What the fossil record tells us about trends in pterosaur diversity

[David Marjanovic <david.marjanovic@gmx.at>]

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. :-)