The skeletal elements of cartilaginous fishes are composed of a thin layer of mineralized tissue, ‘prismatic cartilage’, overlaying a hyaline cartilage core. Cartilage, even with a surface layer of mineralization, is far less stiff and strong than bone. Nevertheless, several species of stingray, including Rhinoptera and Aetobatus, subsist by crushing hard-shelled mollusks and crustaceans in their cartilaginous jaws. The jaws of these stingrays are composed of a previously undescribed form of cartilage. This tissue, ‘trabecular cartilage’, has mineralized struts which run through the central hyaline core. The struts, or trabeculae, are hollow tubes, made of calcified blocks, arranged as in a brick chimney. They serve to prevent buckling and bending of the jaws while prey is being crushed. The struts are present in late term embryos, indicating that feeding on hard prey does not cause them to form. As the animal grows the struts lengthen and thicken though they do not appear to become more numerous. Trabecular cartilage appears to have evolved at the base of the clade containing the hard prey specialists. This clade also includes Manta, a planktivorous species, which retains trabecular cartilage.

The newly resurgent field of evolutionary developmental biology integrates the study of evolutionarily important anatomical changes and developmental biology to describe the genetic and developmental changes that have led to anatomical changes. In this dissertation I describe candidate developmental mechanisms in the context of axial elongation and pectoral fin musculature evolution in fishes. Both axial elongation and increase in pectoral fin muscle subdivisions have important ecological correlates. Elongate fishes tend to be found in highly structured environments and fishes with an increased number of fin muscles tend to use fin-based locomotion to swim. Both of these morphologies have evolved multiple times within the ray-finned fish radiation. In Chapter 1 I focus on a specific predator avoidance behavior that is only seen in elongate fishes. Deeper-bodied fish tend to perform a unilateral bend of the body and swim away whereas elongate fish, when startled, bend bilaterally and hide. Although all elongate fishes perform head retraction, their specific anatomy indicates multiple explanations for how elongation occurs. In Chapter 2, I describe changes in the vertebral column in lineages of actinopterygian fishes that have elongate members. Elongation occurs through three different mechanisms: addition of abdominal vertebrae, addition of caudal vertebrae, and lengthening of all the vertebral cents. This study suggests that the number of abdominal vertebrae, number of caudal vertebrae, and length of the vertebral cents are controlled by separate developmental modules. Fin-based locomotion has evolved multiple times independently within actinopterygian fishes and is correlated with a modification of the pectoral fin musculature. In order to increase the understanding of fin muscle development, in Chapter 3 I describe the wildtype anatomy and embryology of the pectoral fin musculature in the zebrafish, Danio rerio. Zebrafish have six muscles in the pectoral fin. Early in development, the fin musculature consists of two muscle masses, one on each side of the fin. The arrector ventralis is the first muscle to individuate from the initial abductor muscle mass, and the adult musculature is present by 3 weeks postfertilization. This study provides a basic understanding of the embryology of the fin muscles and will provide a baseline for examining mutant fin muscle morphologies in zebrafish and diverse fin muscle morphologies in other species.

Canids have long been considered to be conservative in their postcranial anatomy, so there are few studies examining individual canid taxa for locomotor adaptations. Canids are generally considered to be the most cursorial of the carnivorans. The limbs of large canids are generally adapted for rapid terrestrial locomotion, as these animals frequently rely on speed for prey capture. The prey animal is captured and killed using the jaws and teeth. Smaller canids, such as the red fox Vulpes and gray fox Urocyon, do not use their limbs primarily for fast running. The red fox appears to have many adaptations for running, including long slender legs, but these foxes do not run in their daily activities except when chased. The red fox uses its forelimbs to help in prey capture and its hind legs for leaping. The gray fox is an unusual canid since it regularly climbs trees. The limbs of the gray fox, especially the forelimb, are utilized in climbing. This dissertation contains a detailed description of the postcranial osteology and myology Vulpes and Urocyon cinercoargenteus and includes an analysis of these anatomical features in a functional framework. An examination of both the osteology and myology of the fore and hind limbs of these two foxes reveals that their behavior is reflected in a number of anatomical characters. Adaptations for leaping in the red fox include the presence of unusually long hind legs relative to the front legs, and an increase in the length of the distal bony limb elements relative to more proximal ones. In addition, the limb bones are very slender. Muscle bellies of tarsal and digital flexors and extensors are restricted to a proximal position on the limb, and muscles in general are emphasized that act along the long axis of the limbs. Adaptations of the gray fox for climbing include the presence of relatively short legs, a greater ability to rotate the radius on the ulna relative to other canids, and a relatively greater ability to abduct the hind limb. In addition, both red and gray foxes are able to retract their claws, an ability that is not generally associated with canids.