xxvii. 5 CREODONTS 683 



that move the head. The clavicle is reduced. The tail, well developed 

 for the maintenance of balance in wild cats, tends to become reduced 

 under domestication, the extreme being the Manx variety, with only 

 three caudal vertebrae. 



As in so many carnivores, the alimentary canal is short and the 

 stomach never complex or the coecum large. The uterus retains the 

 primitive mammalian bicornuate form. The chorio-vitelline placenta 

 is important early in pregnancy. The chorio-allantoic placenta is of 

 a type known as vasochorial with the villous portion of the chorion 

 restricted to a characteristic band around the embryo (hence 'zonary' 

 placenta). 



5. *Suborder Creodonta 



Besides animals such as the cats, adapted in this detailed way for 

 hunting live prey, the order Carnivora contains a variety of less- 

 modified forms, such as the dogs and their offshoot the bears, which 

 are partly scavengers. Others are suited for special types of carni- 

 vorous life, such as the weasels, mongooses, and other small animals. 

 The seals and walruses are carnivores much changed by aquatic life. 



Great numbers of fossil carnivores are known and we can trace 

 much of the history of the order. The *Creodonta (= 'flesh-tooth') 

 of the Palaeocene and Eocene included four distinct families, one, the 

 *Arctocyonidae, is perhaps close to the ancestry of the whole Fer- 

 ungulate stock, the other three are more specialized. The earliest creo- 

 donts, such as *Tricentes of the North American Palaeocene, were 

 small semi-plantigrade creatures, very like the contemporary small 

 insectivores, which were the prototype of all eutherian mammals. 

 The skull was long and low, with a small macrosmatic brain, but 

 already having sagittal crests for the temporalis muscle. The denti- 

 tion included the full number of teeth and these carried sharp cusps, 

 arranged in the tritubercular pattern, with the beginning of the 

 development of a hypocone in the upper molar. There was no car- 

 nassial, however; animals of this type could therefore well have given 

 rise to non-carnivorous forms, such as the ungulates. Other differences 

 from modern carnivores were that the scaphoid and lunate were not 

 fused and there was no ossified auditory bulla. 



It is not surprising that these early creodonts were for a long time 

 classed as Insectivora. Their descendants soon began to show various 

 specializations. Thus *Arctocyon of the Upper Palaeocene of Europe 

 was a large animal, with tuberculated molars, probably omnivorous 

 like a hear. Some Eocene descendants of this type, such as *Mesonyx 



