Phylum Chordata (chapter 3)

• Notochord is present during early embryonic life, is a primitive endoskeletal structure, is located along the middorsal line of the body, gives support, is replaced by vertebral column in vertebrates, and becomes part of our intervertebral cartilage disks as adults (fibrous cartilage).
• Doral hollow nerve cord lies above the notochord, contains a hollow canal filled with fluid.
• Postanal tail is an extension of the body, present only during the embryonic stage in some chordates.
• Families under Order Urodela include Proteidae, Sirenidae, and Salamandridae.
• In 1938, the first fish was caught in the east coast of South Africa, Latemeria chalumnae, which belongs to the Superorder Dipnoi, also known as true lungfish.
• The first tetrapods evolved from crossopterygian fishes, including lobed-finned fishes such as coelacanth and lungfish.
• Urodela have two weak limbs, possess true teeth in both upper and lower jaws, and are perennibranchiate, retaining larval gills and gill slits throughout life.
• Neoceratodus, an Australian lungfish, is a member of the Superorder Dipnoi.
• Some amphibians, like mud puppy, Necturus, remain completely aquatic and retain their gills throughout life, known as perennibranchiates.
• The body of Urodela is elongated with three regions: head, trunk, and tail, and they retain the tail throughout life.
• Proteidae, or mudpuppies or waterdogs, are aquatic with large red, maroon or purple filamentous external gills and compressed fin-like tail.
• Propterus, an African lungfish, is also a member of the Superorder Dipnoi.
• Lepidosiren, a South American lungfish, is also a member of the Superorder Dipnoi.
• Amphibians are tetrapods which clearly indicate the transition from aquatic to terrestrial life.
• Urodela (Caudata), also known as tailed amphibians, are found mostly in temperate and subtropical climates in the Northern Hemisphere.
• Tetrapods have a cornified or horny outer layer skin, nasal passages connected with mouth cavity that transport air, lungs used in respiration, and a bony skeleton.
• Sirenidae are neotenic aquatic salamanders with a very small forelimbs but no hindlimbs.
• Amphibia representatives include salamanders, newts, frogs, toads, and are the first vertebrates to live on land.
• In some tetrapods, limbs are modified and evolved as a five-toed or pentadactyl appendage.
• Swim bladder is well-developed and used as a lung during respiration, with air passing through the mouth.
• Superclass II Tetrapoda have paired appendages in the form of limbs rather than fins.
• During metamorphosis, external gills develop from the newly hatched eggs in some amphibians, while in others, lungs develop, supplementing the vascular skin as organs of respiration.
• There are four classes of Tetrapods: Amphibia, Reptilia, Aves, and Mammalia.
• Presence of gill slits or pharyngeal pouches is sometimes during life, with gill slits present in chordates that breathe by gills and pharyngeal pouches present in early human embryos.
• Early human embryos show a series of folds, or pouches, that look just like those of early fish embryos, which develop into the eustachian tube, middle ear, tonsils, parathyroid, and thymus.
• Mammalian embryos temporarily have pharyngeal pouches, reflecting the fact that mammalian ancestors were once aquatic gill-breathing vertebrates.
• The pharyngeal pouches of modern fish embryos eventually become perforated to form gills.
• Some of the branchial arches in jawless fish later evolved into the bones of the jaw, and, eventually, into the bones of the inner ear.
• Infraclass II, Eutheria, includes true (chorioallantoic) placental mammals.
• Mammals are homoiothermous, have hair and mammary glands (specialized skin glands), a well-developed nervous system (cerebral hemisphere), and few are egg-laying (oviparous), but most give birth to living young (viviparous).
• Birds have a reduced length large intestine.
• Birds have reduced numbers of bones in the wrist, palms and digits.
• Presence of feathers offers effective resistance to air when in flight.
• Prototheria are egg-laying (Oviparous mammals) and their youngs are nourished by milk from mammary glands without nipples, which open directly onto the surface of the skin.
• Archaeornithes are the first primitive reptile-like birds, represented by Archaeopteryx lithographica, which is linked between reptiles and birds.
• Archaeopteryx lithographica was found in the quarry at Solenhofen in Bavaria, Germany.
• Birds have a thinned skull.
• Dermoptera, or flying lemurs, have a well-developed fold of skin which extends along either side of the body from neck to tail, enclosing the limbs, and they have webbed feet.
• Birds have a constant body temperature and are homoiothermous.
• Chiroptera, or bats, are the only mammals that can actually fly, and their fold of skin extends from the elongated fingers to the body and legs forming a wing.