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Fig. 22 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 22. Periostracal extension of the ventral shell wall (median section, growth direction to the right, centrifugal). A. Phylloceras (Euphylloceras) cf. velledae (Michelin, 1934), BSPG MAo-1770, early Albian, Cretaceous, Ambatolafia, Mahajanga Basin, NW Madagascar; a scythe-like extension of the ventral organic periostracum forms an organic radial lirae (Radtke and Keupp 2016); the dorsal inner prismatic layer of the succeeding whorl smoothes out the periostracum relief. B. Phylloceras (Euphylloceras) sp., BSPG MAo-1769, early Albian, Cretaceous, Ambatolafia, Mahajanga Basin, NW Madagascar; the same as in A. C. Phylloceras (Phylloceras) plicatum Neumayr, 1871, BSPG MAn-4509, late Oxfordian, Jurassic, Sakaraha, Morondava Basin, SW Madagascar; the ventral organic periostracum forms convex periostracal extensions; the dorsal inner prismatic layer of the succeeding whorl smoothes out the periostracum relief. D. Desmophyllites diphylloides (Forbes, 1846), BSPG MAo-1838, Campanian, Cretaceous, Teshio-Nakagawa area, Hokkaido, Japan; the same as in C. Abbreviations: dipl, dorsal inner prismatic layer; if, infilling; ipl, inner prismatic layer, ncl, nacreous layer, opl, outer prismatic layer, per, periostracum.

Fig. 18 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 18. Construction of the complete dorsal shell wall (transversal section, centrifugal). Hoploscaphites nicoletii (Morton, 1842), AMNH-FI-99143, Maastrichtian, Cretaceous, Fox Hills Formation (Loc. 3272), S Dakota, USA. A–C. Prior to the detachment of the living chamber, the dorsal shell wall is already complete and consists of a wrinkle layer, a dorsal outer prismatic layer, a dorsal nacreous layer and a dorsal inner prismatic layer. B. Close-up of A. D. In the detached living chamber, at least a dorsal nacreous layer is formed. The dorsal outer prismatic layer and the dorsal inner prismatic layer are not preserved. Abbreviations: dipl, dorsal inner prismatic layer; dncl, dorsal nacreous layer; dopl, dorsal outer prismatic layer; if, infilling; ipl, inner prismatic layer; ncl, nacreous layer; wl, wrinkle layer.

Fig. 17 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 17. Construction of the complete dorsal shell wall (median section, growth direction to the left, centrifugal). A. Choffatia (Grossouvria) sp. 1, BSPG MAn-4520, late Callovian, Jurassic, Dubki near Saratov, Russia; A1, the dorsal shell wall consists of a dorsal outer prismatic layer, a dorsal nacreous layer and a dorsal inner prismatic layer; A2, close-up of A1. B. Divisosphinctes besairiei Collignon, 1960, BSPG PA-10151b, late Oxfordian, Jurassic, Sakaraha, Morondava Basin, SW Madagascar; B1, the ventral shell wall (vsw) is overgrown by an encruster (enc) which is in turn overgrown by the succeeding whorl (dsw); B2, the thin early complete dorsal shell is formed in contact with the ventral shell wall; it consists of (a wrinkle layer), a dorsal outer prismatic layer, a dorsal nacreous layer and a dorsal inner prismatic layer; B3, the dorsal outer prismatic layer; B4, the older, thick, detached dorsal shell wall consists of the same three layers as in B2; B5, close-up of B4. Abbreviations: dipl, dorsal inner prismatic layer; dncl, dorsal nacreous layer; dopl, dorsal outer prismatic layer; dsw, dorsal shell wall; enc, encruster; if, infilling; ncl, nacreous layer; opl, outer prismatic layer; s, septum; vsw, ventral shell wall; wl, wrinkle layer.

Fig. 21 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 21. Construction of the seemingly complete dorsal shell wall (transversal section, centrifugal). Quenstedtoceras henrici Douville, 1912, BSPG MAn- 4768, early Callovian, Jurassic, Dubki near Saratov, Russia. A. At the contact of two whorls the outer prismatic layer and the nacreous layer of the attaching whorl wedge out but a "new" dorsal outer prismatic layer is formed towards the spiral plane which covers the wrinkle layer; the inner prismatic layer is continuous. B. The (dorsal) nacreous layer and the (dorsal) inner prismatic layer attach to the "new" dorsal outer prismatic layer which compensates the relief of the wrinkle layer. C. The dorsal shell wall consists of a wrinkle layer, a dorsal outer prismatic layer and a dorsal inner prismatic layer. D. The wrinkle layer left imprints in the dorsal outer prismatic layer. Abbreviations: dipl, dorsal inner prismatic layer; dopl, dorsal outer prismatic layer; ipl, inner prismatic layer, ncl, nacreous layer, opl, outer prismatic layer; wl, wrinkle layer.

Fig. 16 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 16. Construction of the complete dorsal shell wall (transversal section, centrifugal). Lobolytoceras costellatum (Pavia, 2002), BSPG MAn-3059, late Oxfordian, Sakaraha, Morondava Basin, SW Madagascar. A. The dorsal shell wall consists of a dorsal outer prismatic layer, a dorsal nacreous layer and a dorsal inner prismatic layer. B. Close-up of A; the thick dorsal inner prismatic layer consists of two sub-layers. C. Close-up of A; the dorsal outer prismatic layer. Abbreviations: dipl, dorsal inner prismatic layer; dncl, dorsal nacreous layer; dopl, dorsal outer prismatic layer.

Fig. 19 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 19. Construction of the complete dorsal shell wall (A, median section, growth direction to the right, centrifugal; B, transversal section, centrifugal). A. Scaphites whitfieldi Cobban, 1951, AMNH-FI-99144, Touronian, Cretaceous, Turner Sandy Member (Loc. 3190), Wyoming, USA; A1, shortly before complete detachment of the living chamber, the dorsal nacreous layer is repeatedly reinforced by new generations of the dorsal nacreous layer (dncl A–C); A2, close-up of A1. B. Ancyloceratoidea indet., BSPG MAo-1813, Aptian, Cretaceous, Shilovka near Volga River, Russia; B1, contact of both dorsal shell portion of two succeeding shafts; the dorsal shell wall consists of a dorsal outer prismatic layer, a primary dorsal nacreous layer, a primary dorsal inner prismatic layer and a secondary dorsal nacreous layer; the secondary dorsal inner prismatic layer is not preserved; B2, close-up of B1. Abbreviations: dipl, dorsal inner prismatic layer; dipl 1/2, primary/secondary dorsal inner prismatic layer; dncl, dorsal nacreous layer; dncl 1/2, primary/secondary dorsal nacreous layer; dncl A–C, generations of the dorsal nacreous layer; if, infilling; ipl, inner prismatic layer; ncl, nacreous layer; ol, organic layer; s, septum.

Fig. 9 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 9. Occurrences of dorsal shell wall types in Mesozoic ammonoid superfamilies (after Rouget et al. 2004; cf. Tables 1, 2, SOM: table A). The wide distribution of reduced dorsal shell walls in Mesocoic taxa suggests a plesiomorphy. In general, nacreous reduced dorsal shell walls or complete dorsal shell walls follow a stage of a prismatic reduced dorsal shell wall. The wide distribution of nacreous reduced dorsal shell walls and complete dorsal shell walls in Mesozoic ammonoid taxa suggests that the ability to form dorsal nacre is also a plesiomorph feature. Note: The dorsal nacreous layer of Eoderoceratoidea (Amaltheidae) has a prismatic appearance (*). The complete dorsal shell walls in Stephanocertatoidea, Haploceratoidea, and Hoplitoidea lack a dorsal nacreous layer, i.e., seemingly complete dorsal shell wall (**). The complete dorsal shell walls of Anclyceratoidea and Douvilleiceratoidea can be reinforced by additional pair of nacreous and prismatic layers, i.e., reinforced complete dorsal shell wall (***).

Fig. 11 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 11. Construction of the dorsal shell wall (median section, growth direction to the left, centrifugal). A. Puzosia saintoursi Collignon, 1963, BSPG MAo-1797, early Albian, Cretaceous, Ambatolafia, Mahajanga Basin, NW Madagascar; A1, the wrinkle layer forms an unusual cone-like thickening; the compensating thick dorsal inner prismatic layer forms nacreous inclusions; A2, close-up of A1; the organo-prismatic structure of the wrinkle layer thickening; A3, close-up of A1; the thickening of the dorsal inner prismatic layer shows nacreous inclusions. B. Perisphinctes (Kranaosphinctes) sp., BSPG MAn- 4756, late Oxfordian, Jurassic, Sakaraha, Morondava Basin, SW Madagascar; B1, the dorsal inner prismatic layer bridges the relief of two ribs forming a crescent hollow space; the ventral nacre layer of this shell portion is diagenetic altered; B2, close-up of B1. Abbreviations: dipl, dorsal inner prismatic layer; if, infilling; ncl, nacreous layer; opl, outer prismatic layer; wl, wrinkle layer.

Fig. 14 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 14. Construction of the nacreous reduced dorsal shell wall (A–C, E, median section, growth direction to the right, centrifugal; D, transversal section, centrifugal). A. Aspidoceras sp., BSPG MAn-3193, late Oxfordian, Jurassic, Sakaraha, Morondava Basin, SW Madagascar; the dorsal shell wall consists of a primary dorsal inner prismatic layer, a secondary dorsal nacreous layer and a secondary dorsal inner prismatic layer; the dorsal shell wall becomes thinner towards the aperture (A1–A3) and vanishes completely (A4). B. Eupachydiscus sp., BSPG MAo-1831, Campanian, Cretaceous, Teshio-Nakagawa → area, Hokkaido, Japan; the early secondary nacreous layer is part of the secondary inner prismatic layer. C. Euaspidoceras sp. 2, BSPG MAn-4751, late Oxfordian, Jurassic, Sakaraha, Morondava Basin, SW Madagascar; same as in B. D. Colombiceras sp., BSPG MAo-1884, Aptian, Cretaceous, Caucasus region, Russia; the dorsal shell wall cover of the flanks of the preceding whorl consists of a dorsal outer prismatic layer, a primary dorsal inner prismatic layer, a secondary dorsal nacreous layer (and a secondary dorsal inner prismatic layer). E. Desmoceras (Desmoceras) latidorsatum (Michelin, 1838), BSPG MAo-1787, early Albian, Cretaceous, Ambatolafia, Mahajanga Basin, NW Madagascar; the dorsal shell wall can develop nacreous material within the dorsal inner prismatic layer. Abbreviations: dipl 1/2, primary/secondary dorsal inner prismatic layer; dncl 2, secondary dorsal nacreous layer; hbl, heringbone layer; if, infilling; ipl, inner prismatic layer; ncl, nacreous layer; opl, outer prismatic layer; wl, wrinkle layer.

Fig. 8 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 8. Construction of the prismatic reduced dorsal shell wall (A–C, F, median, section, growth direction to the left, centrifugal; D, E, transversal section, centrifugal). A. Argonauticeras besairiei Collignon, 1949, BSPG MAo-1772, early Albian, Cretaceous, Ambatolafia, Mahajanga Basin, NW Madagascar; the dorsal shell wall consists of an outer wrinkle layer and a dorsal inner prismatic layer which has two sub-layers; the relief of an injury of the preceding whorl is overgrown by both layers. B. Calliphylloceras sp., BSPG MAn-4512, late Oxfordian, Jurassic, Sakaraha, Morondava Basin, SW Madagascar; the wrinkle layer left imprints in the dorsal inner prismatic layer. C. Desmoceras (Desmoceras) latidorsatum (Michelin, 1838), BSPG MAo-1839, early Albian, Cretaceous, Ambatolafia, Mahajanga Basin, NW Madagascar; the same as in B. D. Cadoceras stupachenkoi Mitta, 1998, BSPG MAn-4790, early Callovian, Jurassic, Makaryev on Unzha River, Russia; the dorsal wrinkle layer is completely replaced by pyrite, i.e., diagenesis. E, F. Aconeceras sp. 1, →

Fig. 6 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 6. Construction of the prismatic reduced dorsal shell wall (median section, growth direction to the left, centrifugal). Ptychophylloceras cf. dacquei Joly, 1976, BSPG MAn-4516, late Oxfordian, Jurassic, Sakaraha, Morondava Basin, SW Madagascar. The dorsal shell wall consists of an outer wrinkle layer and dorsal inner prismatic layer. The dorsal inner prismatic layer becomes thinner towards the aperture (A, B) and vanishes completely (C). Abbreviations: dipl, dorsal inner prismatic layer; ipl, inner prismatic layer; ncl, nacreous layer; opl, outer prismatic layer; s, septum; wl, wrinkle layer.

Fig. 5 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 5. Construction of the prismatic reduced dorsal shell wall (median section, growth direction to the left, centrifugal). A. Desmoceras (Desmoceras) latidorsatum (Michelin, 1838), BSPG MAo-1786, early Albian, Cretaceous, Ambatolafia, Mahajanga Basin, NW Madagascar; A1, the early dorsal shell wall consists of a smooth organic layer and (prismatic) septal mural parts; A2, later in ontogeny, the septal mural parts extend and seem to form the first dorsal inner prismatic layer; A3, the prismatic mural part of a nacreous septum can form an own layer which is separated from the ventral inner prismatic layer; the nacreous and prismatic materials of a septum merge. B. Neosilesites ambatolafiensis Collignon,1963, BSPG MAo-1779, early Albian, Cretaceous, Ambatolafia, Mahajanga Basin, NW Madagascar; the prismatic mural part of a nacreous septum can form an own layer which is separated from the dorsal inner prismatic layer; the nacreous and prismatic materials of a septum merge. C. Argonauticeras besairiei Collignon, 1949, BSPG MAo- 1705, early Albian, Cretaceous, Ambatolafia, Mahajanga Basin, NW Madagascar; C1, the septal mural part seems to be the origin of the inner sub-layer of the dorsal inner prismatic layer; C2, close up of C1. Abbreviations: dipl, dorsal inner prismatic layer; dspl, dorsal septal prismatic layer; ipl, inner prismatic layer; ncl, nacreous layer; ol, organic layer; opl, outer prismatic layer; s, septum; spl, septal prismatic layer; wl, wrinkle layer.

Fig. 2 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 2. Schematic drawing of general dorsal shell wall types (A1, B1, transversal section, centrifugal; A2, B2, median section, growth direction left, centrifugal). A. Reduced dorsal shell wall. The lateral shell wall wedges out at the contact with the preceding whorl. The dorsal wall is omitted at the aperture. B. Complete dorsal shell wall. The ventral, lateral, and dorsal shell walls form a continuum. The dorsal wall is present at the aperture. Colouring: black, ventral/lateral wall of the succeeding whorl; dark grey, dorsal wall of the succeeding whorl; light grey, septum of the succeeding whorl; white, ventral wall of the preceding whorl.

Fig. 3 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 3. Schematic construction of the dorsal shell wall (A, D, E, median section, growth direction right, centrifugal; B, C, F, G, transversal section, centrifugal). A, B. Complete dorsal shell wall. D, G. Seemingly complete dorsal shell wall. C. Complete dorsal shell wall of Amaltheidae. E, F. Reinforced complete dorsal shell wall. Abbreviations: dipl, dorsal inner prismatic layer; dipl 1/2, primary/secondary dorsal inner prismatic layer; dncl, dorsal nacreous layer; dncl 1/2, primary/secondary dorsal nacreous layer; dopl, dorsal outer prismatic layer; ipl, inner prismatic layer; ipl 1/2, primary/secondary inner prismatic layer; ncl, nacreous layer; ncl 1/2, primary/secondary nacreous layer; opl, outer prismatic layer; so, spiral ornament; vsw, ventral shell wall of the preceding whorl; wl, wrinkle layer.

Fig. 1 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 1. Schematic construction of the ventral and dorsal shell wall (A, B, D, E, median section, growth direction right, centrifugal; C, F, G, transversal section, centrifugal). A. Simple ventral shell wall. B. Ventral shell wall with a doubling. C, E, G. Nacreous reduced dorsal shell wall. D, F. Prismatic reduced dorsal shell wall. Abbreviations: dipl, dorsal inner prismatic layer; dipl 1/2, primary/secondary dorsal inner prismatic layer; dncl, dorsal nacreous layer; dncl 1/2, primary/secondary dorsal nacreous layer; ipl, inner prismatic layer; ipl 1/2, primary/secondary inner prismatic layer; ncl, nacreous layer; ncl 1/2, primary/secondary nacreous layer; opl, outer prismatic layer; per, periostracum; vsw, ventral shell wall of the preceding whorl; wl, wrinkle layer.

Fig. 62 in The Changhsingian (Late Permian) ammonoids from Baghuk Mountain (Central Iran)

Fig. 62. Stoyanowites aspinosus Korn & Ghaderi, 2016. A. Lateral and dorsal view, specimen MB.C.30100, section C, -1.60 m. B. Whorl profile proportions. Scale bar units = 1 mm.

Fig. 60 in The Changhsingian (Late Permian) ammonoids from Baghuk Mountain (Central Iran)

Fig. 60. Abichites infirmis Korn & Hairapetian sp. nov. A. Lateral and dorsal view, holotype MB.C.30086, section G, -0.40 m. B. Suture line, holotype MB.C.30086, at 21.5 mm dm, 9.1 mm wh. Abbreviations: see Material and methods. Scale bar units = 1 mm.

Fig. 61 in The Changhsingian (Late Permian) ammonoids from Baghuk Mountain (Central Iran)

Fig. 61. Stoyanowites dieneri (Stoyanow, 1910). A. Lateral and dorsal view, specimen MB.C.30090, section E, float. B. Lateral and dorsal view, specimen MB.C.30089, section E, float. C. Suture line, specimen MB.C.30090, at 12.4 mm ww, 17.4 mm wh. D. Suture line, specimen MB.C.30089, at 14.4 mm wh. E. Whorl profile proportions. Abbreviations: see Material and methods. Scale bar units = 1 mm.

Fig. 63 in The Changhsingian (Late Permian) ammonoids from Baghuk Mountain (Central Iran)

Fig. 63. Stoyanowites parallelus Korn & Hairapetian sp. nov. A. Lateral and dorsal view, holotype MB.C.30102, section C, -1.70 m. B. Suture line, holotype MB.C.30102, at 17.5 mm wh. Abbreviation: see Material and methods. Scale bar units = 1 mm.

Fig. 58 in The Changhsingian (Late Permian) ammonoids from Baghuk Mountain (Central Iran)

Fig. 58. Abichites ovalis Korn & Hairapetian sp. nov. A. Lateral and dorsal view, holotype MB.C.30059, section B, float. B. Lateral and dorsal view, paratype MB.C.30071, section G, -0.40 m. C. Suture line, holotype MB.C.30059, at 14.2 mm wh. D. Whorl profile proportions. Abbreviation: see Material and methods. Scale bar units = 1 mm.