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Re: Therizinosauroids (was Re: Giant Birds)
>...and a radius over 90% of metatarsal length**.>
Jaime Headden wrote-
> I see no functional reason to include this in an
>analysis of bipeds when the only possible
>radius/metatarsal correllation I can percieve would be
>among quadrupedal animals. Shortening of the forelimb
>or lengthening thereof is probably quite variable
>among all sorts of taxa, not just dinosaurs. A
>possible correllation might be nonhumans [definition:
>all apes excluding *Homo* (specifically, *H. sapiens
>(sapiens)*) -- good use of a paraphyletic term] where
>the lengthening of the arm compares well with
>shortening of the leg, in relation to increased use of
>the former and lack of complete use of the latter,
>thus elongate forelimb elements is related to
>shortened hindlimb elements. But these animals in
>question are not such taxa to need the use of their
>forelimbs to hang from trees and not use the legs.
This character was included because Xu et al. (1999) use "ulna longer than
metatarsal III" (their # 104) to group dromaeosaurids and birds to the
exclusion of troodontids. In my analysis, troodontids are closer to birds
and I wanted to see if this added character (among others) affected this
After examining radius/metatarsal ratios (I used radii instead of ulnae
because a hypertrophied olecranon could throw the results off) in every
coelurosaur I could, I adjusted it to "radius at least 90% of metatarsus"
because the "Velociraptor" sp. (= Saurornitholestes?) from the Two Medicine
Formation has a radius slightly shorter (~97%) than it's third metatarsal.
Therizinosauroids and Oviraptor just also happen to have this synapomorphy,
and my analysis coded them thus.
As for the functional reason to include the character, it may be very close
to your primate example. Avians obviously elongated the arm (and forearm in
particular) to aid in flight, while their hindlimbs were less important for
running, so they shortened the metatarsus (possibly to aid in perching).
Comparing these two trends to each other in one character (as opposed to a
radius/humerus or metatarsus/femur ratio for example) makes the shift from
running to flying more obvious. Perhaps non-avian ancestors to birds would
show the beginnings of this discrepansy and thereby help prove their avian
relations. Or alternatively, the presence of this discrepancy in droms,
ovis and therizs could help prove secondary flightlessness, wherin the
character was kept after it wasn't needed. Then again, maybe it isn't
correlated at all. Droms could have elongated their arms for grasping and
shortened their metatarsus because of some requirement for sickle-claw
slashing. Therizs could just have done it all to be quadrupedal. Oviraptor
could also have elongated it's arms to grasp and shortened it's feet for
who-knows-what-reason. Maybe it proves relationships to therizs, maybe no
other oviraptorid has the proper ratio and it's parallel evolution. Unless
the character is used in an analysis so that it can be mapped on the
resulting phylogeny, we won't know which answer is more plausible. The
point is, there are at least some evolutionary possibilities for this
character that would be applicable to maniraptorans and it has as much place
in an analysis as any other character.
Thanks for the criticism, it made me think about the reasoning behind this
character when I hadn't before.