2346 THE TIN AM US, FLIGHTLESS BIRDS, ETC. 



TOOTHED AND LIZARD-TAILED BIRDS 



There remain for brief consideration certain extinct birds, from 

 formations of earlier age than the Tertiary, which differ from the 

 whole of those of the present day either in the possession of teeth in the jaws, or of 

 these, coupled with the retention of a long lizard -like tail, and certain other fea- 

 tures in the skeleton indicative of affinity with reptiles. 



Of the toothed birds ( Odontomithes) , as distinct from the lizard-tailed birds 

 which are likewise provided with teeth, there are two very well-marked modifica- 

 tions, both of which have been obtained from strata in the United States, corre- 

 sponding approximately in age with the Chalk and associated formations of Europe, 

 and hence frequently spoken of as Cretaceous birds. In their general organization 

 these birds approximate so closely to the ordinary Carinate birds of the present day, 

 that they may well be included in the same subclass, of which they will constitute a 

 separate series characterized by the possession of teeth, and likewise by the circum- 

 stance that the two halves of the lower jaw remain completely separate in front, in- 

 stead of having a solid bony union. Of these toothed birds the one type is known 

 as Ichthyornis, and comprises somewhat gull-like birds characterized by having 

 a numerous series of teeth implanted in distinct sockets, and also by the vertebrae or 

 joints of the back bone articulating with one another by means of cup-like surfaces, 

 whereas in the neck (and generally also in the back) of all existing birds, such sur- 

 faces are saddle shaped. Although the osteology of Ichthyornis has many resem- 

 blances to that of the gulls, this being especially shown in the skull, which is 

 regarded by Dr. Schufelt as coming very close to that of the skimmer, the skeleton 

 differs, among other points, by the circumstance that there is no projecting process 

 on the outer side of the lower end of the humerus. Hence, although it is quite 

 within the bounds of probability that these birds may be ancestral types of the mod- 

 ern gulls, it is by no means certain that they should be included in the same group. 



With Hesperornis we are confronted with a totally different type, in which the 

 teeth were implanted in an open groove, while the wings were rudimentary, and the 

 keel of the breastbone was wanting, although the vertebras resembled those of exist- 

 ing birds in articulating by saddle-shaped surfaces. In general organization 

 Hesperornis approximated indeed very closely to the modern divers, with which 

 it agrees in the general conformation of the skull and limb bones, as well as of the 

 pelvis. Whereas, however, the modern divers, have the long spike-like kneecap, 

 or patella, united with the tibia, in the extinct bird these two bones remained dis- 

 tinct. In dimensions, Hesperornis was a bird of large size, attaining a height of 

 rather more than a yard when in the upright position. That it was thoroughly 

 aquatic in its habits is self-evident; while it may with considerable probability 

 be regarded as a specialized and flightless offshoot from the ancestral stock of the 

 modern divers, although this would not justify its inclusion in the same family 

 as the latter. An apparently allied, although very imperfectly-known type of bird 

 (Enaliornis) is represented in England, where its remains have been obtained from 

 a thin stratum lying at the base of the chalk, known as the Cambridge green sand. 



