Evolution of Animals
(Metazoa)
BIOL 1407
Animal Body Plan
• Tissues
– Absent =
Parazoa
– Present =
Eumetazoa
Radial Symmetry
• Encounter
environment equally
from all sides
• Sessile, sedentary or
planktonic
• Sea Anemone
Feeding Video
•
•
http://www.mbayaq.org/efc/video_library/vid
eo_library.aspx
Then click on “Anemone Feeding”
• Jellyfish Swimming
•
http://www.youtube.com/watch?v=760lUxyle6I
Bilateral Symmetry
• Central nervous
system in head
• Active movers
• Frilled lizard video
•
http://video.nationalgeographic.com/video/pl
ayer/animals/reptilesanimals/lizards/lizard_frilled_ontherun.html?f
s=animals.nationalgeographic.com
• Crocodile gallop video
•
http://www.flmnh.ufl.edu/natsci/herpetology/
brittoncrocs/images/cj-gallop2.mpg
Number of Germ Layers
• Diploblastic: has two germ layers
– Endoderm
– Ectoderm
• Triploblastic: has three germ layers
– Endoderm
– Mesoderm
– Ectoderm
Question?
Body Cavities
• What is a body cavity?
– Fluid-filled cavity separates digestive tract
from body wall
Body Cavities
• Advantages:
– Fluid cushions organs
– Acts as hydrostatic skeleton
– Allows internal organs to move independently
of body wall
– Allows internal organs space for folding
Development
• Protostome
– Fate of blastopore
– Type of cleavage: spiral and determinate
– Coelom formation
• Deuterostome
– Fate of blastopore
– Type of cleavage: radial and indeterminate
– Coelom formation
Animation of Spiral and Radial Cleavage
http://worms.zoology.wisc.edu/urchins/rad_spir.html
Schizocoelous
Enterocoelous
Sister Taxon
Model of Early Animal Evolution
Evolution of Animals
• Earliest animal
fossils
• Fossilized
embryos from
China
• 575 mya
Ediacaran Fauna
• 565-550 mya
• Australia
• Soft-bodied
animal fossils
• What type of
symmetry?
Ediacaran Fauna
•
•
•
•
Animal fossil
Many body segments
Head
What type of
symmetry?
Cambrian Explosion
• 535-525 mya
• Animal diversity ↑↑
• 50% extant animal
phyla in fossil
record
Burgess Shale Fossils
Cambrian Explosion
• First animals with
hard mineralized
skeletons
• 1st arthropods,
chordates &
echinoderms
Hypotheses for Cambrian
Explosion
(1) Predator-prey coevolution
(2) Rise in atmospheric oxygen levels 
↑ metabolic rate and body size
(3) Evolution of Hox genes  developmental
flexibility
Traditional Phylogenetic Tree
• Was based on body plans
– Tissues absent or present
– Type of symmetry
– Types of body cavities
– Protostomes versus deuterostomes
Modern Phylogenetic Tree
• Based on molecular data
Modern Phylogenetic Tree
• Reinforces some of traditional tree
– Parazoa vs. Eumetazoa
– Radial vs. Bilateral
– Deuterostomes are a clade
Modern Phylogenetic Tree
• Radical affects on other parts
– Body cavity characteristics are analogous
– Two main lineages for most invertebrates
• Lophotrochozoa
• Ecdysozoa
Lophotrochozoa
• Clade named for
presence of either a:
– Lophophore
(horse-shoe
shaped ciliated
feeding apparatus)
– Trochophore larva
Lophotrochozoa
Ecdysozoa
• Clade was named
for presence of
• Ecdysis = molting
• Produce an
exoskeleton
• Must be shed as
animal grows
The End
Unless otherwise specified, all images in this presentation came from:
Campbell, et al. 2008. Biology, 8th ed. Pearson Benjamin Cummings.
Slides 19 and 28 are from Campbell, et al. 2005. Biology, 7th ed.