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Obolella crassa
Taxonomy
Orbicula crassa was named by Hall (1847) [Orbicula? crassa. Late Early Cambrian, middle Dyeran Stage (Botomian) of North-East Greenland. Late Early Cambrian, eastern United States and Canada]. It is not a trace fossil.
It was recombined as Obolella crassa by Skovsted and Holmer (2005), Peel (2021).
It was recombined as Obolella crassa by Skovsted and Holmer (2005), Peel (2021).
Synonymy list
| Year | Name and author |
|---|---|
| 1847 | Orbicula crassa Hall p. 290 fig. 79.8a |
| 2005 | Obolella crassa Skovsted and Holmer pp. 340 – 342 figs. pl. 5 f. 1–15 |
| 2021 | Obolella crassa Peel pp. 9 - 11 fig. 6 |
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
†Obolella crassa Hall 1847
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Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| C. B. Skovsted and L.E. Holmer 2005 | Shell biconvex, circular to ovate; ornamentation of marked concentric ridges and fine growth lines; ventral pseudointerarea catacline with deep, parallel-sided, delthyrium; ventral valve interior with low visceral platform and widely divergent vascula lateralia; dorsal valve with broad median ridge.
Description. Shell circular, slightly to moderately biconvex in small individuals, strongly biconvex in large valves. Ornamentation of concentric growth lines and faint radial striae, the latter commonly more pronounced towards the lateral margins. Ventral valve with low, catacline interarea bisected by deep, parallelsided, delthyrium. Delthyrium usually open, but sometimes developed into a tube by overgrowth of the delthyrial margins. Ventral beak marginal. Dorsal valve with short orthocline interarea with thin propareas separated by triangular notothyrium. Dorsal beak marginal. Ventral visceral field forming a low platform, bisected by median ridge in larger specimens. Ventral posterior adductor scars deeply inserted medianly, immediately below propareas. Ventral anterior adductor and internal oblique scars not differentiated. Ventral vascula lateralia submedian, strongly curved and divergent. Dorsal visceral area bisected by prominent median ridge. Posterior dorsal adductor scars deeply impressed below propareas. Elongated dorsal anterior adductor scars separated by median ridge. Dorsal vascula lateralia submarginal, usually weakly developed. First-formed shell small (c. 0Æ3 mm across), smooth and circular. Early adult shell ornamented by fine growth lines and occasionally radial striae, while raised concentric ridges are present in larger specimens. Internal moulds of both valves sometimes covered with small (5–10 lm across), circular, knob-like, projections corresponding to minute pits on the internal surface of the original shells. Internal moulds of a few valves also have impressions of a fibrous shell structure, with fibres on average 2Æ5 lm in width. |
Measurements
No measurements are available
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| Source: g = genus, o = order, c = class, p = phylum, uc = unranked clade | |||||
| References: Hendy 2009, Nesnidal et al. 2013, Aberhan et al. 2004 | |||||
Age range: Dyeran or 515.30000 to 509.70000 Ma
Collections (11 total)
| Time interval | Ma | Country or state | Original ID and collection number |
|---|---|---|---|
| Dyeran | Greenland | Obolella crassa (49456 49457 49460 49461 49463 49464 49471 67776 67781) | |
| Dyeran | Greenland (Peary Land) | Obolella crassa (210618) | |
| Dyeran | Canada (Newfoundland and Labrador) | Obolella crassa (50783) |