Leptomaria niloticiformis ( Schlotheim, 1820 )

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 65-66

Leptomaria niloticiformis ( Schlotheim, 1820)

Figs 20 N–P

1820 Trochilites niloticiformis Schlotheim : 156–157.

1902 Pleurotomaria niloticiformis v. Schlotheim sp. [partim]—Ravn: 215 (not Pl. 1, figs 3 and 4).

1903 Pleurotomaria niloticiformis v. Schlotheim sp. [partim]—Ravn: 380 (other species included).

1933 Pleurotomaria niloticiformis (Schlotheim) —Ravn: 25, Pl. 1, fig. 10.

2014 Leptomaria niloticiformis (von Schlotheim 1829) —Lauridsen & Schnetler: 36–37, fig. 3A–D.

Diagnosis. Very large, relatively high-spired Leptomaria with nearly straight sides dominated by fairly smooth spiral ribs on later whorls. Umbilicus wide (20–25 % of whorl diameter) on internal moulds. Selenizone located approximately 1/3 of the distance between the whorl sutures from the adapical suture (emended from Pacaud (2004) and Schlotheim (1820)).

Material. A large specimen MGUH 33095 from the Korsnaeb Mb. infilling at the base of the Cerithium Limestone Mb. at Højerup, and a smaller specimen, ØSM.10042-73 from a Thalassinoides burrow in the Cerithium Limestone at Rødvig. A further specimen with a diameter of 89.5 mm and a height of more than 68 mm has been examined from the private collection of Claus Heinberg. That one came from the Thalassinoides burrows cutting through the Cerithium Limestone Member.

Type stratum and type locality. Middle Danian Coral Limestone from Faxe Quarry, Denmark .

Occurrence. This species occurs in the lower Danian Cerithium Limestone Member of the Rødvig Fm. at Stevns Klint, where the shells are found in Thalassinoides burrows containing material from the succeeding Stevns Klint Formation. The specimens, however, belong to a now eroded upper layer of the Cerithium Limestone Member as evidenced by their internal moulds consisting of Cerithium Limestone (pers. comm. Claus Heinberg Clausen, Roskilde University, Denmark). It is furthermore reported from the middle Danian Faxe Formation and upper Stevns Klint Formation at Faxe, Denmark ( Pacaud 2004; Ravn 1902).

Description of Cerithium Limestone material. Shell cyrtoconoid with a spire angle of between 70 and 80˚; umbilicus narrow or completely closed, but taking up between 20 and 25 % of total width on internal moulds; whorls with moderately distinct shoulder, resulting in a somewhat stepped shell outline. Whorl surface adapically and abapically of shoulder nearly straight to weakly convex, but may become slightly concave. Shell periphery with moderately pronounced, sharply rounded keel. Abaxial part of whorl fairly weakly convex. Selenizone narrow, taking up approximately 7 % of whorl height measured from suture to suture; selenizone generally indistinct, located immediately above shoulder about 1/3 of distance between keel and adapical suture from adapical suture. Selenizone replaced by open slit around 2/3 of a whorl from aperture. Aperture wide, subtriangular with flattened outer wall. Teleoconch sculpture above keel consisting of 10 weak spiral threads abapically of selenizone. Adapical part of whorl with about four weak spiral threads on adapical half and a more or less smooth abapical half adjoining selenizone. Growth lines very weak, mainly seen on shell base, but may produce a slightly grainy sculpture on the very early whorls.

Measurements. The most complete specimen examined from the Cerithium Limestone Member has a diameter of 89.5 mm and a height in excess of 68 mm (apex missing), but specimens of more than 10 cm in height are known from the middle Danien coral limestone of the type locality.

Remarks. This species seem first to have moved out into the Danish Basin shortly before the marked sea level drop, which terminated the muddy Cerithium Limestone environment, and has thus not been found in situ in the Cerithium Limestone but only as redeposited shells in Thalassinoides burrows reaching down from the top of the formation. The material from the Cerithium Limestone Member may deviate slightly from the typical form from the middle Danian limestone at Faxe Quarry, Denmark, by a slightly more high-spired shape (spire angle below 80˚) and perhaps relatively finer spiral threads.

Leptomaria niloticiformis ( Schlotheim, 1820) is readily distinguished from L. meyeri Pacaud described below by the largely smooth spiral sculpture, the nearly straight whorl sides with only a weak shoulder and no pronounced concavity adapically of the selenizone, and by the location of the selenizone.

Figures

FIGURE 20. A–B. Palaeoloxotoma sp., inner mould of MGUH 33087. Length 17.2 mm. C–I. Anatoma sp. A. C–E. Silicone casts of MGUH 33088. Width 1.3 mm. F–G. Silicone cast of MGUH 33089. Width 1.9 mm. H. Silicone cast of MGUH 33090. Preserved width 1.35 mm. I. Silicone cast of MGUH 33091. Preserved width 1.35 mm. J. Anatoma? sp. B, Silicone cast of MGUH 33092. Preserved width 1.05 mm. K–M. Temnotropis stevniensis n. sp. K–L. Silicone cast of holotype MGUH 33093. Width 3.5 mm. M. Umbilical view of paratype MGUH 33094. Width 2.1 mm. N–P. Leptomaria niloticiformis Schlotheim, 1820. N–O. Inner mould of MGUH 33095. Width 44 mm. P. Silicone cast of MGUH 33096. Middle Danian Coral Limestone from Faxe, Denmark. Height nearly 11 cm. Q. Leptomaria meyeri Pacaud, 2004. Silicone cast of MGUH 33097. Cast 14.5 mm wide, 12.5 mm high.