2 Classroom ExerciseLook at Figure 17.6 on page 340, a phylogenetic treeshows hypothetical evolutionary relationshipsShows criteria by which groups were categorizedPresence/absence of tissuesType of body symmetry (radial or bilateral)During the lecture, each group should construct a similar tree for the animals, showingthe relationships among the groups discussedthe criteria for separationWe will share them at the end of the class period.
3 Definitions Animals are eukaryotic,multicellularheterotrophic organisms that obtain nutrients by ingestionable to digest their food within their bodies.Animal cells lack the cell walls that provide strong support in the bodies of plants and fungiMost animalsHave muscle cells and nerve cells that control the muscles.are diploid,reproduce sexually, andproceed through a series of typically similar developmental stages
4 Early Animals and the Cambrian Explosion Scientists hypothesize that animals evolved from a colonial flagellated protistThe oldest animal fossils found are 550–575 million years oldThe molecular data suggest a much earlier origin for animalsAnimal diversification appears to have accelerated rapidly from 525 to 535 million years ago, during the Cambrian periodBecause so many animal body plans and new phyla appear in the fossils from such an evolutionarily short time span, biologists call this episode the Cambrian explosionThe Cambrian explosion may have been ignited byincreasingly complex predator-prey relationshipsan increase in atmospheric oxygen.The genetic framework for complex bodies, a set of “master control” genes, was already in place
5 Animal Phylogeny Biologists categorize animals by “body plan,” general features of body structure and,more recently, genetic data.One major branch point distinguishes sponges from all other animals because, unlike more complex animals, sponges lack true tissuesA second major evolutionary split is based on body symmetryRadial symmetry refers to animals that are identical all around a central axis.Bilateral symmetry exists where there is only one way to split the animal into equal halves.Animals also vary according to the presence and type of body cavity, a fluid-filled space separating the digestive tract from the outer body wall. There are differences in how the body cavity developsIf the body cavity is not completely lined by tissue derived from mesoderm, it is called a pseudocoelom.A true coelom is completely lined by tissue derived from mesoderm.
6 Sponges represent multiple phyla are stationary animals, lack true tissues, andprobably evolved very early from colonial protists.The body of a sponge resembles a sac perforated with holeschoanocyte cells draw water through the walls of the sponge where food is collected
7 Cnidarians Cnidarians (phylum Cnidaria) are characterized by the presence of body tissues,radial symmetry, andtentacles with stinging cells.basic body plan = a sac with a gastrovascular cavity, a central digestive compartment with only one openingThe body plan has two variations:the stationary polyp andthe floating medusa.Cnidarians are carnivores that use tentacles, armed with cnidocytes (“stinging cells”), for defense and predation
8 Molluscs soft-bodied animals and usually protected by a hard shell. Many molluscs feed by using a file-like organ called a radula to scrape up foodThe body of a mollusc has three main parts:a muscular foot used for movement,a visceral mass containing most of the internal organs, anda mantle, a fold of tissue that secretes the shell if present.three major groups of molluscsgastropodsinclude snails whichare protected by a single, spiraled shell,have no shell at all, as with slugs and sea slugs.bivalvesinclude clams, oysters, mussels, and scallops andhave a shell divided into two halves hinged togethercephalopodssquids and octopus,typically lack an external shell, andare built for speed and agility
9 FlatwormsFlatworms (phylum Platyhelminthes) are the simplest bilateral animalsFlatworms include forms that areparasites or free-livingmarine, freshwater, or damp habitats.The gastrovascular cavity of flatwormsis highly branched andprovides an extensive surface area for absorption of nutrients.
10 AnnelidsAnnelids (phylum Annelida) have body segmentation, a subdivision of the body along its length into a series of repeated partsthree main groups of annelidsearthworms, which eat their way through soil,polychaetes, marine worms with segmental appendages for movement and gas exchange, andleeches, typically free-living carnivores but with some bloodsucking forms.body includesa coelom anda complete digestive tract withtwo openings, a mouth and anus, andone-way movement of food.
11 Roundworms Roundworms (phylum Nematoda) are cylindrical in shape, tapered at both ends, andthe most numerous and widespread of all animals.roundworms (also called nematodes) areimportant decomposers anddangerous parasites in plants, humans, and other animals
12 ArthropodsArthropods (phylum Arthropoda) are named for their jointed appendagesThere are over 1 million arthropod species identified, mostly insectsArthropods are a very diverse and successful group, occurring in nearly all habitats in the biosphereThere are four main groups of arthropods:arachnids,crustaceans,millipedes and centipedes, andinsects.General Characteristics of ArthropodsArthropods are segmented animals withspecialized segments andappendages for an efficient division of labor among body regions.an exoskeleton, an external skeleton that providesprotection andpoints of attachment for the muscles that move appendages.
13 Arachnids and Crustaceans usually live on land,usually have four pairs of walking legs and a specialized pair of feeding appendages, andinclude spiders, scorpions, ticks, and mites.Crustaceansare nearly all aquatic,have multiple pairs of specialized appendages, andinclude crabs, lobsters, crayfish, shrimp, and barnacles.
14 Millipedes and Centipedes millipedes and centipedes have similar segments over most of the bodyMillipedeseat decaying plant matter andhave two pairs of short legs per body segment.Centipedesare terrestrial carnivores with poison claws andhave one pair of short legs per body segment.
15 InsectsInsects typically have a three-part body : head, thorax, and abdomen.The insect head usually bearsa pair of sensory antennae anda pair of eyes.mouthparts are adapted for particular kinds of eatingFlight is one key to the great success of insectsInsect DiversityInsects outnumber all other forms of life combinedInsects live in almost every terrestrial habitat, fresh water, and the air.Many insects undergo metamorphosis in their developmenthemimetabolous insects have juvenile formst that appear to be smaller forms of the adult orholometabolous species change from a larval form to something much different as an adult.
16 Echinoderms Echinoderms (phylum Echinodermata) lack body segments,typically show radial symmetry as adults but bilateral symmetry as larvae,have an endoskeleton, andhave a water vascular system that facilitates movement and gas exchange.Echinoderms are a very diverse group. include such well-known animals as starfish, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone lilies".Marine organisms that occupy every ocean depth.No freshwater or terrestrial representatives
17 ChordatesChordates (phylum Chordata) all share four key features that appear in the embryo and sometimes the adult:a dorsal, hollow nerve cord,a notochord,pharyngeal slits, anda post-anal tail.Another chordate characteristic is body segmentation, apparent in thebackbone of vertebrates andsegmental muscles of all chordates.Chordates consists of three groups of invertebrates:lancelets are bladelike animals without a cranium,tunicates, or sea squirts, also lack a cranium, andhagfishes are eel-like forms that have a cranium.All other chordates are vertebrates
18 Fishesfirst vertebrates were aquatic and probably evolved during the early Cambrian period, about 542 million years ago.lacked jawsare represented today by lampreys.have a lateral line system that detects minor vibrations in the watertwo major groups of living fishescartilaginous fishes (sharks and rays), with a flexible skeleton made of cartilage, andbony fishes, with a skeleton reinforced by hard calcium salts.Bony fishes, include ray-finned fishes and lobe-finned fishes.To provide lift off the bottom,cartilaginous fish must swim butbony fish have swim bladders, gas-filled sacs that help them be buoyant.
19 Amphibians exhibit a mixture of aquatic and terrestrial adaptations, usually need water to reproduce, andtypically undergo metamorphosis from an aquatic larva to a terrestrial adult.the first vertebrates to colonize landdescended from fishes that hadlungs,fins with muscles, andskeletal supports strong enough to enable some movement on landterrestrial vertebrates are collectively called tetrapods, which means “four feet.”amphibiansreptilesmammals
20 Reptiles amniotes, producing amniotic eggs, which are fluid-filled,have waterproof shells, andenclose the developing embryo.Include snakes, lizards, turtles, crocodiles, alligators, and birds.Reptile adaptations to living on land includea. an amniotic egg andb. scaled waterproof skin.Nonbird Reptilesectotherms, sometimes referred to as “cold-blooded,” which means that they obtain body heat from the environmentcan survive on less than 10% of the calories required by a bird or mammal of equivalent sizeReptiles diversified extensively during the Mesozoic eraDinosaurs werethe most diverse reptile group andthe largest animals ever to live on land.Reptiles, the class Reptilia, are an evolutionary grade of animals, comprising today's turtles, crocodilians, snakes, lizards and tuatara, their extinct relatives, and some of the extinct ancestors of mammals. Due to their evolutionary history and the diversity of extinct forms, the validity of the class is not universally supported in scientific circles, though in practice, it remains in use by some biologists and more laymen, especially in mass media. The study of reptiles, historically combined with that of amphibians, is called herpetology.
21 Birds Birds have many adaptations that make them lighter in flight: honeycombed bones,one instead of two ovaries, anda beak instead of teeth.Unlike other reptiles, birds are endotherms, maintaining a warmer and steady body temperatureBird wings adapted for flight are airfoils, powered by breast muscles anchored to a keel-like breastbone
22 Mammals First arose about 200 million years ago and were probably small, nocturnal insect-eaters.Most are terrestrial, although dolphins, porpoises, and whales are totally aquaticMammals have two unique characteristics:hair and mammary glands that produce milk, which nourishes the young.There are three major groups of mammals:monotremes, egg-laying mammals,marsupials, pouched mammals with a placenta, andeutherians, also called placental mammals.Eutherian placentas provide more intimate and long-lasting association between the mother and her developing young than do marsupial placentas
23 HumansHumans and chimpanzees have shared a common African ancestry for all but the last 5–7 million yearsPresent-day humans and chimpanzees clearly differ in two major physical features. Humansare bipedal andhave much larger brains
24 Who Were the Hobbit People? Observation: The hominin fossils on the island of Flores did not belong to any known speciesQuestion: Where does this hominin fit in our evolutionary history?Hypothesis: The hobbits evolved from an isolated population of Homo erectusPrediction: Key traits of the new species, such as its skull characteristics and body proportions, would resemble those of a miniature Homo erectusExperiment: Detailed measurements and other observations of the new fossils were compared with data from Homo erectus fossilsResults: Not shownConclusion: The initial results supported the hypothesisNote: Other analyses including additional specimens suggest alternate hypotheses:Homo floresiensis is most closely related to Homo habilisthe hobbits are not a species at all, but Homo sapiens with a disorder that caused bone malformations.
25 Discussion QuestionsDescribe the fossil discoveries on the Indonesian island of Flores and relate the findings to modern humans.Define what it means to be an animal and describe common aspects of animal development.Describe the significance of the Cambrian explosion.Distinguish between the nine major animal phyla according to the presence of tissues, type of body symmetry, presence of a body cavity, type of digestive tract, and presence of segmentation.
26 Discussion QuestionsDescribe the body structure and feeding strategies of sponges, cnidarians, molluscs, and flatworms.Describe the general structure of annelids and nematodes. Compare the lifestyles and feeding habits of earthworms, polychaetes, leeches, and nematodes.Describe the general structure of arthropods, and discuss the advantages and disadvantages of an exoskeleton. Distinguish between arachnids, crustaceans, millipedes, centipedes, and insects.Describe the general structure of echinoderms and explain the significance of the water vascular system.
27 Discussion QuestionsDescribe the four defining characteristics of the phylum Chordata.Distinguish between the following groups: invertebrate chordates, jawless vertebrates, cartilaginous fishes, ray-finned fishes, and lobe- finned fishes. Describe the significance of jaws and a swim bladder.Describe several aquatic and terrestrial adaptations of amphibians.Describe the adaptations of reptiles to life on land.Describe three adaptations for flight found in birds.Describe the characteristics common to all mammals. Distinguish between monotremes, marsupials, and eutherian mammals, and provide examples of each.
28 Discussion QuestionsDescribe the primate adaptations for life in trees. Compare the three main groups of primates, noting examples of each.Compare Old World monkeys and New World monkeys.Explain why it is incorrect (a) to consider chimpanzees as our ancestors, (b) to think of human evolution as a ladder, and (c) to think that human traits evolved together.Describe the traits of each of the following species and the relationships between them: Australopithecus afarensis, Homo habilis, Homo erectus, Homo neanderthalensis, and Homo sapiens, and the hobbit people of Flores.Describe the evolution and impact of our species as we spread across the world
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