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Re: Torosaurus NOT Triceratops--? resent
> Body size (one genuine aspect of individual variation) is a
> big question mark. However,
> we can narrow down the issue by first pulling out the
> stratigraphic and ontogenetic signals.
> Obviously I'm biased towards strat, but this data is
> absolutely essential, and Longrich's study
> doesn't have it.
That is discouraging.
Generally I'd make it "strat and loc[ality]", but in this case locality is
probably resolved. Are there any pertinent specimens from outside the prairie
belt? IIRC, no. Can they be expected, given the density of known fossil
localities of correct age and depositional environment (e.g. in California, or
in Appalachia)? I'd go with "no" here. All the animals in question seem to have
been endemic to the warm-temperate to subtropical (at that time) lowlands and
foothills of eastern Laramidia.
That leaves strat; my first thought on reading the comments was in fact "did
they figure in the temporal range?" It's not good to hear they didn't
Using Plio-Pleisto-Holocene taxa as proxy, I'd guesstimate that for a large
terrestrial animal, 0.1 Ma of evolutionary time is when you start getting
morphological differences that exceed individual variation within in any
exactly coeval population (it's definitely so for 1 Ma, and for small land
mammals it's already so after 0.01 Ma, so it's got to be the order of magnitude
Might try to get "exact" data from elephants; you need something with a roughly
comparable generation time and ideally a comparable metabolism (these things
are what affects mid/long-term rate of evolutionary change most; in the short
term fluctuations in background mutation rate are often dominant). So
elephants, possibly rhinos, are probably the closest we can get, and I'd think
the quantitative value, while not terribly exact or representative, would at
least be better than one order of magnitude, seeing that the values for *all*
terrestrial mammals *no matter their generation time* barely span two OOM
(meaning that the value of any one particular lineage with stereotyped
evolutionary rate would be significantly lower).
So I think the temporal resolution necessary to resolve this question can be
narrowed down to one order of magnitude, with an uncertainty of 0.1 OOM
perhaps. If not better. Whether the strat sample is precisely dated and dense
enough to fulfil this requirement I don't know, but at least we should be able
to get a pretty good quantitative estimate for the hypodigm needed to resolve