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Re: too quiet on the western front
> I just read somewhere that someone ... had figured out that
> the many *species* of hadrosaurs (based on different head crests)
> were actually just a few species, with gender and age differences.
> Can anyone tell which
> *species* or *genera* of hadrosaurs are no longer considered true,
> and how they relate to accepted species? (Fictional example:
> ex-Anatosaurus now determined to be a female or immature male
> example of Corythosaurus.)
The article that you read about must have been the one a number
of years back that studied Corythosaurus, Lambeosaurus and relatives.
Prior to this study, there were *14* described species of
two described species of Lambeosaurus, and some large number of
described species of Prochenosaurus (supposedly a small form with a
low, incipient crest).
He did what is known as allometric analysis to show that all but
one or two of the described species of Corythosaurus belonged to
a *single* species, Corythosaurus casuarius, that those one or
two other species were female Lambeosaurus specimens, and that
all of the described Prochenosaurus species were juveniles of
either Corythosaurus or Lambeosaurus.
As a results there are two valid genera, Corythosaurus and
Lambeosaurus, and three valid species.
All of these forms are crested forms from a single time period,
called the Belly River stage in North America.
As a side effect of this study, the classification of some similar
forms from the succeeding Edmonton Group was revised. The genus
Chenosaurus (similar to Prochenosaurus) was recognised as the
juveniles of Hypacrosaurus (similar to Corythosaurus). So now
there is but a single species in this cluster of specimens, a
species of Hypacrosaurus.
[Because all three of these genera are so similar, an argument
could be made to place all four species in a single genus, but that
has not acutally been done].
Another, more recent revision, of a similar nature, involved
Anatosaurus and Edmontosaurus. These forms were *non*-crested
forms from the Lancian Age and the Edmonton Group respectively.
A study showed that, of the circa 4 species of Anatosaurus,
the type species and all but one of the others were identical
to one of the species of Edmontosaurus. Since the name
Edmontosaurus is older, that is now the correct name, and Anatosaurus
is a junior synonym of Edmontosaurus. (Edmontosaurus is currently
considered to consist of two species, *both* of which span the
entire Edmontonian + Lancian stages - each picked up some former
Anatosaurus specimens - but I am skeptical, I suspect there may
only be one species).
Now, this left the odd-ball species of "Anatosaurus" without a
valid generic name, so a new one had to be coined. Thus "Anatosaurus"
copei (I think) is now named *Anatotitan* copei. [This species
is truly different - it is also the most frequently pictured
species of the former Anatosaurus - it is the most "duck-billed"
of all of the duck-billed dinosaurs].
There *is* no genus Anatosaurus anymore.
[PS. Since I have gotten some stuff lately, is Horton having
The peace of God be with you.