Haploceras sp.

Pandey, Dhirendra Kumar, Fuersich, Franz T., Alberti, Matthias, Das, Ranajit & Saez, Federico Oloriz, 2022, First population-level study of the ammonite genus Hildoglochiceras Spath, and the Lower Tithonian record of the Hildoglochiceras Horizon in the Kachchh Basin, India, Zitteliana 96, pp. 1-49 : 1

Haploceras sp.

Fig. 6H-K, O

Material.

Two specimens, Hildoglochiceras Bed of Jara Dome (Lower Tithonian); KSKV2019Jara/65, 67 (both figured).

Description.

Shell small, incomplete, compressed, involute subquadrangular whorl section with almost flat to slightly arched lateral surface, slightly arched ventral region, indistinct umbilical shoulder and short, steeply sloping umbilical wall.

Remarks.

These are moderately preserved, small specimens that show abraded external surfaces. Specimen no. KSKV2019Jara/65 consists of the phragmocone and body chamber, whereas specimen no. KSKV2019Jara/67 is only a part of the body chamber. Except for the umbilical diameter, which is larger in the present specimen, other dimensional proportions are within the range of variation in Haploceras staszycii (Zeuschner) (Fig. 7 ), however, the subquadrangular whorl section and the umbilical diameter do not match any of the specimens of the present collection nor the species of Haploceras described by Waagen and Collignon, most probably due to their small size.

Biostratigraphy.

The genus Haploceras shows a long biostratigraphic range from the latest Kimmeridgian to Early Berriasian. The interpreted age of the described specimen is Early Tithonian (three-fold division), in accordance with the biostratigraphic interpretation of described Hildoglochiceras , Aulacosphinctoides and an incomplete virgatosphinctin.

Figures

Figure 6. A-G, L-N. Haploceras staszycii (Zeuschner, 1846). A. KSKV 2019 Jara / 63, left side view of phragmocone, note well preserved suture lines; B, C. KSKV 2019 Jara / 64; B. Left side view of phragmocone; C. Apertural view showing broken aperture along a septum; D. KSKV 2019 Jara / 66, apertural view; E. KSKV 2019 Jara / 69, apertural view showing broken surface along a septum; F, G. KSKV 2019 Jara / 62; F. Left side view of phragmocone, note well preserved suture lines; G. Apertural view; L-N. KSKV 2019 Jara / 61; L. Right side view of phragmocone; M. Apertural view; N. Outline of whorl-section; H-K, O. Haploceras sp.; H, O. KSKV 2019 Jara / 65; H. Apertural view along a broken surface of phragmocone; O. Right side view showing phragmocone and a part of body chamber; I-K. KSKV 2019 Jara / 67; I. Vental view; J. Apertural view; K. Left side view of body chamber; P-T. Hildoglochiceras kobelliforme (Bonarelli, 1894) (m); P-S. KSKV 2019 Jara / 1, inner cast with epigenized shell preserved; P. Right side view of moderately evolute specimen (U ≈ H), with subtle uncoiled outer whorl (probable adult), body chamber 180 ° with peristomal vestige (dorsal branch on inner cast?); Q. Suture lines at the end of phragmocone, note increased density at the end of phragmocone; R. Apertural view, note epigenized shell clearly identifiable on the ventral region; S. Oval whorl section with narrow venter, wide lateral groove on the body chamber; T. KSKV 2019 Jara / 2. inner cast, left-side view of nearly complete adult specimen with clear final uncoiling, partial preservation of epigenized shell, ca. 180 ° of preserved body chamber on inner cast of comparatively fine-to-medium sandstone.

Figure 7. Scatter plot showing D: H / T ratios of some related species of Haploceras.