Tibetothyris johnstoni MACFARLAN 2023, new species
Creators: name: MACFARLAN, DONALD ALEXANDER BANKIER
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Brachiopoda
Rhynchonellata
Terebratulida
Dielasmatidae
Tibetothyris
Tibetothyris johnstoni

description: Tibetothyris johnstoni new species
Fig. 5: 1–8. Fig. 6 A–B.
Holotype. BR 3420 a double-valved internal mould from N28/f7454, GS 196, Eighty-Eight valley Nelson; collected A. McKay 19/3/1898.
Derivation of name. This species is named for Dr Mike Johnston, geologist, of Nelson.
Material. The data series consists of thirteen specimens, eleven of which yielded valid measurements.
New Caledonia. île Hugon NC/f109a (AU 7165).
Nelson. Eighty-Eight Valley N28/f7454 (GS 196), Ram Creek; N28/f0045 (PGS 40).
Southland. Taringatura Hills E45/f6635 (JDC 241).
Description. Small to medium sized terebratulide with rounded-pentagonal outline. The dorsal valve is moderately convex posteriorly and has a distinct shallow, rounded sulcus anteriorly.
The ventral valve is strongly convex posteriorly, with two close-spaced rounded plicae which diverge behind the beak, separated by a shallow rounded central sulcus. The flanks are broad and slightly concave. The anterior part has a high fold and a narrow, shallowly concave central part. The anterior commissure is strongly sulcate. The shell surface is smooth apart from a few strong, stepped concentrics.
The beak is large and triangular with a bluntly rounded tip. The foramen is large, circular, and mesothyrid, with a short pedicle collar (Fig. 5.1d, 6A). The beak ridges are strong and bluntly rounded. The deltidial plates are small and widely disjunct (Fig. 5.1a, 6A). The dental plates are short, divergent and widely separated. (Fig. 5.2a, 5.7a, b).
The dorsal valve has a hingeplate with a deep U-shaped septalium (Fig, 5.1a, 6A, B), a broad, shallow median septum with longitudinal grooves which appear to be muscle attachments (Fig. 5.1a, 5.2a). A small, high, striated cardinal process is present, and is close to the anterior of the foramen (Fig. 5.2a, 6B).
The shell is coarsely and densely punctate.
Dimensions. Dimensions of the holotype and representative specimens, and statistics for all measurable specimens are shown in Table 1. A length vs width graph is shown in Fig. 9A.
Range and Distribution. Otapirian, early Otapirian in New Caledonia and Southland, late Otapirian in Nelson. Of the 13 specimens measured, nine come from one early Otapirian locality (E45/f6635 (JDC 241) in the South Taringatura Hills, western Southland.
Remarks. This species is close to Tibetothyris depressa in shape, but the folding differs. T. depressa has strong rounded lateral folds and two weak central folds on the dorsal valve, and a weak central fold on the ventral fold. The anterior commissure is sulciplicate to bisulcate (Jin et al. 1976, Jin et al. 2006, Sun et al. 2017). T. johnstoni is more strongly folded. The dorsal valve has similar strong rounded lateral folds and a central sulcus. The ventral valve is strongly convex with two low, incipient or poorly developed rounded folds anteriorly. The anterior commissure is unisulcate. T. depressa has long dental plates whereas in T. johnstoni the dental plates are short and widely separated.
description: Published as part of MACFARLAN, DONALD ALEXANDER BANKIER, 2023, Otapirian (Rhaetian) Terebratulida (Brachiopoda) of Zealandia, pp. 1-34 in Zootaxa 5374 (1) on pages 7-9, DOI: 10.11646/zootaxa.5374.1.1, http://zenodo.org/record/10148159