Futakami and Haggart—early Albian (Early Cretaceous) douvilleiceratid ammonites


47


Figure 3. Whorl sections of Douvilleiceras mammillatum (Schlotheim) from Haida Gwaii. (1), GSC No. 21239, GSC Loc. 7598. (2), GSC No. 10657, GSC Loc. C-303724.


Table 1. Dimensions of specimens of Douvilleiceras mammillatum (Schlotheim, 1813) from Haida Gwaii, British Columbia


Specimen D H B B/H U U/D NR NT


GSC No. 10657 79.6 29.8 (36.8) (1.23) 27.8 0.35 26 7 +1* GSC No. 21239 (70.0) (29.2) (33.0) (1.13) -


All measurements in millimeters. Measurements in parentheses are approximate. *Indicating an additional row on each side of the venter.


than the ribs themselves. There are occasional intercalated ribs on the outer whorl of GSC No. 10657. The ribs number 26 per whorl on the outer whorl of GSC No. 10657. This specimen has eight rows of tubercles on each rib on the body chamber, but the inner row of ventrolateral tubercles on the left side of the shell is fainter than the other rows. This specimen shows an ontogenetic change in the number of tubercles on the outer whorl: six at less than approximately 50mm in diameter, seven at approximately 50–70mm, and eight at over 70mm diameter.


Dimensions.—See Table 1.


Material.—GSC No. 10657, from a sandy calcareous concretion collected at GSC Loc. C-303724. The specimen consists of approximately two-thirds of a whorl of an intermediate-sized individual, as well as the very well-preserved internal mold of the remainder of the whorl. A composite plaster cast-latex rubber mold recreates the full specimen of GSC No. 10657. Another specimen, GSC No. 21239 (figured previously as D. spiniferum (Whiteaves) byMcLearn, 1972, pl. 10, figs. 3a–c; illustrated herein in Fig. 2.1, 2), comes from GSC Loc. 7598.


Occurrence.—Whereas this species is found rarely in the lower part of the Haida Formation in Skidegate Inlet, it is widely distributed in the upper lower Albian (the mammillatum Zone) of the Mediterranean region.


Remarks.—The shell ornamentation of GSC No. 10657 (Fig. 2.3–2.8), such as mode of tuberculation and ribbing, is similar to the neotype specimen of D. mammillatum, illustrated by Casey (1962, pl. 41, figs. 5a–b), from southeast England.


- 14x2 7+1*


pl. 10, figs. 3a–c) as a specimen ofD. spiniferum, has eight rows of tubercles on the outer whorl in middle growth stage, including an additional row on each side of the venter that is not seen in typical examples of the species, and fine and delicate tuberculation and fine ribbing on the outer whorl; consequently, this specimen appears to fall outside of the range of morphological variation for D. spiniferum. It is closely similar to a specimen illustrated by Casey (1962, p. 272, text-figs. 94–d, e) as D. mammillatum var. praecox, and we herein include it within material assigned to D. mammillatum.


The present specimen, however, has a more slender whorl compared with the neotype. GSC No. 21239 (Fig. 2.1, 2.2), figured by McLearn (1972,


Douvilleiceras spiniferum (Whiteaves, 1876) Figures 4–9


1876 Ammonites stoliczkanus var. spiniferus; Whiteaves, p. 24, pl. 3, fig. 3, pl. 4, fig.1.


1900 Acanthoceras spiniferum; Whiteaves, p. 273, pl. 35, figs. 2, 3, 3a, text-fig. 14.


?1938 Douvilleiceras restitutum; Anderson, p. 175, pl. 54, fig. 2.


1962 Douvilleiceras leightonense var. pringlei; Casey, p. 277, pl. 41, figs. 3a–b, text-fig. 102j.


1967 Douvilleiceras charshangense; Mirzoyev, p. 54, pl. 7, figs. 1–5.


1972 Douvilleiceras spiniferum; McLearn, p. 62, pl. 10, figs. 1–3, pl. 11, figs. 1–2.


1972 Douvilleiceras sp. b; McLearn, p. 67, pl. 13, figs. 1A–B, pl. 26, fig. 1.


1979 Douvilleiceras tarapacaense; Etayo-Serna, p. 54, pl. 7, fig. 5, pl. 8, figs. 2, 6.


Types.—GSC No. 5014b, the lectotype selected by McLearn (1972) and illustrated byWhiteaves (1876, pl. 3, fig. 3;McLearn, 1972, pl. 11, figs. 1A–C; illustrated herein in Fig. 4), from Skidegate Inlet, west of Alliford Bay, exact locality not recorded


(Coll. J. Richardson, 1872). GSC No. 5014a, a paralectotype also figured by Whiteaves (1876, pl. 4, fig. 1; McLearn, 1972, pl. 10, figs. 1A–C), was collected from the same locality.


Ontogenetic description.—The ontogenetic development in the relatively early stage of D. spiniferum (lessthan35mminshell diameter) has been studied on selected specimens (GSC No. 10708 and GSC No. 10711) fromMaude Island. The protoconch appears roughly ellipsoidal in shape. A clear primary constriction exists at approximately 0.9mm diameter. The shell surface before the primary constriction is smooth, without any trace of ribs or tuber- cles on the whorl. After the primary constriction, a faint lateral tubercle, or possible spine, begins to appear on the mid-flanks. These tubercles number eight per whorl at approximately 2.5mm of shell diameter (Fig. 5.1). The whorl at this stage is greatly depressed, the height being much smaller than the width, and the whorl section is trapezoidal in form. The ontogenetic changes in the whorl section after about 1.5mm in shell diameter are shown in Figure 5.2. At approximately 4.2mm in diameter, faint and numerous ribs appear on the venter, lacking tubercles. They appear to be


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