Elasmobranchii, Bonaparte, 1838
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publication ID |
https://doi.org/ 10.4202/app.2012.0101 |
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persistent identifier |
https://treatment.plazi.org/id/6B2D1521-EF62-1221-FC9B-177FB4E05B64 |
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treatment provided by |
Felipe |
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scientific name |
Elasmobranchii |
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Elasmobranchii View in CoL indet. fam., gen. et sp. B sensu Burrow et al. 2009
Fig. 10 View Fig .
Material.— NYSM 17791–17799 About NYSM ; 17898–17958, scales from Plattekill Formation , Cairo quarry, Cairo, Greene County, New York State, USA .
Description.—The body scales are characterized by a simple rhomboid crown and, in most cases, bear lateral flanges. In lateral view, these flanges extend upwards from anterior to posterior ( Fig. 10E–I View Fig ). The crown can be asymmetric; in some cases only one flange is visible ( Fig. 10F View Fig ), while in others the lateral halves can be antero-caudally displaced relative to each other ( Fig. 10G View Fig ). The posterior edge tapers and extends only slightly beyond the base. The anterior edge generally has a single median depression; however, there might be from zero to three depressions ( Fig. 10H View Fig ). A concentric pattern is observed in the crown of some specimens and suggests areolar growth. The crown is smaller than the base, and its anterior edge does not reach the anterior margin of the base. Consequently, the base has an anterior U-shaped plateau when viewed from above. The base is smooth and generally rhomboid, but rounded in some specimens. In lateral view, the anterior half of the base is bulbous whereas the posterior half is flattened. The bulbous part generally occupies about half of the length of the base, but variation is observed among the scales ( Fig. 10E, I, J View Fig ). One specimen
Fig. 10D View Fig ) is a flattened, very wide scale that appears to be the result of a fusion, as the base of the scale has three bulbous structures that are aligned laterally.
Scales identified as head scales are characterized by an irregular, almost stellate crown ( Fig. 10A–C View Fig ). The crown outline varies from oval to circular, and may cover the whole surface of the base, but can also recede from the anterior margin of the base. The base may be more rounded and symmetrical, but in some cases retains the shape described above for the body scales. In lateral view, the base ranges in shape from that present in body scales to a massive, block-like form ( Fig. 10A–C View Fig ).
Although investigation with the micro-CT scan was inconclusive, the internal structure was partly revealed by SEM of damaged specimens ( Fig. 10K, L View Fig ). The crown appears to be composed of superposed layers ( Fig. 10K View Fig ); these layers are organized similar to the semicircular growth zone observed in the crown of Elasmobranchii indet. fam., gen. et sp. B of Burrow et al. (2009: fig. 10m). Unoriented bundles of fibres are observed in the base ( Fig. 10L View Fig ).
Similar head and body scales have been described from the Middle Devonian of Antarctica ( Burrow et al. 2009). Burrow et al. (2009: 86) mentioned that these specimens could belong to either Portalodus or Aztecodus . As Aztecodus has not been identified at Cairo, despite extensive sampling and fieldwork, these scales are tentatively assigned to P. mannoliniae sp. nov. However, the pustulous base, one of the characteristics noted by Burrow et al. (2009), is not observed in the Cairo material.
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