Squalus undetermined
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publication ID |
https://doi.org/ 10.5070/P939056976 |
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publication LSID |
lsid:zoobank.org:pub:13E6A6E9-DE0F-4C71-BE40-2957F48D9F70 |
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persistent identifier |
https://treatment.plazi.org/id/03DF0849-4130-FFDE-3C81-FC38FB12FD8A |
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treatment provided by |
Felipe |
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scientific name |
Squalus undetermined |
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FIG. 6A–E View Figure 6
Type species — Squalus acanthias Linnaeus, 1758 View in CoL ; Recent.
Referred specimens (n=4) —SC2007.36.3 ( Fig. 6A–C View Figure 6 ), SC2007.36.130, SC2015.29.9, SC2015.29.17 ( Fig. 6D, E View Figure 6 ).
Description —SC2007.36.3 ( Fig. 6A–C View Figure 6 ) is the only complete specimen in our sample. The crown is very low, and its total width measures 1.8 mm. The mesial cutting edge is smooth, elongated, sinuous along its length, and forms a sharply pointed cusp with the distal cutting edge. The cusp itself is highly distally directed, and the distal cutting edge is very short, straight, and smooth. A distal heel is elongated, and the cutting edge on this structure is smooth and somewhat angular, with a low apex that is located beyond the apex of the main cusp.The labial face is rather flat, devoid of ornamentation, with a somewhat thickened crown foot and medially located, basally directed protuberance ( Fig. 6B View Figure 6 ). This protuberance extends beyond the basal attachment surface of the root. The lingual crown face is convex and smooth, and it has a medially located basal protuberance ( Fig. 6A View Figure 6 ). This protuberance is very short, perpendicular to the lingual crown face, and directed mesially. There is a distinct constriction below the crown base on the labial and lingual sides, after which the thin root flares laterally a short distance. The basal attachment surface is narrow and weakly concave. A large centrally located nutritive foramen opens lingually ( Fig. 6C View Figure 6 ).
SC2015.29.17 is a well-preserved crown ( Fig. 6D, E View Figure 6 ) measuring 1.5 mm in width, the cusp angle is acute, and the apex of the distal heel lies beyond the apex of the main cusp. This crown is somewhat lower than that of SC2007.36.3.
Specimens SC2007.36.130 and SC2015.29.9 are both represented by only the posterior half of a tooth crown. Both specimens show that the highest point on the distal heel is beyond the main cusp apex. The main cusp of SC2015.29.9 is broken, but the cusp angle of SC2007.36.130 is acute.
Remarks —The Ashley Formation specimens represent the first reported fossil occurrence of Squalus from South Carolina. The genus has been reported from the Oligocene of Oregon ( Welton 1972), and S. alsaticus ( Andreae, 1890) was tentatively reported by Müller (1999) from the Oligocene of Virginia. The latter species is well known from the Rupelian and Chattian of Europe, having been documented in Poland ( van den Bosch 1981), Belgium ( Hovestadt and Hovestadt-Euler 1995, Baut and Génault 1999, Mollen et al. 2016), the Czech Republic ( Brzobohaty and Kalabis 1970, Cappetta et al. 2016), France ( Génault 1993), and Germany ( von der Hocht 1978a, 1978b, Reinecke et al. 2001, Reinecke et al. 2005). Although the Ashley Formation sample size is small, these Oligocene teeth differ from S. alsaticus in two key respects – the apical angle of the main cusp (i.e., the angle formed at the cusp apex by the mesial and distal cutting edges) and the morphology of the distal heel.
Within the jaw of an extant Squalus acanthias Linnaeus, 1758 we examined (SC96.77.4), we observed that cusp inclination increases and, correspondingly, the crown height decreases from the symphysis to the commissure. We also observed that the apical angle was variable and decreased mesiodistally along the jaw. Reinecke et al., (2005) documented variation in the apical angle of S. alsaticus teeth, which ranged from 50˚ to 64˚, but they noted that the variation was not related to jaw position. Our examination of specimens shown in Reinecke et al. (2005:pl. 4-6) and Reinecke et al. (2001: pl. 6-7) showed this statement to be accurate, as anterior, lateral and posterior teeth of S. alsaticus can have angles in the 60˚ to 64˚ range.The apical angle of SC2007.36.3 measures only 41˚, that of SC2015.29.17 measures 47 ˚, and SC2007.36.130 is 53˚, all of which are at the low end of, or less than, the range of S. alsaticus teeth. The crown of SC2015.29.17 is slightly lower than that of SC2007.36.3, indicating that it was from a more distal jaw position.
With respect to the distal heel, that of S. alsaticus generally has a very convex to angular cutting edge with an apex that is located directly under the main cusp apex or closer to the base of the distal cutting edge. This morphology is seen on the Squalus aff. alsaticus specimens discussed by Müller (1999). In contrast, the heel apex of the South Carolina specimens lies beyond the apex of the main cusp. Although the Ashley Formation specimens may represent an undescribed species of Squalus , a larger sample is needed to accurately identify this Oligocene taxon and interpret its dentition.
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