The Sub-class NEORNITHES may be arranged, as above stated, in three divisions, (A) Neornithes Ratitae, (B) Neornithes Odontolcae, and (C) Neornithes Carinatae. The first of these contains the Ratite Birds proper and possibly part of the so-called Stereornithes of Patagonia (p. [43]), with several fossil forms of doubtful position from England, France, and New Mexico, as will be seen below; the second the Hesperornithes of the Cretaceous Shales of Kansas, the Enaliornithes of the Cambridge Upper Greensand, and Baptornis of the American Chalk; the third the Ichthyornithes of the aforesaid Kansas deposits, and all other existing Birds, with various extinct species closely allied to them.
Of the points of distinction between the Neornithes and the Archaeornithes the most important are that the metacarpals are fused together, the second digit being the longest, and the third more or less reduced; and that the number of caudal vertebrae does not, as far as is known, exceed thirteen, of which the last five or six combine together to form a pygostyle, except in the Hesperornithes, Ratitae, and Tinamidae, where such is seldom the case.[[14]] The centra of the vertebrae also are concave on one side only, except in Ichthyornis, and perhaps in Enaliornis. The possession of teeth is, of course, exceptional, as is the remarkable loss of the keel of the sternum in the Ratitae.
It is now generally, if not universally, agreed that Flightless Birds were developed from those that could fly. It does not, however, necessarily follow that the Neornithes are direct descendants of the Archaeornithes, as each may be a separate offshoot from the same parent stem. All we can safely assert is, that the former were in existence about the end of the Jurassic times, that teeth were still retained in some cases during the Cretaceous Epoch, and that not only normal forms, but also flightless forms without keel or pygostyle,[[15]] had arisen by that date.
(A) The Ratitae are commonly characterised as Birds with no keel to the sternum; but this will not hold as a definition, since Hesperornis has also that peculiarity, while such genera as Didus, Stringops, Cnemiornis, and Notornis are nearly in the same condition. It is no one point, therefore, but the sum of many, which enables us to draw so clear a line of demarcation between this primitive group and the remainder of existing forms; nevertheless it is convenient to preserve the name unaltered, as it is well understood to what members of the class it is more especially meant to apply. The rhamphotheca, or horny sheath of the bill, instead of being simple, is composed of several more or less separate pieces, as in the Procellariidae, Tinamidae, and Steganopodes; the quadrate bone, by means of which the lower jaw is articulated to the skull, in place of two proximal knobs has only one, as in Hesperornis, Ichthyornis, and the Tinamidae; the coracoid and scapula are fused together, and meet at an obtuse, as opposed to an acute or right, angle; and the last six or seven caudal vertebrae do not coalesce into a pygostyle, or upright triangular expansion to carry the rectrices, a state of things found elsewhere in Hesperornis and the Tinamidae.[[16]] The reduced wings preclude flight; the tail is functionless, as in the Podicipedidae and Tinamidae; the tongue is very small; the oil gland is absent; the penis is large and erectile, being comparable to that of the Anseriformes; while in the adult the feathers are evenly distributed over the whole surface, as in the Spheniscidae and Palamedeidae, no down being present. Claws are found on the pollex and index in Struthio and Rhea, or occasionally on the third digit; in Casuarius, Dromaeus, and Apteryx they occur only on the index.
Ratite Birds proper are comprised in six groups, Struthiones or Ostriches, Rheae or Nandus, Megistanes or Cassowaries and Emeus, Apteryges or Kiwis, Dinornithes or Moas, and Aepyornithes or Rocs.
I. STRUTHIONES.
Fam. Struthionidae.–These birds are distinguished from all others by having only two toes–the third and fourth–the terminal phalanges of which are shortened and bear thick stunted claws, that of the outer toe being commonly absent. The whole foot, including the long scutellated metatarsus, is exceptionally stout, and the toes are padded beneath. The beak is short, broad, and depressed, with deeply split gape; the head is small, with large eyes; the neck very long; the wing- and drooping tail-feathers–the plumes of commerce–are large and soft, with broad equal vanes. The furcula and syringeal muscles are wanting, nor is there any aftershaft.
Struthio camelus, the Ostrich or "Camel-bird" of North Africa, now extends from Barbary to Arabia, and even to Mesopotamia, though no longer found, as of old, in Egypt or Central Asia, its former occurrence in Baluchistan being somewhat open to question. It is black with white wings and tail, having a flesh-coloured neck covered with brownish down, and partially bare tibiae of the same hue. The female and young male are almost entirely cinereous, while the chicks are clothed with bristly yellowish-white down with blackish stripes. The eggs of the typical northern bird have a surface like ivory, while those from Southern Africa are marked with close-set pits, whence some authorities recognise a different species (S. australis) in the latter region, distinguishable, moreover, by the bluish colour of the naked parts. Examples from Somaliland and the adjoining districts of East Africa to Lake Tanganyika are separated as S. molybdophanes, on account of the leaden colour of the unfeathered portions, coupled with a red patch on the front of the metatarsus. The eggs are smoother than in the southern species, but similarly pitted. The fossil forms S. asiaticus from the Pliocene of the Siwalik Hills of India, and S. karatheodori from the Upper Miocene of Samos complete the family, while S. (Struthiolithus) chersonensis has been founded on a petrified egg from the government of Cherson in South Russia.
Fig. 8.–Ostrich. Struthio camelus. × 1⁄19.