Lecture 18 Flashcards
Tetrapoda def
- evolved from four limbed ancestors
- Not all extant tetrapods have four limbs
- All vertebrates that aren’t fish
Movement onto Land evolution
• 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
Differences between Aquatic and Terrestrial Environment:
- Oxygen content (air»_space; water)
- Fluid density (air < water)
- Temperature regulation (more complicated on land)
- Habitat diversity (more diverse on land)
Origin of Tetrapods
• Paired fins of lobe-finned fishes are homologous to amphibian limbs
Modern Amphibians classes and order
- Phylum: Chordata
- Class: Amphibia
- 3 Major Orders
- Order Gymnophiona – Caecilians
- Order Urodela – Salamanders
- Order Anura - Frogs (includes toads)
General Characteristics of Amphibians
- 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
‘Typical’ Characteristics of Amphibians
• 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
Respiration in Amphibians
- 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
External Gills in amphibians
- Develop from pharyngeal slits (one of the hallmarks of chordates)
- External gills are exposed to the environment
- found in all amphbian larvae
Order Gymnophiona - Caecilians
- Elongated, limbless, burrowing animals
- Mostly found in South America
- Eyes small and can be covered over with skin
- Some species are blind
Order Urodela - Salamanders
• Most have limbs set at right angles to the
trunk
• In some aquatic and burrowing forms, limbs are rudimentary or absent
Salamanders vs lizards
Salamanders • amphibians • Moist skin • No claws or scales • 4 front toes
Lizards • reptiles • Dry skin • Scales and claws • External ear openings • Five front toes
Aquatic Salamanders
- 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
Paedomorphosis
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
Amphiumas Aquatic Salamanders
- 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
Terrestrial Salamanders
- 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
Salamanders – Double Metamorphosis
Some species
• Gilled larvae -> red eft juvenile (lungs) -> aquatic adult (lungs)
Respiration in Salamanders - summary
• 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)
Order Anura - Frogs
frogs are ectothermic and need to stay close to water
• Specialized for jumping
• What about Toads? They are Frogs!
Order Anura - Respiration
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
Order Anura - Development
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
