Re: Bone density in mustelids

Marc Verhaegen <m_verhaegen@xxxxxxxxx> wrote in
news:C37A1872.9F2D%m_verhaegen@xxxxxxxxx:

Op 03-12-2007 17:48, in artikel
Xns99FB69D3EC80Fmujinomega@xxxxxxxxxxxxx, Mujin
<umwinkl0@xxxxxxxxxxxxxxxxxxx> schreef:

...

FE Fish & BR Stein 1991 Zoomorphol.110:339-345
Functional correlates of differences in bone density among
terrestrial and aquatic genera in the family Mustelidae (Mammalia)
"the costs of maintaining an increased skeletal mass increases
according to locomotor function as follows : swimmers, sedentary
forms, slow runners, fast runners, and flyers"
No reason why erectus must be an exception, IOW, the H.erectus
endurance running hypothesis is pure nonsense.

...

H.erectus has pachyostosis,

"In some specimens [of tapinocephalian] this boss is of only moderate
thickness, while in others it has become greatly thickened into a
huge mass of bone (pachyostosis). It has been suggested that these
animals engaged in intra-specific head-butting behaviour (left),
presumably for territory or mates. A similar thickening of the skull
occurs in pachycephalosaur ("boneheaded") dinosaurs, and it is
speculated that all these animals practised head-butting behaviour
like modern goats and bighorn sheep, and late Eocene Titanotheres."
http://www.kheper.net/evolution/therapsida/Tapinocephalidae.htm

Yes, thanks, "it is speculated".
Others in the link speculated these animals were semi-aquatic.

But did not link pachyostosis to the speculation.

I don't know anything of these animals, but why would they be an
exception?

You are missing the point, which is of course that pachyostosis is not
restricted to buoyancy adaptations, but occurs for other reasons (such as
stress) as well.

Did you know some PAs even speculated that H.erectus were head-banging
each other, or ate too much honey, or carnivore livers, or had hyper-
or hypo-thyroidy, or -parathyroidy, or other far-feched &
uniquely-human just-so "explanations"...? They must have head-banged
each other on the occiput alone, because there were air sinuses in the
frontal bone... :-D

There are sinuses in other entirely terrestrial mammals as well. What's
your point?

As it happens, I am aware that it has been speculated that the pachyostosis
of H.erectus skulls may have been related to behavior (specifically
combat):

http://www.naturalhistorymag.com/master.html?http://www.naturalhistorymag.c
om/0204/0204_feature.html

I'm not sure what to think of this speculation, but it does seem to explain
two facts:

1. Only Asian specimens of H.e. have unusually robust skulls.

2. The rest of the H.e. skeleton isn't markedly different from our own.


osteosclerosis

"Most of the sabertoothed cat vertebral specimens we studied
exhibited diffuse osteosclerosis on both conventional radiographs and
CT images." www.ajronline.org/cgi/reprint/148/4/779.pdf

Interesting. IIRC, Mario at s.a.p speculated on I don't know what
arguments (no time to read them) that sabretooths were semi-aquatic.
Who knows he's right?

Oh, please. You're grasping at straws here in order to evade the point:
that the bone development phenomena you *claim* are unique to aquatic
animals in fact occur for other reasons as well. Or would you like to
claim that cervids and other ruminants are also slow-diving aquatic
mammals?

But of course, localised osteosclerosis is seen in the human (& other
animals') os petrosus (very dense, but also brittle(!) bone): has
probably to do with hearing.

So you *do* concede that osteosclerosis isn't specific to aquatic mammals?


, medullary stenosis

As medullary stenosis is properly a pathological condition compared
to the

I wouldn't call it pathological in, eg, the right arm of right-handed
tennissers.

In the literature with which I am familiar, the phenomenon isn't referred
to as medularry stenosis if it is a natural response to stress.

general population, I presume that what you mean is that H.erectus
*as a population* has greater cortical thickness and reduced
medullary cavity. Two problems:
1. To which other population are you comparing H.erectus?

To *all other* primates (incl.Hs, apes, apiths...), of course.

How about to other H.e.? Note that cranial thickness/density is *much*
higher among east Asian H.e. specimens than those found in Africa. You
claim that diving behaviour accounts for H.e. spread along the south coast
of Asia and among islands such as Flores, but even if we accept the claim
that increased thickness in the skull is necessarily linked to a diving
behaviour you're left with the fact that this feature doesn't appear to
emerge until *after* H.e. has spread East. Why not?


2. Increased cortical thickness and decreased medullary volume don't
seem to mean what you think they mean:
"Conclusions: Running, a weight-bearing exercise, is associated with
more favorable geometric and biomechanical characteristics in
relation to bone strength, compared with the weight supported
activities of swimming and cycling. Differences may reflect skeletal
adaptations to the specific mechanical-loading patterns inherent in
these sports"
http://www.acsm-msse.org/pt/re/msse/abstract.00005768-200204000-
00018.htm;jsessionid=HJxhg51XTP76vm2Q2tjGNy9JTQCZFcv3xHG8Qh2XL470Kzjk7
kPB!- 1601909834!181195629!8091!-1

Not comparable to bone densening & thickening as in He.
Long-distance runners (Hs) are very lightly-built.

The *musculature* of long-distance runners is lightly built. The bones of
long-distance runners are dense and strong; in fact, the runners in the
sample studied were *not* sprinters. You simply assumed they were because
doing so would support your hypothesis.


Clearly weight bearing, high impact activity increases cortical
thickness and decreases medullary cavity sizes. More importantly:
"SWIM[swimmers] and CYC[cyclists] had significantly larger (P < 0.05)
size- adjusted medullary cavity CSA than RUN[runners] and
TRI[triathletes]" (ibid)

Of course:
1) To be expected: less stress on bones. We all know this: see
possible causes of osteoporosis in old women. This is ontogenetic &
localised, due to heavier muscles etc. Has nothing to do with
pachyostosis & osteosclerosis as seen in H.erectus.

On the contrary. The increased density of long bones and vertebrae of H.e.
is within the normal range of variation within H.s., but at the end of the
scale which corresponds with modern humans who are engaged in activities
placing high stresses on those bones - particularly running and lifting
heavy weights. Swimmers, on the other hand show much less deviation from
the norm among sedentary modern humans. This is a *direct* contradiction
of your claim.

That the phenomenon in modern humans is ontogenetic is irrelevant. The
presence of the same phenomenon among H.e. might well be ontogenetic as
well, or it could be genetic. We have no way of assessing, except by
comparing the various specimens we have available to see if the pattern is
consistent with behavioural variation within the population. AFAICT, the
only comparison is between Asian and African variants, which could well be
either a regional genetic variation or a behavioural one. Can you
demonstrate a statistical consistency among specimens at a single site that
would contradict the idea that bone density was ontogenetic?

2) We're not speaking here of surface swimmers, but to the contrary,
of slow *bottom* diving animals (abalones etc.are on the bottom
AFAIK). Surface swimming ducks have a spec.weight of 0.6 only, with
extremely light bones! Underwater swimming animals have the density of
the surrounding water (ie, heavier in sea water). Bottom-divers are
fat & slow & have heavy bones (to compensate for the lungs & SC fat
etc.). It's thought the dense bones (eg, heavy limb bones in
sea-otter) help them anchor on the bottom.

Slow shallow divers such as the manatee and sea otter have nearly absent
medullary cavities in the ribs to locally compensate for the buoyancy
provided by fully charged lungs. H.e. does not appear to have this feature
when compared to earlier human ancestors or modern humans. How do you
explain this discrepancy?

Also, a *very* important reason why sea otters require ballast is the fact
that they carry a significant quantity of air trapped in their pelt for
insulation. This buoyancy needs to be counteracted. Since your hypothesis
attributes hairlessness in humans to an aquatic adaptation, this is not an
issue that H.e. would have needed to address in your model.

Moreover, the source you cited earlier in this thread (Fish & Stein) also
states:
"the association of increasing bone density with increasing adaptation to
an aquatic environment is tempered by the realization that increasing body
size may also influence bone density in larger, terrestrial mammals."

IOW, they added caveats to the pattern they noted - specifically that there
are numerous other factors that can influence bone density.


So while you may be correct that H.erectus medullar cavity size is
smaller (than what?) the pattern appears to show that this would mean
H.erectus spent *more* time walking and running, not less.

You're right that localised (eg, right arm bones in tennis) medullary
stenosis *alone* (esp.without osteosclerosis (= usu.brittle!)) could
be explained by physical activity, but this is localised & it's
difficult to imagine what physical activity they were doing with their
extremely dense occipita.

While sprinting primarily places stresses on the points of muscle
insertion, lower impact distance running places repetetive stress on a
variety of bones - all those which are likely to absorb the vertical impact
of the stride. i.e. tibia, humerus, vertebrae, and occipital bone.

Note also that gymnasts may have higher *localized* bone density than
runners and triathletes, but that the latter two groups have higher
*generalized* bone densities. In fact, sporting activities have been found
to promote a generalized increase in bone density as well as site specific
increases associated with loading:

http://www.ingentaconnect.com/content/tandf/rjsp/2004/00000022/00000007/art
00007
"multivariate and univariate analyses of covariance were performed to
compare the BMD of the nine sports groups with controls (at all sites)
using body mass and age as covariates. Our results confirmed a greater
adjusted BMD in the arms of the upper-body athletes, the right arm of
racket players and the legs of runners (compared with controls), supporting
the site-specific nature (i.e. specific to the externally loaded site) of
the bone remodelling response (all P <0.01). However, evidence that bone
mass acquisition is not just site-specific comes from the results of the
rugby players, strength athletes, triathletes and racket players. The rugby
players' adjusted BMD was the greatest of all sports groups and greater
than controls at all nine sites (all P <0.01), with differences ranging
from 8% greater in the left arm to 21% in the lumbar spine. Similarly, the
strength athletes' adjusted BMD was superior to that of controls at all
sites (P <0.05) except the legs. The adjusted BMD of the triathletes was
significantly greater than that of the controls in both the arms and the
legs as well as the thoracic and lumbar spine. The racket players not only
had significantly greater right arm BMD compared with the controls but also
a greater BMD of the lumbar spine, the pelvis and legs. "

Sprinters can have thicker leg bones &
muscles, but long-distance fast-runners are lightly built overall.
Just look at the Ethiopian etc.marathon runners.

No. This is simply not true according to the sources I have provided.
Yes, sprinters do have heavier, thicker leg bones, but long distance
runners also have denser bone structure than other athletes. In fact, the
"slight" build you attribute to marathon runners is entirely a feature of
their musculature, not their bone density.


- all these are *only* found in slow divers.

Apparently you are incorrect.

Not me. If you think the authors I quoted are incorrect, please tell
them. I'll place a number of papers on pachyostosis etc. in the AAT
files. http://groups.yahoo.com/group/AAT

Don't be obtuse. The authors you cite have noted a correspondence between
the aquatic lifestyle of certain animals and bone density increases. But
it is *you* who have inferred a general law that animals with various types
of increased bone density *must* be aquatic. Yours is the hypothesis under
scrutiny, so you're the one who has to defend it.



Unless you can explain these, keep your big mouth shut.

H.erectus in Mojokerto was found in a river delta amid freshwater &
marine shells. In fact, AFAIK all erectus lay next to shells.

And? Neither diving nor even wading are necessary for taking advantage of
shellfish food sources. Moreover, the evidence is that a very specific
range of shells were used by H.e., apparently as a non-lithic tool
material, and that the primary food sources identified at these sites were
terrestrial animals, including bovids:

http://dx.doi.org/doi:10.1016/j.jas.2006.03.013

AFAICT there is no evidence that the primary food source for this
population of H.e. was shellfish, let alone that they dove to get them.
Anyone who has ever been to a beach is probably familiar with the huge
quantities of shells that accumulate at the tide lines. These would serve
quite well as a tool material. Also, the primary shell noted in the paper
I cited above was a type of clam - clams live in the intertidal region, and
are most easily harvested by *digging* for them when the tide is out, not
by diving.


Unless you can explain why counterexamples to your "absolute"
evidence don't count, perhaps you should take your own advice?

Counter-examples?? None of these "examples" can be compared to the
generalised osteosclerosis & pachyostosis in H.erectus. All animals
with these features are slow divers.

This is simply not true, as I have demonstrated by reference to the
literature. Slow divers have these features, but these features are not
unique to slow divers.

We know erectus dispersed to
Java & Flores. Why wouldn't they adapt to collecting shellfish?

Why would they? Plenty of other animals dispursed to Java and Flores, and
yet did not become slow-diving shellfish eaters. Archaeological evidence
tells us that on Java at least H.e. was making significant use of
terrestrial animals, and many of the finds on Java are inland, far from
potential shellfish sources.

Wouldn't you?

Personally? No. Among other reasons, there are much more energy efficient
food sources available for a cooperative species.

[snip]

--
Bon nou mujin sei gan dan
.