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KINGDOM ANIMALIA Phylum Chordata Subphylum Vertebrata Class Aves. A Separate Taxon?. Molecular and fossil evidence has convinced most biologists that birds are actually reptiles.
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KINGDOM ANIMALIAPhylum ChordataSubphylum VertebrataClass Aves
A Separate Taxon? • Molecular and fossil evidence has convinced most biologists that birds are actually reptiles. • The evidence indicates that crocodilians and birds are more closely related to each other than either one of them is to snakes and lizards.
Characteristics of Birds • Endothermic • Bony beak, no teeth • Large muscular stomach • Bipedal • Large, yolked, hard-shelled, amniotic eggs • The parent bird provides extensive care of the young until it is grown • Strong, lightweight skeleton • Specialized adaptations for flight: • Keratinous feathers (modified scales) that function in both flight and insulation • Specialized wing shape that produces lift • Numerous weight-reducing features
Wings • Most birds have airfoil-shaped wings. • Wing shape is closely related to wing function.
High Metabolic Rate • Birds have a system of branching air sacs that function with their lungs in respiration. • The system of air sacs supplies the high levels of oxygen needed to support a high rate of metabolism for the hard-working flight muscles. • This high metabolic activity also provides heat for endothermy.
Weight-Reduction • The air-sac system reduces the overall density of the bird • Bones have a honeycombed structure that makes them lightweight but strong • Birds are missing some of the internal organs found in other vertebrates: • Females have one ovary instead of two • No teeth (a hard beak and a gizzard with stones for grinding food)
Circulatory System • Bird circulatory systems efficiently deliver oxygen to cells. • Like amphibians and reptiles, birds have two pathways of blood flow: one from the heart to the lungs and back, and the other from the heart to the rest of the body and back. • Unlike amphibians and most reptiles, birds have a four-chambered heart with two separate ventricles that keep oxygen-rich blood from the lungs separate from the oxygen-depleted blood that passes through the heart.
Caudipteryx zoui Microraptor gui Sinornithosaurus millenii The Origin of Birds • Most paleontologists agree that the common ancestor of all existing birds was a type of small, feathered dinosaur. • Recent fossil discoveries of feathered dinosaurs in China support this hypothesis.
Archaeopteryx • Represents an animal that lived about 150 million years ago. • Unlike modern birds, Archaeopteryx had clawed forelimbs, teeth, and a long tail with vertebrae—all reptilian characteristics. • In fact, if the feathers had not been preserved in the fossil, Archaeopteryx probably would have been identified as a small dinosaur.
Bird Biodiversity • There are about 9,000 species of birds living today, far outnumbering mammal species. • Tremendous diversity of flying styles, beak and foot adaptations, and behavioral characteristics.
Flying Styles • Different styles of flying: • Cardinals and finches rapidly change altitude as they fly, a behavior that helps them avoid predators. • Falcons and albatrosses are hunting birds that soar, using their wings to gain altitude and then gliding on air currents without flapping. • Hummingbirds flap their wings as many as 80 times per second, enabling them to hover. • Penguins are flightless diving birds that use the same basic flight stroke to swim. • Chickens belong to a group of birds that can fly short distances, but are incapable of long flights. • Ostriches, emus, and kiwis are cannot fly at all.
Beak Adaptations • Also called “bills” • Made of keratin • Nostrils function in breathing • Variety of beak shapes reflects a wide range of functions • Beaks are not used for chewing, though some are used to break food into smaller pieces
Foot Adaptations • Various birds use their feet for walking, perching on branches, wading, paddling through water, grasping food, in defense, and in some courtship rituals • Most bird feet are covered in scales • Most birds have four toes on each foot, though the arrangement varies from species to species
Behavioral Adaptations • Bird brains are relatively highly developed, with a brain to body size ratio second only to mammals. • Birds are capable of complex behavior, especially in elaborate courtship rituals, caring for their young, and communication.
