Chapter 34. Vertebrates. Overview: Half a Billion Years of Backbones By the end of the Cambrian period, some 540 million years ago An astonishing variety of animals inhabited Earth’s oceans One of these types of animals Gave rise to vertebrates, one of the most successful groups of animals.
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Echinodermata(sister group to chordates)
Chondrichthyes(sharks, rays, chimaeras)
Reptilia(turtles, snakes,crocodiles, birds)
Lungs or lung derivatives
Jaws, mineralized skeleton
Dorsal edgesof neural plate
(a) The neural crest consists of bilateral bands of cells near the margins of the embryonic folds that form the neural tube.
(b) Neural crest cells migrate todistant sites in the embryo.
Migrating neuralcrest cells
Figure 34.7a, bDerived Characters of Craniates
(c) The cells give rise to some of the anatomical structuresunique to vertebrates, including some of the bones and cartilage of the skull.
(a) Blacktip reef shark (Carcharhinus melanopterus).Fast swimmers with acute senses, sharks have paired pectoral and pelvic fins.
(b) Southern stingray (Dasyatis americana).Most rays are flattened bottom-dwellers thatcrush molluscs and crustaceans for food. Some rays cruise in open water and scoop food into their gaping mouth.
Figure 34.15a, b
(c) Spotted ratfish(Hydrolagus colliei). Ratfishes, or chimaeras, typically live at depths greaterthan 80 m and feed on shrimps, molluscs, and sea urchins. Some species have a poisonous spine at the front of their dorsal fin.
Cut edge of operculum
(b) Order Anura. Anurans, such as this poison arrow frog, lack a tail as adults.
(c) Order Apoda. Apodans, or caecilians, are legless, mainly burrowing amphibians.
(b) The tadpole is an aquatic herbivore witha fishlike tail and internal gills.
(c) During metamorphosis, the gills and tail are resorbed, andwalking legs develop.
(a) The male grasps the female, stimulating her to release eggs. The eggs are laid and fertilized in water. They have a jelly coat but lack a shell and would desiccate in air.
Chorion. The chorion and the membrane of the allantois exchange gases between the embryo and the air. Oxygen and carbon dioxide diffuse freely across the shell.
Allantois. The allantois is a disposal
sac for certain metabolic wastes pro-
duced by the embryo. The membrane
of the allantois also functions with
the chorion as a respiratory organ.
Yolk sac. The yolk sac contains the yolk, a stockpile of nutrients. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo. Other nutrients are stored in the albumen (“egg white”).
Amnion. The amnion protectsthe embryo in a fluid-filled cavity that cushions againstmechanical shock.
Amniotic cavitywith amniotic fluid
(b) Australian thorny devil lizard (Moloch horridus)
(d) Eastern box turtle (Terrapene carolina carolina)
(b) Bone structure
(c) Feather structure
Airfoil wing with contour feathers
Long tail with many vertebrae
(b) Mallards. Like many bird species, the mallard exhibits pronounced color differences between the sexes.
(c) Laysan albatrosses. Like most birds, Laysan albatrosses have specific mating behaviors, such as this courtship ritual.
(d) Barn swallows. The barn swallow is a member of the order Passeriformes. Species in this order are called perching birds because the toes of their feet can lock around a branch or wire, enabling the bird to rest in place for long periods.
Grasping bird (such as a woodpecker)
Swimming bird(such as a duck)
Perching bird (such as a cardinal)
(a) The lower jaw of Dimetrodon is composed of several fused bones; two small bones, the quadrate and articular, form part of the jaw joint. In Morganucodon, the lower jaw is reduced to a single bone, the dentary, and the location of the jaw joint has shifted.
Incus (evolvedfrom quadrate)
Malleus (evolvedfrom articular)
(b) During the evolutionary remodeling of the mammalian skull, the quadrate and articular bones became incorporated into the middle ear as two of the three bones that transmit sound from the eardrum to the inner ear. The steps in this evolutionary remodeling are evident in a succession of fossils.
Figure 34.32a, b
(a) A young brushtail possum. The young of marsupials are born very early in their development. They finish their growth while nursing from a nipple (in their mother’s pouch in most species).