VERTEBRATE EVOLUTION AND DIVERSITY – Vertebrates have unique endoskeletons composed of: A cranium (skull) A backbone made of a series of bones called vertebrae

Vertebra Cranium (protects brain) Figure 17.26

Characteristics of Chordates – Chordates (phylum Chordata) all share four key features that appear in the embryo and sometimes the adult: A dorsal, hollow nerve cord A notochord Pharyngeal slits A post-anal tail

Muscle segments Notochord Dorsal, hollow nerve cord Pharyngeal slits Brain Mouth Anus Post-anal tail Figure 17.27

– Another chordate characteristic is body segmentation, apparent in the: Backbone of vertebrates Segmental muscles of all chordates

– Chordates consists of three groups of invertebrates: Lancelets are bladelike animals without a cranium. Tunicates, or sea squirts, also lack a cranium. Hagfishes are eel-like forms that have a cranium. – All other chordates are vertebrates.

Mouth Tail LanceletTunicates Figure 17.28

Ancestral chordate Tunicates Lancelets Hagfishes Lampreys Cartilaginous fishes Bony fishes Amphibians Reptiles Mammals Chordates Vertebrates Tetrapods Amniotes Figure 17.29

(a) Hagfish (inset: slime) Figure 17.30a

– Lampreys: Are vertebrates Have a cranium But lack jaws

(b) Lamprey (inset: mouth) Figure 17.30b

– The two major groups of living fishes are the: Cartilaginous fishes (sharks and rays) with a flexible skeleton made of cartilage

(c) Shark, a cartilaginous fish Lateral line Figure 17.30c

And bony fishes with a skeleton reinforced by hard calcium salts – Bony fishes include: Ray-finned fishes Lungfishes Lobe-finned fishes

(d) Bony fish Lateral line Operculum Figure 17.30d

– Cartilaginous and bony fishes have a lateral line system that detects minor vibrations in the water. – To provide lift off the bottom: Cartilaginous fish must swim but Bony fish have swim bladders, gas-filled sacs that make them buoyant

Amphibians – Amphibians: Exhibit a mixture of aquatic and terrestrial adaptations Usually need water to reproduce Typically undergo metamorphosis from an aquatic larva to a terrestrial adult Were the first vertebrates to colonize land Descended from fishes that had lungs and fins with muscles

(a) Tadpole and adult golden palm tree frog (b) Frogs and salamanders: the two major groups of amphibians Red-eyed tree frogTexas barred tiger salamander Figure 17.31

– Terrestrial vertebrates are collectively called tetrapods, which means “four feet.” – Tetrapods include: Amphibians Reptiles Mammals

Reptiles – Reptiles (including birds) and mammals are amniotes, which produce amniotic eggs that consist of a fluid-filled shell inside of which the embryo develops. – Reptile adaptations to living on land include: Amniotic eggs Scaled, waterproof skin

– Reptiles include: Snakes Lizards Turtles Crocodiles Alligators Birds

Figure Snake Lizard Turtle

Birds – Recent genetic evidence shows that birds evolved from a lineage of small, two-legged dinosaurs. – Birds have many adaptations that make them lighter in flight: Honeycombed bones One instead of two ovaries A beak instead of teeth – Unlike other reptiles, birds are endotherms, maintaining a warmer and steady body temperature.

Mammals – The first true mammals: Arose about 200 million years ago Were probably small, nocturnal insect-eaters – Most mammals are terrestrial although dolphins, porpoises, and whales are totally aquatic. – Mammalian hallmarks are: Hair Mammary glands that produce milk, which nourishes the young

– There are three major groups of mammals: Monotremes, egg-laying mammals

Monotremes (hatched from eggs) Echidna adult and egg Figure 17.35a

Marsupials, pouched mammals with a placenta

Marsupials (embryonic at birth) Kangaroo newborn and mother Figure 17.35b

And eutherians, placental mammals

Eutherians (fully developed at birth) Wildebeest newborn and mother Figure 17.35c

– Primates are distinguished by characteristics that were shaped by the demands of living in trees. These characteristics include: Limber shoulder joints Eyes in front of the face Excellent eye-hand coordination Extensive parental care – Hominoids, the ape relatives of humans

Ring-tailed lemur Tarsier Black spider monkey (New World monkey) Patas monkey (Old World monkey) Gorilla (ape) Gibbon (ape) Chimpanzee (ape) Orangutan (ape) Human Figure 17.37

– Upright posture and an enlarged brain appeared at separate times during human evolution. – Different human features evolved at different rates.

Australopithecus and the Antiquity of Bipedalism – Before there was the genus Homo, several hominid species of the genus Australopithecus walked the African savanna. – Fossil evidence pushes bipedalism in A. afarensis back to at least 4 million years ago.

(a) Australopithecus afarensis skeleton (b) Ancient footprints(c) Model of an Australopithecus afarensis male Figure 17.39

Homo Habilis and the Evolution of Inventive Minds – Homo habilis, “handy-man”: Had a larger brain, intermediate in size between Australopithecus and modern humans Walked upright Made stone tools that enhanced hunting, gathering, and scavenging on the African savanna

Homo Erectus and the Global Dispersal of Humanity – Homo erectus was the first species to extend humanity’s range from Africa to other continents. – The global dispersal began about 1.8 million years ago. – Homo erectus: Was taller than H. habilis Had a larger brain Gave rise to Neanderthals © 2010 Pearson Education, Inc.

The Origin and Dispersal of Homo Sapiens – The oldest known fossils of our own species, Homo sapiens: Were discovered in Ethiopia Date from 160,000 to 195,000 years ago DNA studies strongly suggest that all living humans can trace their ancestry back to a single African Homo sapiens woman who lived 160,000 to 200,000 years ago.