Thylacodes contendis, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 107-108

Thylacodes contendis n. sp.

Figs 27 F–J

2014 Serpulorbis sp. Hansen & Surlyk: 339, fig. 6: 1, tab. 3.

Diagnosis. Young shell regularly curled with coarse transverse ribbing on concave flanks and equally coarse spiral ribbing on abapical side. Transition between the two sides sharp.

Derivation of name. Refers to the contrasting sculpture of spiral ribs and transverse ribs on coiled shell.

Type material. Holotype MGUH 33187 is an external and internal mould of a coiled juvenile shell . Paratype MGUH 33188 is an external mould of a coiled juvenile shell attached to a cephalopod and found at Skeldervig . Paratype MGUH 33189 is from just south of Højerup Church , while paratype MGUH 33190 is from Rødvig , Stevns. All three paratypes belong to the same horizon as the holotype .

Additional material. ØSM.10042-199-c , ØSM.10042-244-c, and 29 informally catalogued specimens with sample numbers SH.2.A, SH.41, SH.42, SR.778, SR.779, SR.780, SR.783.B, SR.787.D, SR.914, SR.916.A, SR.926. B, SR.934.A, SR.984, SR.987, SR.1017, SR.1054, SR.1055, SR.1056, SR.1057.A–B, SR.1058.A–B (2 specimens), SR.1060.A–B, SR.1076.A–B, SR.1110, SR.1111.A–B, SR.1119, SR.1121, SR.1127 (2 specimens). A last small specimen is found together with the holotype .

Type stratum and type locality. Lithified top of the upper Maastrichtian Højerup Member of the Tor Formation from just north of Holtug Quarry .

Occurrence. Lithified top of the Maastrichtian Tor Formation at Rødvig, Skeldervig, Højerup Church, Mandehoved and Holtug Quarry, Stevns.

Description. Young shell regularly coiled, very low with flattened spire attached to hard substrate (cheilostome bryozoans); whorl strongly widening adapically on peripheral side, increasing attachment surface; lateral flank slightly concave, changing to moderately convex on abapical side. Aperture obliquely oval. At least third whorl carrying pronounced, fairly coarse spiral ribs on abapical side, abruptly changing to equally strong and evenly distributed, forwardly inclined oblique transverse ribs. Shell wall moderately thin, strongly thickening peripherally on apical side. Mature shell irregularly coiled; abapical surface covered by more or less unevenly distributed, fairly coarse spiral ribs and fine growth lines; sides covered by pronounced and fairly regular growth increments or ribs and weak to nearly effaced spiral ribs. Spiral ribs may be substituted by relatively fine and short transverse ribs.

Measurements. Coiled young shell, paratype MGUH 33189, 1.1 mm high and 2.8 mm wide with an aperture width of 1.0 mm.

Remarks. The uncoiled teleoconch resembles somewhat Vermetus sp. described above from the succeeding Rødvig Formation, but differs in the pronounced division between spiral ribbing in the abapical side and transverse ribbing or growth increments on the lateral sides and in the coarser transverse ribs. The general outline of the present species resembles some specimens of the recent Thylacodes adamsii ( Mørch, 1859) except for the strong transverse ribs.

To the knowledge of the author this is the oldest described possible representative of this genus, which previously has been reported from the mid to late Danian de Vigny deposits in France ( Pacaud et al. 2000).

Figures

FIGURE 27. A–B. Melanella? sp., Silicone cast of MGUH 33183. Width 1.4 mm. C–E. Vermetus sp., C. Silicone cast of attached tube MGUH 33184. Largest diameter 6.6 mm. D. Inner mould of protoconch and initial teleoconch inside bryozoan ball. MGUH 33185. Protoconch 0.5 mm wide. E. Silicone cast of MGUH 33186. Width 3.5 mm. F–J. Thylacodes contendis n. sp. F. Attached holotype mould MGUH 33187. Width 2.4 mm. G–H. Silicone cast of paratype MGUH 33188. Width 2.9 mm. I. Silicone cast of paratype MGUH 33189. Width 3.0 mm. J. Silicone cast of free whorl paratype MGUH 33190. Tube diameter 1.8 mm. K–M. Thylacodes? sp., Silicone cast of MGUH 33191. Width 2.4 mm. N. Dendropoma sp., Protoconch and initial teleoconch tube of MGUH 33192. Width 1.7 mm. O. Laxispira sp., Silicone cast of MGUH 33193. Width 3.6 mm. P–R. Epetrium s.l. skeldervigensis n. sp. P. Silicone cast of holotype MGUH 33194. Width 2.4 mm. Q. Silicone cast of paratype MGUH 33195. Width 4.0 mm. R. Silicone cast of paratype MGUH 33196. Width 3.6 mm. S. Triphoridae genus et sp. indet. Sinistrally coiled protoconch MGUH 33197. Width 0.7 mm. T–W. Cerithiopsis restemlongis n. sp. T. Silicone cast of holotype MGUH 33198. Width 1.0 mm. U. Silicone cast of paratype MGUH 33199. Width 1.5 mm. V. Silicone cast of paratype protoconch MGUH 33200. Width 0.5 mm. W. Silicone cast of paratype protoconch MGUH 33201. Width 0.6 mm and height 1.1 mm. X. Cerithiopsis? sp., Silicone cast of MGUH 33202. Width 0.6 mm. Y–AE. Thereitis carlsbergi n. sp. Y–Z. Silicone cast of holotype specimen MGUH 33203. Width of protoconch 0.6 mm and teleoconch 1.4 mm. AE. Silicone cast of paratype MGUH 33204. Width 0.7 mm.