Ichthyornis validus (YPM, 1740)

CLARKE, JULIA A., 2004, Morphology, Phylogenetic Taxonomy, And Systematics Of Ichthyornis And Apatornis (Avialae: Ornithurae), Bulletin of the American Museum of Natural History 2004 (286), pp. 1-179 : 42-43

Ichthyornis validus

Ichthyornis validus was named in Odontornithes. The holotype was not described, differentiated, or diagnosed, although it was figured ( Marsh, 1880: pl. XXX, figs. 11–14).

HOLOTYPE SPECIMEN: YPM 1740 is a nearly complete right ulna (fig. 12). Brodkorb (1967) noted the holotype to be comprised of an ulna and radius; however, no radius is currently known to exist for this specimen. Marsh (1880) also did not mention a radius as part of this specimen. Additionally, the original YPM label of the specimen mentions only an ulna, as does the unpublished YPM catalogue undertaken by Thorpe (1937).

LOCALITY AND HORIZON: The holotype is described ( Marsh, 1880: 198) as being ‘‘discovered in September, 1877, by Mr. S. W. Williston, near the Solomon River in north­ western Kansas.’’ Brodkorb (1967) further specified that it was from Graham County, Kansas, information also listed as part of the original label associated with the specimen.

DISCUSSION: The holotype of Ichthyornis validus (YPM 1740) is considered subadult primarily because of the unfinished bone on the epiphyses. Compatible with this interpretation are the comparatively weakly developed follicular ligament scars and lack of detail in the morphology of the distal condyles and muscular attachments. It is intermediate in size between specimens corresponding to the majority of the YPM material and the holotype of Ichthyornis dispar (figs. 9, 10). This intermediate size can clearly be seen if the distance between the nutrient foramen and the proximal tip of the olecranon is compared or if total ulnar length is compared (fig. 10). The length of the ulna in Ichthyornis dispar is 61.5 mm ( Marsh, 1880, reported 62.0 mm); in YPM 1740 it is 68.5 mm (consistent with Marsh, 1880); and YPM 1453 measures 73.8 mm ( Marsh, 1880, reported 75.0; fig. 9). YPM 1453, an isolated ulna, is inferred to be the size of the Ichthyornis victor holotype, and the size of the majority of the YPM specimens through comparison with a third specimen, YPM 1757, which has elements overlapping those of the Ichthyornis victor holotype that are the same size.

If a larger species is recognized associated with further evidence concerning how Ichthyornis grew, the holotype of Ichthyornis validus , as a subadult individual of a larger species, would probably be recommended as a junior synonym of the named larger species (e.g., Ichthyornis victor ). Further discussion of the significance of this specimen is presented in the Taxonomic Revision, in the section Evidence for the Presence of Distinct Ontogenetic Stages.

REFERRED SPECIMENS: An isolated partial coracoid (YPM 1446) was referred to this taxon. There is no evidence to support this referral to Ichthyornis validus as it cannot be compared to the holotype. This large coracoid is notably larger than the holotype of Ichthyornis validus . Thus, these two specimens do not have even relative size in common.