Progress in Mammalian Palaeontology . — Osborn. 215 
LAW OF LOCAL ADAPTIVE RADIAT/OtV 
Confcnporary Evotufion of U-S P/iy/a of Horses , O/t'foeene So Pfeisfocene 
J IV Cidteo . 'SO* 
/ Side p/iy/un, I /Jim* 
re tated f £ . pny/u 
'// .J Efuus, * Ptionippus 5 HypoAippui iSidc p/wlcu' 
l° /i 9<'"» pAy/um . pALLm relate fo S 
P/e/itocen, 
F.fuui 
Pfi'oeene 
Hipuarmii 
/Yeorf</>/>* r '<> n 
Miocene 
JY(rucj 
ippus 
ProtoAinpus 
Mtryc^jpu 
I nstatu t 
iejunctu.s 
P/,oA,yfru-. 
l\{erycAippu J 
_____i 
Hypohtpfx* 1 
dalotcnsis 
HlfpoflipP"* 
eauinus 
i/iif. 
_Z_____ 1 
Pais hi, 
ParaAippus 
Miotiiapusilld/ti 
M.aitnecttns 
M r____f___ 
MtSo/t'/jpuS 
rattdas 
M. ArarAysti/fu 
McsoAipp w. 
meftufopAus 
Of, 
foecne 
MesoA 
ifi^US 
hat rd, 
Mesonippu 1 
AiesoAippuS 
Mcsonippus 
ob/iyuidctu 
MesoAipvus 
eu/opAu. 
Me so A, 
ifanensis 
ygu 
pro feu lop A u 
V 
Cusps separated. 
Profocenc ieeomcs isofated '.' 
Sfyfcs prominent 
Cusps mocferatc/u 
united info crests. 
Ec to/op A 1 styles /fattened , 
Casus united into perfect crests 
fill those in Tapir us iVhmoeeraS 
FIG. 4. 
The Polyphyletic Law Illustrated in the Evolution of the Equidae of North America 
In the Miocene are at least four contemporary phyla of horses, the 
extremes being represented by the forest-living- horse Hypohippus, and 
the light-limbed Neohipparion; the central form, Protohippus, apparently 
leading to Equus. 
This true Equus line separated off from other horses as far back 
as the base of the Oligocene. In this period again five distinct contem- 
porary phyla have already been found. 
are not exactly determined (Wortman, Matthew).. The 
supposed ancestry (Wortman) of the Felidae in the Eocene 
in the prohlematical genus Aelur other iioa has been dis- 
proved (Matthew). 
Still undiscovered or unrecognized in the Eocene both 
of America and Eurasia are the ancestors of the true Rhin- 
ocerotidse which suddenly appear in the Oligocene. The 
Basal Eocene ancestry of the Rodentia is still satisfied only 
provisionally by the family Mixodectidse*, belonging to the 
somewhat hypothetical Proglires (Osborn 1 ) ; the teeth seem 
to be approaching those of the Rodents but knowledge of 
2 The Extinct Camc/idae Bull. Amor. Mus. Nat. Hist., vol. x. L898, 
pp. 93-112. 
3 Bull. Amer. Mus. Nat. Hist., xvi, 1902. 
