I assume all mammals are nourished in the womb through a placenta and
umbilical cord.  If this is the case, what happens to the cord of
other animals at birth?  Do all primates/mammals, then, have navels?

What an unusual and interesting question. A question alot of us
probably never thought about.

The belly button, or umbilicus, represents the site where the
umbilical cord attaches to the fetus during development. The umbilical
cord transports blood between the fetus and the placenta. All
placental mammals have a placenta, and an umbilical cord. In the
placenta the fetal circulation releases wastes in exchange for oxygen
and nutrients from the mother. In the case of animals which carry more
than one fetus at a time, each fetus must have an umbilical cord in
order to survive. However, these multiple umbilical cords do not
usually get tangled. The main reason is that each embryo is contained
in the mother’s uterus as a single unit. There are a series of
membranes that surround the developing embryo and the umbilical cord,
thus isolating them from neighboring structures. After the baby is
born, the umbilical cord is usually broken or tied off and cut. The
stump attached to the baby falls off within a few days, leaving the
belly button behind as the only reminder of life 'in utero'.

Virtually all mammals have umbilical cords and hence navels, which are
simply scars left at the site where the umbilical cord was attached to
the body. The difference between human navels and animalnavels is the
appearance. Cats navels are basically an elongated scar located just
astern of the rib cage. It's quite understandable that they are often
overlooked since it is hidden by hair. In dogs they appear as small
scars along the stomach, rather than indented belly buttons. These
scars usually fade away after a few years, but you can still see them
in puppies

Information was found on the following sites:

"BBCi - Science Shack"
http://www.bbc.co.uk/science/scienceshack/articles/questions/q_ou74.shtml

"The Life Museum"
http://www.fiocruz.br/emvida/porque_resp5_jogos_e.html

"The Straight Dope"
http://www.straightdope.com/classics/a1_001a.html

"MadSci Network"
http://www.madsci.org/posts/archives/aug98/902945879.Zo.r.html

"Reeko's Mad Scientist lab"
http://www.spartechsoftware.com/reeko/qanda.htm

Keywords used:
mammals "umbilical cords" navels
://www.google.com/search?sourceid=navclient&q=mammals+%22umbilical+cords%22+navels

Best of luck,
rainbow-ga

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Request for Answer Clarification by etterman-ga on 13 Jun 2002 15:42 PDT

This is a great start.  But, I'm still not understanding how animals
can "tie off" and "cut" the cord from the placenta.  Do they use
scissors, teeth....?

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Clarification of Answer by rainbow-ga on 13 Jun 2002 17:08 PDT

Hi Etterman,

Many domestic mammals will be in the care of humans while giving
birth. This is the time the umbilical cord is cut and then tied. But
amongst wild animals, "the first thing that the mother will do is to
clean the babies by licking them dry. She will also cut the umbilical
cord by biting through it near the baby's body. No blood will be lost
because the umbilical cord does not function any more. Finally, the
mothers of many species of wild mammals often clear away the amnion,
placenta and umbilical cord by eating them. This is important because
the blood in the placenta could attract predators to the helpless,
new-born offspring"

"The Open Door Website"
http://www.saburchill.com/chapters/chap0038.html

Regards, 
rainbow-ga

http://www.madsci.org/posts/archives/sep2000/967827843.Zo.r.html would
have been good, too.

my understanding is that when the babies are born, the mother
typically licks the baby clean, and bites the umbilicus.

I wonder at the reference of "placental mammals"... does this indicate
that there are non-placental mammals that use a different system of
nutrient transport?

There are a couple of aplacental mammals, including monotremes
(platypuses) and marsupials (kangaroos, etc).

See:  http://www.ucmp.berkeley.edu/mammal/monotreme.html for more
info.

((you have to love ap biology))

Ingesting the placenta also gives the mother an nutrient-rich protein
boost after her labor efforts, as she will have been isolated and her
energy spent during the birth. This is not limited to "wild animals,"
as several human societies still eat the placenta after giving birth.
I believe this practice is coming back into style in Europe. There are
some recipes out there for freeze-dried or pate-style placenta.
Really. http://www.dear-midwife.com/faq.html

butterfly said:
"There are a couple of aplecental mammals, including monotremes
(platypuses) and marsupials (kangaroos, etc)."

I think this is perhaps a misleadingly simplistic statement.  There
are currently considered to be 276 species of mammals that are
monotremes or marsupials, as opposed to placentals.  However. . .

Monotremes (platypuses and echidnas) lay eggs and nutrients are
provided to the embryo from the yolk sac (the direct evolutionary
basis of the placenta).

Most marsupials (with the exception of bandicoots) have very simple
placentas (choriovitelline placentas) that are more or less yolk sacs
without eggs.

Bandicoots, (true) placental mammals, and some snakes have more
complex placentas (chorioallantoic placentas).

Yes, some snakes give live birth, in fact "viper" comes from
"viviparous", "bearing live young".  Some people have estimated that
live birth has evolved 75 different times among reptiles.

I really couldn't say how all this fits in with navels, though.  I've
never heard of a snake with a belly button.

My personal favorite site for zoology information is the Animal
Diversity Web:
http://animaldiversity.ummz.umich.edu/index.html

Its sections on mammals and crocodiles are particularily informative.