Decazella vetteri ( Heyler, 1964 )

Decazella vetteri ( Heyler, 1964)

( Figs 5; 6)

Aeduella – Heyler 1964: 6-14 – Vetter 1968: 154.

Decazella Heyler, 1967a: 87 – Heyler 1969: 175-185. – Poplin & Dutheil 2005: 20.

MATERIAL. — A postrostral associated with an operculum ( MHNT. PAL. 2023.9.14 [ Fig. 5A, B, G, H]) , an isolated parietal ( MHNT. PAL. 2023.9.30 [ Fig. 5E, F]) and an isolated suboperculum ( MHNT. PAL. 2023.9.18 [ Fig. 5I, J]) .

DESCRIPTION

Specimen MHNT.PAL. 2023.9.14 shows an association of two bones, each other distant from 13 mm. The first bone ( Fig. 5A, B) has a rectangular to pentagonal shape, with a straight posterior edge and a rounded anterior edge. It is 17 mm long and 9 mm wide (length/width ratio 1.9). Its right lateral edge and anterior edge are damaged and difficult to distinguish. A strong ornamentation of elongated ridges is visible on the lateral face of the posterior edge, and diminishes towards the anterior edge. Although the anterior part of this bone is damaged, several flat tubercles can be distinguished. We identified this bone as a postrostral. The second bone ( Fig. 5G, H) is an operculum, which is well recognizable by its shape and large size (8 mm long and 17 mm high). It is almost complete, only its dorsal end was destroyed during its delicate extraction. This operculum, with a 180° bending angle, has a straight anterior and ventral edge and a slightly rounded dorsal and posterior edge, giving it a very rectangular appearance. The ratio between the width of the ventral part and the width of the dorsal part of this operculum cannot be measured with confidence due to the slight incompleteness of the postero-ventral part of the bone. It is ornamented with ridges parallel to the edges of the bone (growth lines), but no flat tubercles are visible. Even if these operculum and postrostral of MHNT.PAL. 2023.9.14 are both attributed to Decazella vetteri (see below), it is difficult to know whether they belong to the same individual or not, because they are disarticulated.

MHNT.PAL. 2023.9.30 ( Fig. 5E, F) is a slightly oblong bone, measuring 10 mm long and 6.5 mm wide (length/ width ratio 1.5). Only the posterior part of the bone is preserved, the anterior part being discernible only as a counterpart. Its anterior and posterior edges are straight, while its lateral edges are slightly concave. The bone is slightly ornamented with rounded to oval pores on its lateral surface. Two pit lines are present, but it is not possible to determine whether they join or not, as the bone is not complete enough. These pit lines form a V oriented towards the left lateral edge of the bone. The morphology and presence of pit lines in MHNT.PAL. 2023.9.30 allow us to identify it as a parietal.

MHNT.PAL. 2023.9.18 ( Fig. 5I, J) is clearly a suboperculum, as shown by its ornamentation of small flat tubercles on its lateral surface, its large size (12 mm long and 8 mm high) and its shape. One half of the bone is fully preserved, the other half appearing as a counter part. It is parallelogram-shaped, with opposite sides perfectly parallel and the same size. It is therefore impossible to determine its orientation in the anterior-posterior direction.

COMPARISONS

The postrostral of MHNT.PAL. 2023.9.14 is a large bone, ornamented with elongated ridges on its posterior part and flat tubercles on its anterior part, with a roughly pentagonal shape and rounded edges. These features enable us to assign it to Aeduellidae (e.g. Heyler 1969; Poplin & Dutheil 2005). MHNT.PAL. 2023.9.14 is extremely similar to the postrostral of MNHN.DEC.32 ( Fig. 5C, D; Heyler 1969: 183, 184, fig. 135) assigned to Decazella vetteri by Heyler (1969). These two specimens share very similar dimensions and morphology, notably with the straight posterior margin and the anterior margin forming a rounded median tip. The straight posterior margin distinguishes MNHN.DEC.32 and MHNT.PAL. 2023.9.14 from Aeduella blainvillei , Bourbonnella hirsuta Štamberg, 2007 , B. jocelynae Mickle, 2011 and Neslovicella spp. (e.g. Heyler 1969; Štamberg 2007, 2010; Mickle 2011). MNHN.DEC.32 and MHNT. PAL. 2023.9.14 are very similar to the postrostral of Westollia crassa ( Pohlig, 1892) , with the exception of the posterior end, for which the character is ambiguous (either straight or slightly wavy) ( Štamberg 2024). The postrostral of other Aeduellidae is poorly known or unknown, but Heyler (1969) hypothesised that the posterior edge of the postrostral of Decazella vetteri should be straight, based on the shape of its frontal. It is therefore entirely possible to assign MHNT.PAL. 2023.9.14 to Decazella vetteri .

The parietal MHNT.PAL. 2023.9.30 has a short rectangular shape and shows two pit lines forming a V-shaped pattern, allowing us to assign it to Aeduellidae (e.g. Heyler 1969; Poplin & Dutheil 2005). The anterior margin of MHNT. PAL. 2023.9.30 is straight, unlike Neslovicella spp. , Bourbonnella hirsuta and Aeduella blainvillei , which have V-shaped anterior margins ( Heyler 1969; Poplin & Dutheil 2005; Štamberg 2007, 2010). Decazella vetteri, Amelangia ornata Štamberg & Werneburg, 2023 , Westollia crassa , Bourbonnella fourrieri Poplin, 2001 , B. guilloti Heyler, 1967a , B. jocelynae and B. sottyi ( Anonymous, 1972) have straight anterior and posterior edges ( Heyler 1969; Poplin & Dutheil 2005; Mickle 2011; Štamberg & Werneburg 2023; Štamberg 2024). MHNT.PAL. 2023.9.30 can be distinguished from the parietal of A. ornata because in the latter, the parietal is pentagonal with a V-shaped contact with the dermopterotic ( Štamberg & Werneburg 2023). The parietals of W. crassa , B. fourrieri , B. guilloti , B. jocelynae and B. sottyi are similar to those of D. vetteri . However, MHNT.PAL. 2023.9.3 is closer to the morphology of D. vetteri parietals, for example that of holotype MNHN.DEC.25 ( Fig. 6; Heyler 1969: 176, fig.121, pl. XLIII, fig. 2).

The operculum of MHNT.PAL. 2023.9.14 can be assigned to the Aeduellidae clade based on its large size, rectangular shape and ornamentation (e.g. Heyler 1969; Štamberg 2018). It is twice as high as long, which distinguishes it from the operculum of Puertollanichthys ritchiei Forey & Young, 1985 , proportionally shorter ( Forey & Young 1985). It can also be distinguished from the operculum of Amelangia ornata , which has a very characteristic ornamentation with pointed tubercles, the apex of which is oriented posteriorly ( Štamberg & Werneburg2023). It differs from Platysella spp. in which the ventral edge of the operculum has a medial hump ( Heyler & Poplin 1983). The straight and horizontal ventral margin of MHNT.PAL. 2023.9.14 and its 180° bending angle are highly characteristic: indeed, the operculums of Bourbonnella spp. , Neslovicella spp. , Spinarichthys dispersus ( Fritsch, 1895) , Westollia crassa and Aeduella blainvillei have oblique ventral margins and/or a bending angle between 140° and 160° ( Heyler 1969; Poplin 2001; Štamberg 1986, 2007, 2010, 2018, 2024). The straight and horizontal ventral margin of MHNT.PAL. 2023.9.14 is present only in the operculum of Decazella vetteri ( Fig. 6; Heyler 1969; Poplin & Dutheil 2005). Note that among the isolated operculums from the Decazeville Basin attributed to Aeduellidae indet. by Heyler (1969), none have an horizontal ventral margin like MHNT.PAL. 2023.9.14. The operculums of D. vetteri show some variation in their bending angle, amounting to 170° in MNHN.DEC.24 but 140° in the holotype MNHN.DEC.25 ( Fig. 6; Heyler 1969: 176, 178, figs 121, 122, pl. XLIII, fig. 2 and pl. XLIV, fig. 5). The 180° bending angle of MHNT.PAL. 2023.9.14 may therefore fall within the range of intraspecific variation of this character in D. vetteri (which could be between 140° and 180°). We therefore refer the operculum of MHNT. PAL. 2023.9.14 to Decazella vetteri .

The suboperculum MHNT.PAL. 2023.9.18 has a morphology characteristic of Aeduellidae , with a trapezoidal to rectangular shape (e.g. Poplin & Dutheil 2005). Among Aeduellidae , only Decazella vetteri ( Fig. 6) and Amelangia ornata have a parallelogram-shaped suboperculum with a straight suture to the operculum ( Heyler 1969; Poplin & Dutheil 2005; Štamberg & Werneburg 2023). However, the suboperculum of A. ornata has very characteristic ornamentation with pointed tubercles, with the apex oriented posteriorly ( Štamberg & Werneburg 2023). This specimen is therefore attributable to Decazella vetteri due to its parallelogram shape and lack of characteristic ornamentation.