Re: getting a handle on Dinosaur taxonomy

[Christopher Taylor <ck.taylor@auckland.ac.nz>]

On 11/10/04 7:33 am, "Eric Martichuski" <herewiss13@hotmail.com> wrote:

> I'm having a hard time wrapping my brain around the relationships between
> dinosaurs, and I was hoping someone might be able to clarify matters in
> terms of modern species comparisons.
> 
> When we talk about two different hadrosaur species, would it be like
> comparing two antelope?  Or do you need to go further out to a comparison
> between all two-toed hoofed mammals.  Or is it just the variation between
> mule deer and white-tailed deer?
> 
> Are T. Rex and some other large contemporary theropod carnivore (I'm
> blanking on names) like Lions and Tigers?  Indian and African Lions?  Or
> more like Bears and Wolverines?
> 

    We're risking simplifying an, as you point out, complex issue, but a
couple of pointers you might find helpful:
    In practice most workers just treat palaeospecies as equivalent to
neospecies, but it seems to be generally agreed when people think about it
that most palaeospecies are just as likely to be 'species complexes' as
single species. Palaeospecies can generally only be distinguished by
skeletal characters, whereas neospecies may exhibit a wide range of other
characters that may indicate species distinctions, such as external
appearance (colouration, crests, etc.) or behaviour (vocalisations,
displays, etc.) An example where this is directly relevant to palaeo is the
recent separation of the moa species _Dinornis novaezealandiae_ and _D.
robustus_ by analysis of mitochondrial DNA. To the best of my knowledge, no
osteological characters are known which can distinguish these two species,
but in life there may have been other distinguishing characters.
    Obviously, this possibility varies from species group to group. In
lambeosaurines and ceratopsians, for instance, with complex, probably
display-related frills and crests that may be preserved as fossils,
'species' differences are more likely to correspond to actual individual
species. Small theropods or hypsilophodont-type ornithopods may be much more
osteologically uniform between 'actual' species, and so the chance that a
palaeospecies represents a species complex may be higher.
    Above all, remember that this is all largely theoretical, and you should
be careful how far you take it :-)

    Cheers,

        Christopher Taylor