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Re: Type material: does it have to look pretty?



In a message dated 97-11-30 03:00:48 EST, bettyc@captivation.com writes:

<< How then are the same species designated when there are recognised (or
assumed) to be two morphs, such as male and female characteristic dimorphism.
 If the type (say one of the good 'ol Oviraptors) has a big crest and is a
large
 animal but another from the same local and horizon is pretty dang close in
looks
 and MUCH of the diagnostic features, but the crest aint so big or as fancy
and
 that other one is considereably more petite...how does one indicate this is
a
 supposed same species but different sex?>>

When the sample size is small--one or two individuals--the problem is
virtually insoluble; significant sexual dimorphism easily results in the
description of two species, and even two genera (and occasionally two
families). Likewise significant morphological change from juvenile or
subadult to adult.

Only after a reasonably large sample size is available can one do the
statistical morphometric analyses to see whether the specimens fall into two
sets, or as they say, "form a bimodal cluster." If the specimens are
sympatric, seem closely related, are of roughly equal numbers, and are split
into species diagnosed primarily by features that likely had a display
function, then one can argue plausibly that one has two sexes in hand rather
than two taxa. This is essentially how Dodson argued his analysis of the
numerous sympatric species of _Lambeosaurus_, _Corythosaurus_, and
_Procheneosaurus_, showing them to be "male," "female," and juvenile of
either _Lambeosaurus lambei_ or _Corythosaurus casuarius_. (Incidentally, as
I shall note in MM #2 third edition, if Dodson is correct and the type
specimen of _Procheneosaurus praeceps_ is from a juvenile _Lambeosaurus
lambei_, then the genus _Procheneosaurus_ has priority over _Lambeosaurus_ by
three years and must become the correct generic name of the type species
_Lambeosaurus lambei_, as in _Procheneosaurus lambei_.)

<< Or do you have to identify this other one as another species offcially?
 Can you just describe BOTH sets diagnostic features of the crest under one
 species?  (Ie; this dinosaur has a little bitty crest and sometimes a big
honkin
 crest, and all the requesite bumbs on it's elbows besides....)>>

Yes, you can state in your diagnosis that supposed females have such and such
features, whereas supposed males have such and such features. The diagnosis
relies on the hypodigm--all the good material from a horizon--not just the
type specimen.
 
<< Juveniles found with an adult would seem to be a problem if such
late-developing
 things such as crests are diagnostic of that species. So what happens with
them?
 Wouldn't the juvenile features need to be considered dagnostic as well so
when
 other juveniles are found, they can be compared.>>

If juveniles possess diagnostic features that are lost with the onset of
adulthood (as undoubtedly happens with some insects), then these features
should nevertheless become part of the species diagnosis. Generally, however,
adult dinosaurs are the ones that develop the prominent crests, horns,
plates, and so forth that serve to diagnose the species. Among
pachyrhinosaurine (= centrosaurine) ceratopians, juvenile and subadult skulls
are very similar among the genera, which develop their diagnostic cranial
horns and crest features only as adults. Thus _Monoclonius_ is a _nomen
dubium_, because the type specimen of the type species, _Monoclonius
crassus_, is a partial subadult crest that cannot be distinguished from the
crests of juveniles of either _Eucentrosaurus_ (=_Centrosaurus_),
_Styracosaurus_, or _Einiosaurus_.
 
<< Is "hypodigm" from the same root as paradigm?>>

Yes.