PHYLUM CHORDATA CLASS AMPHIBIA “AMPHIBIOUS” – (1) able to live both on land and in water (2) combining two characteristics
PHYLUM CHORDATACLASS AMPHIBIA
“AMPHIBIOUS” – (1) able to live both on land and in water (2) combining two characteristics
Q: Tetrapods did something remarkable … what??
A: They left water and invaded land
Why such a big deal??
- life originated in water- all phyla evolved in water- animals are mostly water- all cellular activities occur in water
CLASS: List environmental differences between water & land that demanded change
1) Air is less dense … less supportive
New supportive skeletonsNew musculature to move the new bones
2) Land air temps fluctuate widely & quickly
Amphibs have limitations in latitudes and elevations (poikilotherms)
3) Air has much more O2 (20%) … but how to get it??
Needed: respiratory and circulatory change
4) Air is dessicating
Needed: new skin and new kidney
5) Air carries different “information”
Needed: new sensory systems
Lateral lines lost – Ears gained
Gas detection gained (olfaction)
DEVONIAN: alternating floods and droughts…
Streams & ponds were subject to poor water quality … and disappearance
Fishes able to move short distances on land to another pond may have been favored
Devonian survivors were fishes with gills AND “lungs”
Suggested similarities in the locomotion of sarcopterygian fishes (a) and salamanders (b)
http://www.youtube.com/watch?v=SvRtOYGMWV8
Eusthenopteron – lobe-fined fish from the late Devonian Period. Note pectoral fin attached to the skull. Acanthostega – early Devonian
tetrapod – Note forelimb bones (nota strong walker)
Ichthyostega – Devonian tetrapod. Note limbs (probably a walker)
Limnoscelis – Carboniferous tetrapod - Note pentadactyl limbs
Unpredictable Devonian led to the stable CARBONIFEROUS
Warm-swampy-mosses-ferns (amphibian friendly)
Large tetrapod radiation in the Carboniferous
CHARACTERISTICS OF AMPHIBIANS
1) Bony endoskeleton – variable number of vertebrae
2) Usually 4 limbs – forelimb usually with 4 digits
3) Smooth skin w/many glands – pigment cells common
4) Mouth large w/teeth on one or both jaws
5) 2 nostrils open into mouth cavity
6) Respiration by some combination of lungs, skin, and gills
7) 3-chambered heart with a double circulation through the heart
8) Predominantly oviparous – mesolecithal eggs w/gelatinous membrane coverings
ChromatophoresColor intensifies when cytoplasm “streams” throughout the cell distributing pigment granules
Pigment Diversity: brown, green, red, yellow, blue
Alkaloid – 200X morepowerful than morphineas an analgesic
One of the most toxic knownsubstances - lethal dose forhumans < 200 μg (cardiac arrest)
AmphibianSkin Toxins
Aposematic (warning) Display – showing off colorful, conspicuous skin which reminds experienced predators about toxicity (dorsal skin is camouflaged)
Newton’s Law of Universal Gravitation applied to amphibians on earth
9.8 m/s/s
Why is gravity so “punishing” to terrestrial animals??
NITROGENOUS Waste Products of Animals
Ammonia Urea Uric Acid
Cost of Synthesis none low high
Toxicity high moderate low
Solubility high high very low
Diffusion Coefficient high intermediate low
N per osmotic particle 1 2 4
(bugs)
Na+ and Cl- are reabsorbedTubule is water permeable
Na+ and Cl- are reabsorbedTubule is water impermeable
DiluteUrine
Class AmphibiaOrder Anura (without tail)
- > 5000 species of frogs & toads- radical metamorphosis- tailed larval stage- jumpers- toads: dryer skin & shorter legs
bullfrogRana catesbeianna
leopard frogRana pipiens
American toadBufo americanus
Class AmphibiaOrder Urodela (w/tail)
-Salamanders (~ 500 species)- 4 legs of ~ equal size- carnivores- internal fertilization- terrestrial species use a direct
development
Northern dusky salamanderDesmognathus fuscus fuscus
Spotted salamanderAmbystoma maculatum
Redback salamanderPlethodon cinereus