the Sinemurian and not in the Pliensbachian. On the basis of the transverse serial sections, the first Elvis taxon was found in the Hungarian paleontological record (Lobothyris ? subgregaria). The outer morphological features of this Early Jurassic species are very similar to those of the Late Triassic Rhaetina gregaria, but the inner morphological features are quite different.