Similotheca bastionensis, Malinky & Skovsted, 2004
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publication ID |
https://doi.org/ 10.5281/zenodo.13522197 |
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persistent identifier |
https://treatment.plazi.org/id/03F8878E-FF91-FF99-FF94-F93AFECDFA83 |
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treatment provided by |
Felipe |
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scientific name |
Similotheca bastionensis |
| status |
sp. nov. |
Similotheca bastionensis sp. nov.
Fig. 2B View Fig ,?C.
Holotype: MGUH 27082 View Materials from GGU sample 314835.
Type horizon: Bastion Formation, Lower Cambrian.
Type locality: North−East Greenland.
Etymology: From the Bastion Formation in North−East Greenland where the type material was discovered.
Material.—MGUH 27082–27083 and six additional specimens from GGU samples 314807 and 314835.
Diagnosis.— Similotheca having coarse transverse rugae on the dorsum and narrow longitudinal concavities immediately adjacent to the dorsal keel.
Description.—Conch orthoconic with large apical angle such that conch has wide appearance; venter flat, grading into sharp, bluntly rounded lateral edges; dorsum low with prominent, well−developed median ridge; side of ridge marked by prominent ribs; each dorsal flank has a narrow, shallow longitudinal concavity adjacent to the median ridge, and the flanks overall are only slightly inflated, with a gentle slope away from the ridge. Venter flat, with faint transverse growth lines on shell; ligula seemingly long and rounded at anterior edge, with steeply dipping sides.
Dorsum with two prominent longitudinal ridges on each flank that subdivide the flanks into three discrete parts of about the same width. Transverse growth ribs are convex toward aperture and are subdivided into distinct segments by longitudinal ribs. Aperture apparently orthogonal but with slight median indentation in middle of dorsal rim. Cross−section with pronounced triangular shape.
Remarks.—The concavo−convex dorsal flanks and longitudinal elements of sculpture on the dorsum support assignment to Similotheca . Similotheca similis possesses a distinctly concavo−convex dorsum, with a well−developed longitudinal concavity adjacent to the median dorsal ridge, and has much fainter transverse ornament on the dorsum. In contrast, S. bastionensis sp. nov. has a narrower dorsal concavity and much coarser transverse dorsal sculpture.
A specimen ( Fig. 2C View Fig ) with a large apical angle bears limited resemblance to Similotheca bastionensis , but its venter is slightly more inflated and convex, creating a more rounded triangular cross−section ( Fig. 2C View Fig 1 View Fig ). In addition the apical angle is not constant, but increases toward the apertural region, giving the conch a flaring appearance. There is no sculpture on the specimen, but whether this is a biological or taphonomic trait cannot be determined. Thus, its assignment to S. bastionensis can only be tentative. Specimens with a similar cross−section and apical angle from Australia were assigned by Bengtson (1990a) to “ Hyolithes ” conularioides Tate, 1892 but that taxon has a distinct dorsal indentation in the centre of the apertural rim, which is lacking in C 1 –C 4. “ Hyolithes ” conularioides is similar to the Lower Cambrian Yankongovitus Qian, 1978 from South China and India, and the Middle Ordovician Sulcavitus Syssoiev, 1958 from Sweden and Estonia, in having a longitudinal depression in the centre of the dorsum.
Stratigraphic range and distribution.—Lower Cambrian, North−East Greenland.
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