Late Devonian: Rhipidistians From Sea to Slime: Evolution of Amphibians Lungs were developed in two groups of lobe-finned fishes - Rhipidistians and lungfishes . The Rhipidistians are considered to be the ultimate ancestors of later land animals. Rhipidistians such as Eusthenopteron had evolved "land animal-like features": Eusthenopteron Skeletal Modifications An Important Link: Tooth Structure Labyrinthodont tooth Labyrinthodont tooth of Rhipidistian fish of early amphibian (Eusthenopteron) (Archegosaurus) Labyrinthodont tooth structure (with complexly infolded enamel) is shared between Rhipidistian fishes and the earliest amphibians. This strongly supports a close relationship between the two groups. 1 Late Devonian: Ichthyostega and Acanthostega -Ichthyostega was a cross between a fish and an amphibian -Ichthyostega had legs and walked and was a true tetrapod. -With true legs, it could live on land for extended periods. -The primitive amphibians like Ichthyostega had a special kind of skin that helped them retain bodily fluids and deter desiccation. -Stronger skeletons allowed the primitive amphibians to live more comfortably with the increased gravity on land. -Animals like Ichthyostega used their limbs for locomotion and their tails for balance. Ichthyostega Carboniferous to Permian Evolution of neck and ear · Amphibian nostrils became increasingly functional for breathing air. · Amphibians evolved "hands" and "feet" with five digits. · Amphibian tails became reduced in size. · Amphibian backbones grew stronger (this enabled amphibian bodies to grow bigger). · Amphibians obtained eardrums. -Fishes need limbs to support bodies and ears to hear sounds in the air. -Fins changed to limbs -Several bones of the skull changed to the shoulder bones -Tongue cartilage (part of the jaw in fish) became an ear bone. 2 Amphibian Diversification Advantages for amphibians living on land: Diplocaulus Less competition for food (1 m long) Avoidance of large predatory fishes. Disadvantages for amphibians living on land: Eryops Amphibians have gas-permeable skin to aid their (1.5 m long) inefficient lungs. This skin must be kept moist ! They must have water to reproduce, Water is needed for the external fertilization that is characteristic of amphibians. By the Permian Period, amphibians had become Amphibian jelly-like eggs can not survive out of water. quite diverse (and some were very large). Modern Amphibians: 1.Anura (frogs and toads) 2.Caudata(salamanders and newts) END OF LECTURE 3.Apoda (caecilians) 3.