Alligator gar have a unique appearance that sets them apart from other types of gar. Their bodies are heavier and broader, and their snouts are short and broad, adorned with numerous large and sharp teeth. While most of their teeth are needle-sharp at the tip, some fish may have less sharp, pre-molar-like teeth, possibly due to heavy use or age. The number, rows, and locations of their teeth are highly variable, with some fish having teeth in and outside of their closed mouths, arranged in what appears to be revolving rows for the replacement of lost teeth.
When their mouths are closed, the teeth are seated into recessed openings on the corresponding jaw. Alligator gar, along with other members of the Atractosteus genus, have two rows of teeth on their upper jaws, with the second row located inside the mouth, which can be easily mistaken for the externally visible teeth when the mouth is closed. While some shortnose gar may also exhibit double rows of teeth on the upper jaw, they can be distinguished from alligator gar through other morphological differences that become apparent upon closer examination.