Classification of vertebrate animals

An Evolutionary Tree of the Vertebrates Tetrapods Chondrichthyes (sharks, rays) (coelacanths) Actinistia (ray-finned fish) Actinopterygii Petromyzontiformes (lampreys) (lungfishes) Dipnoi salamanders) Amphibia (frogs, (turtles, snakes crocodiles, Reptilia birds) Mammalia (mammals) Dorsal nerve cord, notochord, pharyngeal gill slits, post-anal tail Vertebral column Jaws Lungs Skull Lobed fins Limbs Amniotic egg Hair, milk An Evolutionary Tree of the Vertebrates

Vertebrate Adaptations Several adaptations have allowed vertebrates to successfully invade most habitats presence of an internal skeleton that can grow and repair itself allowed for greater size and mobility, enabling these animals to invade most habitats Jaws evolved to allow these animals to exploit a much wider range of food sources than jawless animals that preceded them The development of paired appendages (fins, legs, wings) helped to stabilize movement The increased size and complexity of the brain and sensory structures allowed these animals to perceive their environment in detail and to respond in a variety of ways

What Are the Major Groups of Vertebrates? Today, vertebrates include the following groups: Lampreys Cartilaginous fishes Ray-finned fishes Lungfishes Amphibians Reptiles Mammals

lampreys Some lampreys parasitize fish jawless rounded sucker that surrounds the mouth spinal cord is protected by cartilaginous segments live in both fresh and salt waters

Cartilaginous fishes Cartilaginous fishes are marine predators They are of the class Chondrichthyes, and include sharks, skates, and rays Most are marine They possess jaws and a cartilaginous skeleton Their body is protected by a leathery skin embedded with tiny scales

Bony fishes the most diverse vertebrates Bony fish are found in nearly every watery habitat, both freshwater and marine This group includes: Ray-finned fishes, such as the angler fish, the moray eel, and the sea horse Lobe-finned fishes, which include the lungfish and the coelacanth

The Diversity of Ray-Finned Fishes most diverse and abundant group of vertebrates Fins which are formed by webs of skin supported by bony spines bony skeleton skin is covered with interlocking scales two-chambered heart gills are for respiration Most have a swim bladder

Lobed-finned fishes fleshy fins that contain rod-shaped bones surrounded by a thick layer of muscle Some of these modified fleshy fins could be used to drag the fish from a drying puddle to a deeper pool This gave rise to the first vertebrates to invade land—the amphibians Some of the lineages of lobefins left descendents that survive today and are the tetrapods (amphibians, reptiles, and mammals)

Amphibians: frogs, toads, salamanders, and caecilians Amphibians begin life adapted to an aquatic environment (e.g., tadpoles have gills) They later mature into semi-terrestrial adults with lungs three-chambered heart adults respire through lungs and moist skin Most have four limbs Most are confined to moist habitats use of external fertilization requires water eggs, protected only by a jelly-like coating, are vulnerable to water loss

Reptiles class Reptilia and are adapted for life on land These animals evolved from an amphibian ancestor about 250 million years ago Reptiles include lizards, snakes, alligators, crocodiles, turtles, and birds They respire exclusively through lungs tough scaly skin that protects the body and resists water loss internal fertilization with shelled amniotic egg three- or four-chambered hearts efficient lungs and do not use their skin as a respiratory organ

Birds distinctive group of reptiles They appear in the fossil record 150 million years ago They are distinguished from other reptiles by feathers, which are highly specialized reptilian body scales Modern birds retain scales on their legs, which is evidence of the ancestry they share with the rest of the reptiles The earliest known bird is called Archaeopteryx

Archeopteryx, the Earliest-Known Bird Fig. 24-13

Mammals Mammals are warm-blooded with high metabolic rates Mammals appeared in the fossil record about 250 million years ago They did not diversify and dominate terrestrial habitats until the dinosaurs became extinct (65 million years ago) Mammals are warm-blooded with high metabolic rates a four-chambered heart hair that protects and insulates legs designed for running rather than crawling provide milk to their offspring sweat, scent, and sebaceous (oil-producing) glands, which are not found in other vertebrates Mammals are subdivided into three groups Monotremes Marsupials Placental mammals

Monotremes are egg-laying mammals This group includes only three species, the platypus and two species of spiny anteater (echidnas), and are found only in Australia and New Guinea Platypuses forage for food in the water and eat small vertebrate and invertebrate animals Echidnas are terrestrial and eat insects and worms they dig out of the ground Monotremes lay leathery eggs rather than giving birth to live young The newly hatched young are nourished from milk secreted by the mother

Marsupia Species include the opossums, koalas, kangaroos, wallabies, wombats, and the Tasmania devil In marsupials, embryos begin development in the uterus of the female Young are born at a very immature stage and must crawl to and grasp a nipple to complete development Post-birth development, in most, is completed in a protective pouch

Placental mammals inhabit land, air, and sea This highly diverse class includes bats, moles, impalas, whales, seals, monkeys, and cheetahs The uterus contains a placenta that functions in gas, nutrient, and waste exchange between circulatory systems of mother and embryo In placental mammals, young are retained in the uterus for their entire embryonic development