[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Feather Flap
Scott Hartman wrote:
Right...but colugos and draco have other specializations for living in
trees, such as limbs that can be laterally splayed, (realitively) shorter
manus and pes (for better leverage while climbing), highly flexible ankle
and wrist joints, and flexible backs.
But colugos and dracos evolved within lineages that were already specialized
for arboreality. In these groups gliding evolved as a means of commuting
from tree to tree. The same is true for most gliding tetrapods, including
gliding marsupials and rodents. I'm not sure this holds for the first
gliding theropods, who may have evolved gliding ability as means of getting
from trees to the ground. In this case, it would make sense to retain a
morphology that was suited for terrestrial bipedal locomotion. Of course,
this scenario is a "just-so" story, and not evidence - but I don't see any
reason to assume that you have to be specialized for arboreality in order to
be an effective glider.
And their gliding surface is confluent with the abdomen, like essentailly
any other gliding arboreal organism. Winged dinosaurs lack all of these,
including the fact that the phylogenetically earliest wings appear distally
on the limbs, and are not confluent with the abdominal airfoil...exactly
the opposite of arboreal gliding animals.
This is not true for all arboreal gliders. Some gliding amphibians have
flaps on the distal limbs, such as "flying frogs" (_Rhacophorus_ spp.) which
have huge webbed feet for gliding. The "flying geckoes" (_Ptychozoon_ spp.)
have gliding surfaces on the abdomen and feet that are not confluent.
Having said that, there is the argument that the reason why _Archaeopteryx_
and _Caudipteryx_ lack an "inner wing" is a preservation artefact. The
argument runs that these festhers are less likely to be preserved with the
skeleton because the attachment is not as strong, given that these proximal
feathers have a lesser role in thrust-generation.
Again, it's not that Archaeopteryx could not have gotten in a tree...it's
that it shows no specializations for doing so relative to its closest
Nevertheless, certain maniraptorans do show some traits that might be
associated with arboreality - or at least scansoriality. There's small body
size, for one (yeah, I know this one's a stretch). There's possible
scansorial/arboreal traits in the manus and pes, including (for example) an
enlarged hallux that has shifted distally on the foot compared to other
theropods. Still not a reversed hallux, just a longer and lower one.
Play games, earn tickets, get cool prizes. Play now?it's FREE!