Entogonites bucheri, Klug & Baets & Korn, 2016

Klug, Christian, Baets, Kenneth De & Korn, Dieter, 2016, Exploring the limits of morphospace: Ontogeny and ecology of late Viséan ammonoids from the Tafilalt, Morocco, Acta Palaeontologica Polonica 61 (1), pp. 1-14 : 9-10

Entogonites bucheri sp. nov.

Figs. 2C , 5A , 6C .

Etymology: Honoring Hugo Bucher (Zürich) for his numerous, thorough and profound contributions to ammonoid paleobiology and stratigraphy.

Type material: Holotype, subadult specimen, PIMUZ 31509 , paratype, juvenile specimen, PIMUZ 31508 .

Type locality: 12 km southeast of Dar Kaoua, southeast of Erfoud, eastern Anti–Atlas, Morocco.

Type horizon: Early late Viséan ( Entogonites assemblage).

Material. — 6 individuals: 2 specimens in PIMUZ 31509 (the subadult holotype and a smaller individual); 3 juvenile to subadult specimens in PIMUZ 31512 (associated with about 100 other juvenile ammonoid conchs); a very small juvenile conch in PIMUZ 31520 (in the body chamber of a mature conch of Maxigoniatites ) .

Diagnosis.— Entogonites with largely regularly coiled whorls. Only the third whorl displays faint tetragonal coiling. Expansion rate of juvenile and adult whorls exceeds 2.0. The uw/dm ratio is below 0.4. Ornamentation begins after the nepionic constriction with simple ribs, followed by bifurcating and intercalatory ribs (>30 per whorl).

Description. —The small subevolute specimen PIMUZ 31520 measures about 1.8 mm in diameter. It comprises the initial chamber and the initial 2.5 whorls ( Fig. 2C ). The embryonic shell measures less than 1 mm and has a smooth surface. Only one side is exposed and thus, the thickness cannot be measured. At the presumed position of the nepionic constriction, the fine ornament commences. At 1.8 mm diameter, there are 25 simple and rectiradiate ribs per half whorl.

The ontogenetically slightly older specimen PIMUZ 31508 measures 5 mm in diameter. Its conch is subinvolute with a high whorl expansion rate ( Table 4 ). As in the other specimen, the conch is only partially exposed and hence, conch thickness is unknown. The tetragonal coiling is only very faintly developed in early whorls and the last of the preserved (preadult) whorls is completely regularly coiled. At 5 mm diameter, there are 20 primary ribs per half whorl. Most of these ribs bifurcate near the midflank, but there are a few trifurcating ribs as well (or bifurcating with an associated intercalatory rib).

The holotype PIMUZ 31509 has a diameter of almost 9 mm. At this size, the subevolute conch is thinly discoidal with a high whorl expansion rate. The initial chamber measures approximately 0.4 mm across. The first two whorls are regularly coiled followed by one vaguely tetragonally coiled whorl. The last two whorls are again normally coiled. The ornamentation consists of 34 primary ribs on the last half whorl. Most of these ribs bifurcate in the middle of the flank, some are simple but then often associated with intercalatory ribs. The rib course begins with a deep ventral sinus, which is nearly twice as wide as it is deep measured from the tips of the adjacent ventrolateral projections, which are rounded and asymmetric. The ribs are the most strongly developed in the ventrolateral projections. Most of the flank is covered by a broad and shallow sinus. None of the specimens displays the suture line.

Remarks. —Although the suture is not visible, the combination of coiling, ornamentation and stratigraphic origin confirms the genus assignment. The new species differs from all other species in the extremely reduced tetragonal coiling of the inner whorls. Additionally, it has a clearly higher whorl expansion rate (values partially from the online database GONIAT (http://www.goniat.org, accessed September 7 th 2015) and Korn et al. 2010) than all other species ( E. bucheri , 2.0–2.15; E. grimmeri , 1.5–1.7; E. saharaensis , 1.5–1.65; E. tetragonus , 1.8–1.9) and, as can be expected from the covariation of these characters, the umbilicus is narrower ( E. bucheri , <0.4; E. borealis , 0.41; E. grimmeri , 0.45; E. saharaensis ,>0.48; E. tetragonus , 0.5).

Stratigraphic and geographic range. —Early late Viséan, so far only known from the Tafilalt ( Morocco).

Figures

Fig. 2. Juvenile (neanic) specimens of Goniatites lazarus Korn, Klug, and Mapes, 2005, Entogonites saharensis Korn, Klug, and Mapes, 2005, and Entogonites bucheri sp. nov. All from the early late Viséan, 12 km SE of Dar Kaoua (Tafilalt, Morocco). A. PIMUZ 31512, two neanic G. lazarus specimens (white arrows) in ventral views (A1), note the associated E. saharensis and orthocones. Enlarged G. lazarus in lateral view (A2); the narrow umbilicus and the umbilical ridge (A3). B. PIMUZ 31512, a juvenile G. lazarus, a small juvenile and a subadult E. saharensis; G. lazarus in ventral (B1) and lateral (B2) views. C. PIMUZ 31520, detail of a fully grown Maxigoniatites saourensis (Pareyn, 1961) with G. lazarus, 3 juvenile E. saharensis, and a subadult E. saharensis and a hatchling of E. bucheri sp. nov. (arrowed); C2, detail of C1, showing G. lazarus and E. bucheri sp. nov. All specimens whitened with NH4Cl-sublimate. Scale bars 10 mm.

Fig. 5. Ammonoids from the early late Viséan, 12 km SE of Dar Kaoua (Tafilalt, Morocco). A, C. Calygirtyoceras darkaouaense Korn, Klug, and Mapes, 1999. A. PIMUZ 31516 (A1), Goniatites lazarus with a juvenile specimen in oblique-ventral (A2), lateral (A3), and ventral (A4) views. C. PIMUZ 31513, fragmentary adult in lateral view (C1), cross section (C2). B. Entogonites bucheri sp. nov., PIMUZ 31509, holotype in lateral (B1) and ventral (B2) views. All specimens whitened with NH4Cl-sublimate.

Fig. 6. Mass occurrence of juvenile ammonoids from the early late Viséan, 12 km SE of Dar Kaoua (Tafilalt, Morocco). A. PIMUZ 31518 with 4 specimens of Nomismoceras sp., 3 Prolecanites sp., 4 Entogonites saharensis Korn, Klug, and Mapes, 2005, 1 Calygirtyoceras darkaouaense Korn, Klug, and Mapes, 1999, and 2 Bollandites sp. B. PIMUZ 31508, overview; many taxa are indicated in the figure. All specimens whitened with NH4Clsublimate.