The Nif files you need are the Tapir ones...Adult and Young both follow the same protocal
Okay, the Nif files say which files to read when they are looking for the .dds files. IF you are making a new animal, you ALWAYS have to open up these. You will need a program such as WinHex to open them and read them.
Inside the NIF, look for .dds, and it should take you to Tapir_Adult.dds or whatever it is. Now, the thing about the NIFs is that you can't change the amount of letters in there, or you will get an error. So, for example, when I did the African Crowned Crane from the Secretary Bird, I had to change BirdSecretary into CraneAfricanC. If you have a name that is SHORTER than the original one, use underscores _ to fill in the spaces. Make sure to ONLY change places that say .dds; usually there is only one unless you are doing an animal with 2-D parts, like the peafowl, etc.
Now, make sure that you like the NIF in the .bfm file. You only change 3 places in that file, and they will look something like these:
CraneAfricanCrowned\CraneAfricanCrowned_Adult_F.NIF">
and
Now, you have to go to the main .dds file and make sure that it is named the same way as you told the NIF file that it would be. After you do that, go to the main XML file and do a "Find: .dds" thing, and make sure that that is linked right as well.