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


>The semilunate carpal is a winglike characteristic of dromaeosaurid
>forelimbs. Remember that the wings of _Archaeopteryx_ retained a good
>grasping function; the digits were all separate and movable (although there
>may have been ligamentous locking mechanisms that kept them extended straight
>when the wings were being flapped). So a flightless descendant of
>_Archaeopteryx_ or a similar dino-bird would likely have retained the
>grasping function, too.

OR: the semilunate carpal is a feature of dromaeosaurid forelimbs retained
in Archaeopteryx that proved to be important in the evolution of the avian
wing, though it did not serve that function originally.

Now: how do you tell these views apart?  How do you test them, other than
finding more fossils?

>The main problem I've always had with the BADD/ground-up scenario is getting
>a 20-50 kg theropod with relatively small forelimbs to evolve into a 2-5 kg
>dino-bird with grasping wings. It _could_ happen, but in my opinion it is
>_far_ less likely than having a 2-5 kg dino-bird with grasping wings to
>evolve into a 20-50 kg theropod.

I may be ignorant here but I have never heard anyone claim that the
ancestors of birds weighed 20-50 kg - only that LATER non-avian maniraptors
did.  Why couldn't both lines - the avian and non-avian - have evolved from
a smallish ancestor?

Also - though it is perhaps more common for size to increase with time there
is no rule that it need do so, and dwarfism can evolve relatively rapidly
(eg the pint-sized insular elephants and mammoths known from various
islands).  Also close relatives can vary considerably in size, so an
ancestral line could have closely related large and small forms.  Consider,
for example, the bird family Phasianidae, whose members range in size from
Coturnix chinensis (12-15 cm in length) to things like Pavo muticus at
190-250 cm (without the train); the size range in hawks is even greater,
from the male Tiny Hawk (75 g) to the female Harpy Eagle (7600-9000 g).
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
International Wildlife Coalition              Fax/Modem: (905) 569-0116 (home)
Home: 1825 Shady Creek Court                  Messages: (416) 368-4661
Mississauga, Ontario, Canada L5L 3W2          Internet: ornstn@inforamp.net
Office: 130 Adelaide Street W., Suite 1940    
Toronto, Ontario Canada M5H 3P5