Evolution of Animal DiversityChapter 18
Animal Evolution BasicsAnimal Evolution was rapid, occurring ~ 600 million years ago (Precambrian Era)Evidence suggests that animals have evolved from protists that lived as colonies of cells.Colonies form when cells divide, but do not separate.These cells differentiated and became specialized.
ProtoanimalsModel of blastula and grastula used to represent these early animals.Sources: http://farm3.static.flickr.com/2372/2121294845_dab7667079.jpg?v=0; http://www.dkimages.com/discover/previews/800/912525.JPG
Cambrian Explosion (545 mya)Time period in which all the major body plans seen today developed.Occurred during a short, 10 million year period of time.Why??Ecological (food), Geological (atmosphere), Genetic (reg. genes)
Animal Specs.Multicellular, eukaryotes that are heterotrophic (utilize ingestion).
Animal cells lack cell walls, utilize intercellular junctions, proteins.
Utilize muscle cells for movement
Animal ReproductionReproduce sexuallyMitosis & Meiosis involvedBlastula -> Grastula -> Ectoderm (epidermis) -> Endoderm (lines digestive tract) -> Mesoderm (internal organs)Larval stages & Metamorphosis sometimes presentHox genes = reg genes that control development.
Invertebrates / VertebratesInvertebrates = lack vertebral columnVertebrates = have vertebral column
Animal AncestryAncient Choanoflagellates = ancestor of all animals species today.Colonial protist.Fig. 18.3 E
Radial SymmetryAnimal body parts are arranged in a pie-like shape (around central axis).Ex: Phylum Cnidaria: jellyfish Phylum Porifera: Cylindrical spongesFig. 18.3 B
Sponge Nutrition (Phylum Porifera)Suspension Feeders = animals that collect food particles from water passed through some type of food-trapping mechanism.Choanocytes: Trap and obtain bacteria from water via mucus.Amoebocytes: digest food packaged in vacuoles.Package food via phagocytosis (engulfment)
Cnidarians Have gastrovascular cavityIncomplete digestion: undigested foods exit through mouth.Classified as polyp or medusaEx: Sea anemones, jellies
Bilateral SymmetryAnimal can be divided equally by a single cut; left & right mirror image.Anterior (Head) - houses brain, sensory organs, and mouth.Posterior (Tail)Dorsal (Back)Ventral (Bottom)Lateral (Side)
Bilateral SymmetryAnimals with this symmetry are very active and travel headfirst through its environment.Most have complete digestive tract (mouth to anus) & a body cavity between digestive tract and body wall.
*Importance in evolution of animals*
Body Cavity*Fluid-filled space between the digestive tract and the body wall was important in the evolution of animals*Pseudocoelom = body cavity not completely lined by tissue derived from mesoderm.Coelom (sea-lum) = body cavity completely lined by tissue derived from mesoderm (complete digestive tract)
Advantages to having a Body CavityFlexibilityAllows use of muscles by force derived from hydroskeleton.Allows internal organs to develop and move independently of outer body wall.Fluid aids in protecting internal organs.Circulate nutrients and oxygen.Aids in waste disposal
Complete Digestive TractAnterior portions of body churn and mix food with digestive enzymes.
Posterior portions of body absorb nutrients and dispose of wastes.
Circulatory SystemAn organ system that distributes nutrients and oxygen throughout the body.
SegmentationSubdivision of the body along its length into a series of repeated parts.Allows for grouping of specialized cells.Flexibility = adaptation for movementEx: Earthworm - grooved rings (external), coelom partitioned by walls (internal)Ex: Dragon fly (head, abdomen, & thorax) human (vertebrae & abdominal muscles)
ArthropodsHave an exoskeleton = hard external skeleton.Consists of layers of protein and chitin (polysaccharide)Serves as protection and points of attachment for muscles.Shedding of exoskeleton = molting.
EchinodermsEndoskeleton - hard internal skeleton.
ChordatesHave the following features:Dorsal, hollow nerve chordNotochordPharyngeal slitsPost-anal tailVertebrate chordatesInvertebrate chordates (tunicates & lancelets)
Vertebrates (Chordates)Have the following features:Skull & Backbone (encases brain and main parts of nervous system)Endoskeleton (cartilage / hard bone)
*Evolution of jaws were of great importance in fish development*
Amphibians1st terrestrial vertebrates*Evolution of lungs and appendages were major evolutionary advances in fishes and allowed evolution of amphibians / adaptation to land*Adapted to living in shallow aquatic habitats and waters edge.Proliferated during Carboniferous period.
ReptilesAdaptations to living on land:Skin with scales (keratin)Eggs that retain waterAmniotic eggs = self-contained nourishment.Exothermic = absorption of heat externally.
ReptilesDinosaurs:Endothermic animals = use heat generated by metabolism to maintain constant body temperature.Mass extinction ~65 myaEvolution of Birds
BirdsRelationship to Reptiles: Presence of amniotic eggsScales on legs of birdsToenails of keratinSimilar body structuring to reptilesFlight Structures:No teeth, hollow shafted feathers, honeycombed bones (strong, but light)
BirdsHigh Metabolic RateEndothermic (feathers ensure insulation of body temperature)Efficient circulatory system
MammalsEvolved about 220 mya from reptiles.Mass extinction of dinosaurs allowed for a proliferation of mammalsExposure to greater resources & lack of predation)Endothermic, high metabolic rate, presence of hair, and mammary glands.
Mammals3 Groups: Monotremes EX: duck-billed platypus (egg-laying).2) Marsupials EX: kangaroo (External pouch)3) Eutherians EX: dogs, cats, humans(Reptile Homologous structure = amniotic tissues)
MammalsPlacenta = structure joining mother & embryo within uterus (#2 & #3)Placentas provide long-lasting association between mother and developing young.