BIOEE 1780 Lecture 23: Lecture 23
7 May 2018
School
Department
Course
Professor
Tetrapods: marine, freshwater, or terrestrial
• Synapomorphy: 4 legs
• Fin bones gradually changed to evolve the 1-2-5 pattern found in all living tetrapods
o 1 = humorous
o 2 = radius and ulna
o 5 = more than 5 little bones
o Tiktaalik was the first transitional form to have a wrist. The evolution of joints had a functional
basis.
o Once the 1-2-5 pattern evolved, diversity involved adjusting the pieces:
• What made the colonization of terrestrial habitats by tetrapods successful?
o Professor's Answers
• Legs
• Eggs
• Skulls
o Class Answers
• Limbs → motility, supporting body in the absence of buoyancy
• Preventing desiccation → skin, amniotic egg, excretory system that reduces the loss of
water
• Circulatory system → oxygenation; blood movement
• Two major groups:
o Amphibians
o Amniotes
Amphibians
• Freshwater/terrestrial
o Eggs are enclosed by a water permeable membrane, so they must be laid in water or they will
desiccate
o This is how they differ from all other tetrapods.
• Predators
• Some graze as larvae
• Examples:
o Salamanders
o Frogs
o Toads
o Caecilians: lack legs; look like large worms/snakes
Amniotes: reptiles and mammals
• Synapomorphy: amniotic egg (can be laid on land → adaptation to dry, terrestrial habitat)
o Separates the egg from the environment
o Egg doesn’t require water in the environment
• Series of membranes in the amniotic egg:
o Shell: protects embryo
o Amniotic Membrane: filled with fluid, supports embryo
o Allantois: collects wastes
o Chorion: helps regulate oxygen
Lepidosaurs: lizards and snakes
• More closely related to each other than to other reptiles
Document Summary
The evolution of joints had a functional basis: once the 1-2-5 pattern evolved, diversity involved adjusting the pieces, what made the colonization of terrestrial habitats by tetrapods successful, professor"s answers. Limbs motility, supporting body in the absence of buoyancy: preventing desiccation skin, amniotic egg, excretory system that reduces the loss of water, circulatory system oxygenation; blood movement. Freshwater/terrestrial: eggs are enclosed by a water permeable membrane, so they must be laid in water or they will desiccate, this is how they differ from all other tetrapods, predators, examples: Some graze as larvae: salamanders, frogs, toads, caecilians: lack legs; look like large worms/snakes. Synapomorphy: amniotic egg (can be laid on land adaptation to dry, terrestrial habitat: separates the egg from the environment, egg doesn"t require water in the environment. Series of membranes in the amniotic egg: shell: protects embryo, amniotic membrane: filled with fluid, supports embryo, allantois: collects wastes, chorion: helps regulate oxygen.
