34.1 Attaching muscles to an internal framework greatly improves movement.
The Chordates
• Four features characterize the chordates: (1) single, hollow nerve cord; (2) a flexible notochord present at some developmental stage; (3) pharyngeal pouches connecting the pharynx and the esophagus; (4) a postanal tail at least during embryonic development. (p. 684)
34.2 Nonvertebrate chordates have a notochord but no backbone.
The Nonvertebrate Chordates
• Tunicates possess a notochord and a nerve cord as larvae, but exhibit no major body cavity or segmentation as adults. (p. 686)
• Lancelets are fishlike marine chordates with a permanent notochord running the entire length of the dorsal nerve cord. (p. 687)
34.3 The evolution of vertebrates involved invasions of sea, land, and air.
Characteristics of Vertebrates
• Vertebrates differ from tunicates and lancelets in that they have a vertebral column instead of a notochord and a distinct, well-differentiated head. (p. 688)
• The history of the vertebrates includes a series of evolutionary advances that allowed them to invade the sea and then the land. (p. 689)
Fishes
• Fish were the first vertebrates and are the most diverse and successful vertebrate group. (p. 690)
• Key characteristics of fish include a vertebral column, jaws and paired appendages, gills, single-loop circulation, and nutritional deficiencies. (p. 690)
• The first fish had heads made of bone and internal skeletons made of cartilage. Jaws later evolved from cartilage arch supports. (pp. 692-693)
• Sharks eventually became dominant sea predators, partially due to a skeleton composed of calcified cartilage. Sharks were also among the first vertebrates to develop teeth. (p. 695)
• Bony fish evolved at the same time as sharks, but adopted a heavy internal skeleton made of bone. Such ossification provided a strong base for muscle attachment and evolved in fresh water. (p. 696)
• Bony fishes also evolved important adaptations such as a swim bladder for buoyancy, a lateral line sensory system, and a gill cover (operculum) to permit water to be pumped over the gills. (pp. 696-697)
Amphibians
• Key characteristics of living amphibians include legs, cutaneous respiration, lungs, pulmonary veins, and a partially divided heart. (p. 698)
• Paleontologists believe amphibians must have evolved from lobe-finned fishes. Amphibians today include frogs and toads, salamanders, and caecilians. (pp. 699-701)
Reptiles
• Key characteristics of reptiles include the amniotic egg, dry skin, and thoracic breathing. (p. 702)
The Rise and Fall of Dominant Reptile Groups
• Four major forms of reptiles took their respective turns as the dominant large terrestrial vertebrates: pelycosaurs, therapsids, theocodonts, and dinosaurs. (pp. 704-705)
• Other important characteristics of reptiles are that they practice internal fertilization, have an improved circulatory system, and are ectothermic. (p. 707)
• Only four reptilian orders survive today: turtles, lizards and snakes, tuataras, and crocodiles. (pp. 707-709)
Birds
• Modern birds retain many reptilian characteristics, but lack teeth and have vestigial tails. They are distinguished from living reptiles by feathers and the presence of a thin, hollow flight skeleton. (p. 710)
History of the Birds
• Archaeopteryx was probably the first bird, arising 150 MYA and likely a direct descendant of dinosaurs. (pp. 712-713)
• Aves continues to be listed as a separate class due to the evolutionary novelties of feathers and hollow bones and to physiological mechanisms such as efficient lungs capable of sustaining powered flight. (p. 713)
Mammals
• Key mammalian characteristics include hair, mammary glands, a placenta, heterodont dentition, the ability to digest plant material, keratinized hooves and horns, and flight capability (in bats). (pp. 714-716)
The Orders of Mammals
• Mammals were not common until dinosaurs disappeared. Modern mammals fall into one of three categories: monotremes, egg-laying mammals; marsupials, pouched mammals; and placentals. (pp. 717-718)
34.4 Evolution among the primates has focused on brain size and locomotion.
Primates
• Grasping fingers and toes and binocular vision are two features that allowed primates to flourish. (p. 720)
• Modern prosimians include lemurs, lorises, and tarsiers, while anthropoids include monkeys, apes, and humans. (pp. 720-721)
Australopithecines
• Bipedalism marked the beginning of hominid evolution, although the reason for such evolution remains controversial. (p. 722)
• Currently, two philosophical approaches, lumping and splitting, are used to characterize African hominid fossils. (p. 723)
The GenusHomo
• The first humans (Homo habilis) evolved from australopithecine ancestors about 2 MYA. (p. 724)
• Homo erectus replaced H. habilis, and is believed to have come out of Africa. (pp. 724-725)
• Homo sapiens is both the only surviving species of the genus Homo and the only surviving hominid. (p. 726)
• Humans are the only animals that can effectively make tools, that have refined and extended the ability to use conceptual thought, and that can use symbolic language and shape concepts and experiences with words. (p. 726)