220 



SCIENCE 



N. S. Vol. XXX. No. 763 



Equns sivalensis of the Siwalik deposits of 

 northern India is the oldest true horse known 

 to science (i. e., the oldest one-hoofed horse 

 ■with long (hypsodont) molars), and as it 

 measured about fifteen hands, it is the largest 

 of the old world " fossil " horses. This an- 

 cient Siwalik horse was characterized by long, 

 fairly slender limbs and a long tapering face 

 deflected to form an angle of nearly 20° with 

 the base of the cranium. In addition to hav- 

 ing a large head, a convex profile and long 

 limbs, E. sivalensis seems to have been char- 

 acterized by a long neck, high withers and a 

 tail set on so high that the root was well in 

 front of the point of the buttock. 



Nothing is known of the ancestors of the 

 horse which suddenly made its appearance in 

 Pliocene times amongst the foothills of the 

 Himalayas, but it may be safely assumed that 

 it very decidedly differed from PKohippus, the 

 small " fossil " horse of the late Miocene and 

 early Pliocene deposits of America from which 

 some believe all the recent Equidse are de- 

 scended. 



It used to be said that E. sivalensis could 

 not be regarded as an ancestor of domestic 

 horses because of the shortness of the ante- 

 rior pillar of the cheek teeth. I find, however, 

 that in some modern horses, the anterior pil- 

 lars are decidedly shorter than in E. sivalensis, 

 and that in some of the short-pillared do- 

 mestic horses the face is nearly as strongly 

 deflected on the cranium as in E. sivalensis. 

 There is hence no longer any reason for as- 

 suming that this ancient Indian species had 

 no share in the making of domestic breeds. 

 But in the absence of a large and representa- 

 tive collection of skulls of domestic horses, it 

 is impossible to say which modern breeds are 

 most indebted to the large-headed, long- 

 limbed race, which in Pliocene times fre- 

 quented the area to the east of the Jhelum 

 Eiver, now occupied by the Siwalik Hills. 



Mr. Lydekker thinlre E. sivalensis or some 

 closely allied race " may have been the an- 

 cestral stock from which Barbs, Arabs and 

 Thoroughbreds are derived." When more 

 skulls are available for study and when the 



phases through which equine skulls pass dur- 

 ing development and growth have been worked 

 out, it will probably be ascertained that broad- 

 browed horses with a prominent interorbital 

 region — a forehead convex from side to side 

 as well as from above downwards — and a long 

 tapering strongly deflected face have in great 

 part descended from a species closely allied 

 to E. sivalensis, but that slender-limbed horses 

 with a broad flat forehead, and the face short 

 and nearly in a line with the cranium, are at 

 the most only remotely related to E. sivalen- 

 sis. 



Further enquiries will probably also show 

 that some Indian breeds, as well as some of 

 the unimproved races of Central Asia (e. g., 

 certain long-faced Kirghiz horses with a 

 sloping forehead and long ears) in many of 

 the points agree with E. sivalensis of the Plio- 

 cene deposits of northern India. 



The second possible ancestor mentioned is 

 Equus stenonis of the Pliocene deposits of Eu- 

 rope and North Africa. In a typical specimen 

 of this species with the teeth in an inter- 

 mediate state of wear, all the anterior pillars of 

 the premolars and molars are shorter than in 

 E. sivalensis, while in a specimen with the teeth 

 well worn, the longest pillar may be only one 

 third the length of the grinding surface of the 

 crown — at no age are the pillars of the molars 

 more than half the length of the crown. 

 Whether the face was long and tapering and 

 strongly deflected in E. stenonis has not yet 

 been determined, but from the limb bones col- 

 lected, it is evident that the horse with short- 

 pillared molars, which in Pliocene times fre- 

 quented the valley of the Arno, sometimes 

 reached a height of nearly fifteen hands. 



It is generally supposed E. stenonis either 

 became extinct towards the close of the Plio- 

 cene age or was modified to form varieties 

 with long-pillared molars. It is conceivable 

 that some of the descendants of E. stenonis 

 acquired long-pillared molars, but it by no 

 means follows that all the Pleistocene horses 

 of Europe with the anterior pillai-s more than 

 half the length of the crown are related to or 

 derived from E. stenonis — some of them may 

 have been the descendants of E. namadicus. 



