Ch. 26 : Animal Evolution and Diversity. 26.1 Invertebrate Evolution and Diverisity.
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Transcript of Ch. 26 : Animal Evolution and Diversity. 26.1 Invertebrate Evolution and Diverisity.
Ch. 26 : Animal Evolution and Diversity
26.1Invertebrate Evolution and
Diverisity
Origins of the Invertebrates
• 3 billion years ago, prokaryotes and eukaryotes were single-celled.
• Animals evolved from ancestors they shared with organisms called choanoflagellates
Traces of Early Animals
• The first animals were tiny and soft-bodied, so few fossilized bodies exist.
• As animals became larger and more complex, specialized cells joined together to form tissues, organs, and organ systems that work together to carry out complex functions.
• Trace fossils are tracks and burrows made by animals whose body parts weren’t fossilized
The Ediacaran Fauna
• Fossils from The Cambrian Period date back roughly 565 to about 544 million years ago.
• They show little evidence of cell, tissue, or organ specialization, and no organization into a front and back end
• Many of the organisms were flat and lived on the bottom of shallow seas.
The Cambrian Explosion
• Cambrian fossils show that over a period of 10-15 million years, animals evolved complex body plans, including specialized cells, tissues, and organs
• Many had body symmetry; segmentation; a front and back end; and appendages, structure such as legs or antennae protruding from the body.
• By the end of the Cambrian Period, all the basic body plans of modern phyla had been established.
Modern invertebrate Diversity
• All invertebrates except sponges exhibit some type of body symmetry—either radial symmetry or bilateral symmetry.
• Invertebrates with cephalization can respond to the environment more quickly and in more sophisticated ways than can simpler invertebrates.
• Worms, arthropods, and mollusks are protostomes, and echinoderms are deuterostomes.
Nonchordate Invertebrates
• The cladogram of nonchordate invertebrates presents current hypotheses about evolutionary relationships among major groups of modern invertebrates.
• These features include body symmetry, cephalization, segmentation, and formation of a coelom.
26.2 Chordate Evolution
and Diversity
Origins of the Chordates
• Chordates are the animals we know best because they are generally large, often conspicuous, and strike us as beautiful, impressive, cute, or frightening.
• Some we keep as pets, others many of us eat as sources of protein.
The Earliest Chordates
• Embryological studies suggest that the most ancient chordates were related to the ancestors of echinoderms.
• In 1999, fossils beds from later in the Cambrian Period yielded specimens of Myllokunmingia, the earliest known vertebrate.
• Cartilage is a strong connective tissue that is softer and more flexible than bone.
Modern Chordate Diversity• Modern chordates are very diverse, consisting of six groups: the
nonvertabrate chordates and the 5 groups of vertebrates- fishes, amphibians, reptiles, birds, and mammals.
• About 96% of all modern chordate species are vertebrates.
• Among vertebrates, fishes are the largest group by far,
Cladogram of Chordates• The cladogram of chordates presents current hypotheses about
relationships among chordate groups.
• It also shows at which points important vertebrate features, such as jaws and limbs, evolved.
Nonvertebrate Chordates
• The nonvertebrate chordates are tunicates and lancelets.
• Adult tunicates look more like sponges than us.
• They have neither a notochord nor a tail, but their larval firms have all the key chordate characteristics.
Jawless Fishes
• Lampreys and hagfishes both lack vertebrae and have notochords as adults.
• Lampreys are filter feeders as larvae parasites as adults.
• Hagfishes have pinkish gray, wormlike bodies, secrete incredible amounts of slime, and tie themselves into knots!
Sharks and their Relatives
• Jaws hold teeth and muscles, which make it possible to bite and chew plants and other animals.
• Fins were attached to limb girdles, which are supporting structures made a cartilage of bone.
• These adaptations launched the adaptive radiation of the class Chondrichthyes: the sharks, rays, and skates.
Bony Fishes
• Ancient fishes evolved skeletons made of hard, calcified tissue called true bone.
• Ray-finned fishes are aquatic vertebrates with skeletons of true bone; most have paired fines, scales, and gills.
• Lobe-finned fishes are a different group of bony fishes that evolved fleshy fins supported by larger, more substantial bones.
Amphibians
• The word amphibians means “double life”, referring to the fact that these animals live in water as larvae but on land as adults.
• Several fossils indicate that various lines of lobe-finned fishes evolved sturdier and sturdier appendages, which resembled the limbs of tetra pods.
• Early amphibians evolved ways to breathe air and protect themselves from drying out.
Reptiles
• Reptiles, which evolved from ancient amphibians, were the first vertebrates to evolve adaptations to drier conditions
• Dinosaurs lived in the Triassic and Jurassic period, and lived all over the world.
• About 66 million years ago, a worldwide mass extinction occurred at the end of the Cretaceous Period.
Birds
• Birds are reptiles that regulate their internal body temperature.
• Recent fossil discoveries strongly support the hypothesis that birds evolved from a group of dinosaurs.
• Modern birds by themselves, the traditional class Aves, from a clade within the clade containing dinosaurs.
Mammals
• Characteristics unique to mammals include mammary glands in females, which produce milk to nourish you, and hair.
• Mammals breathe air, have four-chambered hearts, and regulate their internal body temperature.
• After birth, most placental mammals care for their young and nurse them to provide nourishment
26.3Primate Evolution
What Is a Primate?
• Primates, including lemurs, monkeys, and apes, share several adaptations for a life spent in trees.
• In general, a primate is a mammal that has relatively long fingers and toes with nails instead of claws, arms that can rotate around shoulder joints, a strong clavicle, binocular vision and a well-developed cerebrum.
Fingers, Toes, and Shoulders
• Primates typically have 5 flexible fingers and toes on each hand or foot that can curl to grip objects firmly and precisely.
• This enables many primates to run along tree limbs and swing from branch to branch with ease.
• In addition, most primates have thumbs and big toes that can move against the other digits.
Binocular vision
• Many primates have a broad face, so both eyes face forward with overlapping fields to view.
• Binocular vision is the ability to combine visual images from eyes, providing depth perception and a three-dimensional view of the world.
• This comes in handy for judging the locations of tree branches, from which many primates swing.
Evolution of Primates
• Human and other primates evolved from a common ancestor that lived more than 65 million years ago
• Primates in one of these groups look very little like typical monkeys
Tarsiers and Anthropoids
• Anthropoids or humanlike primates, include monkeys, great apes, and humans.
• New world monkeys also have a long, prehensile tail that can coil tightly enough around a branch to serve as a “fifth hand.”
• Great apes, also called hominoids, include gibbons, orangutans,
gorillas, chimpanzees, and humans.
Hominine Evolution
• Hominines led to humans, and include modern humans and all other species more closely related to us than to chimpanzees.
• Hominines also evolved much larger brains.
New Findings and New Questions
• Since the 1990’s, new discoveries in Africa have doubled the number of known hominine species.
• Hominine fossils date back to 7 million years.
• There are various hypotheses on how these hominines relate to humans.
Relatives versus Ancestors
• All hominine species relate to modern humans, but not all are human ancestors.
• Distinguishing relatives from ancestors in the hominine family is an ongoing challenge.
The oldest hominine?
• In 2002, paleontologists in central Africa discovered a skull 7 million years old.
• This fossil is called Sahelanthropus.
• Scientists are still debating whether this fossil represents a hominine.
Australopithecus
• This type of hominines lived from about 4 million to about 1.5 million years ago.
• Lucy, is a female skeleton discovered in 1974, which lived about 3.2 million years go.
• In 2006, an Ethiopian researcher announced the discovery of some incredibly well preserved 3.3 million year old fossils of a very young female hominine.
The Road to Modern Humans
• Hominines lived millions of years before modern humans.
• Many species in our genus existed before our species, Homo sapiens, appeared; furthermore, at least three other Homo species existed at the same time as early humans.
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