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

Re: Microraptor hanqingi, new species from China.


Good points. At least we see some things eye to eye ;-)

My whole thesis boils down to this:

"If it didn't have [insert arboreal character of choice], it wasn't
arboreal,"... but how does selection work for [insert arboreal
character of choice] if they weren't up in the trees enough to make it
a selective situation?

Let's pick on everyone's favorite, perching... Of course they were up
in the trees a great deal before perching was developed to
'standards', and using a manus to assist in climbing, along with a
modified second toe, are parts of a sound hypothesis dealing with how
this most likely played out.

Character acquisition... (A) Climbing with front and back limbs to (B)
better balance develops along with increased perching abilities due to
variations and selection, allowing for the manus, at the same time, to
decrease its ability to grasp (including using the claws on the
hands). Then and only then is perching fully developed, and only after
the animal had been arboreal for quite a while. Like I've said before,
a whale doesn't evolve flippers, and THEN jump into the ocean… It
starts out with getting its feet wet (as in non-flipper feet), then
flippers are selected for in the new environment. ;-)

This is a perfectly workable hypothesis, and I believe it takes
gold-medal mental gymnastic of someone firmly set in his ways to argue
that this hypothesis is any less likely.

Good discussion...



On Fri, May 25, 2012 at 3:05 AM, Tim Williams <tijawi@gmail.com> wrote:
> K Kripchak <saurierlagen1978@gmail.com> wrote:
>> "True" arboreality... If we are leaning toward the notion that "true"
>> arboreality arose with the perching pes, no discussion necessary. It's
>> what I see as those "pseudo"- arboreal or "near" arboreal critters
>> that came before (and were often still around)...
> Archaeopterygids, jeholornithids and many small deinonychosaurs might
> indeed qualify as incipiently arboreal.  _Jeholornis_ was found with
> seeds in its stomach.  Maybe it scaled trunks to get to the seeds far
> from the ground, then glided back down.
>> Alright... Microraptorans are considered to have been gliders.
>> Confuciusnornithids are considered to have been gliders.
>> Confuciusornithids are considered to have been "true" arboreal because
>> they had a foot morphology that enabled a degree of perching.
>> Therefore, Confuciusornithids... gliders... were climbers (had to get
>> "up" there somehow) and were "true" arboreal since they had perching
>> feet.  Microraptorans... gliders... *may* have been climbers... and
>> they couldn't have been arboreal to any degree since the characters
>> (pleural) they did possess are ambiguous and they lacked the foot
>> morphology to enable perching?
> Something along those lines, yes.  But their lack of arboreality in
> these theropods is not just due to the pedal morphology.  Their
> overall morphology (limb proportions, degree of motion at the joints)
> is inconsistent with arboreal behavior.  Spider monkey, my foot.
>> It's hard not to interpret the perching foot as being the linchpin for
>> arboreality when it is repeatedly referred too during most discussion.
>> Sure, they weren't *perfect* hands, or feet, or ungul geometry, or
>> limb/digit length ratios, or whatever for grasping branches... But why
>> expect animals in transition to have the perfect anything or fully
>> functioning whatevers for behaviors or niches they were in the process
>> of adapting to/being selected for to exploit?
> I agree.  Arboreal behavior had to start somewhere.  But IMHO it's
> significant that the overall proportions of _Archaeopteryx_,
> _Microraptor_ etc are those of a bipedal, cursorial theropod.  They
> all had a long neck, a long tail (although generally shorter than the
> ancestral condition), and long legs for terrestrial locomotion.
> This brings me to the petrel example.  Certain petrels can and do
> roost in trees, in spite of the reduced or absent hallux.  The webbed
> feet are capable of gripping branches.   My guess is that the anterior
> digits toes wrap over the branch.  Cormorants do the same thing, with
> rocks and branches.
> But petrels, as typical for procellariform birds, have bodies built
> for flight and life at sea.  They have short necks, short tails and
> short legs.  All neornitheans have the benefit of being descended from
> an arboreal, perching bird.  Comparing these advanced birds with
> _Archaeopteryx_, _Microraptor_ etc is inappropriate, given just how
> different the bauplans are.  It's just as bad as using the juvenile
> hoatzin as an analog for tree-climbing behavior in _Archaeopteryx_.
> Tinamous are known to roost in trees, in spite of the reduced or
> absent hallux.  They don't really perch, and use their tarsi to help
> them "sit".  But again, although terrestrial, the bauplan is that of
> an advanced modern avian.
>> My approach is not opinion-based. My approach is (1) questioning our
>> artificial constructs of (a) and (b) based on a different
>> interpretation of the available evidence and (2) investigating the
>> reasoning behind theories built upon said evidence and constructs.
> No, I didn't intend to direct the "opinion-based" barb at you.  I was
> thinking more of the recent _Microraptor_-as-a-colugo-like-glider
> paper, and similar publications.
>> No, no... I understood what you meant by ambiguous.   "Who or whom"
>> was insinuating that to us, the characters/traits are ambiguous, but
>> if the animal put itself up in a tree, they were anything but.
> If an animal habitually spent its time in trees, then the characters
> wouldn't be ambiguous.
>> Just like everyone else who lays awake critically thinking about this
>> stuff, I'm drawing my own set of conclusions based on our current
>> understandings... not just pulling them out of wishes and desires for
>> coolness. Although arboreal microraptorans are rather cool :-)
> Cool: agreed!  But if we're going to put microraptorans in trees, it
> has to be for the right reasons.
> Cheers
> Tim