Evolution of Animal Diversity

Chapter 18

Animal Evolution Basics• Animal 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.

Protoanimals• Model 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 Reproduction• Reproduce sexually• Mitosis & Meiosis involved• Blastula -> Grastula -> Ectoderm

(epidermis) -> Endoderm (lines digestive tract) -> Mesoderm (internal organs)

• Larval stages & Metamorphosis sometimes present

• Hox genes = reg genes that control development.

Invertebrates / Vertebrates

• Invertebrates = lack vertebral column

• Vertebrates = have vertebral column

Animal Ancestry

• Ancient Choanoflagellates = ancestor of all animals species today.– Colonial protist.

– Fig. 18.3 E

Radial Symmetry

• Animal body parts are arranged in a pie-like shape (around central axis).– Ex: Phylum Cnidaria: jellyfish

Phylum Porifera: Cylindrical sponges

– Fig. 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 cavity– Incomplete digestion: undigested

foods exit through mouth.

– Classified as polyp or medusa

– Ex: Sea anemones, jellies

Bilateral Symmetry

• Animal 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 Symmetry

• Animals 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 Cavity

• Flexibility

• Allows 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 Tract

• Anterior portions of body churn and mix food with digestive enzymes.

• Posterior portions of body absorb nutrients and dispose of wastes.

Circulatory System

• An organ system that distributes nutrients and oxygen throughout the body.

Segmentation• Subdivision of the body along its

length into a series of repeated parts.

• Allows for grouping of specialized cells.

• Flexibility = adaptation for movement– Ex: Earthworm - grooved rings (external),

coelom partitioned by walls (internal)

– Ex: Dragon fly (head, abdomen, & thorax) human (vertebrae & abdominal muscles)

Arthropods

• Have 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.

Echinoderms

• Endoskeleton - hard internal skeleton.

Chordates

• Have the following features:– Dorsal, hollow nerve chord

– Notochord

– Pharyngeal slits

– Post-anal tail

Vertebrate chordates

Invertebrate 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*

Amphibians• 1st 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 water’s edge.

• Proliferated during Carboniferous period.

Reptiles

• Adaptations to living on land:

–Skin with scales (keratin)

–Eggs that retain water

–Amniotic eggs = self-contained nourishment.

–Exothermic = absorption of heat externally.

Reptiles

• Dinosaurs:– Endothermic animals = use heat

generated by metabolism to maintain constant body temperature.

– Mass extinction ~65 mya

– Evolution of Birds

Birds• Relationship to Reptiles:

–Presence of amniotic eggs

–Scales on legs of birds

–Toenails of keratin

–Similar body structuring to reptiles

• Flight Structures:– No teeth, hollow shafted feathers,

honeycombed bones (strong, but light)

Birds

• High Metabolic Rate

• Endothermic (feathers ensure insulation of body temperature)

• Efficient circulatory system

Mammals• Evolved about 220 mya from reptiles.

• Mass extinction of dinosaurs allowed for a proliferation of mammals

–Exposure to greater resources & lack of predation)

• Endothermic, high metabolic rate, presence of hair, and mammary glands.

Mammals

• 3 Groups:

1) Monotremes – EX: duck-billed platypus (egg-laying).

2) Marsupials – EX: kangaroo

(External pouch)

3) Eutherians – EX: dogs, cats, humans

(Reptile Homologous structure = amniotic tissues)

Mammals

• Placenta = structure joining mother & embryo within uterus (#2 & #3)

• Placentas provide long-lasting association between mother and developing young.