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Author: drosen0000drosen0000 Date: Dec 23, 2006 11:36
Questions on pubic bones, an item common in the male members of most
tetrapod species. Humans and bonobos don't have any, but this makes
pubic bones even more interesting.
1) How did pubic bones evolve in tetrapods?
2) Are pubic bones in tetrapods homologous to anal fins in fish?
3) Are there any plausible theories on how pubic bones are used in
extant animals?
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Author: Wirt AtmarWirt Atmar Date: Dec 26, 2006 23:03
> Questions on pubic bones, an item common in the male members of most
> tetrapod species. Humans and bonobos don't have any, but this makes
> pubic bones even more interesting.
> 1) How did pubic bones evolve in tetrapods?
> 2) Are pubic bones in tetrapods homologous to anal fins in fish?
> 3) Are there any plausible theories on how pubic bones are used in
> extant animals?
I presume that you mean the "baculum" (or "os penis") when you say
"pubic bone" (which is actually part of the hip, not part of the
penis).
Most mammals possess bacula, although it is the most morphologically
variable bone in the body. That variation has led to two general
hypotheses for its existence and morphology. The first is that really
serves no purpose other than structural reinforcement in the erect
penis, but because it is polygenic in its encoding, it is also
inherently pleiotropic. As the organism evolves to new environments,
the baculum changes its morphology concommittantly, but with little
selective constraint, thus the variability.
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Author: r normanr norman Date: Dec 27, 2006 13:26
On Wed, 27 Dec 2006 02:03:30 -0500 (EST), "Wirt Atmar"
aics-research.com> wrote:
>> Questions on pubic bones, an item common in the male members of most
>> tetrapod species. Humans and bonobos don't have any, but this makes
>> pubic bones even more interesting...
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Author: dros0000dros0000 Date: Dec 27, 2006 13:26
> I presume that you mean the "baculum" (or "os penis") when you say
> "pubic bone" (which is actually part of the hip, not part of the
> penis).
Yes. Thank you for correcting me. Thank you for the two
theories as to it's use.
Please help with the second question:
>From what bone did baculum descend from in nonamniotic species?
The baculum, variable as it may be, is present in a wide
variety of amniote species. Therefore, I conjecture that something like
it was present in an ancestral species that was nonamniotic. The two
functions you mention make perfect sense in an amniote species, because
amniotic species have internal fertilization. However, nonamniotic
species (e.g., fish and amphibians) have external fertilization.
Nonamniotes don't need a penis for reproduction (although it may be
useful for some amphibians to pee). What would that hypothetical
ancestor use a baculum for? I just raised the conjecture that the
baculum is homologous to an anal fin. However, I don't know enough
anatomy to evaluate that conjecture.
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Author: dhoytdhoyt Date: Dec 28, 2006 10:15
>> I presume that you mean the "baculum" (or "os penis") when you say
>> "pubic bone" (which is actually part of the hip, not part of the
>> penis).
> Yes. Thank you for correcting me. Thank you for the two
> theories as to it's use.
> Please help with the second question:
>>From what bone did baculum descend from in nonamniotic species?
>
> The baculum, variable as it may be, is present in a wide
> variety of amniote species. Therefore, I conjecture that something like
> it was present in an ancestral species that was nonamniotic. The two
> functions you mention make perfect sense in an amniote species, because
> amniotic species have internal fertilization. However, nonamniotic
> species (e.g., fish and amphibians) have external fertilization.
> Nonamniotes don't need a penis for reproduction (although it may be
> useful for some amphibians to pee). What would that hypothetical
> ancestor use a baculum for? I just raised the conjecture that the
> baculum is homologous to an anal fin. However, I don't know enough
> anatomy to evaluate that conjecture. ...
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Author: drosen0000drosen0000 Date: Dec 29, 2006 09:59
Are you sure that there is no "penis bone" associated with
nonmammalian species? I know that the baculum is found in many
mammalian species, but this is the first time that I heard that it
doesn't exist in nonmammalian species. Maybe it is called something
else. Or maybe I am in error.
My knowledge of anatomy is limited. I am not an anatomist, but I
present talks to a private club. I trying to put together a talk on
homologies and analogies between fish and mammal bodies. Specifically,
between the skeletons of sting rays and human beings!
> A Google search also shows that the T. rex "bone" is not a baculum, but
> a difference in the bone tissue of the female related to calcium
> metabolism during egg shell formation.
That difference...
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Author: dhoytdhoyt Date: Dec 30, 2006 21:54
> Are you sure that there is no "penis bone" associated with
> nonmammalian species?
Yes. Among living reptiles the snakes and lizards have paired
hemipenes, hollow, eversible copulatory structures housed in the base
of the tail. Turtles and crocodilians have single, eversible structures
arising from the cloacal wall. Tuataras lack a male copulatory organ,
as do birds. No bones in any of them, although the snake hemipenes
have, in some species, spiny decorations, but these are not baculae.
> That difference in bone tissue was recently discovered. However,
> the researcher knew before making that claim that the skeleton being
> looked at was female. If the skeleton turns out to be...
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