Contitheca, Syssoiev, 1972

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 : 566-568

publication ID	https://doi.org/ 10.5281/zenodo.13522197
persistent identifier	https://treatment.plazi.org/id/03F8878E-FF9D-FF8C-FCDE-FC21FB97FA7D
treatment provided by	Felipe
scientific name	Contitheca
status

Treatment

Contitheca ? sp.

Fig. 9D View Fig .

Material.—MGUH 27111 and 15 additional specimens from GGU samples 314809, 314906, 314908, 314909, and 314933.

Description.—Seemingly slightly cyrtoconic conch with curvature toward venter; apical angle small, giving conch tubular appearance, venter has pronounced, deep longitudinal furrow which is bounded on both sides by well−developed high−standing longitudinal ridges having sides steeply dipping toward furrow; dorsum with high median ridge and steeply dipping flanks adjacent to it, to creating a decidedly heart−shaped cross−section. Surface of conch seems smooth.

Remarks.—This taxon is only known from incomplete specimens, yet its most distinctive features, the deep longitudinal furrow on the venter and resulting heart−shaped cross−section, are easily discernible ( Fig. 9D View Fig 2 View Fig ). It clearly resembles Contitheca Syssoiev, 1972 from the Middle Cambrian of Sweden, Morocco, Korea and Antarctica, and is referred to it with question, owing to incomplete preservation. The high dorsum with slightly inflated flanks and pronounced heart−shaped cross−section suggest that the Greenland material may represent a new species, but given the fragmentary nature of all specimens, assignment to species is not advisable at this time. If better preserved material bears out the contention that Contitheca is present in the Lower Cambrian of North−East Greenland, this genus now ranges into the Lower Cambrian, and its geographic distribution includes North−East Greenland. It is worth noting that the two surviving specimens of Lenatheca groenlandicus ( Poulsen, 1932) from among the Siberian material of Missarzhevsky (1969) resemble Contitheca ? sp. in the depth of the ventral furrow, but because the dorsum is unknown, they cannot be compared further with Contitheca ? sp.

Stratigraphic range and distribution.—Lower Cambrian, North−East Greenland.

“ Orthotheca bayonet var. groenlandica ( Poulsen, 1932) ”

Fig. 10A–C View Fig .

Hyolithus (Orthotheca) bayonet var. groenlandicus Poulsen, 1932: 20 , pl. 3: 1–3.

Material.— MGUH 3526 ( Fig. 10C View Fig 3 View Fig = Poulsen 1932: pl. 3: 3); MGUH 3521 ( Fig. 10A View Fig 3 View Fig = Poulsen 1932: pl. 3: 2); MGUH 3523 ( Fig. 10B View Fig = Poulsen 1932: pl. 3: 1).

Description.—Apical region of conch cyrtoconic, venter appears flat but has very shallow longitudinal furrow; lateral edges bluntly rounded grading into relatively high dorsum with inflated flanks that terminate in pronounced median ridge; crest of ridge nearly angular, and cross−section nearly triangular with slight depression on ventral side. Aperture apparently planar without indentations on either dorsal or ventral rim. Surface of shell has distinct transverse ribs of slightly unequal spacing and intensity on both dorsum and venter.

Remarks.—The planar aperture and shallow longitudinal furrow on the venter indicate that this species belongs within the

Order Orthothecida . It is therefore designated “ Orthotheca ”, not because it represents the genus Orthotheca Novák, 1886 from the Lower Devonian of the Barrandian, but because of its affinity to the order Orthothecida . Poulsen (1932) assigned it to H. (O.) bayonet Matthew, 1899 but placed it into the subspecies groenlandicus because the dorsal flanks are slightly inflated. Matthew’s (1899) species is distinctive because the lateral edges are developed into elongate protuberances which extend away from the shell.

Fig. 10A and C View Fig appear to represent the same species based especially on the dorsal morphology in which growth lines, indicating the presence of a short projection on that side, are present. The venter of Fig. 10C View Fig is not well enough preserved to meaningfully compare it to Fig. 10A View Fig . Fig. 10B View Fig in contrast appears to belong to a different taxon based on the narrower conch, and deep, narrower longitudinal ventral furrow.

Missarzhevsky (1969) designated Poulsen’s species as type species of Lenatheca . Given the poor preservation of Poulsen’s (1932) material, the genus cannot be considered well−founded, and specimens from Siberia included under it by Missarzhevsky (1969) add little to the concept of the taxon. The surviving specimens of Lenatheca (GIN 3593/197 = Missarzhevsky 1969: pl. 10: 17 and GIN 3593/42 = Missarzhevsky 1969: pl. 13: 12, 13) are themselves poorly known. The former is an exposed venter, and the latter exposes the venter and the right lateral edge, but that specimen appears to have been weathered, and no details remain except for the overall shape of the conch. Poulsen’s (1932) material is markedly different from the Siberian Lenatheca in having a larger apical angle. Furthermore, Poulsen’s specimens which are largely incomplete seem to represent two different taxa, neither of which appears to be the same as any Siberian specimen. Thus further use of the name Lenatheca for orthothecid hyoliths is to be discouraged.

Stratigraphic range and distribution.—Lower Cambrian, North−East Greenland.

“ Orthotheca bayonet var. longa ( Poulsen, 1932) ” Fig. 10E View Fig .

Hyolithus (Orthotheca) bayonet var. longus Poulsen, 1932: 20 , pl. 3: 4.

Material.— MGUH 3526.

Description.—Conch seemingly orthoconic with small apical angle, giving conch narrow, gently tapering appearance; venter with shallow median longitudinal furrow bounded on each side by very low longitudinal ridges; surface of shell seemingly smooth without any transverse or longitudinal elements of sculpture.

Remarks.—Comments above under the previous species apply here as well regarding the assignment to H. (O.) bayonet Matthew, 1899 . Poulsen (1932) accorded subspecies status to this specimen because of its smaller apical angle. It also is referred to “ Orthotheca ” for the same reasons as the previous species. Because so little of this specimen is known, confident assignment to any species is impossible. Poulsen (1932: 20) said that he had five specimens of this taxon, but thus far only the illustrated specimen has been located.

Stratigraphic range and distribution.—Lower Cambrian, North−East Greenland.

“ Orthotheca billingsi ( Walcott, 1886) ”

Fig. 10F View Fig .

Hyolithus (Hyolithus) billingsi Walcott ; Poulsen 1932: 22, pl. 3: 6.

Material.— MGUH 3528.

Description.—Orthoconic conch with small apical angle; venter with two shallow longitudinal depressions near each edge with region between depressions slightly convex and inflated; shell smooth; all else unknown.

Remarks.—This species is known from one individual that has the dorsum embedded in matrix. The absence of any apparent growth lines or other elements of sculpture on the shell suggest affinity to the Orthothecida , although the middle of the venter is inflated slightly, owing to the presence of two longitudinal furrows on each side. The morphology of the conch may be accommodated under either Hyolithida or Orthothecida , and confident assignment at this time is impossible due to limited knowledge of this taxon.

Stratigraphic range and distribution.—Lower Cambrian, North−East Greenland.

“ Orthotheca communis ( Billings, 1872) ”

Fig. 10D View Fig .

Hyolithus ( Orthotheca ?) communis Billings ; Poulsen 1932: 20, pl. 2: 10–11.

Material.— MGUH 3524 ( Poulsen 1932: fig. 10 = Fig. 10D View Fig 3 View Fig , fig. 11 = Fig. 10D View Fig 1 View Fig ).

Description.—Orthoconic conch with venter nearly flat having only shallow longitudinal depression; lateral edges tightly rounded grading into inflated dorsal flanks which meet in broad median ridge; surface of shell and internal mould smooth.

Remarks.— One specimen represents this taxon and it appears to have smooth shell entirely lacking growth lines or any other ornament. The generally featureless quality of this specimen suggests that it is preserved as an internal mold, but without doubt this individual possesses shell on the dorsum and part of the venter, because the shell has been broken away partly on the venter to expose a smooth internal mold. The apical end has been cut and polished to reveal the cross−section ( Fig. 10D View Fig 1 View Fig ). Hyolithes communis Billings, 1872 has a tubular conch, but its affinity to the Hyolitha is beyond question, owing to the ventral ligula and interior of the operculum with clavicles and cardinal processes in place. Furthermore, the shell is covered with transverse rugae, which are lacking in the Greenland species. It is unlikely that the Greenland species and H. communis Billings, 1872 from New York belong to the same taxon.

Stratigraphic range and distribution.—Lower Cambrian, North−East Greenland.