Milesacanthus ancestralis Burrow, Lelievre & Janjou 2006
Milesacanthus cf. ancestralis (Fig. 8) MATERIAL. — Nine scales, one of which is lost (M N H N. F.A L D -4 0), a n d o n e t h i n s e c t i o n MNHN.F.ALD-41. DESCRIPTION The crown of these four scales is diamond-shaped and its anterior part may be more rounded as in MNHN.F.ALD-38 (Fig. 8C 2). The c...
| Main Authors: | , |
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| Format: | Other/Unknown Material |
| Language: | unknown |
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2011
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| Online Access: | https://zenodo.org/record/4596946 https://doi.org/10.5281/zenodo.4596946 |
| Summary: | Milesacanthus cf. ancestralis (Fig. 8) MATERIAL. — Nine scales, one of which is lost (M N H N. F.A L D -4 0), a n d o n e t h i n s e c t i o n MNHN.F.ALD-41. DESCRIPTION The crown of these four scales is diamond-shaped and its anterior part may be more rounded as in MNHN.F.ALD-38 (Fig. 8C 2). The convex base, also diamond-shaped, and with anterior and rounded posterior edges is located anteriorly. The scales with a flat crown show sub-parallel grooves (18 for Fig. 8A 1, B 2 and possibly more), diverging in the front part (Fig. 8C 2), like in the material of Milesacanthus ancestralis from Saudi Arabia.The grooves are not really deep but narrower than the ridges. Both grooves and ridges run along the entire crown length of the scale. In the scale MNHN.F.ALD-36 (Fig. 8A 1), grooves and ridges start just at the front edge of the scale, whereas in the scale MNHN.F.ALD-37 (Fig. 8B 2) the ridges start at the vertical edge of the crown and the posterior edge is more crenulated. One scale (ALD-38) shows 13 larger grooves (Fig. 8C 2), but only in its anterior part. Pore openings, located mainly at the beginning of the grooves, connect to an ascending canal system. The grooves begin after the anterior edge of the crown and most lateral grooves undulate, slightly converging in the beginning, then parallel to the diagonal, and stop in the posterior third of the crown. The neck is well marked with a row of foramina posteriorly and anteriorly (Fig. 8A 2, B 2, C 2). Furthermore, wart-like protuberances are visible on the posterior neck (Fig. 8A 2; more evident on Fig. 7F), visible on “young” scales according Burrow et al. (2006: 547). HISTOLOGY The thin section 9 MNHN.F.ALD-41 (Fig. 7G) shows a classical pattern for an acanthodian, with a primordium in the middle of the crown that is made of dentine covered with thin box-in-box growth zones continuing from the crown into the acellular bone base. Contrary to Milesacanthus ancestralis and M. antarctica (Young & Burrow 2004), no vascular canal was found, but only one thin ... |
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