Ammotectonica, Harzhauser & Landau, 2023

Harzhauser, Mathias & Landau, Bernard, 2023, The Architectonicidae and Mathildidae (Gastropoda, Heterobranchia) of the Miocene Paratethys Sea-victims of the Miocene Climatic Transition, Zootaxa 5370 (1), pp. 1-74 : 8

Genus Ammotectonica nov. gen.

Type species. Ammotectonica gregorovae nov. sp.; Middle Miocene , Czech Republic .

Diagnosis. Medium-sized, moderately flattened lenticular shell with low conical spire, angled periphery with rounded keel and convex base. SSC and UPC beaded. Base lacking IPC and PUC, with short axial folds and blunt, tubercular UC ( Fig. 2 ).

Description. Medium-sized, not very solid, moderately flattened lenticular shell with low conical spire. Protoconch medium-sized, convex, <1 whorls visible. First teleoconch whorl flattish. SSC and UPC beaded. LPC faintly beaded to smooth. MCs reduced, mid-whorl with delicate, sometimes beaded spiral threads. LPC forming distinct angulation with convex keel. Base concave immediately adjacent to keel, distinctly convex below. IPC not developed. Basal field bearing fine spiral threads, with short axial folds strengthening towards umbilicus. Short secondary spiral cords may be intercalated between primary folds. No PUC developed. UC delimited from axial folds by weak or prominent groove. UC blunt, tubercular, overhanging umbilicus. Umbilicus wide to very wide (27–38% of MD). Umbilical wall bearing delicate, prosocline growth lines. Aperture small, subquadrate, angled at LPC with moderately deep CG and shallow PG.

Etymology. Referring to the ammonite-like appearance of the base.

Included species. Ammotectonica gregorovae nov. sp.; Solarium emiliae Semper, 1861 ; Solarium deshayesii Michelotti, 1847 ; Solarium soproniense Strausz, 1960 .

Stratigraphic and geographic range. Badenian (Middle Miocene): Central Paratethys Sea (hoc opus); Late Miocene to Pliocene: Mediterranean Sea (Sacco 1892; Chirli 2013).

Paleoenvironment. Middle to outer neritic environments ( Forli et al. 2002; hoc opus).

Discussion. Ammotectonica emiliae (= Solarium plicatulum De Cristofori & Jan, 1832 ) has been placed in Discotectonica Marwick, 1931 by Forli et al. (2002) and Chirli (2013). Discotectonica (type species Architectonica balcombensis Finlay, 1927 ; Miocene, Australia) was described in detail by Bieler (1985a: 241) stating “ shallowly conical to shield-shaped; whorls weakly convex, distinctly concave on both sides of keel […] prominent, sharp keel rib […] concave area near keel with 4-6 fine spiral ribs; ca. 10 spiral ribs broadening towards umbilicus on basal surface; around umbilicus 2-4 broad, mostly flattened beaded spiral ribs, innermost of which (crenae umbilici) widest and ± flat” [translated from German]. Thus, Discotectonica differs from Ammotectonica nov. gen. by the more prominent, slightly flaring keel, the less prominent UC and much more delicate axial folds on the basal field, and the distinctly less convex base, resulting in a much lower position of the keel. In addition, it lacks the spiral cords close to the umbilicus, which were emphasized by Bieler (1985a) as a characteristic feature of Discitectonica. The convexity of the base causes a stubby appearance of the whorls in basal view in Ammotectonica , whereas the base is flattish in Discotectonica .

Ammotectonica is reminiscent of Solatisonax Iredale, 1931 (type species Solatisonax injussa Iredale, 1931 ; present-day, Australia). Aside from the type species, Bieler (1985a, 1993) listed Solarium atkinsoni Smith, 1891 , S. kilburni Bieler, 1993 , S. supraradiata ( Martens, 1904) , Architectonica bannocki Melone & Taviani, 1980 and several other species in that genus. These species are like Ammotectonica in overall shape and spire sculpture, but Ammotectonica differs in the more prominent axial folds on the basal field and the blunt UC. Moreover, Solatisonax has a narrow cylindrical umbilicus, whereas the umbilicus is funnel shaped in Ammotectonica .

Figures

FIGURE 2. Whorl cross-sections of Architectonicidae genera. All modified after Bieler (1993) except for Simplexollata, Basisulcata and Ammotectonica. Solatisonax? refers to Solatisonax? kostejana (Boettger, 1907), Bold genera are represented in the Paratethys Sea. SSC: subsutural cord, MC: mid cord(s), UPC: upper peripheral cord, LPC: lower peripheral cord, IPC: infraperipheral cord; UC: umbilical crenae; PUC: proxumbilical cord.