JOEL - As a spirit being in the pre-existance Adam was known as Michael, the Archangel. The scriptures tell us that God made his body from dust of this earth(Morm. 9: 17, D&C 77: 12, Moses 3: 7), and placed Adam in the Garden as an immortal being with flesh and bone (no blood). Because he was immortal and without blood he could not have come by way of any type of evolution from a lower form of animal, as some might want to believe. So if you take the scriptures literally and God actually formed Adam out of dust, he had no biological parents and therefore would not have needed an umbilical cord, therefore no bellybutton.

However, the book of Moses states that Adam's children were also created from the dust of the earth (see Moses 6:59). The same expression used to describe the bodily creation of Adam's children was used to describe the creation of Adam's body. Does this not suggest the same natural process was used? Adam is also spoken of as being the "son of God" (Moses 6:22). So is it possible that Adam's immortal body was formed by immortal heavenly parents in a similar fashion that Adam and Eve created their own children? If this is true then perhaps Adam did have an umbilical cord atttached to his heavenly mother and therefore did have a bellybutton. Jesus would still be considered the "only begotten son", but in a mortal body.
Since we are told Eve was created from one of Adam's ribs, perhaps a more interesting question would be "Did Eve have a bellybutton?"
The bottom line is ....I don't know..