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Fwd: Fingers and Thumbs (and toes)
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Begin forwarded message:
From: David Peters <email@example.com>
Date: June 24, 2009 7:40:03 AM CDT
Subject: Re: Fingers and Thumbs (and toes)
David M. wrote:
<<< Shrinking of the entire digit and loss of phalanges often seems
to happen at the same time. And from what little we know about
temnospondyls, lepospondyls and lissamphibians, the 5th digit (of
both hand and foot) can disappear at once, though this might be due
to the incomplete fossil record.
However, phalanx counts are remarkably constant throughout limbed
vertebrates. Phalanges don't appear to be easy to lose>>>
In pre-pterosaurs manual digit V appears to shrink to nothingness
without losing phalanges. In nyctosaurs a wing phalanx is lost via
fusion of m4.2+m4.3. Pedal digit V loses a phalanx by fusion of p5.2
In therapsids, as everyone knows, m3.2, m4.2 and m4.3 shrink to
discs, then disappear. In pteros the same phalanges don't disappear,
but do re-elongate in certain taxa, all the bigger beachcombers.
Parallel interphalangeal lines are retained in all tetrapod
extremities, even as certain digits become vestiges and phalanges
are reduced and lost, or for that matter, extras are added.