By Megan Beaton,
Laura Buennemeyer,
and Catherine Romano
Maiacetus inuus- 49-40 million years
ago
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Exploring the
evolution of hind
limbs to a vestigial
structure
Exploring the
evolution of
the inner ear
Dorudon atrox- 41-33 million years ago
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Vestigial Structure- homologous characters in an
organism that has lost all or most of their original
function
Vertigo- extreme dizziness, which can be caused by the
ear
Myosin- motor proteins found in eukaryotic tissues that
are responsible for motility
Myoblasts- a type of stem cell that exists in muscles
Somitic myoblasts- causes the stem cells that develop in
vertebrates to migrate
Cetacean- mammals adapted to aquatic life, including
whales, dolphins, and porpoises
Echolocation- the ability to sense objects in the
environments by hearing echoes from those objects
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Approximately 50 million years ago, the ancestors of modern day
whales were four legged terrestrial mammals about the size of a
raccoon
Thick bone density made it easier escape predators in the water
The inner ear adapted to allow the whales to move quickly under
water and avoid vertigo
Zygorhiza kochii
Late Eocene (39-37)
million years ago
On land- 50 million years ago (Packistis)
Aquatic- 34 million years ago (Dorudon)
Total evolutionary process- approximately 15 million years total
Hind limbs- started 41 million years ago; finished 34 million years ago
(Gaviocetus)
Inner ear- started 47 million years ago (Dalanistes)
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In the 5th week of gestation, the genes responsible
for hind limb development are no longer expressed
Initial limb outgrowth requires…
Apical ectodermal ridge (AER)- signaling center
for the hind limb bud regulated by Fgf8 protein
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Distal margin of limb bud
Zone of polarizing activity (ZPA)- signaling center
that maintains initial limb outgrowth
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Posterior connective tissue
 Hand2 gene- a regulator of Sonic
Hedgehog (Shh) transcription and required
for cell survival
Hand2 is not expressed in the hind limb
developing embryo after the 5th week of
development
Shh- mediates the signaling activity of
ZPA
Fgf8- protein that is coupled with
AER and is not detectable or
functional in the hind limb
development
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Muscles are formed when myosin evades limb buds
Myogenetic cells attracted to limb bud by signals
sent out by the AER and ZPA
Hind limb bud induces somitic myoblasts to migrate
Myogenic cells are found in both the fore limbs and
hind limbs
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The inner ear canal of whales is 3 times smaller than
that of the human ear
The evolution of the inner ear was a key point of no
return
Today, with the size of their ear canal, a terrestrial
whale would only be able to crawl at a slow pace
The ear is extremely specialized for the aquatic
lifestyle
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Examine the relationship between size of hind limbs
and whale length
Explore differences with balance, feeding techniques,
swimming depth, life span, speed, and location in the
ocean.
Study carried out by examination of different whales
and different pods of whales
Examine other species with similar vestigial
structures, and see if the evolutionary paths are
similar
http://www.youtube.com/watch?v=8cn0kf8mhS4&feature=related