Pileograptus pileatus, Lenz And Anna Kozłowska, 2007

Lenz And Anna Kozłowska, Alfred C., 2007, New and unusual upper Llandovery graptolites from Arctic Canada, Acta Palaeontologica Polonica 52 (3), pp. 489-502 : 496-497

Pileograptus pileatus sp. nov.

Figs. 3–5.

Derivation of the name: From Latin pileus, “cap”; referring to cap−like thecal hoods.

Holotype: GSC38912 , Figs. 3A 1 –A 3. Rhabdosome with proximal end well developed five pairs of thecae.

Type locality: Cape Sir John Franklin, Devon Island, Arctic Canada.

Type horizon: Upper Llandovery.

Material.— Twenty specimens, all immature, in various stages of development.

Diagnosis.—As for genus.

Description.—Rhabdosome of most mature specimen with five pairs of thecae 3.7 mm long, maximum distal width 2.4 mm inclusive of thecal hoods. Ancora umbrella deep, bowl−shaped, of Stomatograptus type, about 1.0 mm wide, made up of more or less equal−sized and regular hexagonal meshes; well−developed prosicula present in every specimen, length totalling 0.9–1.0 mm, of which about 0.4 mm of the apical end is preserved mostly as longitudinal threads. Thecal framework consists of zigzag lists present on one side of rhabdosome, transverse rods situated close to the nema ( Fig. 3A 2), concave curved lateral apertural lists inclined overall about 60 ° to axis of rhabdosome, and apertural rims that are well−developed and slightly thickened; ancora sleeve made of fairly dense meshwork of orderly hexagonal meshes, meshes 0.1–0.2 mm in diameter.

A single prominent ancora sleeve stoma of more or less ovate outline developed about level with third thecal pair on both lateral walls, rimmed by well−developed, but loose collar−like meshwork ( Fig. 3A 1 –A 3, B 3). Thecal orifice directed ventrally, with prominent meshwork, genicular hood, reminiscent of the “bill” of a baseball cap. Hood−anchoring lists attached to underside of succeeding thecal lateral apertural lists ( Fig. 3A 1); hood−anchoring lists directed proximoventrally initially, and then abruptly curving ventrally; hood curved ventro−proximally, widening laterally. Lists with weak, parallel micro−ornamentation ( Fig. 3B 1).

Discussion.—The very large and broad thecal hoods of P. pileatus are reminiscent of those of the upper Homerian species e.g., Papiliograptus papilio Lenz and Kozłowska−Dawidziuk, 2002 . In the latter species, however, the hoods are clearly extensions from the geniculum and the thecal structures and thecal framework are completely different.

Stratigraphic and geographic range.—As for genus.