Animals II: The Chordates
Phylum : Chordata Subphylum: Urochordata: Tunicates Cephalochordata: Lancelets Vertebrata: Vertebrates
Chordate Characteristics Bilaterally symmetrical, coelomate animals Complete digestive system and closed circulatory system Four traits of chordate embryos: Notochord: stiff but flexible connective tissue, extends the length of the body and supports it Dorsal, hollow nerve cord Narrow gill slits across the wall of the pharynx Post anal tail Most chordate species are vertebrates (endoskeleton)
Lancelets: have a fishlike shape and retain the defining chordate traits into adulthood Invertebrate Chordates
Tunicates: lose most of the defining chordate traits during the transition to adulthood
Evolution of the Vertebrates
Earliest Lineages of Vertebrates Fishes The earliest fossils of fishes date back to about 530 million years ago Tapered body, a few centimeters long Head with a pair of eyes, but no jaws Skeleton consisted of cartilage
Class Agnatha/Jawless Fishes Hagfishes and lampreys Modern jawless fishes Cartilage skeleton and a cylindrical body about a meter long No fins Hard mouthparts
Hagfishes Most primitive craniate/ Lack jaws & vertebrae Notochord gives the main support Scavenge dead or dying animals Almost blind/excellent sense of smell Slime! Tie their tail into a knot
Lampreys: Vertebrates without hinged jaws Larval stage resembles the lancelets Suspension feeders Adults are mostly parasitic
Evolution of the jaws Hypothesis: jaws evolved from skeletal rods supporting the gill slits
Class: Chondrichthyes/ Cartilaginous Fishes Flexible skeleton made of cartilage to reduce weight Many are predators with powerful jaws and knife-like teeth, fast swimmers Sharp vision and strong sense of smell Sensory organs along the sides of the body that detect prey Cloaca
Class: Osteichthyes/ Bony Fish Osteichthyes have a swim bladder (gas filled sac) used to regulate buoyancy
Class Amphibia First tetrapods Scaleless Limbs that support weight on land Lungs All are carnivores Three-chambered heart Generally tied to water/most lay eggs in water Most are found in damp habitats (skin helps supplement oxygen intake)
Salamanders, newts, frogs, toads and caecilians
Metamorphosis: Gills and tail absorbed, terrestrial adaptations developed
Amniotes Amniotes branched off from an amphibian ancestor about 300 million years ago Traits that adapt them to life in dry places: Lungs throughout life, skin rich in keratin, well-developed kidneys, fertilization within female s body, embryo encased in fluid
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Class Reptilia Lizards, snakes, turtles, crocodiles, and birds Most nonbird reptiles are ectotherms
Terrestrially Adapted Egg Nutrients from the yolk and water from the albumin in the egg sustain the developing embryo
Class Reptilia/ Birds Endothermic Only animals with feathers Excellent vision, large brains, complex behaviors Elaborate courtship displays Hard shell eggs
Flight Adaptations Adaptations to reduce weight: no teeth, tail supported by only a few vertebrae, feathers with hollow shafts, honeycomb bone structure
Class Mammalia Mammary glands Hair or fur High metabolic rate 4-chambered heart Long parental care Most offspring born rather than hatched Endothermic Different shape teeth
Class Mammalia Three major lineages Monotremes Marsupials Eutherians
Monotremes: Egg-laying mammals Australia, New Guinea: platypus & spiny anteater The young licks up milk secreted from mother s fur
Marsupials: Pouched mammals Brief gestation, babies born very early in development and stay in pouch/ nurse in the pouch
Eutherians: Placental Mammals Long pregnancy embryo completely develops inside mother Complex placenta to protect and nourish developing young
Primates Primates: placental mammals that includes humans, apes, monkeys, and their close relatives Shoulders have extensive range of motion Most have both hands and feet capable of grasping (not humans) Most have eyes that face forward Large brain Social groups that include both sexes Females give birth to one or two young at a time
Anthropoids/ Active during the day and have good color vision
Modern Subgroups of Primates Lemurs: oldest lineage; active during day (tropical Africa and southern Asia) Tarsiers: small, nocturnal (southeast Asia)
New world monkeys (central and South America) and old world monkeys (Africa and Asia)
Apes: tailless primates/ gorillas and chimpanzees
Hominins Order: Primates Suborder: Anthropoid Family: Hominidae Tribe: Hominini Bipedalism: Habitual upright walking Several species related to Homo sapiens (only surviving species) Homo nearderthalensis Homo erectus Homo habilis Australopethicus sp.
Evidence of bipedalism in early hominins
Early Hominins Sahelanthropus tchadensis may be the oldest hominin (7 mya) Ardipithecus (5.8-5.2 mya) and Australopithecus (4-1.2 mya) Australopithecus sediba
Genus Homo
Ancestors of humans originated in Africa Oldest known fossils of Homo sapiens are from Ethiopia (160,000 and 195,000 years old) Coexisted with other Homo species including H. neanderthalensis and H. floresiensis
Modern humans have a number of distinctive physical features including: large brain volume/ 1,300 cm 3 lightly built skeleton, adapted to walking on 2 legs skull with a short base and a high braincase small or absent brow ridge chin on the lower jaw Lack thick coat of body hair Precision grip