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.

•