Short answer: nothing whatsoever -- the pterosaur record consists only of
taphonomic biases.
Richard Butler, Paul Barrett, Steven Nowbath & Paul Upchurch: Estimating
the
effects of the rock record on pterosaur diversity patterns: implications
for
hypotheses of bird/pterosaur competitive replacement, SVP meeting
abstracts
2008, 59A
"Pterosaurs formed an important component of terrestrial and marginal
marine
ecosystems during the Mesozoic, and were the first flying vertebrates. The
fossil record appears to indicate a decline in pterosaur taxic diversity
[ =
species count] in the Late Cretaceous, followed by extinction at the
Cretaceous/Paleogene boundary. This reduction in species-richness has been
linked to the ecological radiation of birds in the Early Cretaceous -- it
has been proposed that early birds competitively excluded pterosaurs from
many key niches. Hypotheses of competitive replacement are frequently
posited based on the fossil record, but few have been tested in detail.
Here
we present a detailed examination of pterosaur diversity through time
based
upon a new comprehensive database of the spatial and temporal distribution
of pterosaurs. We use this database to calculate taxic and
phylogenetically
corrected diversity estimates, and compare these estimates with a model
describing temporal variation in rock availability. We use numbers of
pterosaur-bearing formations (PBFs) as a proxy for rock availability;
temporal variation in the number of PBFs is then used to generate a model
in
which rock availability is a perfect predictor of diversity. Both taxic
and
phylogenetic diversity curves are strongly correlated with numbers of
PBFs,
suggesting that a significant part of the signal contained within
pterosaur
diversity patterns may be controlled by geological and taphonomic
megabiases
rather than macroevolutionary processes. Moreover, significant differences
between observed diversity and the diversity predicted by the rock
availability model coincide with the occurrence of sites of exceptional
preservation (Lagerstätten), again indicating major biases in the
pterosaur
fossil record. There is no evidence for a long-term decline in pterosaur
diversity during the Cretaceous, although a reduction in species-richness
might have occurred in the Late Cretaceous. Available data provide little
support for the long-term competitive replacement of pterosaurs by birds."
The talk was pervaded by devastating pessimism. :-)