It was discovered in grey siltstone deposits from the Campanian Hunter Wash Member of the Kirtland Formation of the San Juan Basin in New Mexico.

[1] Joshua Fry questioned the referral in a 2015 masters thesis, with a phylogenetic analysis failing to group it alongside other Pentaceratops specimens.

The name Terminocavus means "coming to the end of the cavity", referring to the parietal embayment being nearly closed off before being lost completely in more derived taxa.

[1] Known from limited material, Terminocavus is distinguished from close relatives such as Pentaceratops and Anchiceratops by the anatomy of its parietal (the upper portion of its frill), which forms a heart shape.

The prominent median embayment (a large notch in the middle of the top of the frill) of earlier relatives is heavily reduced, being very narrow as opposed to wide and U-shaped.

Terminocavus' parietal bars (the top edges of the frill) are thin and extremely broad compared to earlier relatives; they are more plate-shaped than bar-shaped.

The second pair are a larger set of triangles, whereas the third epiparietals have a rounded, "D" shape; both project upwards, angled in line with the rest of the parietal.

The left epijugal horn is known as well, fused to the jugal and quadratojugal bones; it robust and large, but unlike that of Pentaceratops is not especially long.

The genera (in sequence) Utahceratops, Pentaceratops, Navajoceratops, Terminocavus, and Anchiceratops would, under this model, represent a single population of organisms changing in form over time, rather than as a diverse assemblage of close relatives.