Nasiornis messelornithoides was a small messelornithid, an extinct group of terrestrial gruiform birds related to the wider rail and crane radiation. Messelornithids were long legged ground birds rather than specialised aquatic rails, and Nasiornis adds a British representative to a group well known from other early Eocene deposits.

It probably foraged on the forest floor or other vegetated ground, taking insects, other small invertebrates and perhaps plant material. This omnivorous or insectivorous reconstruction is inferred from messelornithid anatomy and ecology rather than direct gut contents. The London Clay material consists of associated partial skeletons and foot material.