62 



KNOWLEDGE & SCIENTIFIC NEWS. 



April, 1904. 



into the fully-developed ones of the dogs) may be 

 explained by the nature of the food of bears, which does 

 not require the action of scissor-like teeth. 



.\t(ain, in the seals and walruses there is no trace of a 

 differentiated pair of carnassial teeth ; such a type of 

 dentition being unnecessary to animals living on a fish 

 diet. In the case of the eared seals and walruses, there 

 is little doubt that the absence of differentiated carnas- 

 sials is due to degeneration, these creatures being 

 apparently related to the bears. The case of the true, or 

 earless, seals is more uncertain : and it has been sug- 

 gested that these creatures inherit their distinctive type 

 of dentition direct from an extinct group referred to 

 below. .Vgainst this is the circumstance that they 

 possess the compound semilunar bone in the wrist, which, 

 on the above view, would imply the fusion of the two 

 elements entering into its composition in two independent 

 instances. 



Reverting to the existing members of the dog tribe, it 

 will be noticed that the skull (fig. i) is characterised by 

 its elongated form and relatively large brain-cavity. The 

 teeth fall short of the typical mammalian number of 44 

 only by a single pair — namely, the last pair of molars in 

 the upper jaw. Consequently there are only two pairs 

 of teeth behind the upper carnassial. In the lower jaw 

 the last molar is \ery small, and evidently on the point 

 of disappearance. As regards the other teeth, it must 

 suffice to mention that the carnassials are strongly de- 

 veloped and possess a perfect shearing action, the lower 

 one having a large tubercular portion for masticating 

 behind the cutting blade ; and that most of the premolars 

 (other than the upper carnassial) carry accessory cusps 

 on either side of the main cone. It may be added that 

 all the existing members of the fatnily are digitigrade — 

 that is to say, they walk on their toes instead of on the 

 sole of the foot, which is raised above the ground and 

 covered with hair. 



A large number of extinct dog-like animals have left 

 their remains in the Tertiary strata of both Europe and 

 North America ; those from the newer formations being 

 nearly allied to existing types, while the older forms are 

 more or less decidedly different. One of the most im- 

 portant of these extinct types is the Oligocene and 

 Miocene genus Cynodictis, which is without much doubt 

 the ancestral type of the true dogs (diiiis) of the present 

 day. Although generally having the same dental formula 

 as the latter, Cynodictis exhibits distinct signs of affinity 

 with the ancestors of the civets. On somewhat the same 

 platform of evolution as Cynodictis is the North American 

 Daphanus, of which the skull is shown in fig. 2. In this 

 animal it will be seen that a small third upper molar 

 (the third tooth behind the carnassial) is retained, thus 



bringing up the number of the teeth to the typical 44. 

 In general characters, the dentition is very similar 

 to that of modern dogs, but there are fewer accessory 

 cusps to the premolars, and the posterior portion of the 

 lower carnassial is adapted for cutting, instead of for 

 grinding. The dogs of this genus are further remarkable 

 for the shortness of their JAws ; and it has accordingly 

 been thought that they may ha\-e been the ancestors of 

 the modern wild dogs (Cyon) of Asia. 



Great interest attaches to another type of Tertiary dog, 

 the A inpliicyon of the Miocene and Oligocene strata of both 

 hemispheres, some of the species of which attained 

 dimensions rivalling those of a bear. This interest is 

 due to the fact that these giant dogs, which had 44 teeth, 

 and partially plantigrade feet, were the actual ancestors 

 of the modern bears, with which they are connected by 

 certain extinct genera. We thus establish the derivation 

 of bears from dogs of a generalised type. 



All the foregoing extinct general types of dogs may, 

 however, themselves be apparently derived from a still more 

 generalised form from the Middle, or Bridger, Eocene of 

 North .'\merica, known as Vulpavus. In this animal, 

 wnich can only be tentatively included in the dog family, 

 the skull (fig. 3) is characterised by its long and narrow 



Fiit. 2.— Skull of iMiili.Tiuit, a primitive Dog from the Middle Eocene 

 strata of the United 5tate.s, with a crown view of first and second 

 lower molars. 'After Dr. Wortman.) 



Fig. 3.— Skull of Vulpai'ui, an ancestral type of Dog from the 

 Bridger Eocene. (After Wortman.) 



form, and the small size of the brain-cavity. The teeth, 

 of which there are 44, are of a decidedly dog-like type, but 

 the outer front angles of the upper molars assume a cutting 

 character, and the bkide of the lower carnassial is much 

 taller and narrower, and also more obliquely placed, 

 than in the dogs, while the second and third lower 

 molars, although much smaller, present a decided re- 

 semblance to the carnassial. Moreover, the lower pre- 

 molars have large fore-and-aft cusps, differing in character 

 from those of the true dogs. Unfortunately, the struc- 

 ture of the wrist is unknown, but it is quite possible the 

 scaphoid and lunar bones may be separate. The hind 

 as well as the fore feet were five-toed. 



More or less nearly allied to Vulpavus are certain other 

 Lower Tertiary Carnivora, exemplified by the genus 

 Vivevravus, which are regarded as forming the most 

 primitive family of Carnassidents at present known. 

 They have five-toed feet, with the scaphoid and lunar 

 of the carpus separate; and the dentition, in which the 

 number of the teeth may be either 44 or 40, difters 

 from that of Vulpavus by minute details, to which it is 

 impossible to refer on this occasion. In certain numbers 

 of the family, such as Oijdectes, the last two lower 

 molars are exceedingly like the carnassial, and have 

 their crowns but little lower, although these teeth retain 

 the essential carnassident feature of being smaller than 

 the latter. In other respects, the dentition of these 

 primitive forms comes very close to that of the under- 

 mentioned creodonts, with which the Viverravida also 



