I'm being good and working on my thesis. Well, I don't mean this very minute (I'm watching the Emmys and cheering for all the wins for John Adams!) So, because I'm writing about the Nauvoo Temple, part of my focus is the baptismal font, which was the very first font built for the newly restored church and installed in the basement of the Nauvoo Temple (built 1840-1846). Joseph Smith had revealed the doctrine of baptism for the dead before the temple was ready, so the first of these ordinances were performed in rivers and lakes. But this sacred ordinance needed a sacred place. So, while the temple was being built, the basement was quickly completed first and dedicated, before the temple's walls were even complete, so that the Saints could get busy and start baptizing.
This first font was carved by Elijah Fordham of joined wooden planks. It was in the form that Mormons are all familiar with today, with the large font resting on the back of 12 life-size oxen. The wooden oxen were painted white and finished with horns of tin. A few years later, this original font was replaced with one carved of stone. To non-Mormons in the 1840s, stories of the temple and its strange font seemed like outlandish and weird tales, and those who saw it called it the 8th Wonder of the World because it was so unusual to them. While some other churches practiced baptism by immersion like the Mormons, it usually took place in rivers as well. Fonts were small and simple, reserved for infant baptism or sprinkling.
While it is accepted that Joseph Smith saw the design for the entire temple in revelation, he must have also been familiar with the description of the "molten sea" in Solomon's temple (1 Kings 7:23-26) which was supported by twelve oxen. The number twelve is highly symbolic, representing among other things the twelve tribes of Israel. Oxen as a symbol might have been chosen because of their extreme strength.
I don't know all the answers, but I did find something interesting when I visited the Victoria & Albert Museum in London back in May. There they have a replica of the baptismal font in the Church of Saint Bartholomew in Liege, France. This is what it looks like:
This font was built between the years 1107 and 1118. Note that the font, which is large enough for total immersion, rests on the back of twelve oxen. (Also note that the high relief imagery and extraordinarily lifelike figures predate Giotto and the Italian Renaissance by more than a century, but that's another story...)
Joseph Smith and probably 95% of the Mormons in 1841 had never been to France or even heard of this church. So there's no question of copying. I believe that the Christians of Liege were influenced by the same sources as the Mormons: the scriptures, and some divine revelation. Its late, so I don't want to get into a huge religious discussion right now, but I just think its interesting.