Progress in Mammalian Palaeontology. — Osborn. 219 
The law of local adaptive radiation with its polyphyletic 
consequences has completely altered our conception of sev- 
eral Oligocene families, as follows. The Titanotheriidae 
(Osborn 3 ) break up into four genera, which evolve inde- 
pendently from the base to the summit of the Oligocene, 
namely, Titanotheriufn, Megacerops, Symborodon, and Bron 
totherium; divergence is indicated by dolichocephaly and 
brachycephaly as well as by other characters (Fig. 7). Sim- 
ilarly the Equidae break up into four and possibly five dis- 
tinct contemporary phyla, and it now begins to appear prob- 
able that the line giving rise to Equus, separated off from 
the other horses as early as the Lower Oligocene (Osborn, 
Gidlev ; Fig. 4). The Oreodontidge, represented by two 
phyla in the Upper Eocene, now present three phyla, name- 
ly, Agriochoerus, Oreodon, Leptauchenia (Matthew). Three 
phyla of Camelidse are also recognized, namely, those repre- 
sented by Paratylopus, Poebrotherium, and Pseudolabis 
(Matthew, Fig. 5). Similarly among the Felidse, the Mach- 
aerodont division, the only felines represented in America at 
this time, breaks up into the stout-limbed Hoplophoneus 
series ancestral to Machaerodus and Smilodon the slender- 
limbed Dinictis *, and a third series represented by Nimravus 
(Fig. 6). 
Among the gaps in the Oligocene is the entire absence 
of Primates, the genera Laopithecus and Menothcrium, for 
merly associated with the Primates, proving to be singularly 
primitive tritubercular Artiodactyls. An important prob- 
lem is the actual relationships of the Artiodactyl genera Pro- 
toceras, Leptomeryx, ITypertragidus, and Hypisodus, which 
according to Scott's theory above alluded to, represent with 
the Oreodontidas an independent radiation of American Arti- 
odactyla wholly without affinity with the European Tragu- 
lines. 
The Miocene Fauna. 
In our Miocene, equivalent to the Langhien (Orleanais), 
Helvetien (Sansan, Simorre), and Tortonien (Grive St. Al- 
ban, Bamboli) stages of Europe, the most exceptional pro- 
3 Bull. Amer. Mus. Nat. Hist., xvi, 1902, pp. 91-109. 
4 Matthew. Fossil Mammals of the Tertiary of Northeastern Colorado 
Mem. Amer. Mus. Nat. Hist., vol. i, pt. vi, 1901. 
