I was learning a bit with Binyamin (who I met at a Melave Malka Motzei Shabbat) and we went over a Taz that explained the opinions about roasting on Shabbat. I created a chart that explains what the Taz says the Mehaber (who the Taz says bases his opinion on the Rambam) and the Rama (who the Taz says bases his opinion on the Tur).
This chart shows where each stands on the difference between the opinions on using an open Tanur vs. a Tanur with the "mouth" sealed by pitch (tar) or a similar substance. The difference between kids and fowl and other meats (like goat or beef) applies only if the meats are cut up into pieces but if the animal is whole, the halakha is like beef and other meats. The reason that a sealed Tanur would be ok is that if you open the Tanur to stoke the coals you would ruin the meat.