Biology 11 Phylum 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
https://www.discovery.co m/tv-shows/discoverypresents/videos/hag-fishslime
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
Tiger Shark Hammerhead Shark
Rays: - Kite shaped - Thin barbed tails - Spines on tail - No thorns on tail and back - Larger - Give birth to live young Skates: - Rounded shape - Thicker heavier tails - No spines on tail - Thorns on tail and back - Elongated nose - Smaller - Lay eggs
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
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 Class Osteichthyes Have a dorsal kidney that excretes mainly ammonia as nitrogen waste
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
Pregnant Males? http://channel.nationalgeographic.com/wild/videos/pre gnant-males/
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
Vertebrates faced many problems moving onto land Problems: Evolution to Land 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 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!