Tiktaalik Fills Another Gap

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Tiktaalik Fills Another Gap
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Searching for Transitionals

• Estuary or tidal flat
• Warm, equatorial climate
• Late Devonian era, around 370 million years ago
• Presently exposed for exploration
• Incorporating knowledge from ecology, geology,
  and paleogeography, a site was chosen

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Transitional Characteristics

• Skull shape
• Mobile neck
• Functional wrists
• Fins with digit-like bones
• Muscled limbs and pectoral girdle
• Development of the ear

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Skull Shape
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Neck Mobility

• Devonian fish have bony gill covers that prevent
  extensive movement immediately behind the head.
• All tetrapods lack a bony gill cover. Amphibians
  have gills but no bony cover.
• Tiktaalik has gills but a reduced bony cover,
  which allows for movement of the neck.

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Functional Wrists
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Digit-like Bones
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Muscled Limbs Pectoral Girdle

• While Devonian fishes have relatively weak fins
  merely for swimming, Tiktaaliks limbs were more
  muscled
• Tiktaalik also had a pectoral girdle that
  supported its forelimbs
• This means that Tiktaalik was capable of lifting
  its own weight out of the water to breathe air

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Muscled Limbs Pectoral Girdle
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Development of the Ear

• Changes in the bony gill cover allow a gill slit
  called a spiracle to be further exapted into a
  component of the ear in later species.
• Though the exaptation of existing characteristics
  to form the ear is well known, especially in the
  amphibian-to-mammal transition, this is yet
  another example of evolutions powerful
  creativity.

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Richard Crowson--The Wichita Eagle
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Intermediate Characteristics

• Neil Shubin, research project leader and Nature
  article author, realizing that the multiple
  intermediate characteristics of Tiktaalik
  demonstrate the transition from fish to tetrapod
  (tetra- meaning four, pod meaning foot) ,
  dubbed the species a
• fishapod.

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Intermediate Characteristics

• Fish
• Gills
• Scales
• Fishapod
• Half-fish, half-tetrapod limb bones and joints
• Half-fish, half-tetrapod ear region
• Tetrapod
• Rib bones
• Mobile Neck
• Lungs

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Creationist Responses

• Ken Ham states in his blog
• I only saw the article briefly tonight, and, of
  course, none of us have seen a detailed analysis
  of what has been foundso until we do that, we
  obviously cant make any detailed comments on
  this particular find.
• http//blogs.answersingenesis.org/aroundtheworld/?
  p696

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Creationist Responses

• Why is Ham not aware that there were two
  Tiktaalik articles published?
• Why does Ham not have access to the information
  in Nature?
• Also, where does he think hell ever find a
  creationist palaeontologist?

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Creationist Responses

• Robert Crowther of Discovery Institutes
  evolutionnews.org writes
• These fish are not neccesarily sic
  intermediates, explain Discovery Institute
  scientists I queried about the find. Tiktaalik
  roseae sic is one of a set of lobe-finned
  fishes that include very curious mosaics--these
  fishes have advanced fully formed characteristics
  of several different groups. They are not
  intermediates in the sense that have
  half-fish/half-tetrapod characteristics. Rather,
  they have a combination of tetrapod-like features
  and fish-like features. Paleontologists refer to
  such organisms as mosaics rather than
  intermediates.
• What is clear is that forms like Tiktaalik sic
  are a melange sic of primitive and more
  developed features. It is not clear whether they
  are true transitional forms.
• http//www.evolutionnews.org/2006/04/latest_fossil
  _find_no_threat_t.html

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Creationist Responses

• alienward on IIDB.org wrote in response
• In One Look dictionary search the quick
  definition for mélange is a motley assortment of
  things. So, were finally starting to see ID
  proponents describe how the intelligent designers
  come up with new designs. Intelligent designers
  hack together motley assortments of primitive and
  more developed features. Ummm
• Super Squirrel on IIDB.org paraphrased
• Discovery Institute They're not transitional
  forms! They are just organisms that share
  characteristics from organisms that came before
  and after them!
• Me ... Smacks forehead How is that not
  transitional?

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