BALANIDAE BRUGUIÉRE, 1797

Charles L. Powell, Ii, Clites, Erica C. & Poust, Ashley W., 2019, Miocene marine macropaleontology of the fourth bore Caldecott Tunnel excavation, Berkeley Hills, Oakland, California, USA, PaleoBios 36, pp. 1-34 : 23-24

BALANIDAE BRUGUIÉRE, 1797 (?) LEACH, 1817

FIG. 40

A very small mold and cast appear to represent a small, short, possibly smooth-sided barnacle. It is not well enough preserved to identify beyond family and that is questionable. The family goes back to the Cambrian

UCMP 218505 is a shark tooth exposed in lingual view and, being mesio-distally wide and concave right in this view, represents an upper tooth from the middle to rear of the tooth row. It is a small, asymmetrical tooth measuring 7.6 mm in crown height, 4.2 mm in crown width and 11.6 mm wide at the root.

The tooth is broadly triangular in shape, but with a concave distal inflection at the juncture of the shoulder and distal cutting edge that gives the crown a falcate appearance. The inflexion point on the mesial side between this convex cutting surface and the rootward shoulder is distinctly higher (i.e., closer to the apex) than the angle between the concave edge of the crown and the shoul- der on the distal side. The labial side of UCMP 218505 is planar, as visible in the cracked portion of the mesial shoulder and root; the exposed lingual side of the crown is gently and uniformly convex. Any labial or lingual curvature is obscured by the surrounding matrix. The relatively flattened blade is strongly serrated, including serrated shoulders tapering to a narrow apex, but with an apical tip free of serrae. The distal side has a shallow notch between the upper and lower part of the crown and the distal shoulder is slightly bowed rather than straight. The root is damaged so the state of the protuberance is difficult to determine, though by outline it would be slightly rounded and not squared-off.

Referral to C. obscurus is supported by the overall morphology described above. In particular the more uniform size of the serrations and their diminution towards the tip on the concave side separates it from Hemipristis Agassiz, 1843 , and the long shoulders, falcate appearance, and thinner, rounded, more concave root from the Charcarodontids. UCMP 218505 can be distinguished from other taxa within Carcharhinus by the presence of a mesial cutting edge with a slight convex curvature terminating at a distally deflected tip (Purdy et al. 2001). A higher inflexion point on the mesial side than on the distal is characteristic of C. obscurus . The smooth tip is unlike most reported upper teeth of C. obscurus which typically has fine serrations along the entire edge but still resembles this taxon most closely. The reduced serrations towards the tip result in the apical end appearing rounded rather than peaked which further allies it with the certain species of Carcharhinus , especially C. obscurus , the dusky shark and C. leucas , the bull shark. It can be distinguished from this last due to its greater asymmetry.

Carcharhinus obscurus has been reported from both coasts of North America ( Applegate 1986, Purdy et al. 2001) and around the world in a distribution that broadly follows occurrences of extant members of the species. The serrations present on UCMP 218505 are finely preserved and the base of the tooth has clear borders; all damage appears to be post-fossilization, suggesting little transport.

Figures

Figure 40. Indeterminate barnacle. Hypotype from UCMP locality IP13002, UCMP 218825.