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

bats



Mike Habib: season's greetings, whatever one's
tendencies. Your two notes were seeds for thought.
I think Jaime is mistaken on several levels. One: I
think it likely, on the basis of available molecular
data when viewed through the prism of cladistic
analyses of chiropteran phylogeny, that bats (perhaps
not as agile and swift as the Cenozoic forms, but
still bats) arose before the end-Cretaceous. Not all
pterosaurs were extinct by the end of the Cretaceous,
and so, two: this means sympatric overlapping of
population dynamics. In other words: the feathered
dinosaurs, the small pterosaurs, the proto-bats (I
don't know what else to call them) were alive during
the same period, viz. may have co-existed in the same
geographical regions.
There is, admittedly, no evidentiary basis for my
supposition, just the "hunch" that the earliest,
well-preserved chiropterans are quite advanced in
morphology, and this is only a "short" 10 million
years, or so, after the extinction events. Moreover,
again without fossil evidence to strengthen my
paradigm, I suspect that not all pterosaurs died at
the end of the Cretaceous, just as non-feathered
dinosaurs may have survived into the Cenozoic
(isolated populations, e.g., hanging on, as it were,
but their gene pools so damaged and depleted that
extinction happened). But the pterosaurs disappeared
as well. Why?  In other words: toward the end of the
Cretaceous, bats appeared, survived with the feathered
dinosaurs, some clades surviving, some dying out. I
think the feathered dinosaurs survived until now
because of a combination of factors: immunocompetency,
parental care, changes in nesting patterns (predator
avoidance strategies = nests high above the ground, or
in the ground, or offshore rookeries). Mammalian
predation killed off the secondarily flightless
Phorushacos in South America probably, ca. 3-4 million
years ago (perhaps in conjunction with the bollide
impact in Argentina).  For me, the profound puzzle is
how diversified bats became during this period.  Bryan
Carstens's recent work on morphology and molecular
data of the Neotropical nectarivorous bats
(Phyllostomidae)is especially intriguing. 
Could it be that chiropterans in the Cenozoic, as it
were, co-opted pterosaur econiches? Were pterosaurs
nocturnal as are the vast majority of bats?
Predator-prey dynamics are replete with numerous
examples of taxa one would think could do well (and
sometimes do), but which survive because they are not
readily available prey. Echolocation could have
initially served two purposes: to locate prey at
night, to avoid becoming prey from flying, hunting
dinosaurs whose visual acuity (like owls) was better
than their own.
One other thought: Gregory Paul has observed that
pterosaurs and bats share similarities,but with one
fundamental difference (as examinations of skulls
demonstrate): bats are bigger-brained. Coupled with
being faster, and able to "out-think" pterosaurs, it
could be that our imaginary end-Cretaceous protobats
survived into the Cenozoic for the same reasons the
feathered, flying and secondarily flightless,
theropods survived.

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