24 



NATURAL UISrORY OF BIRDS. 



necessary in orilor to obtain an intelligent iilea of the state of that scieni-e, and of tlie 

 class it treats of, a full account of these ancestoi-s of the fealhered trilies has been 

 deemed desirable, and, as Professor Marsh's work is the only source of information, 

 the following statements are given as nearly in his own words as jiossible. 



The geological horizon of the known Odontornithes is in the middle cretaceous, 

 and corres])onds to the strata named by 31arsh the ' Pteranodon beds,' situated along 

 the eastern slo])e of the Hocky Mountains, and especially on the adjoining jilains in 

 Kansas and Colorado. These beds consist mainly of a fine yellow chalk and calcare- 

 ous shale, both admirably ailaptedto preserve delicate s|)ecimens. The first bird fossil 

 discovered in this region was the lower end of the tibia of IIcKpa-ornis, found by Pro- 

 fessor Marsh in December, 1870, near the Smoky Hill River, in wester'n Kansas. In 

 June, ISTI, he made the discovery of the skeleton which forms the type of //. ref/dlis. 

 In the autumn, l!^7li, another skeleton of the same was found, and the type of the 

 genus Apatornis. The fossil birds procured in that region between 1870 and 1880, by 

 the different ex])lorations, include remains of more than one hundred individuals of the 

 toothed birds. 



Jt was soon found that these toothed birds were of two different kinds, which, 

 although united under the common heading, Odontornithes, were more different than 

 almost any two living birds of the i)resent day, and which had very little in common 



save the teeth. But even 

 ■ K UH WB I S these were extremely dif- 



ferent, being jdaced, as 

 they were, in a continuous 

 groove in one grou]>, while 

 in the other they were 

 implanteil in individual 

 sockets. The former were 

 therefore styled Odonto- 

 holca' (from the Greek odontoi, teeth, and holkos, a groove) while the others received 

 the name Odont(>torma> (oilotitoi, and toniios, a socket). The latter form the sub- 

 class here under consideration. 



The Odontotorma?, or birds with teeth in sockets, so far as now known, were all of 

 small size, and ])o.ssessed powerful witigs and very small legs and feet. Some of their 

 characters — as, for instance, their vertebras l)iconcave or hollow both behind and in 

 front — separate them widely from all birds recent and e.vtinct. 



The remains of this grouj) jireserved are more or less jineumatic, :nid this fact, in 

 connection with their small size, is perhaps the main reason Avhy .so few have been dis- 

 covered. As might naturally be expected, the hollow bones of flying birds, being 

 filled with air, enable the carcass to float upon the water much longer than it other- 

 wise would, and it is thus li.able to be destrovcd bv fislies or other anim.-ils. Ilence, 

 the chances of complete skeletons being buried entire are greatly diniinished. The 

 plains cast of the TJocky Mountains have yielded remains of not less than seventy- 

 seven different individuals of Odontotorm.T, belonging to two well-marked "genera," 

 Trlillii/oniis and ApaUiriu!i,\\w former rei>resented by several species (some of which 

 were fonnerly referred to the geinis Gracnlavus), and the latter by only one. These 

 were all small birds, scarcely larger than a ]iigeon. In their ]wwerful wings and small 

 legs and feet, they remind one of the terns, and, according to jiresent evidence, they 

 were aquatic birds, of similar life and habits. 



■P UTJ^H^j 



Fici. 8. — Quadrate bone of Ichlhijomls. 



