Unusual brachiopod fauna from the Middle Triassic algal meadows of Mt. Svilaja (Outer Dinarides, Croatia)

Abstract

AbstractLadinian deposits at Mt. Svilaja in Dalmatia (Outer Dinarides, Croatia) yielded an abundant brachiopod fauna of low diversity interpreted as a parautochthonous assemblage representing an ecosystem of dasycladacean submarine meadow. The fauna consists of four named species and one left in open nomenclature. The most common is the spiriferinideFlabellocyrtia flabellulumChorowicz and Termier, 1975 (Spiriferinida) accounting for more than 70% of the material. The athyridideCassianospira humboldtii(von Klipstein, 1845) is the only species known from elsewhere (Anisian of Southern Alps). The new species of SpiriferinidaThecocyrtella dagysiiHalamski, Bitner, Kaim, Kolar-Jurkovšek, and Jurkovšek n. sp. differs from other representatives of the genus in having a deep ventral sulcus.Albasphe albertimagniHalamski, Bitner, Kaim, Kolar-Jurkovšek, and Jurkovšek n. gen. n. sp. is a new brachiopod that possesses a dorsal septum with an intra-septal cavity and dorsal submarginal ridges, both features in common with AalenianZellaniaMoore, 1855 from which it differs in lack of the ventral septum and of ventral submarginal ridges. They are interpreted as members of a sparsely recorded paedomorphic evolutionary line of terebratulides with secondarily lost loop, described formally herein as Gwyniidina Halamski and Bitner n. subordo and subdivided into newly emended Dispheniidae Grant, 1988 (Dispheniinae Grant, 1988 with the only genusDispheniaand Albasphinae Halamski and Bitner n. subfam. withAlbaspheandZellania) and Gwyniidae MacKinnon, 2006 (including RecentGwyniaandSimpliciforma). In contrast to previous interpretations, the trocholophe lophophore ofGwyniais interpreted herein as secondarily simplified.