Early Tetrapod Diversity

Eusthenopteron

•       Crossopterygian fish = First to develop lungs

•       Many terrestrial features

–     More impervious skeleton

–     Enhanced nostril development

–     Leg-like bone features in their fins

Why Did Tetrapods Move to Land

•      “Old Story”: fish are living in habitats that dry up, or that run low on food.

–    Those that survive are the ones that can crawl to new ponds

–    Move to land = natural selection for limbs

•      “New Story”: Acanthostega and others had fully formed limbs, but probably never left the water

–    Limbs were used “after the fact” for moving on, but they originally had a different function

The Rest of the Story

•      Early tetrapods diversified into a large and rather bewildering array of forms in the Mississippian and Pennsylvanian

•      Exactly how they’re interrelated is a contentious matter.  Most are extinct

•      One lineage included the rootstock of the Lissamphibia - the living amphibians

•      Another, the anthracosaurs, led to the amniotes (reptiles, birds and mammals)

Time Line

•      Carboniferous (360 - 290 MYA)

–    Mississipian and Pennsylvanian Subperiods

•      Club mosses, horsetails and ferns appeared

•      Winged insects

•      Reptiles

•      Gymnosperms

•      Gondwana and Laurussia collide forming Pangea

Ichthyostega

Crassigyrinus

Eryops

•      Temnospondyl

•      Generally remained close to their Ichthyostegan labrinthodont roots

•      Better at walking

Seymouria

•      Permian Period

•      Link between reptiles and amphibians

•      Skull was similar to amphibians

•      Rest of the skeleton resembled a reptiles

•      Horny epidermis of overlapping scales

Time Line

•      Permian (360 -250 MYA)

•      Only a single trilobite family remains

•      End of Permian: biggest extinction event of all time

–    90% of all species died out

–    Climate became cooler, enormous volcanic eruptions