[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Fwd: Fingers and Thumbs (and toes)

Sorry, new computer, new software, new preferences. It's now plain text.

Begin forwarded message:

From: David Peters <davidrpeters@charter.net>
Date: June 24, 2009 7:40:03 AM CDT
To: dinosaur@usc.edu
Cc: david.marjanovic@gmx.at
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 and p5.3.

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.

David Peters
after 06-06-09