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VERTEBRATE ZOOLOGY
(VZ Lecture03 – Spring 2012 Althoff - reference PJH Chapters 1,2 & 7)
DIVERSITY,
CLASSIFICATION &
EVOLUTION
PART III
Two Embryonic Features that may
account for difference between
vertebrates and other chordates
In vertebrates:
development of tissue
called ______________. Forms many new
structures found only in vertebrates
Duplication of the ______________________
1
_______________ “migrating” to branchial arches
chicken embryo
I – migrates to
form mandible
II—migrates to
form hyoid
apparatus
III & IV—migrate
to form
outflow tract
of heart
1
Neural Crest Cells
• Originally thought that neural crest was
derived from ectoderm germ layer
• Recently (Hall 2000) proposed that neural
crest actually is a truly “independent germ
layer”—not part of ecto-, endo-, or
mesoderm. If true….
• Vertebrates are the only animals that have
__ germ layers making them ____________
• Helps explain significant advancement in
variety of structures in “true” vertebrates
2
Hox gene complex
• = Homeobox genes that characterize
animals
• Don’t code for specific features, but regulate
expression of the hierarchy of other genes
that control the shape of the body
• Jellyfishes – 1 or 2 Hox genes
Echinoderms & Nonvertebrate Chordates
—7 up to 13
vs. Vertebrates which have undergone
___________ of entire Hox complex
Hox gene complex…con’t
• So, what is the minimum number of Hox
genes in vertebrates? Likely ____
• Mammals appear to have ____ such genes
• Bottomline: “More complex animals usually
have a greater amount of genetic
material…and it is thought that the ________
of this gene sequence at the _______ of
vertebrate evolution made possible the
evolution of a more complex type of animal”
Pough, Janis, & Heiser 2005
Early History & Vertebrate Evolution
• Vertebrates first appeared in the early
Paleozic, about 540 MYA….earth at the
time was mostly water covered, extensive
continental movements, and an O2 rich
atmosphere formed as a result of
________________________ of autotrophs
• Movement of land masses and climatic
differences/changes resulted in major
evolutionary effects on vertebrates.
WHY?
Early History: PALEOZOIC
• Vertebrates first appeared in the early Paleozoic,
about ~________….earth at the time was mostly
water covered, extensive continental movements,
and an O2 rich (in relative terms) atmosphere.
• 490 MYA  443 MYA many shallow seas
appeared, allowed for major radiation among
marine animals, followed by first appearance of
primitive vertebrates—primarily _____________,
followed by _______________
Early History: PALEOZOIC…con’t
• 443  417 MYA vascular plants and arthropods
just starting to appear, Jawless fishes continued
to radiate and jawed fishes (including sharklike
forms) appeared
• 417  354 MYA major freshwater basins
appeared with first tetrapods. End of this period
marked by disappearance of ________________
____________ (ostracoderms)
• 354  290 MYA major glaciation. First
appearance of ___________ and modern types of
jawless fishes. Extensive radiation of nonamniote tetrapods. First __________ appeared.
Early History: PALEOZOIC…con’t
• 290  251 MYA Single continent (Pangea) formed
near end of this period.
-largest non-amniote tetrapods declined
-amniotes radiated
modern reptiles
mammal-like reptiles
first known ___________ tetrapods
• Largest known ______________ event occurred at
end of period—impacting both land and sea fauna:
THE END OF THE PALEOZOIC
MESOZOIC
• 251  206 MYA Single continent high, few shallow
seas, no evidence of glaciation
mammal-like reptiles declined
archosaurian reptiles (including dinosaur
ancestors) diversified
all large nonamniote tetrapods now aquatic forms
true mammals appear
dinosaurs, pterousaurs, marine reptiles,
crocodiles, lepidosaurs, frog-like
amphibians, and teleost fishes appear
• 206  144 MYA Continent breakup. Modern sharks
and rays appear.
_________________________________
PALEOZOIC (late Carboniferous Period)
3
4
2
1
5
Aquatic
nonamniote
tetrapods
Fig. 7-5 p165 PJH
Terrestrial
nonamniote
tetrapods