A new meristid brachiopod genus from the Lower Carboniferous of Guizhou, China

Abstract

The rowleyellinae is a small subfamily of meristelloid athyridid brachiopods, previously with only one genus,RowleyellaWeller, 1911 (Alvarez and Brunton, 1995; Alvarez et al., 1998; Alvarez and Rong, 2002). In this paper we report a new meristelloid athyridid brachiopod genusMuhuathyrisfrom a newly discovered, very diverse Tournaisian brachiopod fauna in South China. It is noteworthy that this newly discovered fauna is slightly older than that reported earlier from the same outcrop (Balinski, 1999). A full discussion of the newly discovered fauna is currently in preparation. Morphological features ofMuhuathyrisn. gen. suggest that it is probably an evolutionary intermediate betweenCamarophorellaHall and Clarke, 1893 andRowleyellaWeller, 1911. The new genus differs fromCamarophorellaandRowleyellaonly in the nature of the structures beneath the septalium in the dorsal valve. InCamarophorellaa shoe lifter is present in front of or beneath the septalium. InRowleyellaa cruralium rests on the dorsal median septum under the septalium and extends to the front of septalium. Lateral to the dorsal median septum, two thin and short plates, asymmetrically disposed, are present posteriorly under the cruralium, which were considered by Carter (1991) as a very posteriorly placed shoe lifter. In the new genus a structure consisting of two plates lateral to the dorsal median septum is attached to the dorsal surface of septalium near the crural bases. This structure extends from the dorsal beak to the posterior of the adductor muscle fields. It may be developed as two vertical plates lateral to the median septum, or, when the plates converge medially, as a sessile or median septum-supported cruraliumlike platform. The structure primarily acts as support to the crural bases and septalium rather than a dorsal adductor muscle platform, but may also serve as part of dorsal adductor muscle attachments in some individuals. It seems probable that this structure might be homologous to the cruralium inRowleyella.For this reason we put the new genus within the subfamily Rowleyellinae.