1. VERTEBRATE ORIGINS Notes 25.1

2. Chordates Share four features at some stage of their development: 1. notochord- a flexible skeletal support rod embedded in the animal’s back (becomes part of the intervertebral discs) 2. hollow nerve cord- runs along the animal’s back (develops into the spinal cord and brain) 3. pharyngeal slits- slits through the body wall in the pharynx ( filter feeders, gills, only in embryonic stage for humans) 4. tail- extends beyond the anal opening, for movement

3. Chordates

4. Vertebrate Endoskeleton Braincase- cranium protects the brain Vertebrae- a series of short, stiff vertebrae that are separated by joints, protects the spinal cord Bones- support and protect the body’s soft tissues and provide points of attachments for muscles Gill arches- found in the pharynx of fish and some amphibians to support the gills

5. Vertebrate Endoskeleton

6. Vertebrate classes 1. agnatha- jawless, lampreys 2. chondrichthyes- cartilaginous fish, sharks 3. osteichthyes- bony fish, perch 4. amphibia- adapted to live in water and on land, frogs 5. reptilia- retain moisture to live on land, snakes 6. aves- birds, feathers 7. mammals- have hair, mammary glands, and three middle ear bones

7. Vertebrate classes

8. Early Vertebrates First recognizable vertebrate were fish Early fish were small, jawless bottom feeders Some had bony head shields, others covered with bony plates and scales Only two groups of jawless fish remain: 1. Lampreys- vertebrates, eel like, mouths surrounded by large sucker, tongues covered by toothlike projections 2. Hagfish- no vertebrae

9. Early Vertebrates