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From: email@example.com (James Shields)
> ... but how can we be sure that
> the large-crested and small-crested forms are the same species?
In Parasaurolophus, we can't, the specimens are too widely scattered
to be sure of much of anything.
In Corythosaurus, a decade or so ago there was a detailed morpho-
metric analysis made of the available specimens, resulting in
the number of species being reduced from 14 to 1, and in recognizing
that Prochenosaurus consisted of juvenile Corythosaurus and
Because of the large number of specimens, all from a single formation,
and thus from a single time and place, we can draw more assured
conclusions. In C. the two morphs really differ only in crest
size. Since they are not different in body size or mouth size,
they are not differentiated ecologically. Since one clear result
of the study of modern ecosystems is the rule that animal species
can only coexist if they partition available resources, and thus
avoid *direct* competition, it is nearly certain that these two
morphs are one species.
[Note, the converse doesn't hold, males and females in some species
differ in ways that involve resource partitioning].
And for some dinosaurs we have even better evidence: single species
mass death sites. In this sort of a situation one can be nearly
certain that the entire range of variation seen falls in one species.
If one then has a bimodal character distribution, it almost certainly
represents sex differences.
Examples of this include: Einolosaurus (?spelling), Chasmosaurus,
Pachyrhinosaurus, Maiasaura, Coelophysis (in the broad sense), and
perhaps a few others.
[For instance, probable male Pachyrhinosaurus have a thicker, more
rounded nasal bump, and the probable females have a flattened bump].
The peace of God be with you.