Biological and stratigraphical significance of the Silurian nautiloid Aptychopsis

Abstract

Turek, Vojtach 1978 04 15: Biological and stratigraphical significance of the Silurian nautiloid Circular or elliptical structures described as the genus Aptychopsis Barrande 1872 (and mostly referred to the Crustacea) represent the opercula of a specialized group of orthoceratids. Their morphology bears a considerable resemblance to the structure of the lower jaws (aptychi) of some Mesozoic ammonoids, particularly of the genus Physodoceras. Because of its size and structure, however, Aptychopsis cannot have functioned as a jaw apparatus. Observation of an operculumin siru supports this assumption as regards its functional and systematic position. The classification of the genus Aptychopsis as given by Jones and Woodward (1872–1893) is purely typological and hardly applicable in palaeobiology. Continuous gradations exist between the various morphological types. The lack of systematically distinctive features explains the unsuitability of Aptychopsis for biostratigraphical use. Aptychopsids occur in the Silurian of Central Bohemia between the Spirograprus turriculatus Zone and the Neodiversograptus nilssoni Zone, inclusive, with maximum frequency in the uppermost Wenlockian.

Boionautilus gen. nov. from the Silurian of Europe and North Africa (Nautiloidea, Tarphycerida)

“…This age is not in contradiction with the verified stratigraphic range of Boionautilus tyrannus in the Prague Basin. In addition, the orthocerid Aptychopsis figured by Turek (1978) comes from older, i.e. Wenlockian horizon of the same locality.…”

“…Dzik (1984, in explanation to pl. 42) assigned them with reservation to Heracloceras Teichert, 1940, preferring to derive this genus from Charactoceras Foerste, 1924. Turek & Marek (1986 classified these coiled nautiloids as Cumingsoceras Flower in Flower & Kummel, 1950, a genus that, according to Dzik (1984, is synonymous with Uranoceras Hyatt, 1884.…”

“…Turek & Marek (1986) assigned species described by Barrande (1865Barrande ( -1877 from Central Bohemia to this genus while Dzik (1984) synonymized Cumingsoceras Flower in Flower & Kummel, 1950 with Uranoceras Hyatt, 1884. Comparison of these coiled nautiloids is difficult especially due to the lack of information concerning the siphuncle and muscle scars in Cumingsoceras.…”

“…Later Novák (1886) added one new species. The stratigraphical range of Boionautilus in the Prague Basin is from upper Ludlow to upper Přídolí (Turek & Marek 1986, Manda in Kříž 1998). …”

Orthoconic cephalopods and associated fauna from the late Ordovician Soom Shale Lagersta¨tte, South Africa

“…A Silurian straight-shelled orthocerid, Aptychopsis prima Barrande, has been described with three flat plates at the entrance to the body chamber. These plates have been interpreted as jaws (Zakharov and Lominadze 1983), as jaws and an operculum (Dzik 1981), and as an operculum only (Holland et al 1978;Turek 1978;Stridsberg 1984). Reticycloceras sp., an orthoconic nautiloid from the late Mississippian Bear Gulch Limestone, has a mandible preserved as a faint carbon film (Mapes 1987).…”