Re: Terramegathermy in the Time of the Titans (not so long...)

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

> So you know, a similar paper on Terramegathermy ... appeared in the 1998
> Modern Geology volume by Greg Paul.  Don't have the ref handy, but could
> send it to you and the list if need be.  I haven't read the 1994 paper you
> quote, but the 1998 one sounds similar.

HP GSP has meanwhile informed me that the 1998 paper is Modern Geology
22(1-4), and that indeed elephants have been measured to be 4 m high at the
shoulders and at least 10 tonnes in weight. I will look for the paper...

> Continuing (P&L):
> "Rather than going belly up when it gets hot, [elephants] use high body
> temperatures of 37°C and bulk to thermoregulate in extreme heat."
>
> What is interesting here is that P&L reject gigantothermy as a hypothesis
> for dinosaur thermoregulation, but use bulk in elephants as a means of
> arguing thermoregulation.

Gigantothermy is understood here as the combination of being bradymetabolic,
bradyaerobic, endothermic, homeothermic, and insulated by size, shape and
fat. In this sense, elephants are not gigantothermic...

> Plus, African elephants have big, thin and flappy
> ears that help them draw heat away from their brains and countercurrent
heat
> exchange in the blood vessels going to their brains to cool themselves.
> Higher core temperatures and bulk alone do not completely explain cooling
in
> these giants.

Well, sauropods had relatively longer limbs than elephants, long necks, damn
long tails, and air sacs for lots of cooling surface!

> P&L continue:
> "... reptile muscles can produce twice as much
> anaerobic power as those of mammals and birds (Ruben, 1991), so even small
> legged lizards and crocodilians sprint at high speeds. However,
> hyperanaerobiosis is an inefficient process (that consumes ten times as
much
> food as aerobiosis) that works only for a few minutes, and is followed by
> toxic effects (Bennett, 1991)."
>
> Weasel words.  Inefficient process in terms of being a mammal or bird, but
> reptiles get by just fine with largely anaerobic muscle metabolism.  Many
> reptiles are sit-and-wait predators who require a few meals a month or
less,
> so I would call this very efficient and endotherms very inefficient in
this
> respect.

I wouldn't consider "hyperanaerobiosis [...] works only for a few minutes,
and is followed by toxic effects" weasel words: they say quite clearly that
while hyperanaerobiosis is perfectly fine for sit-and-wait activities, it
can't be sustained for e. g. migrating.

> P&L:
> "[...] The low capacity and low pressure respiro-circulatory system of
> reptiles can deliver only enough oxygen to supply bradyaerobic muscles.
> [...] [Large, tachyaerobic muscles require good, large lungs and hearts as
> well as high blood pressures.]"
>
> Kinda putting the cart before the horse here.  Crocs and gators have
> four-chambered hearts, like any "good" mammal or bird, with the difference
> that they can control the openings and closing of valves between their two
> aortae [...] Therefore, having a four-chambered heart "preadapts" you to
get
> bigger and place your head further from your heart, but it does not
> necessarily make you endothermic -- again, as evidenced by gators and
crocs.

Sure. But being big requires a heart that is not only four-chambered but
also _big_ and therefore can't be financed by bradymetaboly (see Table 1),
therefore, being big requires being tachymetabolic, P & L write.

> Whew ... well, that's a wrap ... for now. =)

I'm writing Part 2...

> Matt Bonnan, Ph.D.*
> * (defense one week from Thursday!) =)

Good luck! What's the topic?