ODONTORNITHES, the term proposed by 0. C. Marsh for birds possessed of teeth (Gr. 66obs, tooth, apvcs, 6pvtOos bird), notably the genera Hesperornis and Ichthyornis from the Cretace ous deposits of Kansas. In 1875 he divided the "sub-class" into Odontolcae, with the teeth standing in grooves, and Odonto tormae, with the teeth in separate alveoles or sockets. In his magnificent work, Odontornithes: A monograph on the extinct toothed birds of North America (New Haven [Conn.], 188o), he logically added the Saururae,. represented by Archaeopteryx, as a third order. As it usually happens with the selection of a single anatomical character, the resulting classification was unnatural. The Odontornithes, as a matter of fact, are a heterogeneous as sembly, and the fact of their possessing teeth proves nothing but that many types of birds still possessed them in Cretaceous times. These teeth are heritages from their reptilian ancestry, of which abundant evidence is found in various parts of the skeleton. No fossil birds of later than Cretaceous age are known to have teeth, and recent birds possess not even embryonic vestiges.
The best known of the Odontornithes are Hesperornis regalis, standing about 3ft. high, and the somewhat taller H. crassipes. Both show the general configuration of a diver, but whether Hesperornis can be regarded as ancestral to the Colymbiformes or whether the many points of resemblance to this group are due to "convergence" is a moot point. There are about 14 teeth in a groove of the maxilla and about 21 in the mandible ; the vertebrae are typically heterocoelous ; of the wing-bones nothing but the humerus, or upper arm-bone, remained and this was re duced to a vestigial condition; clavicles slightly reduced; cora coids short and broad, movably connected with the scapula; ster num very long, broad and quite flat, without the trace of a keel. Hind limbs very strong and of the Colymbine type, but the outer or fourth capitulum of the metatarsus is the strongest and longest, an unique arrangement in an otherwise typically stegano podous foot. The pelvis shows much resemblance to that of the
divers, but there is still an incisura ischiadica instead of a fora men. The tail is composed of about twelve vertebrae, without a pygostyle. Enaliornis of the Cambridge Greensand of England, and Baptornis of the mid-Cretaceous of North America, are prob ably allied, but imperfectly known. The vertebrae are biconcave, with heterocoelous indications in the cervicals; the metatarsal bones appear still somewhat imperfectly anchylosed. The absence of a keel led the earlier naturalists to regard Hesperornis as one of the Struthious birds, and it has even been described as a "swimming ostrich." But there can be no doubt but that it is to be reckoned as one of the Neognathae which, becoming flight less, lost the keel of the sternum, as some of the land-birds have also done—e.g., the kakapo (q.v.) of New Zealand.
There remain the Odontotormae, notably Ichthyornis victor, I. dispar, Apatornis and Graculavus of the middle and upper Cre taceous of Kansas. The teeth stand in separate alveoli. The ver tebrae are amphicoelous, but at least the third cervical has some what saddle-shaped articular facets. Tail composed of five free vertebrae, followed by a rather small pygostyle. Shoulder girdle and sternum well developed and of the typical carinate type. Pelvis still with incisura ischiadica. Marsh based the restoration of Ichthyornis, which was obviously an aquatic bird possessing full powers of flight, upon the skeleton of a tern, though there is no natural affinity between them. The teeth, vertebrae, pelvis and small brain are all primitive so that the Odontotormae may form a separate order of the Neognathae, near the Colymbomor phous Legion. (W. P. P.) See G. Heilman, The Origin of Birds (1927).