Animal Form and Function Kight Amphibians Class Amphibia (amphibia = living a double life) United by several distinguishing apomorphies within the Vertebrata 1. Skin Thought Question: For whom are integumentary poison glands intended? Why? Thought Question: Do you think the poison is fatal or nonfatal for the intended victim? Why? 2. Forelimb with four digits 3. Two unique modes of respiration a. Cutaneous respiration Thought Question: The skin of amphibians is characterized by a thin epidermis and a highly vascularized (dense capillary beds) dermis. Why? Thought Question: What kind of environment does this constrain skin-breathing amphibians to live in? b. Lungs with bucco-pharyngeal pump Synthesis Question: Why can humans choke to death on food? 4. Mesonephric kidneys that excrete urea - vertebrate kidney discussed later 5. Aquatic eggs with jelly-like membrane coverings - mesolecithal
6. Metamorphosis - juveniles and adults have distinct morphologies. Thought Question: Amphibian metamorphosis is unique among vertebrates, but not among animals (i.e. insects also metamorphose). How does metamorphosis influence the life-history of juveniles v. adults? How is this advantageous? 7. One cervical vertebrum = atlas Thought Question: Fish have no cervical vertebrae (fish have no necks) and amniotes have an atlas + axis. What can amphibians do that fish cannot? What can amniotes do that amphibians cannot? 8. One sacral vertebrum. Review Question: Describe and differentiate cervical, thoracic, lumbar, sacral and caudal vertebrae. 9. Tongue inserts on anterior margin of jaw. Thought Question: Think about the way amphibians capture prey. What is the functional significance of amphibian tongue insertion?
Tetrapoda ( four feet ) - taxon uniting amphibians and amniotes, the terrestrial vertebrates Differences between aquatic and terrestrial environments. 1. Oxygen content Thought Question: How does this influence selection on tetrapod body size? Why? 2. Relative density Thought Question: Why are animals buoyant in water? Thought Question: How does this influence selection on tetrapod body size? Why? 3. Ambient Temperature Fluctuation Thought Question: In which environment does ambient temperature change most rapidly (aquatic or terrestrial). Why? Thought Question: In which environment can animals be relatively homeothermic without being endothermic? Why? Thought Question: How do ectothermic tetrapods cope with rapid changes in ambient temperature? Which tetrapods are ectothermic? 4. Habitat diversity Thought Question: Which environment (aquatic v. terrestrial) has the most diversity of habitats? Describe several examples. Thought Question: How has this diversity influenced the morphology, physiology and behavior of the animals living there? Provide examples.
Several vertebrate apomorphies related to terrestrial existence unite the Tetrapoda. 1. Double Circulation (pulmonary and systemic circuits) - Three chambered heart in amphibians and reptilian amniotes (2 atria, 1 ventricle) Thought Question: Discuss the flow of blood into and out of a three chambered heart. - Four chambered heart in birds and mammals (2 atria, 2 ventricles) Thought Question: Discuss the flow of blood into and out of a four chambered heart. Synthesis Question: Which is more efficient, three or four chambers? Why? Synthesis Question: Non-tetrapod vertebrates have two chambered hearts. Can they have double circulation? Why or why not? Do they need double-circulation? Why or why not? Thought Question: Amphibians have a spiral valve in the ventral aorta (large vessel leaving heart which eventually divides into the systemic artery and pulmonary artery). When closed, most blood enters the systemic circuit and very little blood enters the pulmonary circuit. Why would this valve be adaptive for an amphibian? When?
2. Skeletal apomorphies a. Paired jointed walking limbs b. Reinforced and enlarged appendicular girdles - pectoral girdle with scapulae and clavicles Thought Question: Pectoral girdle does NOT articulate with skull in tetrapods. Why not? - pelvic girdle with ilium, ischium & pubis Thought Question: Why would the appendicular girdles need to be larger in tetrapods? c. Skull smaller with few bones. Thought Question: Why? Thought Question: Tetrapod skulls have specialized musculature that permit not only strong jaw closing, but also holding of prey items. Why would holding prey with jaws be associated with terrestrial existence? d. Zygapophyses Thought Question: The structural integrity of the tetrapod vertebral column is analogous to that of a suspension bridge. How does a suspension bridge work? How is it analogous to the tetrapod body plan? Thought Question: Why would tetrapods need a suspension bridge where non-tetrapods would not? e. Sternum - anterior, ventral trunk region Thought Question: What is the function of the sternum? f. Ratio of appendicular to body-wall musculature Thought Question: What parts of the body do you eat in fish? Birds and mammals? Why? Thought Question: What is the functional significance of these differences in muscular proportions?
3. Ears Thought Question: How do the physics of sound differ in terrestrial and aquatic environments? In which environment would organisms need more sensitive ears? Why? Basic tetrapod ear = tympanic membrane, middle ear & inner ear operculum Fossil Record 400 mya - Rhipidistian Fish (extinct) Thought Question: What conditions would such a fish be adapted to? Thought Question: Modern lungfish share an ancestor rhipidistian fish, but did not descend from them. Are the lungfish of today halffish half-amphibian? Why or why not? 375 mya - Eusthenopteron 350 mya - Ichthyostega = oldest fossil amphibian Thought Question: Jaws were large and relatively heavy. Why does this suggest Ichthyostega was an aquatic predator, despite limbs obviously adapted to walking on land? Two fossil amphibian lineages reach to modern times: 1. immobile skull roof = modern amphibians 2. movement between skull roof and cheeks = gave rise to amniotes
Amphibian Diversity Order Caudata - Salamanders Representative Families Salamandridae = newts Ambystomatidae = tiger salamanders Plethodontidae - lungless salamanders Thought Question: Which salamanders have the most endurance, plethodontids or salamandrids (which have lungs)? Why? (hint: surface area and volume are key). example: humans and tennis courts Order Gymnophiona - Caecilians. Thought Question: Did the ancestors of caecilians have limbs? Justify your answer. Order Anura - frogs and toads Review Question: (from lab) Why is the urostyle adaptive for anurans? toads v. frogs - toads usually defined as anurans with dry warty skin, but this arrangement would be paraphyletic because the group represents several distantly related families. Representative Families Ranidae - bullfrog and relatives Bufonidae - American toad and relative Hylidae - tree frogs Dendrobatidae - poison arrow frogs and relatives curare