A Brief History of Animals

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• A Brief History of Animals
• Origin of animals
• Animal phylogeny
• Comparative anatomy

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Edicarian fauna Early (570mya) Hard to
place -bilateral ancestor? -radial? -no
descendants?
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Origin? 540mya? Earlier, in Ediacarian Organisms
? Earlier, in Larval organisms? Wray paper
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Gondwana finally settled on the South Pole during
the Late Ordovician, massive glaciers formed
causing shallow seas to drain and sea levels to
drop, which likely caused the mass extinctions
60 of all marine invertebrate genera and 25 of
all families went extinct
- Permian Period (286-248 million years ago)-
Terrestrial faunal diversification occurred in
the Permian- 90-95 of marine species became
extinct in the Permian
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The tape of life would play differently Each time
it is rewound
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Animal relationships Phylogeny tree
showing Ancestry/descendent Relationships
among Organisms Morphological based
on comparisons of morphology Molecular based on
com- parisons of DNA sequences
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The major distinctions between deuterostomes and
protostomes are found in embryonic development.
In protostome development, the first opening in
development, the blastopore, becomes the animal's
mouth. In deuterostome development, the
blastopore becomes the animal's anus.
Protostomes have what is known as spiral
cleavage which is determinate, this meaning that
the fate of the cells is determined as they are
formed. T This is in contrast to deuterostomes
which have radial cleavage that is indeterminate.
Blastopore opening into the archenteron
during the embryonic stages of an organism
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Reconstructing phylogenies morphological Charact
ers and molecular characters.
SPECIES 1 AATATTAACG SPECIES 2
AATTTTAACG SPECIES 3 TATATAAAGG Spp. 1 AND 2
90 Spp. 1 AND 3 70 Spp. 2 AND 3 60 Group
closest in a clade (group of Organisms that
share a common Ancestor). Add next closest spp.
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Trochophore larvae two bands of cilia around the
middle that are used for swimming and for
gathering food, and at the "top" is a cluster of
longer flagellae
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Organisms are somewhat Modular in their
construction, They are made up of
semi- Independent parts. Modular systems can
be defined as systems made up of structurally
and/or functionally distinct parts -modules.
While non-modular systems are internally
homogeneous, modular systems are segmented into
modules, i.e., portions of a system having a
structure and/or function different from the
structure or function of other portions of the
system.
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Theme in Animal evolution Duplication
(and Often Divergence) of Modular entities And
of genes
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Homology/Homologs Structures in different
animals that share a common ancestor, under
every variety of form and Function Question
are similarities in Form due to sharing a Common
ancestor or due To convergence (independent Evolut
ion) Novelty new characters Evolving from a
pre-existing Character so different (gills
evolving into wings) that It can no longer be
considered Homologous.
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How do different cells acquire their unique
morphologies and functions required Of different
organs and tissues of the body? Through the
selective expression of distinct subsets of the
many thousands of Genes in an animals genome.
How genes are turned on and off in
different Cells over the course of animal
development is an exquisitely orchestrated
Regulatory program whose features are only now
coming into detailed view If morphological
diversity is all about development, and
development results From genetic regulatory
programs, then is the evolution of diversity
directly Related to the evolution of genetic
regulatory programs? Simply put, yes.
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From Egg to A/P axis formation to segment
identities
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Activators and Repressors act In a
tissue-specific Manner, resulting In the
expression Of genes That create
the Morphologies And functions of Different
tissues.
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Q Why is the activator protein only expressed in
the eye? A It is regulated by an eye-specific
enhancer. This is circular...where does it
start? The Egg.