Mesohedenstroemia olgae, Zakharov & Abnavi, 2013

Zakharov, Yuri D. & Abnavi, Nasrin Moussavi, 2013, The ammonoid recovery after the end-Permian mass extinction: Evidence from the Iran-Transcaucasia area, Siberia, Primorye, and Kazakhstan, Acta Palaeontologica Polonica 58 (1), pp. 127-147 : 137-138

Mesohedenstroemia olgae sp. nov.

Figs. 8A , 9A .

Etymology: Named after Olga P. Smyshyaeva (Far Eastern Geological Institute, Vladivostok).

Holotype: DVGI 3 /851, fully preserved adolescent phragmocone.

Type locality: SMID quarry at Artyom environs, South Primorye.

Type horizon: Mesohedenstroemia bosphorensis Zone, Zhitkov Formation, Olenekian, Lower Triassic (see Zakharov 1978) (found from float block).

Diagnosis.—Laterally compresed Mesohedenstroemia , with broad tabulate venter. Suture with a pair of well developed adventitious lobes.

Description.—The shell is thinly discoidal, extremely involute, with a broad, distinctively tabulate venter, angular ventral shoulders and gently convex flanks with maximum whorl width at about two thirds of whorl height. Umbilicus very narrow and deep with rounded shoulders. Ornamentation consists

http://dx.doi.org/10.4202/app.2011.0054

of fine, sinuous growth lines as well as low and narrow radial folds, curving lightly forward on the lateral sides.

Suture ceratitic with slender lateral saddles. The ventral lobe (V) is very wide and shallow, divided by a medial saddle, in which a pair of adventitious lobes (V 1 and V 2) are well developed on its each side. The outer branch (V 1) of the ventral lobe terminates with two denticulations at its base, one of which is accompanied by two smaller denticulations. The lateral lobe (L) is the largest, and is equipped with five denticulations, one of which is also accompanied by two smaller denticulations; the lobe U 1 is shorter with four denticulations. The shallow lobe U 3 is trident at its base, other auxiliary elements (e.g., U 5 and U 7) remain simple.

Dimensions in mm and ratios:

Remarks.—The new species is distinguished from Mesohedenstroemia bosphorenses ( Zakharov, 1968) from South Primorye by presence of two adventitious lobes, the narrower outer branch of the ventral lobe, deeper lateral lobe and simpler auxiliary series. More complicated adventitious elements, high first lateral lobe and more complicated auxiliary series differentiate it from M. kwangsiana Chao, 1959 , M. planata Chao, 1949 , and M. inflata Chao, 1959 from South China ( Chao 1959).

Stratigraphic and geographic range.— Type locality and type horizon only.

Figures

Fig. 8. Suture lines of some Prolecanitida. A. Mesohedenstroemia olgae sp. nov., DVGI 2/851 (holotype), height 18.4 mm; Lower Olenekian, Mesohedenstroemia bosphorensis Zone; SMID quarry at the Artyom environs, south Primorye. B, C. Hedenstroemia tscherskii (Popov, 1961). Lower Olenekian, Lepiskites kolymensis Zone; Kenyelichi River, Kolyma River basin. B. DVGI 256−3b, height 60.0 mm (B1) and 73.0 mm (B2). C. DVGI 255−19c, height 73.0 mm. Abbreviations: D, dorsal lobe; I, inner lateral lobe; L, lateral lobe; U, umbilical lobe; V, ventral lobe.

Fig. 9. Some Early Olenekian Prolecanitida, Ceratitida, and Phylloceratida from Lower Olenekian, Mesohedenstroemia bosphorensis Zone; SMID quarry at the Artyom environs, South Primorye. A. Prolecantid Mesohedenstroemia olgae sp. nov., DVGI 2/851 (holotype), right lateral (A1) and ventral (A2) views. B. Ceratitid Inyoites sedini sp. nov., DVGI 1/851 (holotype). C. Phylloceratid Subbalhaeceras shigetai gen. and sp. nov., DVGI 2/851 (holotype), right lateral (C1), left lateral (C2), ventral (C3) views.