Calciavis grandei was named by Nesbitt and Clarke (2016) [Calciavis grandei is diagnosed by the following unique combination of character states: pair of distinct furrows on the anterior portion of the dentary and premaxillae (C49:1 and C2:1, respectively); lateral exposure of the ventral process of the lacrimal broad (C13:1); short fingerlike retroarticular process just posterior to the articular facets of the mandible (C60:1); sternum with slightly concave posterior margin (local autapomorphy); deep fossa posterodistal to the pisiform process on the ventral surface of the proximal portion of the carpometacarpus (C135:1); ischium lacking a dorsal process (C155:1); posterior portion of the ischium blunt and not tapered (C156:0); anterior margin of the preacetabular portion of the ilium flat to concave (local autapomorphy); metatarsals IV and II subequal in distal extent (C180:0). Calciavis grandei differs from the holotype of the other Green River Formation lithornithid species, Pseudocrypturus cercanaxius (USNM 424078). The skull is shorter than the humerus in Calciavis, whereas it is longer than the humerus in Pseudocrypturus cercanaxius (based on the proportions of the type and comparing them to the referred specimen). Calciavis grandei has a proportionally narrower shaft of the coracoid and a proportionally longer tarsometatarsus than a referred specimen of Pseudocrypturus cercanaxius (USNM 424078). Calciavis grandei lacks a dorsal process on the ischium that is present in Lithornis promiscuus and the blunt distal end of the ischium of Calciavis grandei contrast with the tapering distal end of the ischium of Lithornis plebius. Calciavis grandei has a smaller preacetabular pectineal process of the pubis than that of Lithornis celetius. Calciavis grandei has less curved and more gracile scapular blade than that of Paracathartes howardae. Calciavis grandei lacks a medial flange of the pterygoid and a less developed flexor tubercle on manual phalanx III-1 in comparison with the Fur Formation lithornithid (MGUH 26770).]. It is not extant. Its type specimen is AMNH 30578, a skeleton (Essentially complete skeleton with soft-tissue preservation including feathers, pedal scales, and claw sheaths). Its type locality is Warfield Springs, which is in a Wasatchian lacustrine deltaic limestone in the Green River Formation of Wyoming.