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

Re: pterosaurs, bats, flying theropods



Stephan Pickering (stefanpickering2002@yahoo.com) wrote:

<The intertwined histories (at least, in my mind) of theropods,
pterosaurs, and bats is yet to be untangled.>

  Of course it hasn't. We have a fossil record to deal with. However, some
points, and the main premise of my reply:

  Bats, pterosaurs, and birds do not overlap in the fossil all together,
relating no point where all three could interact; only birds + pterosaurs,
and birds + bats ever occur in the same area at the same time, never
pterosaurs + bats. Pterosaurs end at the K/T boundary. Birds appear to
have been limited to shorebird or aquatic varieties, being the basal
clades of birds that have been identified from Campano-Maastrichtian
Cretaceous to Danian Paleocene sediments. The Eocene occured well after
this initial _gasp_ in ecological terms and the diversity of birds was
well on its way. There were no Cretaceous bats that we can find, and this
means no enantiornithine + bat competition so far, essentially some of the
best avian fliers before Ornithurae (the oldest members of which being
able to fly well died out in the Campanian [Ichthyornithidae and
*Apsaravis*]).

<No doubt, as Greg Paul has suggested, the flying theropods drove
pterosaurs into extinction, and bats (who are NOT flying primates,>

  Like, who has suggested _this_? It's hogwash, I tell you, and what Greg
Paul actually wrote was (begging his pardon): "We can 'test' this via a
thought experiment ... So, while it is possible that small pterosaurs
would have disappeared without the influence of avian competition, the
proposition can be considered dubious, if not improbable."

  No where in the fossil record except for Solnhofen and Liaoning do
pterosaurs and birds exist in the same sediments where they are even close
to the same size, and for about 50 my, there does not appear to be a
decline in diversity in pterosaurs, but rather an increase in diversity in
both birds and pterosaurs. Paul suggested this was improbable, but the
data does not support contention drove small pterosaurs out, and this has
been discussed on the list extensively. For competition to occur,
similarly both groups must have specializations to the same diet, but this
also does not appear to be the case as the snout configurations and tooth
shapes in the various Solnhofen pterosaurs differ _very_ widely from that
of *Archaeopteryx* as well as in Liaoning, the wicked teeth of
*Dendrorhynchoides* are unmatched in similar-sized birds, which have
smaller, triangular snouts. These thought experiments say no competition
appears to have occured which would lead to such dwindling or extinction.
The K/T wiped out apparently _all_ large pterosaurs _as well as_nearly all
flying birds (i.e., enantiornithines, where ichthyornithids seems to have
disappeared previously in the brief exposure of the Campanian-early
Maastrichtian).

<and have never been secondarily flightless) emerged, so to speak, to
compete with the dinosaurs in the Cenozoic, all three clades sharing
distal airfoils.>

  Only two of these were in the Cenozoic, and by the time the first bat is
recovered in Eocene sediments, birds have diversified into most of the
present orders, and include many specialized fliers, leaving any bat/bird
competition in the drink, as it were. Other arguments seems to focus on
bats becoming nocturnal, to avoid diurnal birds, but this is similarly
bunk as it is first a generality (only most microbats are nocturnal), and
second there are plenty of diurnal bats (all megabats) and nocturnal birds
(owls, swiftlets, etc.) which live in the same areas as microbats. Plus
parrots and megabats are found in the same regions of Africa and South
America eating nearly the same foods.

<Theropods differed, of course, in being bipedal: their hands and legs
being, as it were, separate components for locomotion, whereas in bats,
and presumably most pterosaurs, hands + legs were the foundations for
flight mechanisms.>

  This having nothing to do with bird, bat, or pterosaur competition.

<Dinosaurs, as Greg Paul notes, during the Cenozoic to date, are
surprisingly diverse in morphology, whereas bats are not.>

  Noting this distinct statement, I can see some profound rewriting needs
to occur. Bats, especially the micro kind, are _very_ diverse in both
external morphology, internal anatomy, and skeletal morphology. This
permits them in small areas to specialize among several other types of bat
to types of food. Some take to blod, some to fish, some to fruit, some to
nectar, some to birds. And each one has craniodental and wing adaptations
to suit. Soem bats have a uropatagial muscle from the tail to the leg that
allows them to control the uropatagium tension without moving their legs,
presumably for manuevering. Some have disk-like appendages on their arms,
or a special "slotted" wing, some have elaborate pharyngeal/syringeal
adaptations to producing sound, and some alaborate on their facial anatomy
so much that it has become a joke to be "as ugly as a bat." And don't get
me started about the behaviors. Contentions that bats were "not as diverse
as birds" is a garbage parallel in that bats are incredibly diverse, they
do not need to be as diverse to be either as successful or _more_
successful than birds to be "winners" (look at humans, the greatest
morphological feature we differ in are colorations of the skin, hair, and
eyes, some of which is genetically controlled [eye and hair color are
inherited from your grandparents, essentially], yet we are probably one of
these most successful complex organisms on the planet, with tapeworms and
bacteria and viruses above us, and that's a horrible thought -- Bakker
wrote that it is the unspecialized, undiverse that win through, and this
is _so_ true).

<But, without stepping on scholarly toes, I suggest that bats just might
give some light on ecomorphologies of the cluttered skies at the end of
the Cretaceous: flight adaptations, vision, vocal/chemical signals, etc.
And, this new book edited by Kunz/Fenton just might provide us with
further extrapolation tools.>

  Its a sad thing that in the around 15-20 my after the Cretaceous when
the first "true" bat appears, you get statements like the above. Hoping
for a Cretaceous bat simply has no fundamental grounds. Noting the 15 or
so mya that whales became fully aquatic, it is easily reasonable that bats
did not need to be an efficient, flying phenomenon in the Cretaceous to be
anywhere; they would have started out small and likely arboreal climbers,
not super-fliers.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com