Lecture 18

Question 1

Tetrapoda def

Answer 1

• evolved from four limbed ancestors
• Not all extant tetrapods have four limbs
• All vertebrates that aren’t fish

Question 2

Movement onto Land evolution

Answer 2

• Life originated in water
• Animal bodies are mostly composed of water
• All cellular activities occur in water
• Vertebrates were not the first to transition to land
• Vascular plants, and terrestrial snails and arthropods made this
transition much earlier than did vertebrates
• These organisms were a source of food for early tetrapods

Question 3

Differences between Aquatic and Terrestrial Environment:

Answer 3

1. Oxygen content (air&raquo_space; water)
2. Fluid density (air < water)
3. Temperature regulation (more complicated on land)
4. Habitat diversity (more diverse on land)

Question 4

Origin of Tetrapods

Answer 4

• Paired fins of lobe-finned fishes are homologous to amphibian limbs

Question 5

Modern Amphibians classes and order

Answer 5

• Phylum: Chordata
• Class: Amphibia
• 3 Major Orders
• Order Gymnophiona – Caecilians
• Order Urodela – Salamanders
• Order Anura - Frogs (includes toads)

Question 6

General Characteristics of Amphibians

Answer 6

• need moisture!
• Thin skin is easily desiccated
• Eggs shed into water or moist environment
• Ectothermic
  * body temperature dependent upon environmental temperature and not generated metabolically
  * Fish, non-avian reptiles, and invertebrates are also ectothermic
• Need cool environments

Integument (skin) modified for respiration
eggs have jelly membrane covering

Question 7

‘Typical’ Characteristics of Amphibians

Answer 7

• Dioecious
• Predominantly oviparous
• Eggs are aquatic
• Aquatic larval form (with gills)
• Metamorphose into a terrestrial adult form (with lungs and cutaneous
respiration)

Cutaneous = relating to the skin

Question 8

Respiration in Amphibians

Answer 8

• Cutaneous respiration
• Buccal breathing
• Gills and/or lungs
• Presence of gills and lungs varies by species and by developmental

some species,aquatic larvae lose gills at metamorphosis

Question 9

External Gills in amphibians

Answer 9

• Develop from pharyngeal slits (one of the hallmarks of chordates)
• External gills are exposed to the environment
• found in all amphbian larvae

Question 10

Order Gymnophiona - Caecilians

Answer 10

• Elongated, limbless, burrowing animals
• Mostly found in South America
• Eyes small and can be covered over with skin
• Some species are blind

Question 11

Order Urodela - Salamanders

Answer 11

• Most have limbs set at right angles to the
trunk
• In some aquatic and burrowing forms, limbs are rudimentary or absent

Question 12

Salamanders vs lizards

Answer 12

Salamanders
• amphibians
• Moist skin
• No claws or scales 
• 4 front toes

 Lizards
• reptiles
• Dry skin
• Scales and claws
• External ear openings
• Five front toes

Question 13

Aquatic Salamanders

Answer 13

• Entire life cycle is aquatic
• Internal fertilization
• Lay eggs in the water
• Aquatic larvae have external gills and finlike tail
• Adults retain external gills and remain in aquatic environment
• Also have weak lungs

Question 14

Paedomorphosis

Answer 14

Paedomorphosis = evolution of an adult form that resembles an ancestral juvenile

Unusual pattern:
• reach maturity while retaining their gills, aquatic lifestyle, and other
larval characteristics
• Some species never metamorphose, while others will metamorphose under certain environmental conditions

Question 15

Amphiumas Aquatic Salamanders

Answer 15

• Completely aquatic life history
• Larval form has gills
• Lose gills before adulthood
• Breathe through lungs (raising nostrils above the water surface) • Vestigial legs

Vestigial = body part that has become small or lost through evolution

Question 16

Terrestrial Salamanders

Answer 16

• Entire life cycle is terrestrial
• Internal Fertilization
• Deposit eggs in small, grapelike clusters under logs or in excavations in soft moist earth
• Many species guard eggs
• Direct development (all terrestrial species)
• Lungless! breathes through cutaneous respiration

Question 17

Salamanders – Double Metamorphosis

Answer 17

Some species

• Gilled larvae -> red eft juvenile (lungs) -> aquatic adult (lungs)

Question 18

Respiration in Salamanders - summary

Answer 18

• All salamanders (and all amphibians) use cutaneous respiration
• At various stages in life cycle, salamanders can have gills, lungs, both, or neither
• It’s complicated! General Rules…
• If you hatch in water, you will have gills
• Gills are lost if metamorphosis into a terrestrial form takes place
• If you have lungs they are present from birth (in terrestrial forms)
• Many salamanders are lungless
• includes many entirely terrestrial forms which depend on cutaneous
respiration
• These salamanders also use buccal breathing (pumping air into the mouth where gases are exchanged across the membranes of the buccal cavity)

Question 19

Order Anura - Frogs

Answer 19

frogs are ectothermic and need to stay close to water
• Specialized for jumping
• What about Toads? They are Frogs!

Question 20

Order Anura - Respiration

Answer 20

frogs

internal gills
• Three respiratory surfaces for gas exchange in air (adults) 
• Skin (cutaneous breathing)
• Mouth (buccal breathing)
• lungs
• More reliant on lungs than salamanders

Question 21

Order Anura - Development

Answer 21

frogs

• Most often indirect development
• Eggs of most frogs hatch into a tadpole with: long finned tail
• External and sometimes internal gills
• no legs
• specialized mouthparts for herbivorous feeding
• Bear little resemblance to adult frogs
• Some frogs exhibit direct development (e.g. many tropical frogs)
• Paedomorphosis does not occur in frogs and toads