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Journal of Paleontology 92(2):157–169
marginal plates on each side. Sheet-like muscular mantle on top of conch. Shell wall with or without nacreous layer.
Occurrence.—Early Carboniferous (late Namurian, late Ches- terian, Serpukhovian) to late Carboniferous (Moscovian; early Stephanian).
Remarks.—The diagnosis is emended from that by Doguzhaeva et al. (2007a).Aproostracum-like structure, one of the attributes of the order Donovaniconida, can be assumed for the Carboni- ferous members of the order Aulacocerida as well, although it is so far known only in a single Late Triassic aulacocerid, namely Austrateuthis Jeletzky and Zapfe, 1967 (Jeletzky and Zapfe, 1967, pl. 1). A long body chamber, another character of the order Donovaniconida, could be shared with the order Aulaco- cerida, even though a body chamber has only been described from two juvenile specimens of the late Carboniferous auloco- ceratids Mutveiconites mirandus Doguzhaeva, 2002a and M. milleri Doguzhaeva, Mapes, and Dunca, 2006b (Doguzhaeva, 2002b, pl. 17, figs. 1, 2; Doguzhaeva et al., 2006b, pl. 1, fig. A). A sheath-like rostrum distinguishes the order Donovaniconida from the Aulacocerida. Unlike the short proostracum-like structures in the orders Donovaniconida and Aulacocerida, large, broad, long, and trilobate proostraca associated with short terminal chambers of the phragmocones are developed in the order Phragmoteuthida Jeletzky in Sweet, 1964 (Middle Triassic–Early Jurassic). In Phragmoteuthis, the proostracum has three longitudinal fields (a median field and lateral wings) with concentric ornamentation, like that of a single field in the proostracum-like structures of the Donovaniconida and the Aulacocerida (compare Doguzhaeva and Summesberger, 2012, fig. 1; Doguzhaeva et al., 2003, fig. 2; Jeletzky and Zapfe, 1967, fig. 2).
Family Oklaconidae new family
urn:lsid:
zoobank.org:act:6DB52A18-6B63-43BE-9680- 6623E30CE96A
Diagnosis.—Orthocone compressed, smooth, with flattened lateral, narrowed crest-like dorsal, and broadly rounded ventral sides. Apical angle ~15º. Estimated conch length ~200mm. Proportionally long body chamber and phragmocone. Dorso- ventral diameter maximum width ratio ~1.4:1. Septa deep. Suture line with broad lateral lobe. Mural parts of septa long, ~0.3–0.7 of chamber length. Chambers in phragmocone short, ~0.15 of dorsoventral diameter. Ventral siphuncle small. Septal necks long holochoanitic ventrally, short cyrthochoanitic dor- sally. Connecting rings thin. Shell wall microlaminated with strongly oblique growth lines. Rostrum thin, sheath-like. Proostracum-like structure short, strongly convex. Ink sac pre- sent. Muscular mantle over conch surface.
Occurrence.—Upper Carboniferous (Moscovian).
Remarks.—Three families—Donovaniconidae Doguzhaeva, Mapes, and Mutvei, 2002b, Gordoniconidae Mapes, Weller, and Doguzhaeva, 2010b, and Rhiphaeoteuthidae Doguzhaeva, 2002a—have been referred to the order Donovaniconida. The Donovaniconidae is typified by Donovaniconus having a long
body chamber, a thin sheath-like rostrum, a short proostracum- like structure, a breviconic phragmocone with short chambers and a moderately large apical angle (20–30°), a small ventral siphuncle, a nacreous layer in the shell wall, and an ink sac (Doguzhaeva et al., 2002b, 2003). Saundersites Doguzhaeva, Mapes, and Mutvei, 2007a is provisionally referred to this family because of a long body chamber, a proostracum-like structure, and a thin sheath-like rostrum. Additionally, this genus is known to have arm hooks, a coleoid-type radula, and an ink sac (Doguzhaeva et al., 2007a). The family Gordoniconidae is typified by Gordoniconus Mapes, Weller, and Doguzhaeva, 2010b having a longiconic body chamber of approximately equal length with a breviconic phragmocone with an apical angle of 15°, a long, pointed, weakly mineralized rostrum that covers one-third of the closely septate phragmocone, between six and seven chambers per phragmocone length of the corres- ponding phragmocone width, arm hooks, and ink sac (Mapes et al., 2010b). The Rhiphaeoteuthidae has been provisionally referred to the order Donovaniconida although a body chamber and a sheath-like rostrum have not yet been demonstrated in the late Carboniferous Rhiphaeoteuthis Doguzhaeva, 2002a. It has a breviconic phragmocone with a smooth surface, short, ~0.15 of conch diameter, chambers of the phragmocone; long mural parts of septa about chamber length; shell wall and septa thin, about equal in thickness, and a small marginal ventral siphuncle; sutures with shallow ventral and lateral lobes; septal necks short, cyrtochoanitic dorsally and long holochoanitic ventrally; an ovoid conch section with a narrowdorsal side and inclined apical septa and straight adoral ones (Doguzhaeva, 2002a, pl. 13, figs. 1–4). The morphology of Oklaconus n. gen. does not fitwithin the diagnoses of the three families currently assigned to the order, and therefore a new family is erected to accommodate the genus.
Genus Oklaconus new genus
urn:lsid:
zoobank.org:act:E0F433C4-A71B-4D82- 921F-0D7F1FCF8FFB
Type species.—Oklaconus okmulgeensis new species, by monotypy.
Diagnosis.—As for the type species by monotypy.
Etymology.—Named for the state of Oklahoma, USA where the holotype of Oklaconus okmulgeensis n. sp. (type species) was collected.
Occurrence.—The middle transgressive-regressive cycle of the Wewoka Formation, upper Carboniferous (Moscovian), Oklahoma, USA.
Remarks.—Diagnosis is based on an adult specimen. Oklaconus is assigned to the coleoid cephalopods on the basis of an ink sac within the body chamber, a sheath-like rostrum, and a muscular mantle situated on top of the conch surface. Oklaconus n. gen. is similar to the co-occurring Donovani-
conus (see above) fromwhich it differs by having a smaller apical angle (15º), oval conch in cross section with flattened lateral, narrowed crest-like dorsal and broadly rounded ventral sides, a suture line with a deep broad lateral lobe, and microlaminated
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