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ADVANCES IN PALAEOICHTHYOLOGY
Material. Approximately 170 scales.
Diagnosis. Nostolepis having mid-sized scales with highly raised dominant medial area
on crowns ornamented by one to four short anterior ridges; narrow lateral areas are
outlined by long oblique neck ridges pointed posteriorly. Scale crowns (maximum four
growth lamellae) are composed of dense, finely-networked, cellular simple mesodentine
(dominant tissue) and outer durodentine; no Stranggewebe; vascular canals are well
developed; mesodentine grades into the cellular bone of scale bases without sharp border.
Description. Morphology. Scales have elongated triangular crown plates slightly sloping
down anteriorly with the tapered posterior crown part far overhanging the base. Crown
length varies from 0.38 to 1 mm; most frequently 0.6-0.8 mm. Crown width is 0.2-0.62
mm. A wide medial area forms most of the crown, which is highly raised compared to
the narrow lateral slopes. Only the anteriormost strip of the medial area is sculptured
by a few (one to four) short rounded ridges. The lateral areas are outlined by the oblique
long neck ridges which converge with the medial ones extremely posteriorly (Fig. 5A-
C). The posterior crown overhang can reach a half of its length. Scale necks are low
and bases rhomboidal, of medium convexity, with the deepest point forward of centre.
Histology. Three to four growth lamellae of the crown are composed of simple
mesodentine and durodentine (canalless dentine) which is developed in thin strips
superficially centrally (Fig. 5L). Stranggewebe is lacking in the posterior crown parts.
Simple mesodentine forms a particularly dense and fine network of dentinal canaliculi
(Fig. 5 E-F) incorporating numerous random, large, multi-angular osteocyte cavities.
Mesodentine character in this respect is similar to the base bone pattern except for
more regular orientation of osteocytes along the growth lines in bases (Fig. 5 E-G).
There is no sharp border between the crown and base tissues; mesodentine and bone
make a gradual transition. The system of principal vascular canals in crowns (ascending,
radial and circular) is well developed forming long and wide branches in each lamella
(Fig. 5 I, L).
Remarks. Gross (1947) regarded Diplacanthoides elegans as a junior synonym of
Nostolepis striata. However, as proposed by Vergoossen (1999-2002), the ‘elegans’
group of scales is distinguishable from N. striata by diagnostic morpho- and histological
characters. N. striata sensu Gross (1947, 1971) can not compare with the other nostolepid
taxa or any acanthodian in having so numerous and excessively diverse scale forms,
and undoubtedly incorporates multiple biological species. For more extended
morphological comments on N. elegans scales and comparisons with other nostolepids,
I direct readers to Vergoossen’s (1999-2002) remarks. N. arctica Vieth (1980: pl. 5,
figs 1-9; fig. 20 A-E) differs from N. elegans in having more ornamented scales which
crowns are highly inclined, longer and often longitudinally bent. Now, after a study of
histologic structure of scales (N. elegans was not previously examinated), the differences
from N. arctica are furtherly supported by the absence of Stranggewebe in crowns of
N. elegans.
Occurrence. See Table.