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Terebratulina manchionealensis sp. nov.
Pl. 1, fig. 8; Pl. 3, figs. 3-6.
Holotype – A disarticulated conjoined pair, MGUH 28774a, b (Pl. 3, figs. 5, 6) from the Manchioneal Formation, Christmas River (J3), Jamaica.
Type locality and horizon – Christmas River, Manchioneal Formation (J3) (lower Pleistocene).
Material – About 90 shells of this species have been collected from localities on both Jamaica and Barbados.
Derivation of name – Named after the Manchioneal Formation on Jamaica from whence the majority of the Pleistocene specimens were collected.
Diagnosis – Small, elongately oval to subtriangular Terebratulina species with ventral sulcus and subcarinate dorsal valve. Usually 6-8 ribs per 2 mm at 5 mm growth stage.
Description – Small, dorsibiconvex valves of elongately oval to subtrigonal outline. Maximum width about twice hinge width, occurring at or near mid-valve length; cardinal extremities obtuse and rounded. Anterior commissure uniplicate. Ventral valve about nine-tenths as wide as long and about one-fifth as deep as long. Anterior profile with narrow, relatively deep median sulcus originating near prominent umbo and developing anteriorly; flanks convex medianly with steep lateral slopes. Lateral profile convex with maximum curvature at mid-valve length. Large suboval pedicle foramen perforates shell apex. Dorsal valve about as long as wide and about one-fourth as deep as long. Anterior profile subcarinate with prominent median fold and sloping, slightly concave flanks; lateral profile uniformly convex with marked umbo. Ornament of variably accentuated costae and costellae numbering 5-8 per 2 mm at 5 mm growth stage on 1, 7, 9 and 8 valves, and arising by both bifurcation and intercalation.
Ventral interior with short pedicle collar; large, elongate teeth. Dorsal interior with small transverse cardinal process; socket ridges thin and elevated. Crural processes directed ventrally and medianly, but distal extensions either broken or obscured; anterior part of loop, concave and flattened.
Statistics –
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Discussion – Initial studies of this species suggested that the distinctive outline, development of the dorsal fold and ventral sulcus together with the style and density of the radial ornament invite a close comparison with T.? palmeri Cooper from the Miocene of Cuba. Cooper (1979, p. 7) considered, however, that T.? palmeri was rather anomalous. Apart from having a subcarinate dorsal fold and narrow ventral sulcus, the species lacked a complete loop; the crural processes are directly dorsally, but only slightly medianly, obviating the possibility to unite and form a loop. This same configuration is not apparent in the few dorsal interiors available from Barbados. Both groups of species are thus no longer considered congeneric. Cooper (1979, p. 7) suggested that the loop was much more similar in orientation and structure to that of Chilidonophora rather than that of Terebratulina. The possibility of homoplasy or the reassignment of the T.? palmeri to the Chilidonophoridae requires further material of Cooper’s species together with a rigorous phylogenetic analysis of the group.
The large sample now available indicates that there are further differences between the Pleistocene form and Cooper’s species from the Miocene of Cuba. A PCA analysis of the correlation matrix, based on saglv, sagld, mwi and thickness (= dpv+dpd), of a sample of 25 specimens of the Pleistocene form together with the nine measured specimens of T.? palmeri presented in Cooper (1979, p. 7) suggests first the Cuban specimens are larger (higher scores on the first [size-related] eigenvector), and second the Pleistocene species is on average narrower (most Cuban specimens have lower scores on the second eigenvector that itself has a high negative loading of maximum width). Moreover, the Pleistocene species has a less-narrow ventral sulcus and less-marked carinate dorsal valves. Although Cooper did not present numerical data for the rib density of his new species, measurements on his figured specimens suggest that the rib density of the Cuban species (usually 5 or 6 ribs per 2 mm at the 5 mm growth stage) may be less than that for the Pleistocene species.
The material obtained from the Manchioneal Formation was compared by PCA ordination with specimens of Terebratulina from the ‘newer Pliocene’ within the Lucas Barrett collection (Harper, 1993); no separation was achieved along any of the eigenvectors, thus the two samples are considered conspecific. The new large sample now available from Jamaica was also compared, using PCA, with two specimens from Barbados. Separation was achieved only on the fourth eigenvector, which accounts for only 1 % of the sample variation. The two Barbados specimens have lower scores on this axis than those of the Jamaica material; since the depth of the dorsal valve has a large negative loading on this vector, the Barbados specimens have deeper dorsal valves.
Occurrence – A printing error in Harper (2002a, table 12.1) omitted the symbol ‘J’ (for Jamaica) in the ‘Pleistocene’ column for this taxon. This species is common on Jamaica at Christmas River (J3), and occurs at the type section of the Manchioneal Formation (J2), Cruikshank Bay (J1), San San Bay (J4), Folly Point (J5) and Port Maria (J6); approximately 65 shells of this species are now known from the Jamaican localities. On Barbados, the species is most common at Skeete’s Bay, Whitehaven (B1), but it also occurs at Spring Bay, Ragged Point (B3) together about 25 shells.
Suborder Terebratellidina Muir-Wood, 1955
Superfamily Megathyridoidea Dall, 1870
Family Megathyrididae Dall, 1870
Genus Argyrotheca Dall, 1900
Type species – Terebratula cuneata Risso, 1826, by original designation; from the Recent of the Mediterranean Sea.