Origin of Vertebrates P1

What is a vertebrate?

A vertebrate is an organism with a vertebral column and cranium (neural crest). It must have all the chordate features to be considered a vertebrate. The vertebral column eventually comes in, and it does not need to have bone. The cartilage is actually formed first. Also, vertebrates have muscular pumps for pharyngeal slits, which open and close, and can allow for more oxygen to be taken in. Eventually, jaws are formed (no teeth yet), brain, heart, and 2 lateral eyes, which form more slowly than the rest, so they can now see where they are going.

What are the steps involved in the origin of vertebrates?

1. Pre-vertebrate 

   1. Muscular pump of the gill slits evolves 

   2. Band of muscles moves across the pharynx (helps contract and expand the gills to be more efficient)

• Allows water in and out of the gills  

• Muscular Band Moves Across the Planet 

2. Agnathans (A = without and gnathan = jaw) 

   1. Jawless and armored fish 

• Armor will eventually turn into bone

• Initially starts as acellular 

• Only calcium carbonate 

• Anangram: Are Aliens Calling?

    ii. Modern ones do not have bone 

• Hagfish and Lampreys (Hag & lamp)

• Due to lifestyle

3. Gnathostomes 

   1. Jawed fish 

   2. Now a predator 

• Can get bigger 

• Can move more efficiently because of increased energy

What are the steps involved in the origin of vertebrates?

1. Pre-vertebrate 

   1. Muscular pump of the gill slits evolves 

   2. Band of muscles moves across the pharynx (helps contract and expand the gills to be more efficient)

• Allows water in and out of the gills  

Anangram: Muscular Band Moves Across the Planet

1. Agnathans (A = without and gnathan = jaw) 

   1. Jawless and armored fish 

• Armor will eventually turn into bone

• Initially starts as acellular 

• Only calcium carbonate 

• Anangram: Are Aliens Calling?

    ii. Modern ones do not have bone 

• Hagfish and Lampreys (Hag & lamp)

• Due to lifestyle

1. Gnathostomes 

   1. Jawed fish 

   2. Now a predator 

• Can get bigger 

• Can move more efficiently because of increased energy

Agnathan fish

1. Agnathan fish

   1. Jawless and paired fins, notochord (flexible rod that supports the body), armored, and cartilaginous skeleton.  

   2. Modern ones are cyclostomes 

      1. Hagfish and Lampreys Hagfish --> scavengers (eat dead stuff), rasping tongue, no jaws or teeth 

• Do not have a complex digestive system 

• Knot themselves for leverage 

2. Lamprey --> rasping tongue, "horny" teeth on oral sucker, latch onto living things 

• Munches on blood and body fluids 

• Do not have a complex digestive system

Gnathostome Fish

1. Ex: Dunkleosteus

2. Placoderms (placo = plate, derm = skin)

   1. Form tooth plates (armored)

   2. Head and thorax shield (there were some awful predators back then)

3. Experimental group: impersonators --> nature is playing around with different ideas (natural selection)

   1. Different body designs 

• Shark-like features (claspers) 

• Rays 

• Ratfish

4. Do not give rise to anybody --> no descendants (dead end)

Chrondrichthyan Fish

1. Ex: Sharks, skates, and rays

2. Chondrichthyans --> cartilaginous fish Synapomorphies 

   1. Calcified (hard, but not heavy) cartilaginous endoskeleton 

   2. No bone except teeth + placoid scales (reduced/vestigial bony scales) 

   3. Males have claspers for internal fertilization 

• Insert into the female cloaca (means sewer b/c common exit for all kinds of waste) 

4. Call No Men 

Osteichthyan Fish

1. Ex: Ray fins

2. Bony endoskeleton 

3. Exoskeleton: scales 

4. Gas bladder, which is derived from the lungs - for buoyancy 

5. BEG

Sarcopterygian Fish

1. Ex: lobe fins

2. Fleshy-lobed finned fish that have internal bones and muscles 

3. Oxygen deprived 

4. Live in very shallow water → learned to stand on the bottom floor and gulp air by sticking mouth out of water 

5. Have Internal nostrils (choanae)☆

6. Aestivate ☆: a form of hibernation, referred to as dormancy, which the fish can enter to survive certain environmental conditions. Metabolic rate is slowed down within these fish due to the dry and high temperatures. 

7. FOLIA

Tetrapods

1. Four-legged creatures, presence of lungs and a neck that seperates head from body

2. Tiktalik (fish-a-pod)

   1. Fish fins, gills, lungs, flattened skull, wrist, robust ribs, separate skull from the shoulder girdle

3. Acanthostega (aquatic tetrapod)

   1. Gills, lungs, flat skull, limbs with digits

4. Ichthyostega (biphasic lifestyle)

   1. No gills, lungs, fossilized tadpoles, 1st land ear, robust skeleton, fish fins, scales