Fish and Amphibians Geology 331 Paleontology Phylum Chordata: Subphyla Urochordata, Cephalochordata, and: Subphylum Vertebrata Class Agnatha: jawless fish, includes the hagfish, conodonts, lampreys, and ostracoderms (armored jawless fish) Gnathostomates: jawed fish Class Chondrichthyes: cartilaginous fish Class Placoderms: armored fish Class Osteichthyes: bony fish Subclass Actinopterygians: ray-finned fish Subclass Sarcopterygians: lobe-finned fish Order Dipnoans: lung fish Order Crossopterygians: coelocanths and rhipidistians Class Amphibia Urochordates: Sea Squirts. Adults have a pharynx with gill slits. Larval forms are free-swimming and have a notochord. Chordates are thought to have evolved from the larval form by precocious sexual maturation. Chordate evolution Cephalochordate: Branchiostoma, the lancelet Pikaia, a cephalochordate from the Burgess Shale Yunnanozoon, a cephalochordate from the Lower Cambrian of China Haikouichthys, agnathan, Lower Cambrian of China - Chengjiang fauna, scale is 5 mm A living jawless fish, the lamprey, Class Agnatha Jawless fish do have teeth! A fossil jawless fish, Class Agnatha, Ostracoderm, Hemicyclaspis, Silurian Agnathan, Ostracoderm, Athenaegis, Silurian of Canada Agnathan, Ostracoderm, Pteraspis, Devonian of the U.K. Agnathan, Ostracoderm, Liliaspis, Devonian of Russia Jaws evolved by modification of the gill arch bones. The placoderms were the armored fish of the Paleozoic Placoderm, Dunkleosteus, Devonian of Ohio Asterolepis, Placoderms, Devonian of Latvia Placoderm, Devonian of Australia Chondrichthyes: A freshwater shark of the Carboniferous Fossil tooth of a Great White shark Chondrichthyes, Great White Shark Chondrichthyes, Carcharhinus Sphyrna - hammerhead shark Himantura - a ray Manta Ray Fish Anatomy: Ray-finned fish Osteichthyes: ray-finned fish: clownfish Osteichthyes: ray-finned fish, deep water species Lophius, an Eocene fish showing the ray fins. This is an anglerfish. Osteichthyes, ray-finned fish, Jurassic Leptolepis, ray-finned, Jurassic of Australia Osteichthyes, ray-finned fish, Eocene, Wyoming Fish Anatomy: Lobe-finned fish Osteichthyes, lobe-finned fish, Devonian of Scotland Coelocanth, a living lobe- finned fish: Osteichthyes, Sarcopterygian A Coelocanth Evolution of the tetrapod walking leg from the lobe fin Sauripterus, rhipidistian, Late Devonian, Pennsylvania Late Devonian digits from a lobe-finned fish, Pennsylvania Hindlimb of Ichthyostega, Devonian of Greenland Ichthyostega: Photographs of part and counterpart superimposed to show seven digits Skull roof of the Late Devonian tetrapod Ichthyostega Tetrapods: Acanthostega and Ichthyostega, Devonian of Greenland. Fish or Amphibians? Evolution of Tetrapods South American lungfish in its burrow. The lung evolved in early Devonian bony fish and became the swim bladder of ray-finned fish. Mudskippers, ray-finned fish acting like amphibians. They gulp air into their swim bladder. The evolutionary step from fish to amphibian was not difficult. Looking for water in the Devonian Permian amphibian, Seymouria, with 5 digits.