Animals II: The Chordates

Phylum : Chordata Subphylum: Urochordata:

Tunicates Cephalochordata: Lancelets Vertebrata: Vertebrates

Chordate Characteristics

Ø Four traits of chordate embryos: v  Notochord: stiff but flexible connective tissue, extends the

length of the body and supports it v  Dorsal, hollow nerve cord v  Narrow gill slits across the wall of the pharynx v  Post anal tail

Ø Most chordate species are vertebrates (endoskeleton)

Bilaterally symmetrical, coelomate animals Complete digestive system and closed circulatory system

Invertebrate Chordates

Lancelets: have a fishlike shape and retain the defining chordate traits into adulthood

Tunicates: lose most of the defining chordate traits during the transition to adulthood

Evolution of the Vertebrates

The earliest fossils of fishes date back to about 530 million years ago Ø Tapered body, a few centimeters long Ø Head with a pair of eyes, but no jaws Ø Skeleton consisted of cartilage

Earliest Lineages of Vertebrates Fishes

Class Agnatha/Jawless Fishes

Ø  Modern jawless fishes Ø  Cartilage skeleton and a cylindrical body

about a meter long Ø  No fins Ø  Hard mouthparts

Hagfishes and lampreys

Ø Most primitive craniate/ Lack jaws & vertebrae Ø Notochord gives the main support Ø Scavenge dead or dying animals Ø Almost blind/excellent sense of smell Ø Slime! Ø Tie their tail into a knot

Hagfishes

Lampreys: Vertebrates without hinged jaws

Larval stage resembles the lancelets Suspension feeders Adults are mostly parasitic

Class: Chondrichthyes/ Cartilaginous Fishes

Ø Flexible skeleton made of cartilage to reduce weight Ø Many are predators with powerful jaws and knife-like teeth, fast swimmers Ø Sharp vision and strong sense of smell Ø  Interconnected network of sensory cells/ detecting prey Ø Uncovered gills Ø Cloaca Ø Sharks, rays and skates

Osteichthyes have a swim bladder (gas filled sac) used to regulate buoyancy

Class: Osteichthyes/ “Bony Fish”

The gills are protected by an operculum

Class Amphibia

Ø First tetrapods Ø Limbs that support weight on land Ø Scaleless Ø Lungs Ø All are carnivores Ø Three-chambered heart Ø Generally tied to water for reproduction/Most lay eggs in water Ø 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

Ø Amniotes branched off from an amphibian ancestor about 300 million years ago

Ø Traits that adapt them to life in dry places: •  Lungs throughout life, skin rich in keratin,

well-developed kidneys, 4-chambered heart, fertilization within female’s body, embryo encased in fluid

Class Reptilia

Lizards, snakes, turtles, crocodiles, and birds

Most nonbird reptiles are ectotherms

Nutrients from the yolk and water from the albumin in the egg sustain the developing embryo

Terrestrially Adapted Egg

Class Reptilia/ Birds

Endothermic

Only animals with feathers Excellent vision, large brains, complex behaviors Elaborate courtship displays Hard shell eggs

Adaptations to reduce weight: no teeth, tail supported by only a few vertebrae, feathers with hollow shafts, honeycomb bone structure

Flight Adaptations

Class Mammalia

Ø Mammary glands Ø Hair or fur Ø High metabolic rate Ø Long parental care Ø Most offspring born rather than hatched Ø Endothermic Ø Different shaped teeth

Class Mammalia Three major lineages

Monotremes

Marsupials

Eutherians

Australia, New Guinea: platypus & spiny anteater

Monotremes: Egg-laying mammals

The young licks up milk secreted from the mammary glands through openings in the skin

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/ order under class Mammalia

Ø Primates: placental mammals that includes humans, apes, monkeys, and their close relatives Ø Shoulders have extensive range of motion Ø Most have both hands and feet capable of grasping

(not humans) Ø Most have eyes that face forward Ø Large brain Ø Social groups that include both sexes Ø Females give birth to one or two young at a time

Several species related to Homo sapiens (only surviving species) Homo nearderthalensis Homo erectus Homo habilis Australopethicus sp.

Hominins

Order: Primates Suborder: Anthropoid Family: Hominidae Tribe: Hominini

Bipedalism: Habitual upright walking

Evidence of bipedalism in early hominins 3.6 MYA in Ethiopia