Re: [Re: Insulation does not = "Warm-blooded"]

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

----- Original Message -----
From: <archosaur@usa.net>
To: <david.marjanovic@gmx.at>
Cc: <dinosaur@usc.edu>
Sent: Monday, April 23, 2001 5:29 AM
Subject: Re: [Re: Insulation does not = "Warm-blooded"]


> "David Marjanovic" <david.marjanovic@gmx.at> wrote:
> > > I believe that L.C. endothermy didn't show up in birds until the
> > > enantiornithines (i.e. it probably showed up in some                 >
>
> enantiornithines). I don't think all enantiornithines were L.C.      > >
> endotherms though. Of course since enantiornithines were the sister  > >
group
> to neornithines it doesn't help much with extant avians. I do   > > think
all
> Neornithines were L.C. endotherms, but I don't know enough > > about them
to
> say much more. I will say, though, that I don't believe > > that
> archaeopteryigiformes like _Archaeopteryx_ and _Rahonavis_ were > > L.C.
> endotherms. Everything after them gets confusing.
> >
> > You believe, you think... why?
>
> +++++++++++++++++++++++++++
>
> I base it, right now, off of two controversial pieces of evidence and one
> piece of evidence that I have yet to hear anyone use.
>
> [...]
>
> 3) _Archaeopteryx_ and _Rahonavis_ (do we know of any other
> archaeopterygiformes?) are all long bodied animals. Long bodies are a
problem
> for L.C. endotherms because there is that much more surface area to allow
for
> heat escape. That is why most mammals and all birds are short bodied. The
only
> exception to this rule is in weasels (and otters, which I think are weasel
> relatives) and they probably have higher metabolisms to handle the extra
> length. Meanwhile we have plenty of long bodied non-L.C. endotherms.
Without a
> complete reliance on internal power for heat production, longer bodies are
> possible. Of course we also have short bodied ectotherms as well, so it is
> more like one sided evidence (i.e. usually only non-L.C. endotherms can
> support long bodies).

Long-bodied? I wouldn't say that. Sure, they have long, thin tails, but many
recent birds have extremely long necks in exchange. As long as those
elongated body parts are insulated, I don't see any problem (and even if,
there would still be the warm mesozoic climate), and never mind bird feet,
which are "insulated" only by a counter-current heat exchange system -- even
tiny birds can walk on ice for long periods!

> Anyhoo, by themselves they aren't that supportive, but altogether they
make
> for a stronger argument.

Given that 1) and 2) are very doubtful (IMHO completely useless), and 3)
isn't much more compelling, I'll continue to doubt that.

> _Crocodylus johnstonii_ has been clocked at galloping speeds of 17 km/hr
and
> they grow to only 10-12ft. That's pretty fast for an animal that isn't
even
> built for this type of lifestyle. Just imagine how fast a pristichampsid
could
> have been capable of?

1. It is often stated that alligators can outsprint humans -- are they so
much faster than the Australian freshwater croc, or do these reports
consider rather slow people? :-/

2. A pristichampsid was surely faster, but these were ambush predators
(according to the in-depth research of the article about *Pristichampsus
rollinatii* that has been mentioned onlist some months ago) --
hyperanaerobiosis is a perfect adaptation for this. Many theropods weren't
ambushers.

> Bipedalism (both facultative and obligate) has been observed in dozens of
> lizard species, and we have non-dinosaurian fossil reptiles that were
bipedal
> as well.

This is going to be interesting when more research _will_ be done...

> As for the 1 tonne thing, that all depends on your measurements. As I
> mentioned before, _Testudo atlas_ has been estimated at 4 1/2 tonnes.

:-o
Seems P&L (whose estimates are otherwise always on the high end, IMHO)
disagree.

> HP Tom Holtz brought up a good point in a separate post in this thread
that
> bodyplan might have an effect on size limit. It is quite possible that the
> only reason why varanids didn't exceed one tonne was because sprawling
limbs
> can only hold so much weight. This could certainly explain why
crocodylians,
> with their variable gait, grow and grew to huge sizes (both in and out of
> the water). It also might explain why tortoises can get so big, since they
tend
> to have "more erect" stances than most lizards (even Komodos hold their
legs a
> little more under than other lizards).

Does anyone know about *Megalania*... ?

> Large size does seem to be a good reason for erect stance selection.
> Certainly better than any others that I've heard of.

But large size has appeared after erect stance, at least in dinosauromorphs.
High activity, combined with the absence of a gular or hepatic-piston pump,
may be a better reason. *Eudibamus* the Bizarroid Little Anapsid may also be
such a case.