Higher Chordata: Subphylum Vertebrata: The Fishys Biology 11 Higher Chordata: Subphylum Vertebrata: The Fishys

Phylum Chordata is typically divided into four subphyla: Higher Chordates We are going to spend the next few classes talking about the Subphylum Vertebrata (AKA: the higher chordates!)

Higher Chordata Objectives: Vertebrata Describe the 3 Classes and an example animal Anatomy of the Perch

Subphylum Vertebrata Characteristics: 1. Endoskeleton of bone or cartilage which surround the dorsal nerve cord (a backbone or vertebral column) 2. Notochord absent or reduced in adult 3. Pronounced cephalization 4. A closed circulatory system

Class Agnatha Jawless fishes Much more dominant in the early oceans where they were mud suckers or filter feeders – no articulating jaws Evolved gills to improve oxygen uptake and thus increased activity levels No paired appendages Represented today by Lamprey and Hagfish

Class Chondrichthyes Cartilagenous Fishes Skeleton is made of cartilage not bone (secondarily evolved) Evolved articulating jaws by modification of anterior two pairs of gill slits Have no operculum or air bladder Very streamlined body with paired fins for steering

Class Chondrichthyes Have well developed senses, especially smell Are almost all predators Developed internal fertilization and carry eggs internally (no nutritional connection) as young must swim when born Much more dominant in early oceans They are: sharks, skates, and rays

Hammerhead Shark Tiger Shark

Skates: Rays: Thicker heavier tails No spines on tail Rounded shape Thicker heavier tails No spines on tail Thorns on tail and back Elongated nose Smaller Lay eggs Rays: - Kite shaped Thin barbed tails Spines on tail No thorns on tail and back Larger Give birth to live young

Class Osteichthyes The Bony Fishes Have a calcified skeleton - are dominant water vertebrate Have an operculum and air bladder (formed as a pocket off the pharynx) Developed the structure that evolution would select for in moving the vertebrates to land

Class Osteichthyes 1. Circulatory System Have a two chambered heart that pumps blood to the gills then the rest of the body 2. Nervous system Have the basic organization of a vertebrate brain and well developed senses Behaviours begin

Class Osteichthyes 3. Reproduction Have external fertilization and development with little if any post natal care Young are born able to swim and feed and must fend for themselves 4. Excretory System Have a dorsal kidney that excretes mainly ammonia as nitrogen waste

Class Osteichthyes There are two main groups of fish seen today: 1. Teleosts: true fish with ray finned appendages Evolved in fresh water then moved back to the oceans Most common fish today (salmon, trout etc)

Class Osteichthyes 2. Lung fish and Lobe-finned fish These two fish evolved in fresh water at a time when periodic and severe droughts occurred Lung fish seen today in Africa and South America Use their crude lungs to gulp air to assist gills (usually live in stagnant water)

Class Osteichthyes Lobe-finned fish were mostly bottom dwellers and used their more sturdy fins to grope along the bottom of the swamps and to occasionally move about the muddy shores Both of these fish are well represented in the fossil record

Evolution to Land Vertebrates faced many problems moving onto land Problems: 1. Gas exchange (moist membrane problem) 2. Movement: loss of buoyancy 3. Obtaining food - must adapt to new food especially tough plants

Evolution to Land 5. Reproduction: with motile sperm 4. Dessication 5. Reproduction: with motile sperm 6. Development: all animal embryos develop in water 7. Senses: land is much more transparent than water - can be seen easier - much more to detect and react to 8. Adaptation: to rapid, severe climate changes

Evolution to Land On to Land! The bony fish evolved from the cartilagenous fishes, probably in fresh water During the Devonian, the land became much hotter and drier Water habitats both shrank and became stagnant

Evolution to Land Shallow pools of water would dry up most quickly - problem for fish Competition for food and space also intensified as the habitat shrunk If your pond is drying out, to survive you need to get to another pool of water Nature would select for any structure that would aid short term movement on land

Evolution to Land Fleshy, sturdy fins would allow the fish to “steer” a course between water holes using the muscular tail for propulsion This is very energetically costly: crude lungs were already developing as the stagnant water had too little oxygen (which evolved into air bladders in water fish) Nature would select for better lungs

Evolution to Land One advantage they would discover while in transit was unlimited food (no other major animals on land) This would encourage them to stay longer on land The end result would be a lobe finned, lung fish capable of limited movement on land

A Coelocanth, a lobe-finned fish!