THIRD ANNUAL MEETING 33 



and none in the pre-niaxillae. It is interesting to note that these 

 teeth, which, like those of Hesperornis, may be likened to mosasaur teeth 

 in miniatnre. have vertical successors, and the old teeth are g-i-adually 

 absorbed and displaced by the new. The teeth are set in distinct sockets, 

 and in allusion to this the Greek name Odonlormae has been applied to 

 this sub-order. In most birds thci dentaries of the two rami of the 

 mandible are united at the symphysis, but in Ichthyornis as well as in 

 Archaeopteryx and Hesperornis, the three birds which show the widest 

 divergence known to any age of birds, the rami are loosely connected, 

 which is a reptilian character. Tliey are supposed to have lacked 

 horny beaks. The vertebrae are amphicoelous or biconcave, an extra- 

 ordinarily primitive character, and the caudals, which terminate in 

 a pygostyle, should be compared with the earlier toothed birds. In 

 Archaeopteryx the lizard-like tail, consiting of twenty caudals, was 

 without a pygostjde (Fig. 47). In Hesperornis the caudals number 

 twelve, six of which are united by their centra into an imperfect 

 pygostyle (Fig. 48). In Ichthyornis there are five free caudals, and a 

 small, though perfect, pygostyle. In modern birds the caudals are 

 even more compressed and the pygostyle still more expanded. The 

 size of the brain in both Hesperornis and Ichthyornis is inferior to the 

 nearest allies of their respective sizes. All the other carinates are 

 toothless, although a few still retain ancestral traits to the extent 

 oi' exhibiting germ teeth while young. This is not anomalous for there 

 are many animals which, having descended from toothed ancestors, 

 exhibit the same peculiarities, and the teeth which they possess in the 

 embryonic condition are absorbed in the adult. 



TOOTHLESS CARINATAE 



Though the number of toothless carinates described by the jialaeon- 

 tologist is seemingly large, the records are unfortunately meagre, other- 

 wise the exact relation and classification of certain groups would be 

 less doubtful. In this toothless division the very first bird to engage 

 our attention is a "toothed bird" belonging to the Steganopodes. But 

 we must distinguish between true teeth and teeth-like serrations. 



Among the Steganopodes there is nothing particularly large or 

 unique until we come to Odoxtoptekyx, which by some writers is put in 

 a separate sub-order, Odontopteryges. Odontopterjx, of the Eocene in 

 England, thought by some palaeontologists to be related to the ducks 

 and geese, is so unique in the bony denticulation of its jaws as to 

 constitute another landmark in avian palaeontology. Though appa- 

 rently a toothed bird it is not such in fact, for the teeth are but 

 sharp bony serrations of the jaw itself. As the figure will show there 

 are two sizes of denticles or serrations, the more prominent alter- 

 nating with the less prominent. This denticulation. a peculiarity of 

 this group and unknown since Eocene time, is indicative of fish-eating 

 habits. Some naturalists place Ichthyornis, Apatornis and Odontopteryx 



