H. F, OSBORN — MAMMALIAN PALÆONTOLOGY 95 
only by the addition of many new forms from the Eurasiatic radiation 
hitherto unknown, but also by observing more precisely the time of ar-- 
rival of Eurasiatic migrants in the Lower, Mid- and Upper Miocene and 
of South American in the Pliocene. Fifth, the phylogenetic succession has 
become much clearer and more direct, although a vast amount remains 
to be done. The separate branches of the mammalian phyletic tree have 
been successfully traced back farther and farther toward the beginnings 
of the Tertiary, with resultant changes in our classification. Perhaps the 
most signal taxonomic result of this phylogenetic progress is in the clear 
definition of certain genera, notably among the rhinoceroses (OsBorx ', 
THomas*), as shown in Fig. 3; it has proved to be absolutely neces- 
sary for the sake of clearness to recognize a number of genera which 
many systematists (FLower, Lypekker) have considered simply synonyms 
of the genus Rhinoceros. Sixth, the chief morphological result is the 
discrimination of sexual characters, especially among the male and female 
forms *, which in many cases by Marsa and Cope had been considered as 
distinct species. The recognition (OsBorx ‘) that progressive dolichoce- 
phaly and brachycephaly profoundly modify all the characters of the 
skull and the teeth on the principle of correlation, also represents a mor- 
phological advance. 
The independent and more or less cooperative field or museum work 
of Scorr, OsBorx, WoORTMAN, MATTHEW, HATCHER, DouGLass, GIDLEY, 
PerersoN, has been instrumental in forwarding these chief lines of pro- 
gress. 
Te OLper Mesozorc FAUNA. 
Unfortunately the efforts of the American Museum to find more of the 
Protodonta (Dromotherium, Microconodon) from the Upper Trias or 
Rhætie have proved unavailing. The relation of these animals to the 
Theriodont reptiles has been suggested (Seezev), but the single bone of 
the jaw rather sustains their relation to the mammalia. The groove on 
the inner side of the jaw of all Mesozoic and some recent mammals is 
now recognized as the Meckelian-cartilage groove (BENSsLEY ”). 
? Phylogeny of the Rhinoceroses of Europe. Bull. Amer. Mus. Nat. Hist., Vol. 
xiii, 1900, pp. 229-267. 
? Notes on the Type Specimen of Rhinoceros lasiotis Sclater with Remarks on 
the Generic Position of the Living Species of Rhinoceros. Proc. Zool. Soc., Lond., 
June 4, 1901, pp. 154-158. 
5 The Cranial Evolution of Titanotherium. Bull. Amer. Mus. Nat. Hist., Vol. 
viii, 1896, pp. 157-197. 
* Dolichocephaly and brachycephaly in the Lower Mammals. Bull. Amer. Mus. 
Nat. Hist., Vol. xvi, 1902, pp. 77-89. 
* On the Identification of Meckelian and Mylohyoid Grooves. Univ. of Toronto 
Studies Biol., Ser. 3, 1902, pp. 75-81. 
