Sharks
Skeleton of cartilage, which is calcified (CaCO3) for higher strength
Appendages: first evolutionary step towards paired appendages and fins; pelvic and pectoral girdle
Streamlined body and strong fins ?fast, efficient, superior swimmers ?evolutionary success as top predators
Teeth: first vertebrate teeth are modifiedscales on skin; teeth not anchored in jawup to 20 rows of teeth, constant renewal
Reproduction: only internal fertilization among fish; few sharks lay eggs, most give birth to developed young