Vilkitskilepis valentinae, Märss, 2002
|
publication ID |
https://doi.org/ 10.5281/zenodo.5374651 |
|
persistent identifier |
https://treatment.plazi.org/id/03824E41-756A-FF82-2DA7-4764D9E855BB |
|
treatment provided by |
Marcus |
|
scientific name |
Vilkitskilepis valentinae |
| status |
sp. nov. |
Vilkitskilepis valentinae n. sp. ( Figs 3G; 5 View FIG ; 6 View FIG )
HOLOTYPE. — Trunk squamation, LIG 35-909 A and B, part and counterpart.
TYPE LOCALITY AND HORIZON. — Sample 67-12, Pod’’emnaya River, October Revolution Island, Severnaya Zemlya Archipelago, Severnaya Zemlya Formation, Lochkov, Lower Devonian.
ETYMOLOGY. — Named in honour of Dr Valentina Talimaa, a colleague of mine and a researcher who has studied lower vertebrate palaeontology for many years.
DIAGNOSIS. — Branchial area ends with postbranchial and pectoral(?) plates. The 25 (26?) dorsal ridge scales preserved are large. Each ridge scale straddles four to five trunk scales in the middle of the row. Dorso-lateral, ventro-lateral and ventral scales, and dorsal ridge scales form the trunk squamation. Anal fin is comparatively short, covered with narrow, straight, tiny posteriorly directed scales. Head and caudal skeleton unknown. Scales tuberculated anteriorly, and ridged in the middle of the scales. Dorsal ridge scales covered with elongated tubercles. Microstructure from lamellar aspidine.
DESCRIPTION
In the description, the terminology of Kiaer (1924) and Ritchie (1964) is used. A large portion of the holotype is preserved in part and counterpart (LIG 35-909 A and B; Figs 5 View FIG ; 6 View FIG ). It exposes trunk squamation, partly seen in visceral view; the scale covering is partly displayed as a
vs
natural mould, the sculptured surface lacking. The scales are smooth, with a longitudinal rib internally, and sculptured external surface. Anteriorly the part of the holotype exhibits the area of the branchial band, and posteriorly, behind the anal fin, a fragment of the caudal peduncle. Its counterpart is shorter and broken off at a short distance behind the branchial band. The specimen is laterally compressed. The maximum preserved length is 78 mm; the length between the anterior end of the base of the postbranchial plate and the anterior limit of the anal fin is 40 mm. The maximum (compressed) height is 40 mm; the minimum height, 17 mm, is located behind the anal fin on the caudal peduncle. The height from the base of the postbranchial plate up to above the dorsal ridge scales is 32 mm.
Head
A few rows of head scales are preserved in front of the branchial band (bb, Figs 5 View FIG ; 6 View FIG ), but they are strongly compressed. The latter is a narrow, barren, band-like area, where no finer details can be seen. It forms an oblique area, about 1.5 mm wide and 15 mm high, at an angle of 35°, similar to the branchial band of Pterygolepis Cossmann, 1920 (see Kiaer 1924: 59). Anteriorly to the branchial band, the prebranchial scales (pbs, Figs 5 View FIG ; 6 View FIG ) are compressed and shorter, but have the same direction as the trunk scales. Above the branchial band, the scales are directed more anteriorly. In internal view the postbranchial plate and pectoral plate(?) (pbp and pp(?), Figs 5 View FIG ; 6 View FIG ) are situated at the posterior end of the branchial band.
Trunk
The arrangement and shape of trunk scales are similar to those in the Norwegian Birkeniida . According to Kiaer (1924: 61) and as seen in our material, on the side of the body there is a slightly bent, longitudinal line on the midline of the side of the body. On both sides of this line the scales proceed obliquely backward. On the ventral side, at some distance from the anal fin, the scales run obliquely forward toward the ventral midline ( Fig. 6 View FIG ). Kiaer (1924) divides the trunk skeleton into 1) the median dorsal spines; 2) the upper lateral trunk scales (above the mid-line); 3) the lower lateral scales (below the midline); and 4) the ventral scales.
The median dorsal ridge scales (= median dorsal spines by Kiaer): in Vilkitskilepis valentinae n. gen., n. sp. the moulds of the external surface and internal impression of the scales are preserved (drs, Figs 5 View FIG ; 6 View FIG ) along the whole length of our specimen. There are 25 (26?) dorsal ridge scales; the 5 th to 7 th ridge scales have preserved their natural shape. Each scale arises slightly posteriorly and recedes then, the next scale starting at the lower level. Their height is two thirds of the height of the dorso-lateral scales. They are higher and longer in the middle part of the row, 3 mm long and 6 mm high as a maximum, where each median dorsal ridge scale covers four to five dorso-lateral scales.
The dorso-lateral scales (dls, Figs 5 View FIG ; 6 View FIG ) are arranged in regular rows that run forward and downward. The scale rows are higher in the middle of the body. There are 17 scales per 10 mm, meaning that the width of each scale is about 0.6 mm.
The ventro-lateral scales (vls, Fig. 6 View FIG ) occur in three rows situated below the body midline, running downward and backward. Their total height is larger than for the dorso-lateral scales. The trunk scales, which cover the whole area, become gradually lower and just slightly shorter posteriorly, towards the caudal peduncle.
The ventral scales (vs, Fig. 6 View FIG ), one row on either side, run forward and downward towards the ventral midline of the body. They are situated between the pectoral plate(?) and at some distance from the anal fin. The ventral scale row ends posteriorly with a structure showing scales arranged in concentric oval rows. A spine occurs in the centre of this structure (pas, Fig. 6 View FIG ), which Kiaer (1924: fig. 30) called the preanal spine. In our specimen the trunk with ventral scales and the preanal spine is turned to the same plane as are the dorso- and ventrolateral scales. A very narrow area of ventral scales of the other side is visible. The anal fin (af, Figs 5 View FIG ; 6 View FIG ) is rather well preserved. The minute elongated scales covering it are directed obliquely backward. The base of this fin is 7 to 8 mm long. Between the preanal spine and anal fin, there occur two rows of special scales. In some respects they resemble the scales of Rhyncholepis (see Kiaer 1924: fig. 34b). The upper row comprises low, narrow scales, 15 to 20 in number. Below it, a row of spiny scales (sps) extends to the anal fin.
The scale sculpture of the type specimen is not as well preserved as in other Birkeniida from Severnaya Zemlya. It is broken in the plane of the smooth visceral side and the sculptured side was left in the rock. It was not possible to take scales out without destroying the only specimen. Still, a couple of scales show tuberculated ornamentation anteriorly ( Fig. 3G), and ridged sculpture in the middle of the scales. Microsculpture is not studied. The dorsal ridge scales bear elongated tubercles, each ridge being higher anteriorly and lower towards the posteri- or end of the ridge. They have fine, short ridgelets on the sides. The ridges are coarser anteriorly and in the middle part of the row. Fragments studied in anise oil show typical lamellar aspidine.
REMARKS
The body of Vilkitskilepis valentinae n. gen., n. sp. was approximately 12 cm long. In length, the new species is close to Pterygolepis nitidus ( Kiaer, 1911) (for comparison see Table 1 where measurements after Kiaer 1924 are used). The preserved median dorsal ridge scales number 25 or 26 in our specimen, the total number lying, perhaps, between those of Pterygolepis nitidus and Pharyngolepis oblongus Kiaer, 1911 . In relative size, the median dorsal ridge scales of Vilkitskilepis valentinae n. gen., n. sp., covering four to five dorso-lateral scales, are most similar to those of Pterygolepis nitidus . By the size and direction of the branchial band (at an angle of 35°, being 1.5 mm wide and 15 mm high) the new species is close to Pterygolepis nitidus . The flexible anal fin in our species makes it similar to Pharyngolepis Kiaer, 1911 , while the scales between the pre-anal spine and anal fin resemble those of Rhyncholepis Kiaer, 1911 .
This comparison reveals possible relationships between Vilkitskilepis valentinae n. gen., n. sp. and Pterygolepis nitidus . Still, considering the differences in morphology, we have enough reason to establish a new genus and a new species. There is not enough data to decide to which family it should be referred; thus this question is left open at the present stage of study.
NB: The Norwegian taxa have been revised and the names of Rhyncholepis parvulus , Pterygolepis nitidus and Pharyngolepis oblongus corrected by Blom et al. (in press).
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.