New Pliensbachian rhynchonellide (Brachiopoda) from Livari, (Rumija Mountain, Montenegro): the taxonomic implications of microstructure to disentangle cases of homeomorphism

ABSTRACT

An interesting case of close external similarity (homoeomorphy) is revealed by the study of an Early Jurassic rhynchonellide brachiopod from Livari, Rumija Mountain, southern Montenegro. Shell microstructure was used as the primary diagnostic tool, applied before serial sectioning to study internal characters. Sepkoskirhynchia sphaerica gen. et sp. nov. is erected based on the presence of coarse fibrous shell microstructure and hamiform crura. Because of these primary diagnostic characters, the new genus is placed in the rhynchonellide family Basiliolidae. The shell microstructure of the new taxon is characterised by a differentiated secondary layer of coarse fibrous type. The fibres are rhombic or subquadrate in cross-section, in the external sublayer they are 55–60 μm wide and 40–50 μm thick, internally other sublayers are thinner with fibres 35–40 μm wide and 20–25 μm thick. The main character that distinguishes the new genus is that the secondary layer is differentiated into several sublayers, while in externally homoeomorphic Soaresirhynchia it is built of a single layer. The new taxon was found in the brachiopod and crinoidal limestones from the periplatform facies of the Dinaric Carbonate Platform.

KEYWORDS:

• Brachiopods
• Jurassic
• Sepkoskirhynchia
• Soaresirhynchia
• shell microstructure
• Dinaric Carbonate Platform

Acknowledgments

The author is thankful to the Editor-in-Chief Gareth Dyke and reviewers José F. Baeza-Carratalá (University of Alicante), Fernando García Joral (Complutense University, Madrid), Alfred Dulai (Hungarian Natural History Museum), and anonymous reviewer for their useful comments and remarks that helped to improve the manuscript. Heartfelt gratitude to Michael R. Sandy (University of Dayton) for his constructive remarks and English language improvements. Many thanks to Rajka Radoičić (Belgrade) for discussions on the geology of the area and Vladan Radulović (University of Belgrade) for sharing his palaeontological expertise on brachiopod microstructure and for donating the specimens from Livari. The author is very grateful to Diego A. García-Ramos (University of Ferrara) for donating specimens from Sierra Espuña (Spain). BVR gratefully acknowledges the award of a Paleontological Society Sepkoski Grant.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

BVR was supported by a Sepkoski Grant from the Paleontological Society International Research Program (PalSIRP).