[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Brachiosaur flexibility and face-shape (Was: Terra Nova: thoughts)

It seems to me other reason by which giraffe-like sprawling is
unnecessary is because sauropods do not have legs as relatively long
as giraffes. Giraffes seem to sprawl (or flex) also to shorten
shoulder height so it can be surpassed by neck lenght. The useful
measurement here would be neck/forelimb lenght.

Other thing: is there anything on the vertebral articulations of
sauropod necks which impede the neck from lowering below the
horizontal? Given that sauropod limbs are proportionally short (at
least relative to the neck), I guess the neck do not need to be
lowered by a great angle relative to the horizontal to reach the
ground (the water surface, I mean), probably not necessary to lower it
more than 45º if neck lenght is twice forelimb lenght.

Regarding the possibility of sauropods not drinking at all raised by
David, I think it makes sense because evaporative water loss is
smaller the smaller is the surface/volume ratio, as in smaller
animals, or the respiratory water loss, as relatively less O2 may be
necessary per mass unit given the lower metabolic rate associated with
large size, relative to related smaller taxa. I am not sure how much
elephants need to drink relative to other small animals, but they seem
to be ok. in xeric habitats. Perhaps both long necks and trunks permit
to absorbe respiratory water irrespective of nasal turbinate size, as
I think Gregory Paul stated in his terramegathermy papers, putting
elephants and sauropods at advantage relative to animals with shorter
air passages in addition to undermining Ruben's arguments against
dinosaur endothermy.

Last, relative to sauropods lying on their sides to sleep, I think
there is the problem that torsos seem to collapse wen they surpass
certain size, at least this seems to apply to elephants if they spend
some hours lying down. I do not know it this has to do with lung
collapse or general collapse of viscerae, but seems to relate to the
lack of adequate supporting pillars for the body (at least in
non-testudinates). Parenthetically, lung collapse would not be of the
same kind in saurischians if they had avian-like lungs, but the
problem would persist for air sac collapsement... may association of
air sacs with surrounding axial bones help preventing their
collapsement, in addition to their volume being most likely affected
by rib motion at this position?. Closing parenthesis, the strongest
pillars to avoid collapsement seem to be the limbs, supporting
accepting the possibility they sleeped standing up.

Other alternative is that they rested with the torso being supported
by the proximal limb bones, with the zeugopodia lying on the ground, a
posture sometimes used by lying down elephants. However, it seems to
me that in this way the weight would be transferred to the elbow soft
tissues instead of the ulna, given that the olecranon in derived
dinosaurs (excluding Coelophysis, Heterodontosaurus, and Saturnalia)
generally is not as prominent or does not have such a longitudinally
extended articular surface for the humerus as in mammals. This may put
the extensor tendons under pressure, and as far as I know, tendons are
not good at resisting compression or shearing forces. Something
similar would apply to the knee. As cartilages seem to have supported
part of the body weight, cartilaginous caps (or caps of other soft
tissues, as the caps in elephant feet) may also accomplish this
function at the elbows and knees, but this may require us to
hypothesize the presence of such structures.

Large herbivores seem to sleep less than smaller relatives, because of
needing to expend most of their living time searching for greater
amounts of foods, even when having mass-specific lower metabolic
rates. Parenthetically, I think this required increase in foraging
behaviour is a further argument in favour of Paul's idea that gigantic
dinosaurs have to be tachyaerobic in order to exist, for they have to
spend so much time active and a relatively larger measure of energy
consumption is necessary to keep that increase in activity. I used to
think that it may explain why the more active lepidosaurs are the
largest ones, the varanids, but I do not know if this hold for turtles
or water-based animals. So perhaps sauropods sleeped much less than
elephants. If atonia is necessary for sleeping dinosaurs, the time
required for it may be as small as to permit side-lying before
collapse (if permanently disabling collapse is not also faster as the
volume increases) or resting on elbows and knees before sufficiently
affecting extensor tendons (unless we consider the relatively greater
weight compared with the relatively smaller increase on transvese area
of the tendon will imply the tendons being injured faster than it
would in smaller animals).

Other alternative pointed out by Andreas is great, relative to
one-side brain sleeping, which is present in lizards and birds
according to Wikipedia (sorry not going through the cited literature).
This may solve the problem, because this is the way cetaceans, which
would be in problems if getting atonic, are forced to. Here, we may
not need to expect dinosaurs changing anything from their ancestors
(if the condition is confirmed in crocs, tuataras and turtles).