Chordate Evolution
(Chapter 30.1, and 33)
Please set up your notebook for Cornell Notes
Phylum Chordata
Chordate  an animal that has 4 characteristics for at least part
of it’s life cycle
Dorsal hollow nerve cord – hollow tube running on the dorsal
side of the animal
Notochord  a rigid supporting rod running below the dorsal
hollow nerve cord
Pharyngeal pouch  paired structures in the throat region
Tail that extends beyond the anus
Most chordates are vertebrates  animals with a backbone
Vertebrates have an endoskeleton that grows as the organism
grows
Maintaining homeostasis
Ectotherm  body temp controlled by the environment
Fish, amphibians, reptiles
Low metabolism
Endotherm  generate heat and maintain body
temperature
Birds, Mammals
High metabolism
Form and Function
Feeding
Nonvertebrate chordates – tunicates and lancelets
Filter feeders
Vertebrates
Skull and teeth are adapted to a wide range of food
Have well developed digestive systems adapted for
different eating habits
Respiration
Gills  tunicates, fish, amphibian larva
Lungs  adult amphibians, reptiles, birds, mammals
Alveoli  bubble-like structures in the lings
Thin membranes so that oxygen and carbon
dioxide can diffuse across
Circulation
Single loop  blood travels from heart, to gills, to
body and back to heart
Double loop  oxygen poor blood to lungs, oxygen
rich blood to heart and then to body
Hearts have chambers
Fish and larval amphibians – 2 chambers
Adult amphibians and most reptiles – 3 chambers
Crocodiles, birds, mammals – 4 chambers
Excretion
Nonvertebrate chordates and fish use gills to diffuse
ammonia waste out of body
Other vertebrates use kidneys
Kidneys also help maintain homeostasis by
maintaining balance of water and salt in body
Response
Nonvertebrate chordates have simple nervous systems
with a mass of nerve cells forming brains
Vertebrates have more complex brains with regions that
have specialized functions
Movement
Skeletal and muscular systems support body and make a
wide range of motion possible
Reproduction
Almost all chordates reproduce sexually
External
Nonvertebrate chordates, fish, amphibians
Internal
Reptiles, birds, mammals
After fertilization
Oviparous  eggs develop outside of female body
Most fishes and amphibians, reptiles and all birds
Ovoviviparous  eggs develop inside of mothers body and
are nourished from yolk inside the egg
Sharks
Viviparous  develop in mothers body and get nutrients
directly from mother
Mammals
Nonvertebrate Chordates
Subphylum Urochordata  tunicates (sea squirts)
Marine, filter feeder, adults are sessile
Subphylum Cephalochordata  lancelets
Marine, filter feeder, live in sand with head region above
sand
Closed circulatory system but no true heart
Subphylum Cephalochordata  lancelets
Marine, filter feeder, live in sand with head region
above sand