Conotheca australiensis Bengtson, 1990b

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 : 572-574

Conotheca australiensis Bengtson, 1990b

Fig. 14 .

Conotheca australiensis Bengtson, 1990b: 216 , figs. 143, 144.

Conotheca laurentiensis Landing and Bartowski, 1996: 756 , figs. 7.1– 7.8, 7.20.

Conotheca australiensis Bengtson, 1990b ; Demidenko 2001: 98, pl. 10: 1, 2.

? Conotheca cf. australiensis Bengtson, 1990b ; Wrona 2003: 191, fig. 5A–E.

Holotype: South Australian Museum , Adelaide SAMP30877 .

Material.— MGUH 27121–27129, 69 additional conchs and 314 opercula from GGU samples 314802, 314804, 314806, 314807, 314809, 314835, 314836, 314901, 314904, 314906, 314908, 314909, 314910, 314918 and 314933.

Description.—Gently tapering conch with small apical angle of about 15°; conch may have slight helical coil; aperture is planar and lying in a plane perpendicular to long axis of conch. Shell covered with closely though irregularly spaced transverse lines of varying intensity in different places on conch; apical termination unknown.

Operculum circular in outline; exterior with rounded summit that may be lower than surrounding surface; exterior may have coarse concentric lines; interior with two cardinal processes that diverge at angle of about 50°; cardinal processes broad at base but taper to eventually terminate in blunt rounded surface; emanating from the cardinal processes is a circular ridge set inward from edge of operculum. Interior otherwise smooth.

Remarks.—Specimens of Conotheca from North−East Greenland are assigned to C. australiensis based chiefly on features of the operculum. The interior matches quite well with specimens from Australia in terms of cardinal processes and the ridge that develops in places into tubular clavicles. Without the operculum, assignment to species is far more difficult because diagnostic morphologic features of a tubular conch are relatively few; they are limited mostly to the nature of ornament, apical angle and cross−section. The extensive synonymy under C. subcurvata ( Yu, 1974) given by Qian and Bengtson (1989) well illustrates the problems surrounding recognition of different species among tubular fossils of generally limited morphologic variability. The conchs and opercula are referred to the same species as they co−occur at the same level and localities, and match each other in cross−section. Had only the conchs of the Greenland specimens been discovered, those individuals may just as easily have been accommodated under C. mammilata Missarzhevsky, 1969 . Conotheca circumflexa Missarzhevsky, 1969 and C. subcurvata ( Yu, 1974) both possess pronounced apical curvature, but several Greenland specimens under C. australiensis curve apically as well ( Fig. 14F–I ).

Landing and Bartowski (1996) described Conotheca laurentiensis from the Browns Pond Formation from the Taconic Allochthon of New York State, and distinguished the species from C. australiensis by the longer cardinal processes of the operculum. As this feature appear to be variable in the Greenland material, C. laurentiensis is here regarded as a junior synonym of C. australiensis . Internal moulds from King George Island, Antarctica of more questionable affinity to C. australiensis has recently been described by Wrona (2003).

Stratigraphic range and distribution.—Lower Cambrian; Australia, USA (New York), North−East Greenland and possibly Antarctica.

Figures

Fig. 14. Conotheca australiensis Bengtson, 1990b. A. MGUH 27121, from GGU sample 314933; A1, conch in lateral view; A2, cross−section of conch; A3, enlarged view of ornamentation. B. MGUH 27122, from GGU sample 314835; B1, B2, interior views of operculum. C. MGUH 27123, from GGU sample 314933, lateral view. D. MGUH 27124, from GGU sample 314835, interior view of operculum. E. MGUH 27125, from GGU sample 314835; E1, E2, exterior views of operculum. F. MGUH 27126, from GGU sample 314906, cross−section. G. MGUH 27127, from GGU sample 314804; G1, G2, lateral views. H. MGUH 27128, from GGU sample 314906, lateral view. I. MGUH 27129, from GGU sample 314809, lateral view. All scale bars 0.2 mm, except A1 and A2 which are 0.5 mm.