Chapter 34: Chordates-Amphibians

Front 1

Lobe-fin fishes

Back 1

Include two living groups that have some characteristics of the hypothetical first terrestrial verterbrates

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Lobe-fin fishes include

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coelacanth, Latimeria, a fish within the Actinistia with paired fins at the end of appendages with internal bony elements (rather than the fin rays of the Actinopterygii)

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notochord; jointed braincase

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In addition to the presence of fins supported by substantial skeletal elements, coelacanth retain the _______ as the primary anterior-posterior support and the primitive trait of a ___________.

Front 4

into the early 1900's it was thought that the coelacanth....

Back 4

had been extinct for 65 million years

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lungfishes

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retain a prominent notochord but have well-developed vertebrae as well.
-have functional lungs and can withstand drying of their habitat

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estivation

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lungfish can enter __________, a state of reduced physiological activity during drought, for 7 to 8 months
-air breathe
-lower heart rate
-retain urea and other wastes
-catabolize body, lose weight

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tetrapod

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chordate living on land
-are the ancestrally terrestrial and four limbed vertebrates. Amphibia is the earliest diverging living group

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O2 is more concentrated

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in air than in water

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air is

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1000 times less dense and 50 times less viscous than water
-experiences far greater temperature extremes

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terrestrial environments

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comprise a much greater diversity of habitats than do marine environments

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vascular plants diversified during

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the Devonian Period
-competition and predation increased

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Origins of tetrapods: Osteichthyes (Osteolepiformes)

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-tetrapod skull roof and cheekbones
-stronger axial skeleton
-paired fins with single basal two distal elements
-choanae (internal nostrils)

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choanae

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-internal nostrils
-openings in the roof of the mouth connecting to the external nostrils
-this arrangement allows air to be drawn into the lungs even when the mouth is closed

Front 14

Aquatic tetrapods

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-appear following Kellwasser
-Fusion of bones to form stronger pelvis
-vertebrae braced against each other
-pectoral girdle detached from the back of the skull
-dactyly (development of fingers)

Front 15

modern amphibians

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-there are over 6,000 species of predatory salamanders, frogs, and caecilians
-skeleton is mostly bones (rather than cartilage)
-usually amphibians have four limbs
-skin is moist and functional in respiration

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amphibians exhibit three distinct body forms

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-order urodela
-order anura
-order apoda

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salamanders

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order urodela
-tailed amphibians
-abundant in north temperature regions
-like all amphibians they have a low metabolic rate and therefore ectothermic

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frogs

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order anura

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caecillians

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order apoda

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ectothermic

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can't regulate body temperature via metabolic heat production

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some salamanders are

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aquatic and terrestrial
-the ancestral condition is metamorphosis from aquatic larva to terrestrial adults
-salamander eggs are fertilized internally by sperm passed to the female in a packet or spermatophere

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newts

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have aquatic larva followed by a terrestrial juvenile stage then by a second adult aquatic stage

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paedomorphosis

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-evolution of retention of larval characteristics into adulthood. Many salamanders achieve sexual maturity while retaining external gills and an aquatic habitat
-external gills allow capture of oxygen from water

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cutaneous respiration

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extensive nets of blood vessels in the skin allow for _______ in all amphibians
-at varius life stages salamanders may have gills, lungs, both or neither

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ballistic tongue protection

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some salamander capture prey by...

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frogs and toads (anurans)

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-over 5,200 species primarily adapted to jumping locomotion (reduction of vertebrae, fusion, and elongation of bones)
-anrans have an outer skin layer toughened by the protein keratin
-mucous glands in the skin limit water loss and toxin glands function in defense

Front 27

anuran circulation

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anurans have an efficient, closed circulatory system with a three-chambered heat and separate pulmonary (lung) and systemic (body) circuits.

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anuran reproduction

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-anurans have external fertilization of typically huge masses of eggs deposited in aquatic habitats
-the larval tadpoles first have external than internal gills, the full process of metamorphosis takes 2-3 years in some species

Front 29

caeclians (apodans)

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~170 species of elongate, limbless, burrowing amphibians
-most species are blind and rely on sensory tentacles on the snout to find worm and insect prey
-fertilization of eggs is internal and larval development may occur in the egg, in an aquatic habitat or within the body cavity (viviparity)

Front 30

amphibian declines

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many amphibian species have gone extinct in the last 20 years, at least 40% of species are in decline

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causes of decline include:

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-habitat destruction
-introduced species
-climate change
-atmospheric UV radiation
-chemical contaminants
-disease (fungal pathogens-chytridiomycosis)