Cassitella baculata, Malinky & Skovsted, 2004

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 : 574

Cassitella baculata sp. nov.

Fig. 15 .

Holotype: Phosphatised shell MGUH 27130 ( Fig. 15A ) from GGU sample 314835, Albert Heim Bjerge , North−East Greenland.

Type horizon: Bastion Formation, Lower Cambrian.

Type locality: North−East Greenland.

Etymology: From Latin, baculum, stick, rod, for the sturdy ridges on the interior surface.

Diagnosis.—As for genus.

Material.— Holotype, paratypes MGUH 27131–27135 and 173 additional specimens from GGU samples 314807, 314808, 314809, 314835, 314904, 314906, 314908, 314919, and 314931 .

Description.—Generally cap−shaped shell of near circular to subtriangular outline, with rounded knob−like apex displaced to about one third the distance toward the proximal side of the shell. Angle of dip between apex and both distal and proximal areas equal in some individuals, but other individuals with shell curving upward between apex and proximal edge resulting in a saddle−shaped profile. Surface with fine, widely and generally equally spaced concentric ribs and narrow depressions between ribs. Two rod−like and widely diverging ridges on the internal surface emanating from proximal edge of shell. Ridges are attached to one side of shell but free on the opposite side where they terminate in a straight, rounded edge. Termination of ridges rounded, usually divided into lobes. The shell is relatively thick (up to 0.35 mm) and the interior surface often has a finely pitted ornamentation.

Remarks.—As discussed above, no previously described fossil closely resemble Cassitella baculata from North−East Greenland and no conch or other type of shell from the same suite of samples can be matched with the fossil. Although the function and taxonomic affinity of C. baculata is uncertain, the species is apparently widely distributed in the late Early Cambrian of eastern Laurentia. Undescribed specimens attributable to C. baculata are found in acid−digested limestone samples from the Aftenstjernesø Formation of North Greenland as well as the Forteau Formation of western Newfoundland (Skovsted, unpublished), making this species potentially interesting for regional biostratigraphical correlation.

Stratigraphic range and distribution.—Lower Cambrian, North−East Greenland and possibly North Greenland and western Newfoundland (unpublished).

Figures

Fig. 15. Cassitella baculata sp. nov. A. MGUH 27130, holotype; scale bars 0.2 mm; A1, view from above; A2, lateral view; A3, oblique lateral view showing ridges; A4, view showing fold and ridges. B. MGUH 27131, exterior view from above; scale bar 0.5 mm. C. MGUH 27132; scale bars 0.2 mm except C4 which is 0.1 mm; C1, oblique lateral view showing ridges; C2, view showing fold and ridges; C3, view from above; C4, enlarged view of “protoconch”. D. MGUH 27133, from GGU sample 314807; scale bars 1 mm; D1, oblique lateral view; D2, oblique view of exterior. E. MGUH 27134; scale bars 0.5 mm; E1, lateral view of interior showing diverging ridges; E2, view from above of interior showing diverging ridges. F. MGUH 27135, from GGU sample 314807; scale bars 1 mm except F3 which is 0.2 mm; F1, lateral view of interior showing diverging ridges; F2, view from above of interior showing diverging ridges; F3, enlarged view of termination of ridge. All specimens, except D and F, from GGU sample 314835.