Alphadon lulli was named by Clemens (1966). Its type specimen is UCMP 47047, a maxilla (fragmentary left maxilla with M1-2, alveoli of M3, and parts of alveoli of P3 and P4), and it is not a trace fossil. Its type locality is Lull 2 Quarry (UCMP V-5620), which is in a Maastrichtian terrestrial sandstone in the Lance Formation of Wyoming. It is the type species of Protalphadon.

It was recombined as Protalphadon lulli by Cifelli (1990), Johanson (1995), Johanson (1996), Kielan-Jaworowska et al. (2004).