Re: MRs OF SLOTHS etc

["David Marjanovic" <david.marjanovic@gmx.at>]

> > ...Migrators must be tachymetabolic.
>
> As a generalisation this is nonsense, seeing as gecarcinid crabs, some
> rattlesnakes, monarch butterflies and a million other bradymetabolic
> animals migrate.

1. My error. Not tachymetabolic, but tachyaerobic. Insects are tachyaerobic
because of their respiratory system, but (AFAIK all) bradymetabolic.
2. I wrote "Aren't there some 'exceptions that prove the rule'? They've
slipped my mind..." By this I meant the rattlesnakes. How far do they
migrate, and how long do they need for it?
3. What are gecarcinid crabs?

> > while populations of megamammals are
> > small and unstable and can't easily be refilled by reproduction.
>
> Unfortunately I don't have the literature with me, but some historical
> elephant populations have been huge. 'Can't easily be refilled by
> reproduction'? - you MUST read Clive Spinage's _Elephants_ (Poyser
> Natural History) for detailed discussion on this. Even megamammals
> can breed fast and young and produce populations that cannot then be
> supported by their environment (hence the proposed 'boom and bust'
> model for elephant populations).

I was shortening too much here (however unlikely this sounds). HP Paul &
Leahy's point was, if I have correctly understood that large adults consume
more food than small ones, so an area can feed a smaller amount of larger
adults. The population densities of adult large sauropods must have been so
small that they probably crashed from time to time, which for mammals would
spell extinction because the young are so highly dependent on adults for
such a long time, but not for sauropods.
        Well, I'll try to find that book, anyway.

> > Desert elephants never overheat, so HiMR sauropods shouldn't have
> > either. Therizinosaurs, and maybe early dinosaurs with small ilia,
> > probably had InMRs like giant sloths.
>
> I wasn't aware David Oren and colleagues had finally captured a live
> mapinguary - have they published?

No, I've changed my surname ;-)

> Sarcasm aside, how do you know
> anything about the MR of ground sloths? Extrapolation from extant
> sloths might be reasonable but is obviously speculative.

This seems to be a generalisation from the MRs of living xenarthrans, which
are AFAIK rather intermediate, and from the convergence of therizinosaurs to
ground sloths (and chalicotheres, and homalodotheriids...). Of course this
is rather speculative, but IMHO quite reasonable.