Early Tetrapods & Amphibians Flashcards
1
Q
What are tetrapods?
A
- Evolved from four limbed ancestors
- Not all extant tetrapods have four limbs
- All vertebrates that aren’t fish
- Two major branches (Amphibians and Amniotes)
2
Q
Explain the movement onto land
A
- 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
3
Q
What are the difference between aquatic and terrestrial environment?
A
1) Oxygen content (air»_space; water)
2) Fluid density (air < water)
3) Temperature regulation (more complicated on land)
4) Habitat diversity (more diverse on land)
4
Q
What is the origin of tetrapods?
A
- Paired fins of lobed finned fishes are homologous to amphibian limbs
5
Q
What is Eusthenopteron?
A
- Devonian lobe finned fish
- Foreshadows tetrapod limbs
- Upper arm bone (humerus)
- Two forearm bones (radius and ulna)
- Wrist bone
- Pushed itself along bottom with fins
- Couldn’t walk upright
Limited range of motion of fins
6
Q
What is Acanthostega?
A
- An early tetrapod
- Well formed fore and hindlimb
- 8 fully evolved fingers
- Too weak to walk on land
- Probably exclusively aquatic
7
Q
What is Ichthyostega?
A
- Could walk on land
- Fully developed shoulder girdle and hip girdle
- Well developed muscles
- stronger backbone
- 7 toes
8
Q
What is Limnoscelis?
A
- Terrestrial
- 5 digits on fore and hindlimb
- Became tetrapod standard
9
Q
What are Amphibians?
A
- Dramatic metamorphosis from an aquatic larval form to a terrestrial adult form
- They include the only living vertebrates that have a transition from water to land in both their ontogeny and phylogeny
- Breathe through gills and/or lungs and/or skin
10
Q
What are modern amphibians?
A
Phylum: chordata Class: Amphibian 3 major orders - Order Gymnophiona (caecilians) - Order Urodela (salamanders) - Order Anura (frogs)
11
Q
What are the general characteristics of Amphibians?
A
- Freshwater or moist terrestrial habitats
Need moisture
Thin skin is easily desiccated
Eggs shed into water or moist environment - Ectothermic
Body temp 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
- Mesolecithal eggs with jellylike membrane coverings
12
Q
Typical characteristics of Amphibians?
A
- Dioecious
- Predominantly oviparous
- Eggs are aquatic
- Aquatic larval form (with gills)
- Metamorphose into a terrestrial adult form (with lungs and cutaneous respiration)
- Many exceptions to these typical characteristics
Some salamanders stay in a permanently larval stage
Some caecilians, frogs, and salamanders live only on land (no aquatic larva)
Some amphibians are viviparous or ovoviviparous
13
Q
What is the respiration in Amphibians?
A
- Cutaneous respiration
- Buccal breathing
- Gills and.or lungs (presence of gills and lungs varies by species and by developmental stage)
- In many species aquatic larvae lose gills at metamorphosis (some salamanders retain gills and an aquatic existence throughout life)
14
Q
Explain their external gills
A
- Develop from pharyngeal slits (one of the hallmarks of chordates)
- External gills are exposed to the environment (no operculum)
- Found in all amphibian larvae
15
Q
Explain the order Gymnophiona (caecilians)
A
- Elongated, limbless, burrowing animals
- Mostly found in South America (also Africa, India and Southeast Asia)
- Eyes small and can be covered over with skin (some species are blind)
- Rarely encountered and understudied
16
Q
Explain the order Urodela (salamanders)
A
- Tailed amphibians
- Approx 670 species of salamanders worldwide
- Occur in almost all northern temperate regions (abundant and diverse in North America)
- Most have limbs set at right angles to the trunk (in some aquatic and burrowing forms, limbs are rudimentary or absent)
17
Q
Differences between salamanders and lizards?
A
Salamanders
- Amphibians
- Moist skin
- NO claws or scales
- 4 front toes
Lizards
- Reptiles
- Dry skin
- Scales and claws
- External ear openings
- Five front toes
18
Q
What is the life cycle of the order Urodela?
A
- Ancestral life cycle typical of amphibians: aquatic larvae metamorphose into terrestrial adults
- However, some are aquatic throughout life cycle and some are terrestrial throughout life cycle
19
Q
What is paedomorphosis?
A
- Evolution of an adult form that resembles an ancestral juvenile
- Typical pattern: larvae lose gills when they metamorphose
- Unusual pattern: paedomorphosis
Reach maturity while retaining their gills, aquatic lifestyle and other larval characteristic
Some species never metamorphose, while others will metamorphose under certain environmental conditions
20
Q
Explain Aquatic Salamanders (Amphiumas)
A
- 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
21
Q
Explain terrestrial salamanders (Pygmy salamander)
A
- Entire life cycle is terrestrial
- Internal fertilization
- Deposit eggs in small, grape like clusters under logs or in excavations in soft moist earth
- Many species guard eggs
- Direct development (all terrestrial species)
- Lungless (breathes through cutaneous respiration)
22
Q
What is the double metamorphosis in salamanders?
A
- Some species have an unusual double metamorphosis
- Gilled larvae -> red eft juvenile (lungs) -> aquatic adult (lungs)
23
Q
Explain the order Anura (frogs)
A
- All pass through a tailed stage during embryonic development but adults don’t have a tail
- Like other amphibians frogs are ectothermic and need to stay close to water
- Specialized for jumping
- The distinction is blurry, but in general toads can tolerate drier habitats and then to crawl more than jump
24
Q
What is the respiration of the order Anura?
A
- Larvae breathe through external gills and sometimes internal gills
- 3 respiratory surfaces for gas exchange in air (adults)
Skin (cutaneous breathing)
Mouth (buccal breathing)
Lungs - More reliant on lungs than salamanders
25
Q
What is the development of the order Anura?
A
- 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
- Paedomorphosis does not occur in frogs and toads
26
Q
What is the typical life cycle of the order Anura?
A
- In spring, males call intensively to attract females
- Brief courtship (males clasp the female in a process called amplexus)
- Eggs are fertilized externally during amplexus
- Jelly layer of the egg absorbs water and swells
- Eggs are laid on large masses often anchored to vegetation
- Within a few days the embryos have developed into tiny tadpoles that are visible through the jelly layers
- At hatching tadpole has a distinct head and body with a compressed tail
- Mouth (on ventral side) has keratinized jaws for scraping vegetation (herbivores)
- Swellings occur on each side of the head which become external gills
- Hindlimb appear first, then forelimbs
- Tail is absorbed
- Internal changes as well; intestine becomes shorter, mouth is transformed, lungs develop and the gills are absorbed
- Time to metamorphosis is variable and sensitive to environmental changes
- Adults are carnivores
