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Re: Ah ha! That's where therizinosaurs came from



The biggest problem with GSP's "neoflightless" hypothesis is this:  It
proposes that tree-dwelling theropods had plenty of time to evolve an
extensive list of "flight-related" characters (advanced
scapula-coracoid morphology; foldable forelimbs; shorter and distally
stiffened tails; large contour feathers on the limbs and tail; etc).
But over this same time, these tree-dwelling theropods didn't get
around to evolving any arboreal characters.  I find this perplexing.


For example, maniraptoran theropods had time enough to evolve a
complex arm-folding mechanism, but not a reversed hallux.  The limbs
and tail sprouted enormous wings - but metatarsal I barely shifted its
position on the metatarsus.



Nah, I think exaptation can readily explain the appearance of most
flight-related characters.  We don't require therizinosaurs,
oviraptorosaurs, or deinonychosaurs to be "neoflightless".
Nevertheless, I do accept that certain maniraptorans were engaged in
arboreal and/or aerial behavior(s) long before powered flight kicked
off.





Cheers

Tim



On Mon, Aug 15, 2011 at 11:27 AM,  <GSP1954@aol.com> wrote:
> Hey, glad to see that my post get a nifty discussion going. There has been
> so much stuff I can't address it all, but here's a shot.
>
> Jason I think suggested I might place all the archaeopterygians and sickle
> claws in a single family sort of like in PDW, but I tend to currently go for
> Deinonychosauria including Archaeopterygidae (Archaeopteryx, Anchiornis,
> Xiaotingia), Dromaeosauridae, Troodontidae. Of those the first and last are
> internally currently not very diverse, but dromaeosaurs are all over the place
> with little winged and probably arboreal microraptors, some very large
> runners, and long snouted unenlaginines.
>
> It is possible that loses of flight were relatively rare, with a single
> loss leading to all dromaeosaurs and troodonts, another loss to all
> therizinosaurs, and another to all oviraptorosaurs. That's the most 
> parsimonious
> scenario within the grand neoflightless hypothesis. But evolution is not
> particularly parsimonious. In fact it tends towards the intricate and bushy 
> because
> there is not intelligent goal behind it. The loss of flight in early fliers
> may have been as easy as pie, and multiple losses lead to assorted
> dromaeosaurs and troodonts. For example perhaps dromaeosaurines, 
> velociraptorines and
> unenlagines each descended independently from fliers. It is notable that
> unenlagines include the flier Rahonavis. Perhaps different velociraptorines
> descended from fliers. The presence of very long tailed and shorter tailed
> therizinosaurs may indicate separate descents from different stages of tail
> abbreviation in fliers. It's possible that flight evolved, was lost again,
> reevolved, was lost again. The data is far too poor to test the alterantives 
> and
> is likely to never be sufficient to have more than a poor approximation of
> what went down.
>
> The rather poor success of Cenozoic continental flightless birds is not
> applicable to the  Mesozoic neoflightless protobird hypothesis because derived
> birds may have trouble being competitive without useful arms. And there all
> all the very large brained mammals ground birds have to contend with. Useful
> arms and hands should have given neoflightless protobirds a big advantage
> when competing against never volant dinosaurs with similar or lesser mental
> abilities.
>
> The potential link between jeholornids and therizinosaurs is much weaker
> than that between omnivoropterygids and oviraptorosaurs. The reason that
> jeholornids are interesting is because they show that long tailed herbivorous
> fliers were out and about, and were potential ancestors for neoflightless long
> tailed herbivores like basal therizinosaurs. Jeholornids make poor ancestors
> for therizinosaurs in part because they lacked tooth rows (which are
> unlikey to have reevolved although it cannot be ruled out).
>
> Nor could the omnivoropterygids we know and love be actual ancestors for
> oviraptorosaurs because the latter were already extant. At best there was a
> common ancestor whose morphology would be more transitional than the fossils
> we got. If those creatures existed hopefully they will show up in the earlier
> sediments present in NE China or elsewhere. One can hope -- and it
> basically worked for deinonychosaurs so its not a long shot.
>
> Someone said something about it not being possible to tell if a flightless
> tetrapod with flight related features is neoflightless or not. We know that
> all current flightless birds are neoflightless.
>
> Someone was saying that early boids could not elevate their arms above
> horizontal so they could only glide. As I showed oh so long ago in PDW and 
> later
> in DA even a number of flightless theropods could easily elevate the
> humerus well above horizontal because they had laterally facing scapcoracoid
> glenoids. I had no trouble manipulating casts of Coelophysis rhodesensis to 
> that
> effect (drawing in my books). All winged protobirds and basal birds could do
> the same. What they could not do was elevate the wings all the way to
> vertical as most derived birds can do (as per wing clapping pigeons) due to 
> more
> dorsally facing shoulder glenoids. This is likely to have limited the flight
> abilities of proto/basal birds especially in the climb, but would not have
> barred basic powered flight. As I have shown in detail in my publications
> all large winged proto/basal birds had far more arm musculature than was
> needed for mere gliding, which requires no more muscle power than nonaerial
> locomotion.
>
> And will not rediscuss my extensive discussion in the literature of why
> reversed halluxes are not critical for arboreality, why Archaeopteryx did have
> enough of reversable hallux for climbing (with pictures and everything), why
> forms in the process of becoming arboreal should not be expected to have a
> full suite of arboreal characters, yadda, yadda.
>
> Someone said I am inconsistent in rejecting cladograms that contradict the
> neoflightless hypothesis while accepting those that do. But this is
> illogical. Say the cladograms for years contradict the neoflightless 
> hypothesis and
> I pay them little mind because it is my conclusion that they are defecitve
> due to lack of sufficient fossil data and because the nonneoflightless
> hypothesis does not appear as logical. Say that as new fossils come online 
> some
> cladograms start supporting the neoflightless hypothesis. Am I supposed to
> automatically say that since cladistics is offering support for the
> neoflightless hypothesis I must now reject the latter? I do not think 
> cladistics is
> useless. My concern is that cladistics has become overly dominant to the point
> it prevents thinking outside the box of the cladistic results at any given
> time.
>
> Here's the thing. Are those who oppose my opposition to over reliance of
> cladistics really telling me I should be a cladist? Because if I had been so I
> would not have been able to propose the neoflightless hypothesis when Nancy
> was our 1st Lady, and only when winged microraptors were found in this
> centry would the hypothesis have been invented. Instead I got priority and the
> community was ready for the possiblity when winged dromaeosaurs turned up.
> Seriously, do you really think I should have toed the cladistic line all those
> years? And avoided the logical thinking that led to the hypothesis. Really?
> How would that work, please let me know.
>
> As for the noncladisitic testability of the neoflightless hypothesis I used
> to think alvarezsaurs were neoflightless. But as more fossils have come on
> line that theory is weak at best. In contrast the most basal flightless
> dromaeosaurs, troodonts, therizinosaurs and oviraptorosaurs have lots of 
> flight
> type features that favor their being secondarily flightless.
>
> All that is needed to falsify the grand neoflightless hypothesis is to find
> always terrestrial ancestoral types for therizinosaurs and oviraptorosaurs
> while comparably suitable flying relatives or ancestors remain absent. I of
> course don't think that will happen but you never can tell.
>
> My therizinosaur paper in JVP in 84 actually was a shot at something at
> cladistic analysis -- and look at where that got me. The reason therizinosaurs
> were such a phylogenetic problem was the absence of sufficient fossils. As
> more data became available they proved to be derived theropods after all. Had
> I known the basal forms had folding arms I never would have considered them
> nontheropods.
>
> GSPaul
>
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>