What are amphibians
First terrestrial vertebrates and first tetrapods
Amphibians double life
between water and land in different life stages
tetrapods
Sarcopterygian descendants that possess well-formed forelimbs and hindlimbs
Crown tetrapods
Complicated phylogeny due to tons of extinctions and radiations
Ancient tetrapod like lobe finned fish
Tiktaalik - 375 mya - like lobe finned fish but with stronger forelimbs
Ancient tetrapods fossils
- good fossils
- best are from greenland
- ichthyostega (365 mya)
- had bone fusions to be able to prop itself up and neck vertebrae so head can move
Ichthyostega
- heavy pectoral and pelvic girdle and sturdy limbs
- for movement across ground against gravity
- strong jaws
- probably shallow water predator
Important characteristics of fossils
- mobile neck for feeding
- more rigid vertebral column for gravity
- 4 muscular limbs with discrete digits
- sacral vertebra for gravity (fuses vertebral column and pelvis)
- loss of opercular bones, notochord, fin rays and some cranial bones
Class amphibia 3 orders
gymnophiona
caudata
anura
Order gymnophiona
- caecilians
- tropical burrowers feeding on soil invertebrates
- skin folds (appear segmented)
- internal fertilization
- larval stages within oviducts and young emerge as miniature adults
- others lay eggs with aquatic larvae or embryos that develop on land
Order caudata what are they where are they
Salamanders
Northern hemisphere mostly
Secondary radiation to tropical/subtropical regions
Salamanders 3 traits
tail throughout life
Unspecialized legs
Internal fertilization
Terrestrial salamanders
Live in moist forest floor littered with aquatic larvae
Paedomorphic
retain many larval characteristics when they become sexually mature
Obligate paedomorphosis
- occurs in mudpuppies
- legs and gills and completely aquatic
- do not undergo metamorphosis
Facultative paedomorphosis
- retain larval characteristics as long as pond retains water
- when pond dries, metamorphose into adult terrestrial form
Plethodontidae
- most fully terrestrial salamanders
- most lay eggs on land
- young hatch as mini-adults
Aquatic salamanders
- newts
- most of their lives in water
- may retain caudal fin
Largest north american salamander
hellbender
- reqires fast flowing well-oxygenated water (thin skin for gas exchange with lots of folds for increased surface area)
Order anura are what
frogs/toads
Toads
dry, warty skin and more terrestrial sometimes
family bufonidae
Frogs
smooth skin, more aquatic usually
family ranidae
Adult/larvae toads and frogs
adults lack tails, caudal vertebrae fuse into urostyle
hindlimbs long, muscular and end in webbed feet
External fertilization
Eggs and larvae aquatic usually
Larvae=tadpoles with well developed tails
Larvae are herbivores, adults are not
Rapid metamorphosis
Tree frog eggs
Laid on underside of leaves and tadpoles emerge and drop directly into pond below
Parental care in anurans
backpack frog
