Re: Bone density in mustelids

Marc Verhaegen <m_verhaegen@xxxxxxxxx> wrote in
news:C37DCD66.A110%m_verhaegen@xxxxxxxxx:

Our little boy apparently can't tell us why he believes a tool-using
waterside hominid would not butcher stranded whales or drowned bovids.
He even believes high-arched feet are for running...
Never seen a cursorial animal?

I suppose you have an alternative explanation for the arguments given here:

http://www.nature.com/nature/journal/v432/n7015/full/nature03052.html

Abstract:
"Striding bipedalism is a key derived behaviour of hominids that possibly
originated soon after the divergence of the chimpanzee and human lineages.
Although bipedal gaits include walking and running, running is generally
considered to have played no major role in human evolution because humans,
like apes, are poor sprinters compared to most quadrupeds. Here we assess
how well humans perform at sustained long-distance running, and review the
physiological and anatomical bases of endurance running capabilities in
humans and other mammals. Judged by several criteria, humans perform
remarkably well at endurance running, thanks to a diverse array of
features, many of which leave traces in the skeleton. The fossil evidence
of these features suggests that endurance running is a derived capability
of the genus Homo, originating about 2 million years ago, and may have been
instrumental in the evolution of the human body form."

Table 1 and Figure 3 present a summary of the physical differences between
modern H.s. and Pan that the authors consider indicative of adaptation to
endurance running.

And what of the nuchal ligament?
"Another possible structural modification relevant to running is the nuchal
ligament, a convergent feature in Homo (first evident in KNM-ER 1813) and
other mammals that are either cursorial (for example, dogs, horses, hares)
or have massive heads (elephants). Interestingly, a nuchal ligament is
absent in chimpanzees and apparently in australopithecines (as evinced by
the absence of a median nuchal line)."

How does AAH explain the presence of a nuchal ligament in Homo, but not in
Pan or A'pith? An aquatic animal doesn't need such a ligament for
supporting a massive head, since buoyancy solves that problem, and it
certainly doesn't need it to counteract a tendency for the head to pitch
forwards since swimming doesn't cause the kind of impact that results in
pitching forward.

And here is one critical comparison of Homo sap, Homo erectus, A'pithecus
and Pan:

"Many studies have found that compared to both Pan and Australopithecus,
Homo has substantially larger articular surface areas relative to body mass
in most joints of the lower body, including the femoral head and knee, the
sacroiliac joint, and the lumbar centra. Enlargement of these joints, which
is not matched in the upper limb of Homo, lowers the stresses that impact
forces generate at heel strike during walking, but would contribute more
critically to dissipate the much higher impact loads generated in running.
Another possible modification of the pelvis for resisting the stresses
associated with running is enlargement of the iliac pillar in early H.
erectus"

These features are easily explained by endurance running, but I can see no
way in which they can reasonably be explained by "slow diving" - perhaps
you would like to enlighten us?

Also, would you care to comment on these extracts? Do you have alternative
explanations or *evidence* based objections?

"Although not extensively studied in non-humans, ER is unique to humans
among primates, and uncommon among quadrupedal mammals other than social
carnivores (such as dogs and hyenas) and migratory ungulates (such as
wildebeest and horses)"

"Most humans voluntarily switch to running at approximately 2.3-2.5 m s-1,
which corresponds closely to the intersection of the COT curves for walking
and running in humans (Fig. 2b). At these higher speeds running becomes
less costly than walking by exploiting a mass-spring mechanism that
exchanges kinetic and potential energy very differently (Fig. 1b).
Collagen-rich tendons and ligaments in the leg store elastic strain energy
during the initial, braking part of the support phase, and then release the
energy through recoil during the subsequent propulsive phase. To use these
springs effectively, the legs flex more in running than in walking: flexing
and then extending at the knee and ankle during the support phase (Fig.
1a). Limb stiffness relative to body mass in running humans is similar to
that of other mammalian cursors."

"Well-conditioned human runners exceed the predicted preferred galloping
speed for a 65-kg quadruped and can occasionally outrun horses over the
extremely long distances that constrain these animals to optimal galloping
speeds, typically a canter (Fig 2a)."

"Fit human amateurs can regularly run 10 km, and longer distances such as
marathons (42.2 km) are achieved by tens of thousands of people each year.
Such distances are unknown if not impossible for any other primate, but are
comparable to those observed in specialized mammalian cursors in open
habitats. African hunting dogs travel an average of 10 km per day, and
wolves and hyenas travel on average 14 and 19 km day-1, respectively."

"The mass-adjusted COT of human running is about 50% higher than a typical
mammal, including other primates...Interestingly, other endurance cursors
such as wolves and African hunting dogs also have high mass-adjusted COT
relative to the average mammal."

--
Bon nou mujin sei gan dan
.

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