I only recently was able to distinguish between the 2 most common genus here, Aetobatus and Myliobatis . The latter is often a catch-all name for any kind of grinding ray teeth found, although Brachyzodus , Igdobatis , Apocopedon , and Aetomylaeus are in the same family and have similar teeth. Rhinoptera , or cow-nosed ray, teeth are also found here, though I have only found a single specimen. Like Myliobatis, their teeth are large, flat and arranged in serried, tongue shaped rows creating a continuous surface for crushing and grinding food. These teeth are almost always found singley rather than complete sets or plates.
Some sources claim the slanted angle of the teeth becomes less acute the more recent the species.
The major distinction between Aetobatus species and other rays are the single rows on each plate, thus having closed or rounded ends on each tooth section as illustrated below. The more well know Myliobatis also made its' first appearance in the late Paleocene, and has an even greater number of named species. Again, it is hard to seperate species due to lack of documentation. The teeth are similar to Aetobatus, except there are multiple sections of teeth in a row, fitting together like a puzzle. So instead of having flat ends on each tooth section, they are pointed instead.