Anahoplites sp.

cf. Anahoplites sp.

MATERIAL. — A single specimen preserved as a pyritic uncrushed internal mould corresponding to a juvenile phragmocone. Despite pyrite is oxidized, suture line and overall shape are well preserved. Material deposited in the collections of the Museo de Ciencias Naturales de Álava ( MCNA) with the repository number MCNA-17429. PALEOBIOGEOGRAPHY. — The Anahoplitinae and Hoplitinae Douvillé, 1890 ammonites were restricted to the shallow epicontinental Albian seas of northern Europe during the (e.g., Owen et al. 2010) and characterized the European faunal province. The local occurrences of the European province anahoplitines in the study area suggests their incursion from colder areas and the opening of the seaway connections during the late middle Albian, in a basin typically Tethyan as indicated by its common ammonoid associations (e. g., Agirrezabala & López-Horgue 2017).

OCCURRENCE. — Top middle Albian of Mazo Chico lutites. Valle de Soba, Cantabria, North Spain. Anahoplites occurs in the middle Albian and lower upper Albian of England and Transcaspia. In Russia, Neanahoplites occurs in the middle to upper Albian transitional rossicus Zone (= upper Euhoplites lautus Subzone and Dipoloceras cristatum Zone ).

DESCRIPTION

Oxycone shape. Involute, with outer whorl covering more than a half of flank but coiling loss involution towards the last whorl preserved. Broad and slightly convex flanks are convergent towards venter. Whorl section is compressed, and umbilical wall steep. Umbilicus equals 16% of 18.0 mm diameter. Apparently smooth flanks. Narrow venter looks channeled due to loosing of the siphuncle, which is partially preserved only. Suture with shallowly bifid External lobe and narrower bifid lateral lobe.

DISCUSSION

The lack of preserved ornamentation such as tubercles or ribs may be due to weathering of juvenile delicate structures. However, the well-preserved suture line is indicative of only slight surficial dissolution. Accordingly, the specimen is suggested to be a non- or only slightly ornamented juvenile ( Fig. S1 View FIG ).

The general shape of the specimen, being involute, with broad convergent flanks, high whorls (Wh/Ww = 1.86) and narrow venter are features shared by the genera Anahoplites and Neanahoplites , which are only distinguishable in the middle to adult stages. Namely, Neanahoplites was erected by Cooper & Owen (2011) for the uppermost middle Albian Anahoplites with coarser and sparser ribbing (see Spath 1925, 1926; Owen et al. 2010). The suture line of the studied specimen is simpler than that of Anahoplites , being like Neanahoplites suture by the shallow incisions of the external and lateral lobes (Cooper & Owen 2011: fig. 4).

The specimen occurs in lutites above lower Albian carbonates and below upper Albian siliciclastics and megabreccias (García-Mondéjar & Fernández-Mendiola 1989; López-Horgue 2000; López-Horgue et al. 2009).

Cooper & Owen (2011) included Anahoplites in the subfamily Anahoplitinae and Neanahoplites in Semenoviceratinae, both family Placenticeratidae . Anahoplitinae is a group that arose in the middle Albian and became extinct at the close of the Albian. Neanahoplites occurs in the topmost middle Albian N. daviesi ( type species Anahoplites daviesi Spath, 1926 ) Subzone in Western Europe, and is derived from the longer ranging Anahoplites occurring from the base of the middle Albian to the lower upper Albian H. choffati Subzone ( sensu Owen 2012; see also López-Horgue & Owen 2024). Neanahoplites forms the basal stock of Semenoviceratinae, a group of oxycones with simpler suture line than their ancestor Anahoplites , that gave rise to Placenticeratinae in the upper upper Albian (Cooper & Owen 2011).

The juvenile stage of the specimen prevents more precise assignation. However, its stratigraphical occurrence and the suture simplicity points to a late middle Albian age.

DIMENSIONS ( IN MM)

D Wh Ww U

18.0 9.7 5.2 2.8

11.6 6.0 3.8 1.9

APPENDIX 2. — Figure S1 View FIG : Juvenile ammonoid from the lutites of Mazo Chico, cf. Anahoplites sp. , specimen MCNA 17429 (Museo de Ciencias Naturales de Álava): A, lateral view, SEM image; B, same view highlighting the best-preserved suture lines; C, lateral view of the specimen under natural light; D, ventral view under natural light;ventral groove is a preservational artifact whereas slightly elevated ventrolateral shoulders look original.Normal light photos:Mikel A. Lopez-Horgue/ SEM photos: P. A. Fernandez-Mendiola and Juan Pedro Rodríguez-López.