PHYLOGENY, TAXONOMY, DISTRIBUTION, HABITS, AND ENVIRON- 

 MENT OF THE CERATOPSIA. 



GENERIC A1STD SPECIFIC SUMMARY. 



GENERAL DISCUSSION OF THE PHYLOGENY. 



Of the fourteen genera which have at sundry times and by various authors been referred 

 to the Ceratopsia but seven have survived the process of elimination to which they have been 

 subjected. Of these, three more primitive genera were found in the earlier Judith River 

 beds, and the remaining four, which are much more specialized, were found in the Laramie 

 deposits. That there is a genetic relationship between the earlier forms and their successors 

 is evident, and, as Osborn, Lambe, and Hatcher have suggested, there seem to have been at 

 least two lines of descent, one leading to Triceratops, with its entire bony frill, and the other to 

 Torosaurus, with persistently open parietal fontanelles. 



Professor Osborn's" statement is as follows: 



It is not at all improbable that the horned dinosaurs will prove to be diphyletic, one line, with persistent open fossae, 

 leading from Monoclonius to Torosaurus, the other leading to Triceratops with closed fossa?. 



Lambe, 6 in speaking of the parietal of Ceratops ( Monoclonius) , says : 



The parietal is about one-third the size of that of T. gladius, and would probably represent a proportionately smaller 

 animal, an earlier and more generalized form of the genus, with larger fontanelles than its later Laramie successors. 



In Hatcher's unrevised description of the genus Torosaurus (p. 150) he says: 



As already remarked, the parietals of the present genus most nearly resemble the same elements in the type of Mono- 

 clonius (M. crassus), and there seems but little doubt that the last-mentioned genus was ancestral to Torosaurus. 



In the revised portion of his manuscript, however (p. 100), Hatcher reverses this earlier 

 decision in the following statement: 



The affinities of Monoclonius, as shown in the type species, M. crassus Cope and M. dawsoni of Lambe, are apparently 

 with the later genus Triceratops of Marsh, while Ceratops montanus Marsh, C. recurvicornis Cope, O. canadensis, and C. belli 

 Lambe would seem to be ancestral to Torosaurus. 



Mr. Lambe' s statement is fully in accord with this, while that of Professor Osborn may 

 be reconciled to it if by " Monoclonius" he had special reference to M. canadensis and M. belli, 

 which Hatcher has removed to the genus Ceratops. If, on the contrary, Osborn had in mind 

 the type species, Monoclonius crassus, his opinion as expressed would be at variance with 

 Hatcher's final idea of these relationships. 



The weight of evidence to be reviewed below is certainly in favor of Hatcher's final theory, 

 according to which the genera may be provisionally arranged in two phyla in the following 

 sequence : 



Phyla of the Ceratopsia. 



Geological horizon. 



Triceratops phylum. 



Torosaurus phylum. 



Denver beds. 



Triceratops. 





Laramie of Converse County, Wyo. 

 Laramie of Black Buttes, Wyo. 



Diceratops. 

 Triceratops. 

 Agathaumas. 



Torosaurus. 



Judith River (Belly River). 



Centrosaurus. 

 Monoclonius. 



Ceratops. 



oContr. Canadian Pal., vol. 3 (quarto), pt. 2, p. 31. 

 MON XLIX — 07 11 



b Ibid., p. 67. 



161 



