Re: Ornithodira, breathing with long necks

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

> >>Several SVP abstracts of the last 3 meetings say that in many dinosaurs
the energy costs of breathing surpassed the energy production of metabolism,
means that those dinosaurs couldn't breathe, at least not through their
nostrils, because of the dead space in the long trachea.<<
>
> Does that mean they do not believe the neck air-sacs could act as an
alternate exhaust route to the trachea.  I do not know if any living animals
(most likely with long necks) have an alternate path.  Even if they do not,
why could in not be possible in Sauropods?

Seems they, like AFAIK everyone else, do not believe this. It is surely not
totally impossible (I've read in a Czerkas & Czerkas book, probably
"Dinosaurs: A Global View" in the original, that some birds can breathe
through an opening in each leg that connects to the air-sac system), but
evidence for as well as against this will be hard to find...

> >>Respiratory turbinates or analogs? Are said to be a prerequisite for
both homeo- and endothermy...< <
>
> Why? That feels more like a lawyer&#8217;s argument trying to argue a
particular point of view.

:-( Was not my intent...

> Why would a large animal (or even a small animal) in a warm, possibly
moist climate need turbinates to recover heat or moisture?

The climates where *Lagerpeton*, *Lagosuchus*, *Scleromochlus* etc. lived
were not so moist, if I am correctly informed. Am I?

> If the outside air is warmer than the animal, evaporative cooling is about
the only means of cooling available!

If I have correctly understood, birds do this -- in their air-sacs, they
recover moisture (seemingly not heat) in their respiratory turbinates. I can
imagine all Ornithodira doing likewise. A few mammals (e. g. humans) can
sweat, which has a similar effect but is tied to ludicrous water losses.

> (radiation, conduction, and conduction methods require a cooler
environment or surface.)

> Using moisture to cool the head seems more probable.  Turbinates are more
likely (to me) heat retention improvements for animals whose endothermic
ancestors spent some time in cooler climates as they vary.

I fear this is not testable at the moment... :-|

> <<At the SVP meeting 2000 it was proposed that sauropods held their necks
stiff not with long, superstrong ligaments (no evidence for these can be
found), but with air sacs between and in the vertebrae, just like birds do
it. The abstract sounds very convincing.>>
>
> Interesting!  At least it is a theory that could be tested.  How would
they get pressurized?  Could they get enough pressure? Would it be possible
with 2 air sacs?  Could they then bend the neck?

I'll (probably :-] ) dig up the abstract tomorrow. Anyway, it says that
birds do all this.

> Of course, this use would preclude using them for breathing.

Sure.

> >>The air sac system is a synapomorphy of Ornithodira, and lung + air sac
volume was big
> enough to allow the evolution of 15-m-long tracheae. >>
>
> Do you mean pre and post lung air sacs?  Do you mean post lung and neck
air sacs.

Phew. Neck air sacs are probably quite old, because in basal theropods and
sauropods there are often pneumatic features in the proximal cervical and
cranial dorsal vertebrae (and nowhere else). Some air sacs, however, seem
never to invade bones, so their presence or absence is more difficult to
infer. I don't claim, however, that all air sacs appeared at the same time.

> Was it big enough to allow endothermy.

Very probably. I don't know how to do the maths.

> >>A large, powerful heart requires endo- and hom(o)eothermy.>>
>
> Why?  Does it mean that they are required for the development of a
four-chambered heart?

Not if you regard croc hearts as four-chambered.

> A large, powerful heart implies longer duration of effort to me, or a big
body.  Why can&#8217;t efficient lungs, a 4 chamber heart, an upright gait,
and warm external air mean high, long duration activity levels and rapid
growth could not be achieved?  As much as I want to believe all dinosaurs
were endothermic like mammals, I can&#8217;t convince myself that it is the
only explanation without answering these questions.

These features would be great waste, IMHO, without endothermy. Why
adaptations to, say, long-duration cursoriality when there's never enough
energy to power them?
        I must admit I likewise want to believe that all dinosaurs were
endothermic like mammals and birds, which probably influences what I write,
but IMHO there is some evidence for this.

> In response to > 5.  Freed hands due to the bipedal gait, with skin or
feathers, would lead
> to flight.>
> <<freed hands may facilitate the evolution of flight, even though bats
never
> were bipedal as far as is known... On the other hand, many bipedal animals
> (kangoroos? humans? *Oreopithecus*?) have never evolved flight (but
reasons
> are easy to find here). For pterosaurs, the debate whether they had bi- or
> quadrupedal ancestors continues (I favor the former).
>
> Humans managed flight using machines made by their free hands&#8230;
ground up according to the latest quarters (but not chasing after insects).

Yeah, erm... this is not exactly what I meant... :-)

> As for as pterosaurs.  If they had a bipedal gait, I would doubt it was
very good.  Otherwise, there would probably have been many later flightless
pterosaurs.

*Nyctosaurus* had lost all fingers and metacarpals except no. IV, so it must
probably have been bipedal. Of course, this is a late specialization and
won't end the debates.
Flightless pterosaurs? On the continents all niches possible for them seem
to have been occupied, and if there were flightless pterosaurs on
Hawai'i-like islands, we will most probably never know, because no such
island survives.

> >>HP Gregory S. Paul is onlist, so if he hasn't already done this today
(my mail server is overloaded), he will surely tear any argument that
sauropods didn't need high metabolism to very, very small pieces.
>
> In his Predatory Dinosaurs of the World, he essentially stated that larger
endothermic animals had lower metabolic rates per pound than smaller
animals.  Why would an extremely large animal generate lots of internal heat
when he could not get rid of it?  It would just require more food. With a
large stomach, crop, gizzard and stones, wouldn&#8217;t the breakdown of the
food generate additional heat?  Sauropods may have been endothermic (I
believe they were), I am just looking for a reason why a large animal (or
small for that matter), with a 4 chambered heart, and birdlike lungs would
have to have been endothermic and homeothermic to be active or grow fast if
his body was warm.
>    Alternatively, a high metabolism better explains they large size and
presumably rapid growth rate required to get there.

I'll dig up his Dinofest article too, if he won't enter this discussion
himself; one argument is that a heart required to pump blood up the neck of
an _ectothermic_ *Brachiosaurus* would have needed more energy than a
hypothetical ectotherm the size of the entire *Brachiosaurus*. (He does the
maths.)