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The Eternal Question: Lips or Skin?



Did dinosaurs have lips?

  Mike Hanson seems to adamantly state that they do, for one reason,
apparently: maxillary and dentary mental foramina. These are
extensive in other reptiles (those that hd legs, anyway), but this
issue of lips in lizards is not the same as for mammals. In mammals,
there is a set of facial and oral muscles, that are not involved in
the mental foramina. The nerves that exit the foramina (the maxillary
branch of the maxillopharyngeal nerve) are strictly involved with the
gums. Reptiles have extensive gums, mind, and lizards lack lips in
the mammalian sense. In this way, they resemble other reptiles in
having a tendonous band of tissue that wraps around the oral margin,
with some very few muscles attaching to the margins ... the they are
there to hide the teeth only. They are not conventional "lips" sensu
Mammalia.

  Dan Varner indicates crocodile skulls ... he's right to do so.
Crocodylians have extensively foraminated jaws, but lack even the
flesh that covers the teeth, just the tendonous oral tissue as in
other reptiles. The foramina serve to provide sensory ability
(extensive as it is, very good sense of touch in the snout) and do
not indicate lips.

  Tracy Ford has adamently advocated the lack of lips, for good
reason, based on the strict osseous evidence and comparative biology.
It should be clear the issue is not a fine line of what one feature
indicates lips or not. Thus, we are left with Tracy's many lines of
evidence, and the Extant Phylogenetic Bracket (sensu Witmer, 1993,
1995, 2001).

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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