Pakiluta solangii

Merle, Didier, Pacaud, Jean-Michel, Métais, Grégoire, Bartolini, Annachiara, Lashari, Rafiq A., Brohi, Imdad A., Solangi, Sarfraz H., Marivaux, Laurent & Welcomme, Jean-Loup, 2014, Volutidae (Mollusca: Gastropoda) of the Lakhra Formation (Earliest Eocene, Sindh, Pakistan): systematics, biostratigraphy and paleobiogeography, Zootaxa 3826 (1), pp. 101-138 : 132-133

Pakiluta solangii sp. nov.

Fig. 12 G–M

Etymology. Dedicated to the Professor Sarfraz H. Solangi, Centre for Pure and Applied Geology, University of Sindh, Jamshoro, Pakistan.

Type locality. Stn 4: Lakhra Dome, Lakhra village section, base of the Lakhra Formation.

Type material. Holotype (stn 4: CPAG.RAN. I.51, cast MNHN.F. A50389 ), paratype 1 (stn 4: CPAG.RAN. I.52, cast MNHN.F.A50390), paratype 2 (stn 4: CPAG.RAN. I.53, cast MNHN.F. A50391 ), paratype 3 (stn 5: CPAG.RAN. I.54, cast MNHN.F.A50392).

Other material. 2 spm (stn 4: MNHN).

Description. Shell solid, large, H 75–79, D 36–38 mm (holotype H 70.3 not complete, D 36.2 mm). Protoconch paucispiral, H ca. 1 mm. Teleoconch of 8–9 convex whorls. Coeloconoid spire occupying 20% of total shell height. Five early teleoconch whorls convex, elongate, followed by two shorter whorls. Last whorl moderately wide, convex posteriorly, almost straight-sided in its median part, slightly excavated anteriorly. Suture linear on first whorls, canaliculate on last two whorls. Axial sculpture of weak orthocline ridges on spire, disappearing progressively on last two whorls. First whorl: not preserved; second to fourth whorls: apparently 15–20 ridges; fifth whorl: 24–30 ridges; sixth whorl: 37 ridges; seventh and eighth whorls: ridges obsolete. Spiral sculpture of two or three obsolete cords on base of antepenultimate whorl. Aperture rather narrow, lenticular, occupying 73% of total height, 28% of diameter. Outer lip not thickened externally. Narrow anal sulcus against suture. Parietal callus thin. Four strong, oblique columellar folds, anterior-most weaker. Siphonal canal short. Siphonal fascioles low, weak; siphonal notch shallow.

Comparisons and discussion. This intriguing species superficially resembles members of the turbinellid genus Turbinella Lamarck, 1799 [type species: Voluta pyrum Linnaeus, 1767 by monotypy] in its smooth last whorls and its four strong columellar folds. However, species of Turbinella differ from the present species by having a more sculptured spire displaying true axial costae and by their columellar folds being more widely spaced and placed more posteriorly. In addition, the siphonal canal is longer and gives species of Turbinella a fusiform shape. The shell shape and sculptural pattern of other turbinellids, such as those of the Vasinae or the Columbariinae , are too different to be compared to Pakiluta . Pakiluta displays closer similarities to the volutids than to Turbinella , because of its shorter siphonal canal and the four strong columellar folds, which are more anteriorly placed on the columella than those of turbinellids. Their construction is rather similar to that of Sindiluta and Pseudaulicina. These shared characters suggest an assignment to the volutids rather than to the turbinellids. Nevertheless, the axial sculpture of Pakiluta consisting of numerous ridges and even its shape with a coeloconoid spire are unusual for the volutids and make subfamilial placement difficult. The smooth last whorl of Pakiluta suggests comparison with Scaphella Swainson, 1832 [type species: Voluta junonia Lamarck, 1804 by subsequent designation, Gray 1847: 141) or Caricella Conrad, 1835 [type species: Caricella pyruloides Conrad, 1834 by subsequent designation, Cossmann (1899: 129)] of the Scaphellinae Gray, 1857 , but in Scaphella the spire is more conic, the last whorl is more globose and the columellar folds (usually two or three) are weaker. Caricella is rather similar to Scaphella , but some Cenozoic as well as Mesozoic species of Caricella have four strong folds as in Pakiluta ( Dockery 1977; Bandel 2003). Pakiluta can be distinguished easily from these two genera by its anal sulcus against the suture and by its numerous axial ridges on the spire. Pakiluta has two characters that are more comparable to a Mesozoic subfamily, the Volutodermatinae , than to Scaphellinae . They are a coeloconoid spire with elongate whorls and an anal sulcus against the suture, which are present in most species of Volutoderma Gabb, 1877 [type species: Volutoderma navarroensis (Gabb, 1877) by original designation] (for a complementary discussion, see Saul & Squires 2008: 218). Nevertheless, coarser sculpture and weaker columellar folds (three in most species) are characters distinguishing Volutoderma from Pakiluta . Konistra Saul & Popenoe, 1993 [type species: Gosavia biconica (Anderson, 1958) by monotypy] exhibits a shape rather similar to that of Pakiluta , but differs in its coarser sculpture and its two well-developed, slightly oblique columellar folds. Liopeplum Dall, 1890 [type species: Volutilithes (Athleta) lioderma Conrad, 1860 by original designation] has a smooth last whorl as in Pakiluta , but its early teleoconch whorls have true costae. The volutomitrid Daffymitra Harasewych & Kantor, 2005 [type species: D. lindae Harasewych & Kantor, 2005 by original designation] is a living species displaying strongly convex and ovate whorls, a short siphonal canal and weak sculpture consisting of low axial ridges and obsolete spiral cords. These characters recall the early teleoconch whorls of Pakiluta , but the new genus is distinguished by its stronger columellar folds, its anal sulcus and its coeloconoid spire. Harasewych & Kantor (2005) compared D. lindae to a volutodermatine genus, Volutomorpha Gabb, 1877 [type species: Volutilithes conradi Gabb, 1860 by original designation] in which the sculpture is far more strongly developed than in Pakiluta . As for Daffymitra , conchological similarities to the Volutodermatinae raise the possibility that Pakiluta is a surviving descendent from a group presumed to have become extinct at the end of the Cretaceous.

Stratigraphic range. Lakhra formation: Lakhra Dome.

Figures

FIGURE 12. A – F. Sindhiluta lakhraensis gen. nov., sp. nov., A – B (holotype, CPAG. RAN. I. 48, ventral (A) and dorsal (B) views, stn 4), C – D (paratype 1, CPAG. RAN. I. 49, ventral and dorsal view, stn 4), E – F (paratype 2, CPAG. RAN. I. 50, dorsal view of the broken specimen showing the columellar folds (E) and enlarged view of the spire (F); G – M. Pakiluta solangii gen. nov., sp. nov., G – H (holotype, CPAG. RAN. I. 51, ventral (G) and dorsal (H) views, stn 4), I – J (paratype 3, CPAG. RAN. I. 54, spire (I), and enlarged view of the spire (J), stn 5), K – L (paratype 2, CPAG. RAN. I. 53, spire (K) and enlarged view of the spire (L), stn 4), M (paratype 1, CPAG. RAN. I. 52, ventral view, stn 4). Scale bars: A – I, K, M = 10 mm; J, L = 5 mm.