Szabó János szerk.: Fragmenta Mineralogica Et Palaentologica 21. 2003. (Budapest, 2003)

48 Du: is proportional to the increase of spiriferinids. Within terebratulids, long-looped forms are more frequent than short-looped (26% and 20%, respectively) at the Tölgyhát quarry. Short-looped terebratulids are much more frequent than the long-looped forms at Póckő (36% vs. 8%) but the outstanding number of only one species, Phymatothyris aff. cerasulum influences this ratio. At Kisgerecse, the proportion of the short-looped forms is nearly twice as high as the proportion of long-looped forms (22%) and 14%, respectively). The short-looped terebratulids predomi:,A. nate in Vöröshíd quarry (32%) where only a few longlooped forms were found (5%). These localities yielded very important information about the changes in composition of more or less contemporaneous faunas from the basin towards the horsts. This traverse section will be completed in the near future by the detailed examination of the brachiopods of the Hierlatz Limestone, representing the fauna of the submarine horsts. (However, the Hierlatz Limestone is probably younger, Late Sinemurian). Conclusion 1. The taxonomic composition of the Hettangian faunas of the Transdanubian Central Range clearly show that the niche replacement dated to the Triassic/Jurassic boundary by SANDY (1995a) happened only after the Hettangian. The Hungarian Lower Sinemurian localities generally show very similar taxonomic compositions to the Early Jurassic ratios drawn by SANDY (1995a), whereas the Hettangian assemblages have closer affinities to the Late Triassic faunas from similar environmental settings. Similar taxonomic compositions were also reported from the Hettangian in the literature. E.g.: GAETAN! (1970) described four brachiopod species (with exact specimen numbers) from the Upper Hettangian oolitic limestone of Bergamo. In the uppermost layers of the Calcare di Sedrina Formation, 44% of the brachiopods belong to Lobothyris. An assemblage of Lobothyris (L delta, L andieri, L basilica) was found in the Middle Hettangian Novy Svet Formation of the Krizna Nappe in the Western Carpathians; Lobothyris is the dominant element of the fauna (85%) in this calm, shallow subtidal environment (TOMASOVYCH & MICHALÍK 2000; TOMASOVYCH 2000). It is worth to mention that spiriferinids are absent at both localities (and very scarce in the Transdanubian Central Range, too). Why happened the changes after the Hettangian and not just after the end-Trias sic extinction? The evolutionary intra-phylum niche replacement probably can be attributed to the end-Trias sic mass extinctions but the local environmental factors may have also an effect on this event. E.g. the sedimentation of the large carbonate platform continued in the Bakony Mts during the Hettangian (Kardosrét Limestone) with the same or very similar environments. The first signs of the collapse of this platform can be seen in the Hettangian but the real disintegration of the carbonate platform was at an advanced stage only at the beginning of the Sinemurian. The variable new ecological niches lead to a very rapid diversification of the brachiopod fauna (DULAI 2001). It was probably the adequate time of intraphylum niche replacement for the brachiopods hidden in the refuges. Figure 7 — Proportion of the brachiopod orders at the Lower Sinemurian localities of the Gerecse Mts.