Praebythoceratina deltalata Antonietto & Carmo & Viviers & Neto & Hunt 2016, sp. nov.

Praebythoceratina deltalata sp. nov.

urn:lsid:zoobank.org:act: AEA6A7C1-F7C3-4BCF-B8CB-3CED348DC62F

Fig. 6 G–J

Monoceratina sp. A –? Donze 1964: 148, fig. 7.145.

Diagnosis

A species of Praebythoceratina distinguished by the combination of the following features: ornamentation consisting of irregularly shaped reticulations at the postero-central and ventro-posterior areas, a tubercle in the dorso-central area and an irregularly reticulate spine in the ventro-central area. In dorsal view, the spine presents a widened basis, forming a triangle-shaped ala running from the postero-ventral to the antero-ventral areas.

Etymology

From the Greek delta, meaning “d”, and the Latin alata, meaning “with a wing”. Praebythoceratina deltalata sp. nov. presents a spine in its ventro-posterior region that is shaped like a triangular ala (hence delta, as the letter “d” in the Greek alphabet resembles a triangle).

Type Material

Holotype

CP-683 (right valve), stored dry in a micropaleontological slide.

Paratypes

CP-684 (left valve), CP-758 (right valve) and CP-759 (left valve), stored as the holotype.

Other materials examined

BRAZIL: São José 1 outcrop, Riachuelo Municipality, Sergipe State (samples MP-1551, MP-1552, MP-1554, MP-1558, MP-1559, MP-1561, MP-1564, MP-1565, MP-1567, MP-1568 and MP-1570 to MP-1576), approximate coordinates 10°44' S, 37°13' W.

Type locality and stratum

Sample MP-1680, São José 1 outcrop, Riachuelo Municipality, Sergipe-Alagoas Basin, Sergipe State, Brazil, approximate coordinates: 10°44' S, 37°13' W; Riachuelo Formation, Aracajuia benderi zone (MSA-0), Sergipella viviersae subzone (MSA-0.2), uppermost Aptian–lower Albian.

Measurements

Holotype (CP-683): right valve: length = 0.56 mm, height = 0.29 mm.

Paratype (CP-684): left valve: length = 0.53 mm, height = 0.29 mm.

Paratype (CP-758): right valve: length = 0.47 mm.

Paratype (CP-759): left valve: length = 0.45 mm, height = 0.23 mm.

Description

In lateral view, medium-sized subtriangular to sub-rectangular carapace, with greatest height at posterocentral and greatest length at centro-dorsal regions. Round anterior end, becoming slightly rectilinear close to dorsal margin, where an obtuse cardinal angle is formed. Sharp, supra-curvate posterior end, forming dorsal caudal process. Rectilinear dorsal margin, becoming concave only at centro-posterior region. Regularly straight ventral margin, with slight concavity at oral region. Primary ornamentation consisting of tubercle in dorso-central area, irregularly reticulate spine in ventro-central area and highly inconspicuous, large and low marginal rib running from dorso-posterior to antero-ventral margins. Very shallow S 1 and S 2 sulci. Secondary ornamentation includes irregularly shaped reticulations at posterocentral and ventro-posterior areas. Weakly developed rounded eye tubercle. In dorsal view, strongly sagitiform; spine presents a widened basis, forming wide triangle-shaped ala running from posteroventral to antero-ventral areas. Presence of dorsal ridge creates a flat surface adjacent to hinge line. In internal view, adont hinge, composed in right valve by sulcus running along most of dorsal margin. Weakly developed inner lamella, observable along anterior end and ventral region of posterior end; not visible in oral region, where valve margin bends inwards expressively.

Remarks

Subfamiliar and tribal identifications follow Gründel & Kozur (1971), while the generic is based on Becker (1990). Occurrences herein described correspond to the first early Cretaceous records of Praebythoceratina Gründel & Kozur, 1972, hitherto restricted to the Triassic–Jurassic. Most specimens of Praebythoceratina deltalata sp. nov. were found broken, thereby limiting the designation of type specimens. This species is very similar in general layout to Bythoceratina umbonatoides (Kaye, 1964), B. umbonata (Williamson, 1847) and Monoceratina longispina (Bosquet, 1854) from the Albian– Cenomanian of England (Kaye 1964, 1965; Weaver 1982). However, they differ in the position of the dorsal tubercle (postero-dorsal in the former, antero-dorsal in the latter) and in the carina-like morphology of the spine basis in P. deltalata sp. nov. (absent in B. umbonatoides). Several species, including P. amsittenensis (Andreu-Boussut, 1991) comb. nov. from the Albian of Morocco (Andreu-Boussut 1991), B. tamarae Rosenfeld, 1974 and B. avnonensis Rosenfeld, 1974 from the upper Cenomanian of Israel (Rosenfeld & Raab 1974), are distinguished from P. deltalata sp. nov. by the same features. Donze (1964) illustrated Monoceratina sp. A from the Berriasian of France in dorsal view, which is strongly similar. However, there is not enough information to perform length/height/width measurements of these specimens, and therefore they cannot safely be assumed to belong to P. deltalata sp. nov.

Paleoecology and distribution

Praebythoceratina deltalata sp. nov. is a marine, shelf species occurring in the Angico and Taquari Members, Riachuelo Formation, Sergipe-Alagoas Basin, Brazil, uppermost Aptian–lower Albian, Aracajuia benderi zone (MSA-0), Sergipella viviersae subzone (MSA-0.2).