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Re: Size and longevity



Ah, aging, growth and body size. Some of my favorite subjects. So gather
around the fire kids. 

It appears that animals that grow through life - reptiles, some crustaceans,
etc - literally do not age physiologically. They are perpetual juveniles with
immortal cells, strong immune systems, good nerves and vigorous muscle
contractions. In other words, because they never stop growing, they never get
around to aging! Animals that cease growth - such as we poor humans - have
cells that are literally programmed to die after about 100 cell divisions (as
it happens you can read about this in my new book BEYOND HUMANITY, in the
section that discusses why human immortality probably is possible with the
right genetic engineering maybe with a little nanotech thrown in - and why it
is not the best idea). So we keel over no matter what. Reptiles, however,
always die from something bad happening to them. You know, starvation,
disease, accident, predation. Example, the oldest known animal was a captive
tortoise that died at age 152+ (twas a baby when caught) from an accident. It
appears statistically extremely improbable that any given reptile will live
beyond 100-150 years, maybe less in the dangerous wild. Which is a good
thing, because if the old folks stay around they will compete with their own
young too much. 

Bone microstructure indicates that some dinosaurs had determinate growth and
then aged, they probably lived two to six decades at most. Persistently
cartilagenous joints and bone surface microstructure strongly indicate that
other dinosaurs grew until death, The latter includes sauropods, which may
have had long life spans, but no more than 100-150 years. Past suggestions
that giant dinosaurs lived for many centuries can be dismissed as speculative
and implausible.  

Among fossil proboscideans the most enormous skeletons are not all that much
larger than the norm, maybe 30% heavier. This makes sense considering that
big elephants live only 60 years before dying because their teeth run out, if
not before. Females stop growing at around 40 and rarely exceed 4-5 tonnes,
in males however cessation of growth is often statistically coincident with
death at age 60 and a few males make it to 7-11 tonnes, well above the norm
of 4-6 tonnes. 

Most large sauropod remains come from individuals of 10-35 tonnes. The
remains of 35+ tonners are much scarcer. The skeletons of the very biggest
sauropods - your 80-150? tonne argentinosaurs and amphicoelians - are very
rare. This pattern suggests that the very biggest sauropods were so huge in
part because they were unusually old and kept on growing to at least 60 and
perhaps 100-150. 

However, this does not mean that the great size of super-sauropods can be
attributed simply to adult growth continuing into very old age in animals
with reptilian energetics. The great majority of growth in almost all animals
occurs during the juvenile stage, adult growth is very slow. Super-sauropods
had to reach the majority of their size in a few decades at most. This means
that super-sauropods almost certainly were growing faster than elephants, and
as fast as whales, which also grow to near and over 100 tonnes within 60
years. If so, then growing super-sauropods were putting on 10 kg or more per
day! Only whale calves being fed vast quantities of nutrient dense milk grow
so fast today. It takes about six years for the fastest known growing wild
crocodilians to reach just 50 kg(!!), and fully terrestrial reptiles
(including oras according to new data I have been given access to) grow even
more slowly. It is only birds and mammals that can grow fast enough on land
to become gigantic, probably because only they have an aerobic exercise
capacity high enough to forage and gather enough food to put on all those
pounds. Example, self feeding ostrich chicks grow to full size of over 100 kg
in just over a year! Very probably sauropod chicks had to be about as
energetic as ratitie chicks for them to grow into the towering colossi that
they aspired to be. Yet more evidence dinosaurs were not just scaled up
herps. 

GSPaul