248 



A Milk Dentition in Orycteropus. 



Although called an Edendate, it has always been recognised as pos- 

 sessing many characters exceedingly different from those of the 

 typical American members of the order.* It has in fact been placed 

 with them rather on account of the inconvenience of forming a 

 special order for its reception than because of its real relationship to 

 them. Now, as they are either altogether toothless or else homodont 

 and monophyodont t (apart from the remarkable exception of 

 Tatusia%), it seems more than ever incorrect to unite with them the 

 solitary member of the Tubulidentata, toothed, heterodont, and 

 diphyodont, and differing from them in addition by its placentation, 

 the anatomy of its reproductive organs, the minute structure of its 

 teeth, and the general characters of its skeleton. 



But if Orycteropus is not genetically a near relation of the Eden- 

 tates, we are wholly in the dark as to what other Mammals it is 

 allied to, and I think it would be premature to hazard a guess on the 

 subject. Whether even it has any special connection with Manis 

 is a point about which there is the greatest doubt, and unfortunately 

 we are as yet absolutely without any palseontological knowledge of 

 the extinct allies of either. Macr other ium even, usually supposed from 

 the structure of its phalangeal bones to be related to Manis, has 

 lately proved§ to have the teeth and vertebrae of a Perissodactyle 

 Ungulate, and one could not dare to suggest that the ancestors of 

 Manis or Orycteropus were to be sought in that direction. Lastly, as 

 the numerous fossil American Edentates do not show the slightest 

 tendency to an approximation towards the Old World forms, we are 

 furnished with an additional reason for insisting on the radical dis- 

 tinctness of the latter, whose phylogeny must therefore remain for the 

 present one of the many unsolved zoological problems. 



* On this subject see especially Flower, " On the mutual Affinities of the Animals 

 composing the order Edentata," ' Zool. Soc. Proc.,' 1882, p. 358, et seqq. 



f I have had the opportunity of examining specimens, apparently of a suitable 

 age, of JSradypus, Choloepus, and Dasypus, and can find in them no trace of a milk 

 dentition, while in each case the tips of the permanent teeth are already formed. 

 So careful has this examination been that I feel sure none of these genera ever have 

 calcified rudiments of milk teeth, although the possibility remains that uncalci- 

 fied germs of such teeth may be present in still younger specimens ; and these may 

 yet be discovered by means of section- cutting and thorough microscopical search, a 

 method that I hope will be employed by anyone having the opportunity of doing 

 so. Nor can I find any rudiments of calcified teeth (which would in that case be 

 of the permanent set) in a young specimen of Manis. 



X The tooth-change of this Edentate is so peculiar, so very different from that 

 of all other Mammals, including Orycteropus, that it has been supposed to be a 

 recently acquired and not an inherited characteristic at all. Its presence is, there- 

 fore, no evidence of a near relationship between Orycteropus and the true Eden- 

 tates. — January 3rd, 1890. 



§ See Osborn, ' American Naturalist,' vol. 22, 1882, p. 728. 



