Monday, May 3, 2010

Bird and Pterosaur Wing - Continued (2)

Let's take a look at the pterosaur pteroid bone.

Here we see the pteroid bone which is the thumb but here it is not numbered "one" as it should be. This is because the current (incorrect) opinion is that it is not a thumb. When it is correctly identified as the thumb , then the picture is simple and complete. The five fingers (including the thumb as number one) are present in the pterosaur wing. And the little finger (the pinky finger) is the fifth finger (not the fourth).

For more info on the pteroid bone check here:

"The pteroid bone is a rod-like element found only in pterosaurs, the flying reptiles of the Mesozoic. It articulated at the wrist, and supported a membranous forewing in front of the inner part of the wing spar. The function of this bone, particularly its orientation, has been much debated. It is widely believed that it pointed towards the body, and that the forewing was relatively narrow. An alternative hypothesis states that it was directed forwards during flight, resulting in a much broader forewing that acted as a leading edge flap. We tested scale models in a wind tunnel to determine the aerodynamic consequences of these conflicting hypotheses, and found that performance is greatly improved if the pteroid is directed forwards: the lift drag ratios are superior and the maximum lift is exceptionally high in comparison with conventional aerofoils. This high lift capability may have enabled even the largest pterosaurs to take off and land without difficulty."
"The interpretation by Goldfuss (1831) of the pteroid as the first digit, or thumb, and thus the wing-finger as the fifth digit, sparked off a protracted debate"
"The nature of the pteroid, a rod-like bone projecting from the carpus in pterosaurs, has long been disputed. Three lines of evidence, morphological, developmental and histological, indicate that the pteroid is a true bone, rather than ossified cartilage. The origin of the pteroid is unclear: it may be a modified carpal, the first metacarpal, or a neomorph. " [Or a thumb].
"A  recent  article  by Wilkinson  and  colleagues  (2006)  on  the
function  of the  pteroid bone  of pterosaurs started with a statement  that  the pteroid has
long been  controversial. Perhaps, but there  have been  two separate controversies widely
separated in time. The  first controversy was but  a part  of the  larger  controversy about  the
homology  of pterosaurian fingers. Cuvier (1821– 1824)  interpreted the  manus  as  consisting  of  the  small  Digits I–III  plus the hyperelongate Digit  IV that  supported the  wing, whereas  Goldfuss  (1831) suggested  that  the pteroid represented a vestigial  Digit  I, the small fingers Digits  II–V, and the wing-finger Digit V.
Although Owen  (1869) sided with Cuvier,  most authors (Wagner,  1837; Fraas,
1878; Marsh,  1882; Zittel,  1882; Williston, 1903) sided with Goldfuss, until Williston (1904,
1911) and  Plieninger  (1906) presented convincing  arguments that  the phalangeal formula  of
pterosaurs, 2-3-4-4-x, is essentially  un-changed  from their  non-volant ancestors  except  for
the possible loss of an ungual on the wingfinger. That view has been accepted by almost  all
authors ever since (e.g., Romer,  1956; Kuhn, 1967; Wellnhofer, 1978, 1991a), although Unwin and 
colleagues  (1996) resurrected the  Goldfussian view as a viable  alternative to the
Cuvierian without  actually  supporting it."

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