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The description of a partial but well-preserved head of the sclerorhynchid batoid Sclerorhynchus atavus Woodward, 1889 gave the first clear indication of the presence of a puzzling group of extinct rostrum-bearing rays that resembled both the Pristidae (rays) and the Pristophoridae (sharks). Despite recognizing similarities to and differences from these extant groups, Smith Woodward suggested that Sclerorhynchus be assigned to the Pristidae, although acknowledging that the rostra are very different. Smith Woodward did note similarities of Sclerorhynchus rostrum saw-teeth to those of the Pristiophoridae, including the location of these along the margin of the rostrum, rather than in deep sockets as seen along the pristid rostrum. In addition, the type specimen of Sclerorhynchus has not only very distinct saw-tooth denticles along the rostrum, but also modified denticles along the sides of the head, as in the Pristiophoridae. The enlarged rostral denticles of Sclerorhynchus also appear to rotate into position, another feature seen in the pristiophorids but not in the pristids nor in other sclerorhynchids such as Libanopristis. Although individual fossil rostral tooth-like denticles had been described earlier, Smith Woodward’s description of a rostrum and associated rostral tooth-like denticles meant that for the first time a fossil rostrum could be compared with living forms.

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