ORIGIN AND EVOLUTION OF AMPHIBIA Devonian 408 - 360 mya, Tropical: Equator passed through CA, UT, WY, SD, ND Transition from Epeiric seas to emergent continents increase in amount of freshwater sediments Gondwana assembled, other plates still converging Oceanic plates and arcs converging on NA (Fig. 19.8) caused warping of the North American craton, in eastern North America: Acadian Orogeny convergence advancing with African plate Appalachians prominent sediments shed westward Catskill clastic wedge and Old Red sandstone thick Insects and spiders become more abundant on land Fishes, Ostracoderms, Placoderms, chondrichthyes, Osteichthyes, Actinopterygii, Sarcopterygii ------------------------------------------------ Devonian Ichthyostega of Greenland and similar forms in Russia and Australia ca. 360 m.y.a From lobefin fishes (rhipidistians) , which had the ability to breath atmospheric air and the ability to move about on land Differences in water and land habitats water land ----------------------------- ------------------------- buoyancy gravity O2 <10ppm (less in swamps) O2=19% density = 1000 X air no drag predators abundant predators = rare food abundant rare at first ----------------------------------------------------------------- Terrestrial plants originated in mid Silurian [Chlorophytes colonized freshwater first, then moist land habitats] [First vascular plants were small Psilophytes in mid Silurian = seedless (spore bearing) vascular land plants] Diverse forests by Devonian; "lycopsid trees" to 7 m (club mosses) competition for light drove height increase Horse tail mosses and ferns (spore-bearing) in Carboniferous intermediate stage = Seed Ferns, e.g. Glossopteris Why venture out on land? drying up of habitats hypothesis? (but modern ecology provides examples only in humid habitats) O2 for eggs in shallowest waters no predators in shallowest waters Amphibians today breed in shallowest waters Principle: behavioral changes precede morphological evolution especially behavior related to feeding or reproduction Ichthyostega characteristics = a mixture of fish and amphibian characteristics 1 meter long loss of fins except part of caudal lateral line canals present on head arm: humerus, radius, ulna, wrist bones, fingers; shoulder back leg: femur, tibia, fibula, ankle bones, 7 toes; hip bones vertebrae with arches for support in gravity loss of gill structures in adult Adaptations to new conditions on land: atmospheric oxygen: lungs (gills lost) gravity: supportive vertebrae, walking limbs (fins lost) reproduction still limited to aquatic habitat Animals make behavioral choices under pressure: Predator threat caused animals to seek refuge on land Atmospheric oxygen favored use of lungs gills are expensive to grow; loss was a benefit Locomotion on land aided survival land locomotion increased predator escape-->survival land locomotion increased food capture--> growth -------------------------------------------------------- Diversity of Carboniferous amphibians 360-280 m.y.a. swamp and forest dwelling amphibians some with large heads and tiny legs some long and slender with small or no legs microsaurs many broad flat forms see exhibits some small flat forms with gills possibly larvae of others fish eaters and arthropod eaters Carboniferous world [Mississippian, Pennsylvanian coal measures huge volume of uneaten, unoxidized plant matter buried underwater] southern continent with glacial evidence (Gondwana) North America-Greenland-Europe together on equator (Laurasia) forests with tall club mosses to 40 m horsetails to 15 m seed ferns and conifers in swamps, millipedes, spiders, insects, some huge, wings already developed What kind of selection on amphibians?