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Re: Flightless bat? Flightless pterosaur?



Regarding flightless in bats and pterosaurs

Cheers


Heinz Peter Bredow

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Gregory S. Paul
Dinosaurs of the Air
Page 149

What Makes Birds Special?

The reason that birds have repeatedly experienced the reduction or loss of
flight capability while bats and pterosaurs have not is the fundamental 
differences in their locomotory complexes. Birds fly only with their arms,
and walk and tun only with their legs. They are therefore "two-legged" both in
the air and on the ground. Because their legs are entirely decoupled from the
flight apparatus, their terrestrial locomotory capability is unhindered by
flight needs and therefore high, and birds are able to move about with no help
from their forelimbs. The excellent terrestrial performance of bipedal birds
allows them to easily jettison their other source of mobility, flight.

In contrast, bats use and very probably pterosaurs used their forelimbs for 
walking, and the hindlimb is (or was) an integral part of the flight apparatus.
Bats and pterosaurs are therefore "fourlegged" both in the air and on the
ground. Some bats, especially vampires and the New Zealand short-tails, are
competent on the ground (Nowak 1999). Most pterosaurs were probably good, albeit
flat-footed, walkers (S. Bennett 1997). However, the close coupling of both sets
of limbs into both modes of movement hindered these quadrupeds from becoming as
adept at ground locomotion as bipedal birds. The close links between the fore-
limbs and hindlimbs also complicates the modification of either set for new
purposes.

There are other, more subtle reasons that pterosaurs and bats have been less
prone than birds to evolve flightlessness. Early on, birds evolved large brains,
and birds' exceptionally good vision puts them at least on par with land-bound
creatures. Pterosaur brains, in contrast, remained reptilian in size, and their
eyes do not seem to have become as large as those of birds. Bat brains are not
larger than those of other mammals, and although bats are by no means blind,
their vision is not exceptional. Their best flight-related sensor System is
sonar, which is not of much use to ground dwellers. To the best of our
knowledge, island bats have never lost flight.