CHAPTER 17
The Evolution of Animals
I.
Origins of Animal Diversity
II. Animal Phylogeny
III. Major Invertebrate Phyla
IV. Vertebrate Genealogy
V. Human Ancestry
The blue whale is the LARGEST
ANIMAL that has ever existed
A REPTILE CAN SURVIVE on less
than 10% of the calories required by a
mammal of equivalent size
TAPEWORMS can reach lengths of 20
meters in the human intestine
I. Origins of Animal Diversity
– Animal life began in Precambrian seas
with evolution of multicellular
creatures
Early
Animals
– Animals probably evolved from a colonial
flagellated protist during the Precambrian
– 542 M years ago - the Cambrian period,
animals underwent a rapid diversification
What Is an Animal?
– Eukaryotic, multicellular, heterotrophic
organisms that ingest nutrients
– Most reproduce sexually
• And develop in stages
• A rock python ingesting a gazelle
• 2 weeks to digest its meal
Nutrition by ingestion!
Sexual
reproduction
Development
in stages
Sea star
II. Animal Phylogeny
 3 branches hypothesized
1st defined by presence of true tissues
2nd defined by body symmetry
3rd evolution of body cavities
 led to more complex animals
3
1. Presence of true tissues
2. Body
symmetry
Radial
Bilateral
3. Evolution of body cavities
What is a (body) cavity?
A fluid-filled space separating the digestive
tract from the outer body wall
The body cavity is also called a coelom
No body cavity
Has a body cavity
Flatworm (a tapeworm)
Annelid (earthworm)
III. Major Invertebrate
Phyla
–Invertebrates
• Are animals without backbones
• Represent 95% of the animal kingdom
–Phylum Porifera
• Includes sessile animals once believed
to be plants
• Lacks true tissues; just a loose
assemblage of cells
• Body has pores with central cavity
• Water drawn into cavity collects
food
–Phylum Cnidaria
• Exs: Hydra, Jellies, Sea Anemone
• Characterized by the presence of body
tissues, radial symmetry, and tentacles with
stinging cells
• Body plan = sac with a gastrovascular cavity
• Two life forms
– The sessile polyp and the floating medusa
Anemone
Sessile
Medusa
Floating
Hydra
What type of body symmetry do these cnidarians have?
–Phylum Platyhelminthes
• The simplest animals with bilateral symmetry
• Includes free-living forms such as
planarians
• Some parasitic
• Examples
– Tapeworm and Blood-flukes
Planaria
Tapeworm
–Phylum Nematoda
• ** Two new innovations not found in
previous phyla**
1) Complete digestive tract (2 openings)
2) Body cavity = pseudocoelom
• Most parasitic group of animals
• Examples
– Hookworms, Ascaris, Trichinella
A free living roundworm
Mouth?
Point to the muscle.
Point to the worms.
Anus?
Parasitic roundworms
Have you heard of trichinosis?
–Phylum Annelida
• Worms with body segmentation
• Three main classes
1. Earthworms
2. Polycheates – marine worms
3. Leeches
1. Earthworm
Did you know the
earthworm has a brain?
Giant Australian earthworm
2. Polychaetes
A Christmas tree worm
(a fanworm)
A sandworm
3. Leeches
In January 2004, the U.S.
Food and Drug
Administration (FDA) did
something it had never done
before
It approved the use of a
live animal as a medical
device
Leeches
For the treatment of
circulatory complications
–Phylum Arthropoda
• Organisms with jointed appendages
• Segmented animals with highly
specialized segments and appendages
• Body covered by an exoskeleton made
of chitin
– Phylum Arthropoda
• Total population on Earth: a billion billion
– That’s 1018 individuals
– Or, 150 M for each person!!
• 4 main groups
–
–
–
–
Crustaceans – crab, lobster, barnacles
Arachnids – spiders, ticks, mites, scorpions
Millipeds & Centipedes
Insects – grasshoppers, moths
 Most have 3 body parts
 Undergo metamorphosis
Crustacean
Crustaceans
Fairy shrimp
Barnacles
Arachnids
Scorpion
Black widow spider
Dust mite
Millipede
Insects
Beetle
Mantis
Bee hawkmoth
3 body parts of insects
Metamorphosis
Larva
Emerging adult
Pupa
Pupa
Adult
–Phylum Mollusca
• Soft-bodied animals, protected by a hard
shell
• Body has 3 main parts: muscular foot,
visceral mass, and mantle
• Three major classes
1. Gastropods - snails, slugs
2. Bivalves – clams (shells with 2 halves)
3. Cephalopods – squid, octopus & nautilus
Mollusca
1. Gastropod shells
2. A bivalve (a scallop)
What are these little ‘dots’?
3. A cephalopod (an octopus)
How is the octopus different from other molluscs?
–Phylum Echinodermata
• All marine, usually sessile or slow moving
• Lack body segments
• Endoskeleton
• Have a unique characteristic called a
 Water vascular system (helps movement, etc)
• Ex: sea stars, sand dollars, sea urchins, and
sea cucumbers
Sea urchin
Sea star
Sea star eating
Sea cucumber
IV. Vertebrate Genealogy
–Vertebrates
• Unique vertebrate features include
– Skull
– Backbone (a series of bones called vertebra)
• Represented by fishes, amphibians, reptiles,
and mammals
Observe the skull and backbone. What does that tell you?
Vertebrate
Genealogy
65
Hair & mammary
glands
Amniotic egg
4 legs
Lungs
Jaws
542
Vertebrae
Ancestor
– The first vertebrates - evolved during the early
Cambrian period, 542 mya
– 2 major groups of living fishes
1. Chrondrichthyes = cartilaginous fish
 Ex: sharks, skates & rays
2. Osteichthyes = Boney fish
 Hard boney skeleton, lateral line, good smell and
eyesight
 2 branches – lobed finned and ray finned fish
Cartilaginous fish (a sand bar shark)
A bony fish (a yellow perch)
• Evolved from lobed-finned fishes
• 1st terrestrial tetrapod (four-feet or limbs)
• 1st vertebrate to colonize land
• Usually need water to reproduce
• Have aquatic & terrestrial adaptations
• EX: salamanders and frogs
Lobe-finned fish
Early amphibian
Tadpole
Tadpole undergoing
metamorphosis
Adult frog
– New invention – Amniotic Egg**
• Ectotherms – obtain heat from
environment
• Waterproof skin – benefits/drawbacks
• Now completely terrestrial
• EX: snakes, lizards, turtles, crocodiles
and dinosaurs (now extinct)
Bull snake
Deinonychus (terrible claw)
– Birds evolved from small, two-legged
dinosaurs during the Mesozoic era
– Body modified for flight
•
•
•
•
Hollow bones with struts
Breathing by Counter-current exchange
Wings aerodynamic
Endotherm – maintain warm, constant body
temperature via metabolism
Aerodynamics of bald eagle in flight
– The first true mammals
• appeared 200 million years ago and were
probably small, nocturnal insect-eaters
– Most mammals are terrestrial
– Distinguishing characteristics
• Hair
• Mammary glands
– 3 major groups of mammals:
1. Monotremes, the egg-laying
mammals
2. Marsupials – pouched mammals
Australia’s mammals (kangaroo)
3. Eutherian mammals – Placental
mammals – Horses, lions, tigers,
bears, bats etc
An echidna (a monotreme)
The only mammal that lay eggs
A brushtail opossum (a marsupial)
Born early! Live in mother’s pouch
A zebra, (a eutherian - placental mammals)
V. The Human Ancestry
– Humans are primates
– Primate evolution
• Provides context to understand human origins
• Evolved from insect-eating mammals
• Early primates
– Were small, arboreal mammals
– Distinguishing characteristics
• Secure, limber shoulder joints
• Eyes placed on front of face
• Excellent hand-eye coordination
• Extensive parental care
Orangutan
– Taxonomists divide the primates into
three main groups
1. Lemurs and Lorises
2. Tarsiers
3. Monkeys, Apes and human
Primate
diversity
1. A loris
2. A tarsier
Wooly spider monkey (new world)
Pig-tail macaque (old world)
3. Monkeys (anthropoids)
Orangutan
Gorilla
White banded gibbon
Chimpanzee
3. Humans (hominoids)
Time line of human evolution
Caves
Migrated
Name?
Bipedalism
• Enlarged brain
• Tools
VI. Human
Evolution
– Humans share a common ancestor with
apes approx. 5-7 M years ago
– Australopithecus walked the African
savanna
• Upright posture, brain enlarging
– A. afarensis – bipedal fossil 4 M year ago
– Homo habilis – “handyman”
• Had larger brain
• Probably made stone tools
LUCY, an Australopithecus
afarensis skeleton
Ancient footprints discovered
by Mary Leakey, Laetoli,
Tanzania
– Homo erectus
• 1st species to extend range beyond
Africa approx 1.8 M years ago
– Was taller than H. habilis
– Had a larger brain
– Gave rise to Neanderthals
– Homo neanderthalensis (Neanderthals)
– Lived in caves in Europe, the middle east,
parts of Asia
•
•
•
•
•
Had large brains
Lived from 200,000 to 35,000 years ago
Skilled tool makers
Participated in burials
Very first to create fine art!
Horses
Hand
European bison
Rhino
– Homo sapiens
– oldest known fossils of species H. sapiens
• Discovered in Ethiopia
• Date from 160,000 to 195,000 years ago
The final exam will be comprehensive
(80 questions; 150 points total)
Thursday, December 13, 2007, 11:30 am to 1:30 pm
SC1102
4 stages of life