Chapter 36: Comparing Vertebrates Section 1: Evolution of the Vertebrates

Evolution of the Vertebrates Ever since the first vertebrates appeared more than 500 million years ago, they have been evolving Have developed many new and unusual features Sharper claws Longer hair Amniotic egg Paired front and rear limbs

The Vertebrate Family Tree Most scientists agree that: Amphibians evolved from lobe-finned fish ancestors Reptiles evolved from amphibian ancestors Birds and mammals evolved from reptile ancestors

Trends in Vertebrate Evolution Two general trends appear repeatedly during the course of vertebrate evolution If closely related evolutionary lines are subjected to different forces of natural selection, they tend to become more dissimilar as they evolve If evolutionary lines encounter extremely similar forces of natural selection, they tend to become more similar to one another as they evolve

Trends in Vertebrate Evolution As different vertebrate groups evolved, they utilized the same basic sets of body parts for many uses The pattern of evolution known as adaptive radiation is also known as divergent evolution One species gives rise to many species that appear different externally but are similar internally

Trends in Vertebrate Evolution Convergent evolution is just the opposite Adaptive radiations among different organisms produce species that are similar in appearance and behavior

Body Temperature Control Many chemical reactions work better at certain temperatures When the body temperature is too low, animals slow down and become immobile When the body temperature is too high, body systems are stressed and fail to function properly Many techniques of temperature control have appeared in vertebrates Incorporate three important features A source of heat for the body A way to conserve that heat A method of eliminating excess heat when necessary

Chapter 36: Comparing Vertebrates Section 2: Form and Function in Vertebrates

Form and Function in Vertebrates Vertebrates perform the essential functions of life with a variety of body structures Evolutionary processes have modified certain basic structures over time As you move through the vertebrate classes from fishes to mammals, organ systems tend to become increasingly complex

Movement All vertebrates except jawless fishes have a vertebral column (backbone) made of numerous individual bones called vertebrae Connected to one another by tough ligaments that allow the vertebral column to bend to a certain extent Two pairs of limbs are attached to this basic supporting structure by sets of bones called limb girdles Most of the bones in the body can be made to move through the contraction of muscles that are attached to the bones

Movement Fish and snakes Main body muscles are arranged into blocks that are positioned on either side of the vertebral column Contract in waves, one after another Make the body bend rapidly back and forth Amphibians, reptiles, birds, and mammals The position of the limbs relative to the body shifts toward the center The movement of the vertebral column when the animal runs changes from a side-to-side motion to an up-and-down motion

Feeding The heads of vertebrates show many adaptations for feeding The organs of the digestive systems of vertebrates are equally well adapted for different feeding habits Carnivores Short digestive tracts with special enzymes that break down meat Herbivores Long intestines and stomachs with bacteria that break down cellulose

Respiration Aquatic vertebrates Use gills for respiration As water passes over the gill filaments, oxygen diffuses into the blood in the capillaries and carbon dioxide diffuses from the blood into the water Terrestrial vertebrates Use lungs to breathe When the animals inhale, oxygen-rich air enters the lungs When the animals exhale, carbon dioxide-rich air is expelled

Internal Transport Fishes and larval amphibians Single-loop circulatory system Blood travels from the heart to the gills to the body and back to the heart Two chambered heart Vertebrates with lungs Double-loop circulatory system Heart and lungs Heart and body

Excretion Excretory systems eliminate nitrogenous wastes and regulate the amount of water in the body Most vertebrates rely on kidneys for excretion Nitrogenous wastes are first produced in the form of ammonia Aquatic amphibians and fish Ammonia diffuses from the gills into the surrounding water Mammals, terrestrial amphibians, and cartilaginous fishes Ammonia is changed into urea Reptiles and birds Ammonia is changed into uric acid

Response All vertebrates display a high degree of cephalization The size and complexity of the cerebrum and cerebellum increase as you move through the vertebrate classes from fish to mammals

Reproduction Almost all vertebrates reproduce sexually In some vertebrates fertilization is external In other fertilization occurs inside the body of the female

Reproduction Vertebrates show three different modes of development Oviparous Eggs develop outside the mother’s body Ovoviviparous Eggs develop inside the mother’s body but the embryos receive the nutrients they need from the yolk that surrounds them, not from the mother directly Viviparous Developing embryos obtain nutrients directly from the mother’s body