From Fins to Fists

chordata

• The lobe-fins have muscular pelvic and pectoral fins
• Three lineages survive and include coelacanths, lungfishes, and tetrapods

tetrapod origin

• Old lineages
• Transitional fossils
• Fins shifting to legs
• Gills to lungs
• Coelacanth fossils found in more than 350 MYA

• Derived Characters of Tetrapods
• –Tetrapods have some specific adaptations:
• Four limbs, and feet with digits
• Ears for detecting airborne sounds
• In one lineage of lobe-fins, the fins became progressively more limb-like while the rest of the body retained adaptations for aquatic life

• Amphibians are represented by about 6,150 species of organisms in three orders
• Amphibian means “both ways of life,” referring to the metamorphosis of an aquatic larva into a terrestrial adult
• Most amphibians have moist skin that complements the lungs in gas exchange
• Fertilization is external in most species, and the eggs require a moist environment

• Order Urodela includes salamanders, which have tails
• Order Anura includes frogs and toads, which lack tails
• Order Apoda includes caecilians, which are legless and resemble worms

• Chrytid fungus
• Habitat loss
• Climate change
• Trematodes (cause deformities)
• Pollution and chemicals

• Amniotes are a group of tetrapods whose living members are the reptiles, including birds, and mammals
• Derived Characters:
• –amniotic egg, which contains membranes that protect the embryo–relatively impermeable skin
• –ability to use the rib cage to ventilate the lungs
• The extra-embryonic membranes are the amnion, chorion, yolk sac, and allantois

amniotic egg

• The reptile clade includes the tuataras, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs
• Derived Characters:
• –Reptiles have scales that create a waterproof barrier
• –They lay shelled eggs on land
• Most reptiles are ectothermic
• Birds are endothermic

absorbing external heat as the main source of body heat

capable of keeping the body warm through metabolism

The lepidosaurs include tuataras, lizards, and snakes

lineage produced the crocodilians, pterosaurs, and dinosaurs

• All turtles have a boxlike shell made of upper and lower shields that are fused to the vertebrae, clavicles, and ribs
• Some turtles have adapted to deserts and others live entirely in oceans or ponds and rivers

(alligators and crocodiles) belong to an archosaur lineage that dates back to the late Triassic

Birds are archosaurs, but almost every feature of their reptilian anatomy has undergone modification in their adaptation to flight

• The major adaptation is wings with keratin feathers
• Lack of a urinary bladder
• Females with only one ovary
• Small gonads
• Loss of teeth

• Mammals are represented by more than 5,300 species
• By the early Cretaceous, the three living lineages of mammals emerged: monotremes, marsupials, and eutherians
• Mammals did not undergo a significant adaptive radiation until after the Cretaceous

• Mammary glands, which produce milk
• Hair
• A larger brain than other vertebrates of equivalent size
• Differentiated teeth

are a small group of egg-laying mammals consisting of echidnas and the platypus

• include opossums, kangaroos, and koalas
• –The embryo develops within a placenta in the mother’s uterus
• –A marsupial is born very early in its development
• –It completes its embryonic development while nursing in a maternal pouch called a marsupium

• Compared with marsupials, eutherians have a longer period of pregnancy
• Young eutherians complete their embryonic development within a uterus, joined to the mother by the placenta
• Molecular and morphological data give conflicting dates on the diversification of eutherians

• The mammalian order Primates includes lemurs, tarsiers, monkeys, and apes
• are members of the ape group
• Most primates have hands and feet adapted for grasping

• The study of human origins is known as paleoanthropology
• Hominids are more closely related to humans than to chimpanzees
• Paleoanthropologists have discovered fossils of about 20 species of extinct hominids
• Hominids originated in Africa about 6–7 million years ago
• Early hominids had a small brain but probably walked upright

• –Upright posture and bipedal locomotion
• –Larger brains
• –Language capabilities and symbolic thought
• –The manufacture and use ofcomplex tools
• –Shortened
• –Shorter digestive tract