Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Evolution of the Animal Body Plan Part 2 – Chordates and Vertebrates E. Q. – How has the chordate body plan evolved over time to better suit these animals to their ecological niches? Chordate Characteristics • The members of Phylum Chordata exhibit many different kinds of body plans, but they all have certain characteristics in common. • All chordates, at some time in their lives, have: (1)A dorsal hollow nerve cord (2)Pharyngeal gill slits (3)A stiff rod ventral to the nerve cord called the notochord (4)A muscular post-anal tail. • Some chordates show these characteristics for their entire lives, while in other chordates, they develop into other structures. • In vertebrates, the dorsal hollow nerve cord develops into the brain and spinal cord. • In most vertebrates, the notochord degenerates during the embryonic stage of development. The only remnants appear in adults as the gelatinous disks between the vertebrae. • The pharyngeal gill slits develop into gills in aquatic vertebrates, jaw support, hearing elements, or other functions in higher vertebrates. • Most vertebrates retain the muscular post anal tail as adults. The Simplest Chordates • Tunicates are some of the simplest chordates. They belong to the subphylum Urochordata. • Most tunicates are sessile marine filter feeders. Because they squirt water when disturbed, they are often called sea squirts. • Some others are zooplankton. Some species are colonial. • Adult sea squirts no not resemble other chordates, but as embryos, all chordate characteristics are present. • Lancelets belong to the subphylum Cephalochordata. They are shaped like the blade of a spear, and all of the chordate characteristics appear in adults. • Lancelets burrow into the sand with their mouths exposed. Water enters the mouth and exits the gill slits, while food is filtered out. • Although they don’t swim well, they show the side-toside swimming motion of fishes. Simple Chordates Subphylum Vertebrata • Vertebrates keep the primitive chordate characteristics, but they also have additional characteristics that separate them from the non-vertebrate chordates. • Many of these features are associated with large body size and active lifestyle. • One vertebrate trait is an enlarged brain enclosed within a cranium and a concentration of the sense organs in the head. • Another characteristic of vertebrates is the vertebrate axial skeleton, the main support of the central trunk of the body. • The axial skeleton makes large body size possible as well as fast movements. • Vertebrates have two pairs of appendages (arms and legs). • The vertebrate skeleton is made of bone or cartilage, and is capable of growing with the animal. • Vertebrates have a closed circulatory system with a ventral, chambered heart. • Vertebrates have muscles in their intestinal walls to propel food through the digestive system. • Vertebrates reproduce sexually. Vertebrate Diversity Agnatha Chondrichthyes Reptilia Amphibia Osteichthyes Mammalia Aves Agnatha (Jawless Fishes) • The oldest vertebrate fossils are jawless creatures resembling fish and are about 400-500 m.y.a. • Superclass Agnatha includes some extinct fishlike animals called Ostracoderms. They had circular or slit-like mouths without jaws and were probably mudsuckers or suspension feeders. • Lampreys and hagfish are the only agnathans living today. • Like extinct agnathans, they lack paired appendages. • Agnathans also lack scales. • Lampreys feed on live fish by attaching with their round mouth and using their rasping tongue to penetrate the skin of their host. They then ingest the host’s blood. Lampreys are considered both predators and parasites. They can be freshwater or marine. • Hagfish look like lampreys, but they are mainly scavengers. Some hagfish eat dead or dying fish, but most eat marine worms. Hagfish are entirely marine. Fertilization is external. Jawless Fishes Chondrichthyes • The origin of jaws was a major event in vertebrate history. Vertebrate jaws evolved from changes in the skeletal supports for the most anterior gill slits. • During the Devonian Period (417354 m.y.a.), Chondrichthyes and Osteichthyes both evolved. At the end of the Devonian, the first amphibians also appeared. • Sharks, skates, and rays make up Class Chondrichthyes. • They are called cartilaginous fish because their skeletons are made of cartilage, rather than bone. They have tooth-like scales embedded in their skins. • There are about 750 species in this group. They all have jaws and paired fins. • Sharks have streamlined bodies. Continual swimming makes water pass though the mouth and out the gills. • Sharks have keen eyesight, an excellent sense of smell, and a lateral line system to sense prey. • In sharks and rays, fertilization is internal. Males use claspers to transfer sperm to the female. • Sharks have the largest brain/body size ratio of any fish. Chondrichthyes Osteichthyes • A bony skeleton, an operculum, and a swim bladder are all characteristic of Class Osteichthyes. • There are more members of Class Osteichthyes than of any other class of vertebrates. • They are abundant in the seas and in almost all freshwater habitats. • Members of this class have a skin covered with flattened bony scales different from the toothlike scales of sharks or rays. • Glands in the skin secrete mucus that makes fish feel “slimy” but protects from parasites. • Bony fish breathe by drawing water in through the mouth, over the gills, and out through the operculum. • The muscles attached to the operculum allow the fish to breathe while staying in one place. • Another adaptation is the swim bladder, an air sac that controls the buoyancy of the fish. • Bony fish are maneuverable swimmers because their fins are better for propulsion and steering than those of sharks. Osteichthyes Amphibia • • • • • According to current theories, aquatic vertebrates moved onto the land as shallow pools they live in dried up. These animals faced several critical problems: (1) keep from drying out (2) support the body on land (3) reproduce on land. The oldest known amphibian fossils date from about 370 m.y.a. Amphibians are thought to have evolved from lobe-finned fish. The earliest amphibians had four strong limbs, which evolved from the fish’s fins. The earliest amphibians breathed air through lungs and had sense organs adapted to work on land. • 1) 2) 3) 4) 5) • Modern amphibians have several key characteristics: Most change from an aquatic larval state to a terrestrial adult. Most have a moist thin skin without scales used for gas exchange. Feet, if present, are often webbed and lack claws. Fertilization is external. Eggs lack shells. They are laid in water or moist places. Amphibian hearts have 3 chambers:2 atria and 1 ventricle. Modern amphibians include Order Anura (frogs and toads), Order Urodela (newts and salamanders), and Order Apoda (caecilians, legless amphibians that resemble snakes). Amphibia Reptilia • • • • • Earliest reptile fossils date to the Carboniferous Period, about 350 m.y.a. They diversified rapidly and by the Permian Period had become the dominant land vertebrates. The Mesozoic Era (286-245 m.y.a) is called the “Age of Reptiles” because nearly all of the large vertebrates on Earth were reptiles. During the Mesozoic, dinosaurs appeared and evolved to fill many niches in a variety of environments. Representatives of the 4 modern orders of reptiles survived the mass extinction at the end of the Cretaceous Period: (1)turtles and tortoises, (2)lizards and snakes, (3) tuataras, and (4) crocodilians. • • • • • The success of reptiles on land resulted from their ability to solve the major problems facing land animals: preventing desiccation, locomotion, respiration and excretion of N wastes, and reproduction on land. A thick skin covered by keratincontaining scales prevents water loss. Sturdy limbs with clawed feet support and propel the reptile body. Efficient lungs perform gas exchange, while water is conserved because most reptiles excrete uric acid. Internal fertilization and the amniotic egg keep the embryo from drying out as it develops in a selfcontained watery environment. Reptile Characteristics • • • • Like all terrestrial vertebrates (amphibians, reptiles, birds, and mammals) reptiles have a double loop circulatory system. The pulmonary loop takes blood from the heart to the lungs to be oxygenated, and the systemic loop takes blood from the heart to the tissues of the body where O2 is absorbed and CO2 is released. In all reptiles except crocodilians, the heart has 2 atria and 1 partly divided ventricle. Crocodiles have 2 atria and 2 ventricles. Reptile lungs are large with many small sacs called alveoli that make them much more efficient than amphibian lungs. • • • • The reptile brain is about the same size as an amphibian brain, but the cerebrum, which controls behavior, is much larger. Most reptiles rely on their senses of sight and hearing to detect prey and predators. Reptiles are ectotherms, and control their internal body temperature by changing behavior to control how much heat they absorb. Reptiles have three reproductive patterns: They may be oviparous (lay eggs), viviparous (embryo is incubated within the mother), or ovoviviparous (produce shelled eggs that incubate within the mother’s body). Reptilia Aves • • • • • • • All birds have feathers, and no other living animals have them. The forelimbs of birds are modified into wings. All birds have a lightweight, rigid skeleton with a keel on the sternum. Many bones are thinwalled, hollow, and riddled with air sacs from the respiratory system. All birds are endotherms with a high metabolic rate and a 4chambered heart.. All birds have the most efficient respiratory system yet evolved, that eliminates dead space from the lungs. No bird has teeth, and all birds have a beak. All birds lay amniotic eggs with a hard calcium-rich shell. • • • • Because birds lack teeth, they have a crop for food storage, a proventriculus where digestion begins, and a gizzard for grinding of food. Birds are thought to have evolved from raptor dinosaurs because of three characteristics which both groups share: an S-shaped flexible neck, a unique ankle joint, and hollow bones. The first birds are thought to have descended from small fastrunning carnivorous dinosaurs during the Jurassic Period (208144 m.y.a.) Current theories are that feathers evolved before wings (for insulation), and wings before flight (for stabilization while running). Aves Mammalia • • • • • • There are about 4,400 species of • mammals, and they live on every continent and in every ocean. • Some can fly. Like birds, all mammals are endotherms, with metabolic control of body temperature. All mammals (even whales and dolphins) have hair, which can • serve as an insulator or for camouflage. Like birds and crocodilians, all mammals have a 4-chambered heart. All female mammals produce milk to nourish their young. All mammals have a single jawbone with teeth specialized to perform different functions. The ancestors of mammals appeared more than 300 m.y.a. A major split occurred in the existing reptiles of the time. One group produced the dinosaurs, birds, and all living reptiles. The other group, called synapsids, led to mammals and their closest fossil relatives. Synapsids like Dimetrodon had skulls that were different from pther reptiles and showed some specialized teeth. Mammals • • In the Permian Period, a sub-group of the synapsids, the therapsids, appeared and later gave rise to the earliest mammals. Many features of mammals first appeared in the therapsids— specialized teeth, endothermy, limbs located beneath the body, and hair are examples. • • • • The first mammals and the first dinosaurs appeared at about the same time, during the Triassic Period. Early mammals were small and resembled shrews. With the extinction of the dinosaurs 65 m.y.a. the mammals diversified to fill newly available niches. • Mammals are classified into more than 20 orders. Important orders of mammals are the monotremes and the marsupials. All other mammals are placentals. Monotremes are the only mammals that lay eggs. They are represented by the duck-billed platypus and the echidna, or spiny anteater. Marsupials like kangaroos and the opossum exist today only in Australia, New Guinea, and the Americas. Marsupials give live birth to very underdeveloped young that migrate to the mother’s pouch where they complete development. Placentals include rodents, insectivores, primates, carnivores, proboscideans, and cetaceans, among other groups. Mammalia E. Q. – How has the chordate body plan evolved over time to better suit these animals to their ecological niches? How have the following systems changed from Urochordates and Cephalochordates through the fishes, amphibians, reptiles, mammals, and birds? Nervous system Digestive system Reproductive system Circulatory system Respiratory system Skeletal system