Anisotropic Dirac Fermions in BaMnBi$_{2}$ and BaZnBi$_{2}$*

We report electronic structures of BaMnBi$_{2}$ and BaZnBi$_{2}$ sharing similar structural properties but having different valence configuration of the Mn/Zn-Bi complex. Our angle-resolved photoemission measurements found a strong anisotropic Dirac dispersion in BaMnBi$_{2}$ and a complete departure from the Dirac dispersion in BaZnBi$_{2}$. Our findings, substantiated by the first principle calculations, allow us to understand role of Mn/Zn-Bi tetrahedra in the changes of the electronic structures as well as the effect of varying band filling of Bi-square net.