[D] Graculavus agilis [~/~]
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Avialae Ornithothoraces Ornithurae Cartinatae Ichtyornithiformes
Niobrara Chalk Formation, Kansas, US
Ichthyornis dispar (Marsh, 1872) [= Colonosaurus mudgei (Marsh, 1872) including Ichthyornis agilis (Marsh, 1873); Graculavus agilis (Marsh, 1873); Ichthyornis anceps (Marsh, 1872); Graculavus anceps (Marsh, 1872); Ichthyornis victor (Marsh, 1876); Ichthyornis validus (Marsh, 1880); Ichthyornis antecessor (Wetmore, 1962); Plegadornis antecessor (Wetmore, 1962); Angelinornis antecessor (Wetmore, 1962)
YPM 1209, a proximal left carpometacarpus lacking metacarpal
Graculavus agilis (Marsh, 1873) was named shortly after Ichthyornis dispar (Marsh, 1872) and was subsequently referred to Ichthyornis (Marsh, 1880). It was described in two short sentences, and a holotype specimen was not named in the publication. The holotype specimen was not mentioned to be a proximal carpometacarpus, and the differentiation provided of Graculavus agilis from Graculavus anceps (Marsh, 1872) is unsupported, primarily because the two holotypes are nonoverlapping parts of a left carpometacarpus that cannot be directly compared.
Locality and horizon
Marsh (1880) specified that he collected YPM 1208 from Butte Creek in 1872. Butte Creek, also known as Twin Butte Creek, is a well-known locality of what is now Logan County, Kansas, in the Smoky Hill Chalk Member, Niobrara Chalk Formation (Stewart et al., 1990), representing beds between Marker Units 15 and 19 (Bennett , 1990) of Hattin (1982). Stewart (1990) estimated that the interval containing Hattin’s (1982) Marker Units 8–10 to be upper Santonian in age. Thus, because Marker Units 15–19 are above these units, they must be from, at the earliest, later in the upper Santonian (than Marker Units 8–10) or from the lower Campanian. The top of the Smoky Hill Chalk Member is early Campanian in age (Stewart et al., 1990).
The Ichthyornis agilis specimen differs in size from Ichthyornis dispar. (Clarke , 2004)