E.S.
This is more a response to the woman who mentioned Dr. Weissbluth's book. I can tell you right now that she is a little off on that. He writes that only a small percentage of babies lose their morning nap before 15 months of age, and then after that it goes up dramatically.
I agree that your baby is probably just going through a phase (or perhaps getting sick or teething). Just keep being consistent and eventually he'll go back to his regular routine. I thought my son was losing his morning nap around 13 months but he got pretty sick and then I found out he had an ear infection. Once all that cleared up he went back to taking his naps just fine. Just before 15 months we started having trouble with the two naps again but wasn't sick (this time he would take a long morning nap and then refuse the afternoon nap or he would take a very brief if at all morning nap and then a longer afternoon nap), so we decided to try the one nap schedule. It took a few weeks of him having to go to bed earlier to avoid him getting overtired but we eventually got him adjusted to a one nap schedule.
But again, babies do go through phases. My son was sick again recently and some days it was hard to get him to sleep a total of even 12 hours a day for a couple of weeks. Now that he's better he's been sleeping about 14 hours a day (usually 12-13 hours at night and a 1-2 hour nap during the day).