Aglyptorhynchus sulcatus was a large rostrum-bearing teleost that occupied the open marine waters represented by the London Clay. Its most characteristic fossil is the elongated bill-like snout, a specialised structure indicating a fish adapted for active swimming and predation in the water column. The precise relationship of these Eocene rostral fishes to living billfishes has been debated, so modern billfish behaviour should be used as an ecological analogy rather than a direct model.

The rostrum bears longitudinal canals and a distinctive dorsal groove, showing that it was a complex, vascularised bony structure rather than a simple spine. It probably played a role in feeding or prey interaction, but exactly how it was used is not preserved. Most specimens are isolated rostral fragments, making the animal much better known from this specialised part of the skull than from the rest of the body.