Szabó János szerk.: Fragmenta Mineralogica Et Palaentologica 24-25. 2007. (Budapest, 2007)

VÖRÖS &DULA] Discussion The species number data have been counted by stages and sub-stages. The numbers are plotted in diagrams (Figure 5 and 6) in order to show the temporal changes in species diversity of the Jurassic brachiopod fauna of the Transdanubian Range. The cumulative species diversity diagram of Jurassic brachiopods from the TR is shown in Figure 5. After the end-Triassic extinction, the rapid recovery culminated in the late Sinemurian; this was followed by a slower but steady decrease until the end of the Pliensbachian, and only one species {Unguithyris aspasia) survived to the Early Toarcian. This part of the diagram, updated on the basis of recent findings and results, differs from the figure published by VÖRÖS (1993), where (using the data available at that time) the Sinemurian diversity

7 values were rather low. The Toarcian and Aalenian are almost devoid of brachiopods, whereas a secondary diversity maximum is observed in the Bajocian. After another almost barren interval (Bathonian to Kimmeridgian) the Tithonian is again rich in brachiopods. In Figure 6 the four orders of Rhynchonelliformea (i. e. Articulata in older classification) and the two suborders of Terebratulida are shown in separate columns. They had different histories during the Jurassic, especially in the Early Jurassic. Stages/Ages Brachiopod species Tithonian Kimmeridgian T Oxfordian Callovian Bathonian Bajocian [ Bajocian r Aalenian Toarcian 1 Pliensbachian Pliensbachian Sinemurian Sinemurian Hettangian 40 spcies Figure 5 — Temporal changes in the species diversity of the whole brachiopod fauna in the Jurassic of the Transdanubian Range. Rhynchonellids show a rapid diversification in the earliest Jurassic, culminating in the Late Sinemurian, then a gradual decrease until the end of the Pliensbachian and a sudden disappearance in the Toarcian. They are almost absent in the higher part of the Jurassic, except for a major and a minor reappearance in the Bajocian and in the Tithonian, respectively. The order Spiriferinida experienced its last, modest flourishing period in the Early Jurassic. After the endTriassic crisis, the Spiriferinida showed a rapid recovery and reached their maximum diversity in the Early Sinemurian in the TR. After a gradual decrease, they disappeared in the earliest Toarcian, which almost coincides with the time of the global extinction of the order (ACER 1987, ALMÉRAS & FAURE 1990). The Athyridida are represented by the Koninckinidae in the Early Jurassic. They appeared in the Late Sinemurian in the TR and their diversity increased until the end of the Pliensbachian. This change parallels the general trend recognized for the whole order (VÖRÖS 2002), with the difference that the sudden expansion and diversity

7 peak recorded in the earliest Toarcian in Europe is not documented in the TR. The diversity changes of the order Terebratulida follows roughly the same pattern as that of the Rhynchonellida during the Jurassic in the TR, though its diversity maximum in the Early Jurassic (Late Sinemurian/Early Pliensbachian) is not so pronounced. Within the order, the long-looped terebratulids (Terebratellidina; essentially the zeilleriids) mirror almost perfectly the diversity

7 decline of the rhynchonellids, whereas the short-looped terebratulids (Terebratulidina) seem to keep up more successfully. They remain diverse still in the Late Pliensbachian, persist to the Early Toarcian, and regain rather high diversity repeatedly in the Bajocian and the Tithonian. The gradual diversification of brachiopods in the Early Jurassic is a world-wide phenomenon. Details of this post-extinction recovery

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, as recorded in the TR, were analysed and interpreted by DULAI (2001). The global trend is enhanced by local factors in the TR. Here the fragmentation of the Late Triassic carbonate platform started in the Early Jurassic and the tectonic disintegration resulted in an intricate pattern of submarine horsts and intervening basins (GALÁCZ 1988, VÖRÖS & GALÁCZ 1998). The submarine topographic highs were surrounded by aprons of redeposited material (scarp breccias, brachiopod coquinas, crinoidal calcarenites, etc.: VÖRÖS 1991). The diversity

7 peaks of the brachiopod faunas (in the Early Jurassic, and even more markedly in the Bajocian and Tithonian) coincide with episodes of local tectonic movements along fault scarps bordering the submarine horsts. These might have produced new, barren rock surfaces and talus blocks at the foot of the escarpments, which provided favourable environments and diverse niches for brachiopods (VÖRÖS 1995). The Early Toarcian anoxic event terminated the Early Jurassic flourishing