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Animal Origins
•Bringing it all together
–History of Life
–Basic Animal Body Plan
–Animal Groups: Understanding evolutionary
relationships among phyla of animals
•The Cambrian Explosion
•Other body plan features
–Symmetry
–Segmentation
–Tissue Types
Bringing it all together
• Evolutionary History of Life
• Basic Animal Body Plan—germ layers and
gastrulation
• Animal Groups: Taxonomy and
Systematics
EVENT
TIME BEFORE PRESENT
(BYA--billions of years ago
(MYA--millions of years
ago)
SHEET NUMBER ON
THE TYPICAL ROLL
Formation and Solidification of Earth
4.6-4.0 BYA
1
• Animals show up about
Oldest Rocks Known
3.8 BYA
10
Earliest evidence of life--carbon forms in
rock
3.8 BYA
10
Earliest fossil prokaryotic cells
3.5 BYA
25
Oxygen levels rise steeply due to
increase in photosynthetic activity
2.5 BYA
75
Complex eukaryotic cells appear in fossil
record
1.5 BYA
125
First multicellular organisms in fossil
record
600 MYA
170
Burgess Shale--exposion of multicellular
diversity--most multicellular animal groups
represented in primitive form
515 MYA
176
First land vertebrates
350 MYA
183
Archaeopteryx--precursor to birds (and
other dinosaurs)
150 MYA
192
End Cretaceous Extinction--goodbye
dinos, hello mammalian, bird, flowering
plant diversity
65 MYA
196
Lucy--Australopithecus
4 MYA
1 (last 1/4 of sheet)
Homo erectus, fire
1 MYA
1 (last 1/20 of sheet)
Start of agriculture, settlements
10,000-20,000 years ago
1 (last fibers)
History
of life:
Remember
animals
appear
about 500
MYA
(sheet 176
out of 200)
Basic Animal Body Plan:
• 3 layer embryo
(remember/redo
board drawing)
• Gastrulation
(remember…tube
within a tube…most
important event of our
lives)
Taxonomy and Systematics
• Remember…canimalcules
—finding common shared
characteristics
• Taxonomy of major animal groups (phyla)
reflecting their evolutionary history, is based on
shared common characteristics related to basic
body plan formation during
development…{next slide}
Understanding evolutionary
relationships among animal phyla
• Goal is to see which major groups are
closely related
• Adults are so different that it is difficult to
find shared common characteristics
• Embryos do share many characteristics
and can be easily compared
Animals with no mesoderm
•
•
•
•
•
Least complex groups
Embryo has only ectoderm and endoderm
Called “diploblastic”
Usually have radial symmetry
Include Cnidaria (corals, sea anemones,
jellyfish) and Ctenophora
Three-layer embryos—have mesoderm
• Called “triploblastic”
• Formation of coelom
(body cavity)
– Acoelomate (no body
cavity)
– Pseudocoelomate
(body cavity between
endoderm &
mesoderm)
– Coelomate (body
cavity surrounded by
mesoderm)
Two ways for coelom to form in embryo
Schizocoely in
Protostomes–
mesodermal cells
fill the blastocoel,
forming a solid
band of tissue
around the gut,
then a space
opens inside the
mesodermal
band.
Enterocoely –
portions of the gut
lining form
pockets that pinch
off and form a ring
of mesoderm.
Protostomes
(mouth first)
versus
Deuterostomes
(anus first)
What’s in the fossil record?
The Cambrian Explosion
http://palaeo.gly.bris.ac.uk/Palaeofiles/Cambrian/Index.html
Symmetry
• Radial symmetry
applies when more than
two planes passing
through the longitudinal
axis can divide the
organism into mirror
image halves.
– Jellyfish
• Biradial symmetry –
two planes will divide the
organism.
– Comb jellies
Radiata
• The Cnidarians (jellyfish,
corals & sea anemones)
and Ctenophores (comb
jellies), the radial or
biradial animals,
comprise the Radiata.
– No front/back
– Weak swimmers
– Can interact with
environment in all
directions.
Symmetry
• Bilateral symmetry
is found in organisms
where one plane can
pass through the
organism dividing it
into right and left
halves.
– Better for directional
movement.
– Monophyletic group
called Bilateria.
Cephalization
• Bilateral symmetry is associated with
cephalization, differentiation of a head.
– Nervous tissue, sense organs, and often the
mouth are located in the head.
– Advantages for organisms moving head first –
directional movement.
– Elongation along anteroposterior axis.
Tissue Structure and Function
• A tissue is a group of
similar cells specialized for
performing a common
function.
• Different types of tissues
have different structures
that are suited to their
functions.
• Tissues are classified into
four main categories:
–
–
–
–
Epithelial
Connective
Muscle
Nervous
Epithelial Tissue
• Epithelial tissue
covers the outside of
the body and lines
organs and cavities
within the body.
Connective Tissue
• Connective tissue functions
mainly to bind and support other
tissues.
– Contains sparsely packed cells
scattered throughout an extracellular
matrix.
Muscle Tissue
• Muscle tissue is composed of long cells called
muscle fibers capable of contracting in
response to nerve signals.
– Smooth
– Skeletal
– Cardiac
Nervous Tissue
• Nervous tissue senses
stimuli and transmits
signals throughout the
animal.
• A neuron (nerve cell)
receive signals at the
dendrites and send
them out via the axons.