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Copeâs Rule in the Pterosauria - Hone & Benton 2007

Copeâs Rule in the Pterosauria
Hone & Benton 2007
20 (2007 ) 1164â1170

The remarkable extinct flying reptiles, the pterosaurs, show increasing body
size over 100 million years of the Late Jurassic and Cretaceous, and this seems
to be a rare example of a driven trend to large size (Copeâs Rule). The size
increases continue throughout the long time span, and small forms disappear
as larger pterosaurs evolve. Mean wingspan increases through time. Examining
for Copeâs Rule at a variety of taxonomic levels reveals varying trends
within the Pterosauria as a whole, as pterodactyloid pterosaurs increase in size
at all levels of examination, but rhamphorhynchoid pterosaurs show both size
increase and size decrease in different analyses. These results suggest that
analyses testing for Copeâs Rule at a single taxonomic level may give
misleading results.


Hello, all. I'm new. I hope some experts out there can help me understand 

I had a chance to read this paper. The authors create graphs with these 

<<Fig. 1 Graph of log wingspan vs. time for all pterosaur genera with a
best-fit regression line (formula of line y  )0.0055x + 1.0438),
with the correlation coefficient (R2 Â 0.33) and P value (P Â
0.0001). Wingspans measured from juveniles, and taxa for which
the data are incomplete, were excluded.>>

The fact that Hone and Benton created a straight best-fit regression line is 
what I question. 

1. Aren't typical basal pterodactyloids smaller than typical derived 
2. Why include any taxa at all between Anurognathus and Quetzalcoatlus if a 
straight line (defined by two points) at some inclination is what youâre 
looking for?
3. Wouldn't a sinuous line better represent the actual situation over 100 
million years? â perhaps with a nod toward the overall trend as an 

On a similar note, such a straight line applied to the Synapsida from start 
(Archaeothyris) to finish (Baelenoptera) would miss the major size dip that 
marked the advent of the Mammalia. Would it not?

Then again, wouldn't it have been more to the point of dis/proving Cope's rule 
if Hone and Benton had presented any sort of direct phylogenetic lineage of 
just Quetzalcoatlus or just Pteranodon without including all the other 
unrelated cousins? Doesn't including data from an entire clade as large as the 
Pterosauria just add distracting noise in a case like this?