Loop ontogeny of the Late Triassic (Norian) terebratulid brachiopodPseudorhaetina antimoniensisSandy from Sonora, Mexico and its taxonomic significance

Abstract

Juvenile specimens of the short-looped terebratulid brachiopod genusPseudorhaetinaSandy have been investigated by the use of transverse serial sections. Internal structures indicate a simple brachidium (loop) is present with long flanges in adult specimens; the brachidium is approximately half the length of the dorsal valve; there is no complex loop metamorphosis in the central cavity of the brachiopod (i.e., no median septum). This combination of characters presents a taxonomic problem—Pseudorhaetinacan neither be referred with confidence to superfamily Terebratuloidea, nor superfamily Loboidothyridoidea. ConsequentlyPseudorhaetinais, for the time being, assigned to a new and as yet unnamed superfamily representing a previously unrecognized part of the post-Paleozoic recovery and reradiation of Mesozoic articulate brachiopods (Rhynchonellata of Williams et al., 1996).