Vertebrates in the Sea & on Land Section 32.1

Adaptations of Vertebrates 1.Chordates with a backbone Made of vertebra segments Completely replaces the notochord Provides a site for muscle attachment and protection of the spinal cord Allows for a bony skull to enclose and protect the brain 2.Segmentation 3.Bilateral symmetry 4.Two pairs of jointed appendages 5.Cephalization 6.A true coelom 7.Closed circulatory system with a chambered heart

The First Vertebrates  First appeared about 500 million years ago  Lived in water  Agnathans – early fish without jaws or paired fins  Evolution of fish involved: 1.Improved swimming – flattened bodies became streamlined & paired fins for control 2.Development of jaws – from gill arch supports made of cartilage

Modern Fish  More fish species than any other vertebrate  Three groups: 1.Agnathans – jawless fish; hagfish & lampreys 2.Cartilaginous fishes – skeleton of cartilage; sharks, skates & rays 3.Bony fishes – skeleton of bone (95% of all fish species)

Agnatha – lampreys & hagfish

Cartilagenous fish – Sharks, skates, & rays

Bony Fish – most fish are in this group

Evolution of Amphibians  Appeared about 370 million years ago  Name means ‘double life’ – they live in water as juveniles and on land as adults  Adaptations to land include: 1.Legs – support body & allow movement 2.Lungs – do not need as much water to function 3.Heart – walking on land requires more energy and therefore a stronger pump

Three Groups of Modern Amphibians 1.Frogs & toads – largest group 2.Salamanders & newts 3.Caecilians – less than 1%

Frogs – have smoother skin than Toads

Salamanders & Newts

Caecilian