18.16 Lampreys are vertebrates that lack hinged jaws –Lampreys represent the oldest living lineage of vertebrates Suspension feeders in freshwater streams Have jawless mouth with rasping tongue –The vast majority of living vertebrates have two-part jaws connected by a hinge –Jaws likely evolved from anterior pharyngeal slits

18.17 Jawed vertebrates with gills and paired fins include sharks, ray-finned fishes, and lobe-fins –Three lineages of jawed vertebrates with gills and paired fins are commonly called fishes –Chondrichthyans have changed little in 300 million years Include sharks and rays Flexible skeleton made of cartilage Lateral line system of sensory organs

–The ray-finned fishes include familiar fishes such as tuna, trout, and goldfish Skeleton reinforced with a hard matrix of calcium phosphate Operculi that move water over the gills Buoyant swim bladder –Lobe-finned fishes have muscular fins supported by bones Three surviving lineages including one that gave rise to terrestrial vertebrates

18.18 Amphibians were the first tetrapods— vertebrates with two pairs of limbs –Amphibians were the first tetrapods with limbs allowing movement on land Possibly evolved from lobe-fins during the Devonian period Became very widespread during the Carboniferous period Include salamanders, frogs, and caecilians

–The “double life” of amphibians refers to the metamorphosis of many frogs Larval stage (tadpole): a legless, aquatic algae-eater with gills, a lateral line system, and a long, finned tail Adult: a terrestrial insect eater with four legs and air- breathing lungs –Most amphibians are found in damp habitats, where their skin functions in gas exchange –Amphibian skin usually contains poison glands that function in defense

18.19 Reptiles are amniotes—tetrapods with a terrestrially adapted egg –Reptiles include lizards, snakes, turtles, crocodiles, birds, and a number of extinct groups such as dinosaurs –The major derived characteristic of the clade containing reptiles and mammals is the amniotic egg Embryo develops with a protective, fluid-filled sac Enabled reptiles to complete their life cycles on land

–Reptile adaptations for terrestrial life in addition to the amniotic egg include Scaly, waterproof skin that keeps body from drying out Lungs for obtaining oxygen Ecothermic metabolism (in nonbirds) –Dinosaurs, the most diverse reptiles, included some of the largest animals ever to inhabit land May have been endothermic Died out 65 million years ago but left birds as descendants

18.20 Birds are feathered reptiles with adaptations for flight –Birds likely evolved from a lineage of small, two-legged dinosaurs called theropods Evidence from fossils such as Archaeopteryx

LE 18-20a Wing claw (like dinosaur) Feathers Long tail with many vertebrae (like dinosaur) Teeth (like dinosaur)

–Nearly every part of the body of most birds reflects adaptations that enhance flight Weight-reducing features such as few teeth, strong but light bones Feathers Large, powerful breast muscles Endothermic metabolism, highly efficient circulatory system Acute vision

–Birds have relatively large brains and complex behaviors Male and female cooperation in raising young Migration –A few flightless species of birds exist (example: emu)

18.21 Mammals are amniotes that have hair and produce milk –Main adaptive features of mammals Hair, which provides insulation Mammary glands, which produce milk Endothermic metabolism Efficient respiratory and circulatory systems Differentiation of teeth for different foods Large brain, long period of parental care allowing for learning

–There are three main groups of living mammals Monotremes lay eggs –Examples: echidna, duck-billed platypus The embryos of marsupials and eutherians are nurtured by the placenta within the uterus –Marsupials complete development outside the mother’s body –Eutherians (placental mammals) complete development before birth