1. Introduction
Sharks and rays are cartilaginous fishes that have exploited
a wide variety of diet regimes through geologic time. Many sharks
are piscivores, but a number of cartilaginous fishes have also
evolved to feed on other vertebrates (e.g., sea turtles, birds, and
cetaceans), plankton, and macroinvertebrates (Compagno, 2001).
Among the macroinvertebrate feeders are those that practice durophagy
adapted to feed on shelled animals. Modern forms include
bullhead sharks (Heterodontus spp.) andmyliobatid rays (Summers,
2000; Compagno, 2001), and some extinct forms include the enigmatic
ptychodontid sharks (Elasmobranchii: Hybodontiformes?)
that lived during the Cretaceous and are characterized by pavement-
like dental plates consisting of juxtaposed rows of teeth
(Shimada et al., 2009).
1. IntroductionSharks and rays are cartilaginous fishes that have exploiteda wide variety of diet regimes through geologic time. Many sharksare piscivores, but a number of cartilaginous fishes have alsoevolved to feed on other vertebrates (e.g., sea turtles, birds, andcetaceans), plankton, and macroinvertebrates (Compagno, 2001).Among the macroinvertebrate feeders are those that practice durophagyadapted to feed on shelled animals. Modern forms includebullhead sharks (Heterodontus spp.) andmyliobatid rays (Summers,2000; Compagno, 2001), and some extinct forms include the enigmaticptychodontid sharks (Elasmobranchii: Hybodontiformes?)that lived during the Cretaceous and are characterized by pavement-like dental plates consisting of juxtaposed rows of teeth(Shimada et al., 2009).
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