Progress in ^Mammalian Palaeontology. — Osborn. 209 
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 (Osborn 1 , Thomas"), as shown in Fig. 3; 
it has proved to be absolutely necessary for the sake of 
clearness to recognize a number of genera which many sys- 
tematists (Flower, Lydekker) have considered simply syno- 
nyms of the genus Rhinoceros. Sixth, the chief morpholo- 
gical result is the discrimination of sexual characters, espec- 
ially among the male and female forms 3 , which in many 
cases by Marsh and Cope had been considered as distinct 
species. The recognition (Osborn 4 ) that progressive 
dolichocephaly and brachycephaly profoundly modify all the 
characters of the skull and the teeth on the principle of cor- 
relation, also represents a morphological advance. 
The independent and more or less cooperative field or 
museum work of Scott, Osborn, Wortman, Matthew, 
Hatcher, Douglass, Gidley, Peterson, has been instru- 
mental in fordwarding these chief lines of progress. 
The Older Mesozoic Fauna. 
Unfortunately the efforts of the American Museum to 
find more of the Protodonta (Dromotherium, Mieroconodon) 
from the Upper Trias or Rhaetic have proved unavailing. 
The relation of these animals to the Theriodont reptiles has 
been suggested (Seeley). 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 (Bensley 5 ). 
In the Upper Jurassic or Lower Cretaceous mammalia 
of the Como beds we must also admit that no progress has 
been made to determine whether these animals represent 
both Insectivora and Marsupialia and perhaps Monotremata 
(Osborn), or whether they are all Marsupialia 1 (most Fng- 
1 Phylogenv of the Rhinoceroses of Europe. Bull. Amor. Mus. Nat. 
Hist., vol. xiii. 1900, op. 229-267. 
2 Notes on tie Type Spec/men of Rhinoceros lasiotis Sclafer with 
Remarks on the Generic Position at the Living Species of Rhinoceros. 
Proc. Zool. Soc, Lond., Juni t. 1901, pp. 154-158. 
3 The Cranial Evolution of Titanotherium. Bull. Aiiht. Mus. Nat. 
Hist., vol. viii. 1896, pp. 157-197. 
4 Dolichocephaly and brachycephaly in che Lower Mammals. Bull. 
Amer. Mus. Nat Hist., vol. \vi. 1902, pp. T7-S9. 
5 On the Identification of Meckelian and Mylohyoid Grooves. Univ. of 
Toronto Studies Biol., Ser. 3, 1902, pp. 75-81. 
