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| chordates tunicates Urochordata lancelets Cephalochordata subphylum Vertebrata cartilage endoskeletons jawless fishes bony fishes tetrapods coelom notochord vertebrae dorsal hollow nerve cord embryonic ectoderm anterior dorsal cranium pharyngeal pouches endoderm ectoderm gill slits pharynx postanal tail coccyx Hemichordate tunic Urochordata budding incurrent siphon transitional form atrium ascidians sea squirts excurrent siphons sessile lancelets atriopore vertebrates vertebral column paired limbs cranium vertebrae oviparous ovoviviparous viviparous amniotes ectotherms estuarine gills two-chambered heart hagfishes lampreys ostracoderms placoderms cartilaginous jawed fishes Chondrichthyes chimaeras skates rays sharks lateral line system bony fishes Osteichthyes calcium phosphate swim bladder myoglobin ray-finned fishes lungfishes lobefinned fishes coelacanth amphibian chromatophores paired kidneys urea three-chambered hearts two-chambered heart Anura Urodela Gymnophiona paedomorphosis caecilians reptiles anapsids diapsids synapsids ectothermic amniote egg four-chambered hearts camouflage hard-shelled eggs Aves endothermy precocial altricial sternum pectoralis supracoracoideus carinates ratites feather rachis barbs barbules melanin carotenoids porphyrins biochromes nanostructure ornithologists molt mammals Mammalia monotremes marsupials placental mammals marsupium uterus placenta thecodont mammary glands vibrissae endothermic sebaceous sweat blands cerebral cortex Primates arboreal binocular vision "opposable" thumb Prosimii Anthropoidea prehensile ischial callosities |