Abstract 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.

Abstract Fossils of post-Palaeozoic sharks and rays are common and well known, and have been extensively studied. Early studies, especially the monographic works of Agassiz and Smith Woodward, described species based on macroscopic remains of isolated teeth, fin spines and rostral ‘teeth’ as well as rare specimens of articulated skeletons and skulls. This material was obtained from a range of sources but especially from commercial collectors in Britain and mainland Europe. Additional research over subsequent decades also concentrated on large specimens, giving a very biased perception of the chondrichthyan record. The use of large-scale bulk sampling in the latter part of the twentieth century revealed a previously unknown wealth of small fossils, especially teeth, and vastly improved knowledge of ancient sharks and rays. Widening use of these techniques to obtain small specimens has led to a dramatic increase in the fossil taxa known. In addition, reassessment of previously known taxa has allowed generic diversity of some clades to be appreciated. Detailed work on skeletal anatomy, in part aided by new non-destructive methods, continues to improve knowledge of shark and ray diversity, phylogeny and radiation.