Pseudorutoceras bolli, Barrande, 1866

Turek, Vojtěch, 2009, Colour patterns in Early Devonian cephalopods from the Barrandian Area: Taphonomy and taxonomy, Acta Palaeontologica Polonica 54 (3), pp. 491-502 : 496-497

Pseudorutoceras bolli

Specimen NM−L 449 of Cyrtoceras bolli Barrande, 1866 illustrated by Barrande (1866: pl. 119: 5–9; Fig. 6 herein), repreary pigmentation showing the concentration of dark pigment in narrow transverse or also in longitudinal ridges has also been observed in some Silurian nautiloids. Darker narrow undulating lines represent more conspicuous lamellae repeating in regular intervals on the surface, as is common in some nautilids. A similar case of false colour pattern has been described in Bactrites from the Carboniferous ( Mapes 1979). False colour patterns on cephalopod shells have been discussed in more detail by Mapes and Davis (1996) and Klug at al. (2007).

senting the type species of newly established genus Pseudorutoceras Manda and Turek, 2009 , comes from the Lower Devonian (Dalejan, Daleje−Třebotov Formation, Třebotov Limestone); locality Praha−Hlubočepy. A part of the body chamber with Barrande's inscription represents a weathered and slightly deformed internal mould of an incomplete specimen. The entire surface of the specimen is artificially abraded. The specimen is preserved in a light micritic limestone and is limonitised on the surface .

Dark grey thin transverse lines are seen on the adapical part of the phragmocone in the ventral and ventrolateral regions. The lines are sharp with well−defined edges. Their width is 0.1–0.3 mm, and each is separated by wider interspaces, 0.8–1.2 mm across. Their wavy course shows a marked medially situated shallow ventral lobe. It passes into broad saddles, then into ventrolaterally situated lobes. A short continuation laterally indicates a similar course but these lines fade further laterally.

Foerste (1930), when studying this specimen supposed that these lines extended in the same manner around the dorsal side, and he estimated the total number of waves (sine curve) to be six or seven. Though Foerste (1930) accepted Barrande's (1866) opinion dealing with the nature of these lines, the present author proposes that these lines formed by dark grey calcite represent a false colour pattern. Owing to the translucent abraded surface of the specimen it is evident that they represent projections of incremental lamellae growing below the old shell with the surface, and therefore, these features are not a colour pattern ( Turek 1990). Unfortunately the shell sculpture is not preserved neither on this specimen, nor in Barrande's (1866) another specimens assigned to the same species. The course of the dark grey calcite lines was compared with the course of growth lines in some Devonian rutoceratids, and the two features seem to be generally concordant. Second−

Figures

Fig. 6. False colour pattern in Pseudorutoceras bolli Barrande, 1866. NM−L 449 from Praha−Hlubočepy, Dalejan, Daleje−Třebotov Formation, Třebotov Limestone. A. A part of the body chamber with original Barrande's inscription noticing “test”, aperture up. B. The same specimen in opposite orientation, artificially abraded adapical part with wavy dark lines; ventrolateral view.