Conotheca Missarzhevsky, 1969

Malinky, John M. & Skovsted, Christian B., 2004, Hyoliths and small shelly fossils from the Lower Cambrian of North-East Greenland, Acta Palaeontologica Polonica 49 (4), pp. 551-578 : 571

Genus Conotheca Missarzhevsky, 1969

Type species: Conotheca mammilata Missarzhevsky, 1969 , Tommotian Stage , Lower Cambrian, Siberian Platform .

Diagnosis.—Shell conical with circular cross−section and transverse elements of sculpture on the exterior; aperture planar and operculum with cardinal processes and circular ridges on interior.

Remarks.—This genus was erected for calcareous tubular fossils by Missarzhevsky (1969) from the Lower Cambrian of Siberia. He classified it as an orthothecid hyolith within the family Circothecidae Missarzhevsky, 1969 , an assignment retained by Bengtson (1990b). However, Qian and Bengtson (1989) described Conotheca subcurvata ( Yu, 1974) under the heading “other tubular shells”, and pointed out that morphologic gradations between Conotheca and several other calcareous tubular forms could suggest that Conotheca might even be an anabaritid. If Conotheca indeed is a hyolith, it would be yet another example that seems to combine characteristics of both Hyolithida and Orthothecida . The tubular conch without distinct dorso−ventral differentiation and lack of a ligula, and operculum lacking the rooflets and furrows support affinity to Orthothecida . However, the rounded clavicle−like structures seen on the inner surface of the operculum of C. australiensis Bengtson, 1990b are a feature more closely associated with Hyolithida . Despite generally good overall preservation of Conotheca from North−East Greenland, the specimens shed no new light on the question of affinity, and we considered it a taxon of unknown affinity for the present. Specimens referred to Conotheca from Antarctica were recently described by Wrona (2003).

Stratigraphic range and distribution.—Lower Cambrian in Siberia, Kazakhstan, India, South China, Australia, Antarctica, USA (New York), and North−East Greenland.