Species? or variation within?

[David Peters <davidrpeters@earthlink.net>]

Say I find in one pterosaur specimen a wing only 3/4 the length of the
other of the same nominal species ? are these actually different species
or variation within one species?

Say I find an ilium only half the length of the tibia, but in another it
is nearly the same length as the tibia ? species or variation within?

Say I find a skull that has a 1:3 width to length ratio, while in
another it is 1: 4 ? species or variation within?

Say I find one pterosaur with a tail only 2/3 the length of the other ?
species or variation within?

I've found all of the above within the medium to large Rhamphorhynchus
specimens. About ten years ago Chris Bennett (1995) determined that
they're all the same species, only of different ontogenetic ages. I'm in
a quandary.

There has to be a cutting off point between species, and yet there has
to be gradual transition during phylogeny.  And when can we determine
that distinct specimens found in separate locations represent the same
species expressing allometric change?

Thoughts?

David Peters
St. Louis