Austrotindaria? canalensis ( Catullo, 1846 )

Foster, William J., Danise, Silvia & Twitchett, Richard J., 2017, A silicified Early Triassic marine assemblage from Svalbard, Journal of Systematic Palaeontology 15 (10), pp. 851-877 : 861

Austrotindaria? canalensis ( Catullo, 1846)

( Fig. 2B )

1846 Tellina canalensis Catullo : 56, pl. 4, fig. 4.

1899 Anodontophora (Myacites) canalensis (Catullo) ; Bittner: 23, pl. 3, figs 34–38.

1908 Anoplophoria canalensis (Catullo) ; von Wittenburg: 281, pl. 5, fig. 6.

1963 Unionites canalensis (Catullo) ; Ciriacks: 81, pl. 16, figs 11, 12.

1988 Unionites canalensis (Catullo) ; Neri & Posenato: 94, pl. 2, fig. 8.

2004 Unionites aff. canalensis (Catullo) ; Kashiyama & Oji: 214, fig. 8F.

2009 Unionites canalensis (Catullo) ; Kumagae & Nakazawa: 166, fig. 145, 1–4.

2015 Unionites canalensis (Catullo) ; Hofmann et al.: 481, fig. 4J.

2015 cf. Unionites canalensis (Catullo) ; Foster et al.: 381, fig. 4K.

Material. Three specimens from LD-05 ( NHMUK PI MB 1198 ; NHMUK PE PEI 5493; NHMUK PE PEI 5500) .

Description. Outline subovate to elongate, equivalve, inflated below the umbo; inequilateral with beak lying approximately 62% along the dorsal margin length from posterior; H/L ratio 0.4–0.7. Posterior margin elongated and almost straight, anterior margin narrowly rounded. Escutcheon and lunule indistinct. Umbo orthogyrate, prominent, moderately broad, rounded, projecting above the hinge margin. Ornamented externally with fine concentric growth lines; entire inner margin smooth.

Remarks. The internal characters and hinge in these specimens were not observed and have not been reported for Unionites canalensis . Externally, the shell is virtually identical to those that are typically assigned to U. canalensis (e.g. Hofmann et al. 2015), with a medially placed umbo that is a diagnostic feature of U. canalensis ( Catullo, 1846) and an orthogyrate beak. In contrast, all other species of Unionites have a more anteriorly located umbo, and the beak in Unionites is prosogyrate ( Geyer et al. 2005). Thus, these Early Triassic specimens clearly do not belong to the genus Unionites . The external features of these specimens are most similar to species of Neilonellidae , such as Austrotindaria benthicola ( Dell, 1956) . Austrotindaria is the only genus of the Neilonellidae that is reported from the Early Triassic, and these specimens are, therefore, tentatively assigned to it. Without observation of the internal characters, an unequivocal generic assignment cannot be made. The posterior margin is more elongate than in Austrotindaria svalbardensis sp. nov., and these specimens are therefore considered to represent a separate species.

Mode of life. Shallow infaunal, fully motile, slow, miner (Stanley 1968).

Figures

Figure 2. A, Orbiculoidea winsnesi Gobbet, 1963, NHMUK PI BE 3238, dorsal view, dorsal valve; B, Austrotindaria? canalensis (Catullo, 1846), NHMUK PI MB 1198, external view, left valve; C–G, Promyalina schamarae (Bittner, 1899), external view; C, D, NHMUK PI MB 1204; C, right valve; D, left valve. E, F, NHMUK PI MB 1203; E, right valve; F, left valve. G, NHMUK PI MB 1202, right valve. Scale bars: A, B, G = 2 mm, C–F = 1 mm.