What is the difference between a northern tamandua and a southern tamandua?

The northern tamandua would be Tamandua Mexicana. They always have a black vest and there are some skull differences and differences in gestation.

The southern Tamandua is Tamandua Tetradactyla. They are sometimes vest but not always. They have a gestation of 150 days.

If you are looking at a vested souther anteater and norther tamandua side by side you would not likely be able to tell them appart. Though tamandua m tends to havbe a very definite vest and Tamandua t. tends to have less definite edges.