Trimarginia sp.

Galácz, András, 2017, Bajocian (Middle Jurassic) ammonites of stratigraphical and palaeobiogeographical importance from Mombasa, Kenya, East Africa, Geodiversitas 39 (4), pp. 717-727 : 722

Trimarginia sp.

( Figs 4G ; 5M, N )

? Oecotraustes ? ( Limoxyites ?) aff. O. nivernensis – Westermann 1975: 42, pl. 2, figs 5, 6.

? Trimarginia sp. – Galácz 1990: 202.

REMARKS

This is a septate whorl fragment with flattened and smooth flanks and trimarginate venter. The suture-line is slightly displaced on this specimen (see Fig. 4G ). The actual size of the specimen could have been about 12-14 mm, a diameter at which Arkell (1952: 308) states the presence of tertiary ribbing on the type species. However, Trimarginia iberica Fernández-López, 1985 (Fernández-López (1985: 241, pl. 16, figs 11,12) does not show development of ribs at these sizes.

The specimens figured by Westermann (1975: pl. 2, figs 5,6) are similar by the shape of the venter but differ in having faint ribs and a suture-line with better developed first lateral saddle.

T. sinaitica Arkell, 1952 (the type re-figured in Parnes 1988: pl. 2, figs 35, 36), possibly of Late Bajocian age, is associated with Normannites egyptiacus in the Sinai (see Arkell 1952: 308).

There are some similar oppeliids in the Upper Bathonian previously described as Trimarginia (see ‘ Oppelia [ Trimarginia ] sinaitica ’ in Wendt [1963: 123], and ‘ Trimarginia sylviae ’ in Mangold & Gygi [1997: 502]). They are similar, but regarded here as Bathonian homoeomorphs.

Figures

FIG. 4. — Suture lines of some important species: A, Oecotraustes sp. MR 1, EMNH.2015.249; B, Cadomites (Cadomites) sp. MR 1, EMNH.2015.232; C,?Diplesioceras sp. MR 1, EMNH.2015.180; D, Spiroceras annulatum (Deshayes, 1831) MR 2, EMNH.2015.287; E, Leptosphinctes cf. schmiereri (Bentz, 1924) MR 2, EMNH.2015.224; F, Nannolytoceras polyhelictum (BÖckh, 1881) MR 2, EMNH.2015.257; G, Trimarginia sp. MR 2, EMNH.2015.279. Scale bar: 5 mm.

FIG. 5. — A, B, Phylloceras trifoliatum Neumayr, 1871 MR 1, EMNH.2015.286; C, D, Phylloceras trifoliatum Neumayr, 1871 MR 2, EMNH.2015.285; E, F, Ptychophylloceras lardyi (Ooster,1860) MR 1, EMNH.2015.303; G, H, Calliphylloceras disputabile (Zittel,1868) MR 1, EMNH.2015.304; I, J, Holcophylloceras zignodianum (d’Orbigny, 1848) MR 1, EMNH.2015.259; K, L, Nannolytoceras polyhelictum (BÖckh,1881) MR 2, EMNH.2015.257;M, N, Trimarginia sp. MR 2, EMNH.2015.279; O, P, Lissoceras oolithicum (d’Orbigny,1845) MR 2, EMNH.2015.268;Q, R, Oecotraustes sp. MR 1, EMNH.2015.249;S,?Diplesioceras sp.MR 1, EMNH.2015.180; T, U, Cadomites (Cadomites) sp. MR 1, EMNH.2015.232; V, W, Normannites egyptiacus Arkell, 1952 MR 2, EMNH.2015.288; X, Y, Spiroceras annulatum (Deshayes, 1831) MR 2, EMNH.2015.287. Scale bar: 10 mm.