Chordates

What is a Chordate?  Chordates are animals that are characterized by a notochord, a dorsal hollow nerve chord, and pharyngeal slits at some stage of their development.

Characteristics  Notochord: Flexible rod of specialized cells along its dorsal side Becomes the vertebral column (in vertebrates)  Dorsal Nerve Chord: Hollow tube just above the notochord Eventually becomes the brain and spinal cord  Pharyngeal Slits: Eventually becomes gills in aquatic organisms Becomes throat and ear structures in terrestrial organisms

Contains 3 subphlya:  Urochordates (inverts)  Cephalochordates (inverts)  Vertebrates (verts)

Invertebrate Chordates: Urochordates  2,000 species  Have gill slits as larvae and adults  Have notochord and dorsal nerve cord as larvae  Metamorphosis results in loss of notochord and tail, and the nerve chord shortens  Examples: tunicates (sea squirts)

Invertebrate Chordates: Cephalochordates  28 species  Small fishlike creatures  Have notochord, dorsal nerve cord, and gill slits as adults  Lancelet is the closest living relative to early animals

Vertebrate Chordates: Vertebrates  41,ooo species – 95% of chordates  Bones or cartilage surround the dorsal nerve cord  Contain skull and endoskeleton  Have organs organized into systems

How Vertebrates Regulate Body Temperature  Endothermic – warm-blooded An animal that generates its own body heat Examples – birds and mammals  Ectothermic – cold-blooded Body temperature is determined by the environment Examples – reptiles, fish, and amphibians

Vertebrate Reproductive Development: How long the eggs remain within the female  Oviparous – “egg birth” Lay eggs and eggs hatch outside mother’s body Examples – Most fish, most reptiles, all birds, and 3 species of mammals  Ovoviviparous – “egg-live birth” Fertilized eggs remain inside of mother Nourished by egg yolk – not the mom May lay the eggs and then hatch shortly thereafter OR eggs hatch inside of mother and young are born live Examples – Some fish, some reptiles  Viviparous – “live birth” Young develop within the uterus Nourished by placenta Example – Placental mammals (humans)

Taxonomy of Vertebrates ClassMajor CharacteristicsExamples AgnathaJawless fishLamprey, hagfish ChondrichthyesCartilaginous fishSharks, stingrays OsteichthyesBony fishFlounder, trout, etc. AmphibiansPart life in water, part life on land Frogs, toads, salamanders ReptilesAmniote egg and scalesTurtles, alligators, snakes AvesFeathers, hollow bonesBirds MammalsWarm blooded, hair, produce milk Humans, primates, dogs, etc.

Agnatha – Jawless Fish  AKA cyclostomes (round mouth)  Most primitive living vertebrates  Ostracoderms (extinct); lamprey (extant)  Lack paired appendages  cartilaginous skeleton  rasping mouth to suck blood

Chondrichthyes – Cartilaginous Fish  Sharks, skates, rays  Well developed jaws and paired fins; continual water flow over gills (gas exchange); lateral line system (detects water pressure changes)  Sexual reproduction with internal fertilization

Osteichthyes – Bony Fish  Ossified (bony) endoskeleton; scales; operculum (gill covering); swim bladder (buoyancy); 2 chambered heart with a single circulatory circuit through body  Most numerous vertebrate  Sexual Reproduction, most with external fertilization

Amphibians – “Double Life”  1st tetrapods on land  Frogs, toads, salamanders  3 chambered heart with a double circulatory circuit (travels twice through body for complete trip)  Double life & metamorphosis- aquatic (larva) & terrestrial (adult)  Must have moist skin for gas exchange  Must use WATER for reproduction

Reptiles  Lizards, snakes, turtles, crocs and gators  Amniote (shelled) egg with extraembryonic membranes (gas exchange, waste storage, nutrient transfer)  Waterproof scales of the protein keratin  Well-developed lungs for gas exchange  Most have 3 1/2 chambered heart; crocodilians have 4  No WATER needed for reproduction- first to truly adapt to life on land

Aves – Birds (Flighted Reptiles)  Flight adaptations: wings (honeycombed bone) and feathers (keratin)  Toothless  Airfoil wing  Evolved from reptiles (amniote egg and leg scales)  4-chambered heart – double circuit  Internal fertilization  Archaeopteryx (evolutionary link between reptiles & birds)

Mammals  Mammary glands that produce milk  hair (keratin)  4-chambered heart  large brain  teeth differentiation  Monotremes (egg-laying): duck-billed platypus and echidnas (spiny anteater),  Marsupials (pouch): opossums, kangaroos, koalas  Eutherian (placenta):all other mammals

Vertebrate Chordates Endo/Ecto- therm Circulation (# of chambers) RespirationFertilization (where sperm unites w/egg) FishEctothermsSingle loop (2)GillsInternal or external AmphibiansEctothermDouble loop (3)Larvae-gills Adult- lungs & skin External ReptilesEctothermDouble loop (most 3 1/2 Crocodilians-4) LungsInternal (some external) BirdsEndothermDouble loop (4)Lungs (more complex) Internal MammalsEndothermDouble loop (4)Lungs (most complex) Internal