384 H. F. Osborn — Mammalia in Worth America. 



While Cope overestimates the feet in these larger divisions, 

 many writers in Europe still depend wholly upon the teeth 

 and ignore the wide degrees of divergence such as are indi- 

 cated in the Perissodactyla for example in functional tetra-, 

 tri- and mono-dactylism. By " functional" we refer to tenden- 

 cies which are not expressed in the bare digital formulas — and 

 which have the same relation to the feet that the dental curve 

 has to the teeth. The evolution of a monodactyl tendency is 

 not the work of a century but of a geological period, a princi- 

 ple which we w T holly ignore when we place the monodactyl 

 Anchitheres with the tridactyl Palgeotheres, on the ground 

 that their dental type and digital formulae are identical. 

 How many toes an animal has is of far less importance than 

 how these toes are being displaced and reduced. 



Loiver Mesozoic Pro-Mammalia. 



With the exception of the triassic Theriodesmus of Seelye, 

 no mammal is known by its limbs or skeleton until we reach 

 the basal Eocene ; in studying the first steps in the rise of the 

 mammalia, we are thus practically driven to the teeth and jaws 

 alone In these straits of the fossil-hunter, embryology has 

 lately come famously to aid. 



Assuming their remote reptilian origin, agreeing with Baur 

 and Kukenthal that the theromorph reptiles were parallel with 

 rather than ancestral to the mammals, and therefore placing 

 before both groups the hypothetical Sauro-mammals in or 

 below the Permian, we come to the old question which Huxley 

 discussed in his famous anniversary address: "Was there a 

 succession between Monotremes, Marsupials, and Placentals, 

 or a parallel development from a common pro-mammalian 

 type ?" Then we look to the newer questions, " When were 

 the Edentates and Cetaceans given off ?" 



Modern tooth-science springs first from the recent demon- 

 stration of Putimeyer's hypothesis of 1869, that the teeth of 

 all the mammals center around a single reptile-derived type. 

 With a single exception, which I believe can be disposed of, 

 various stages of trituberculism or a three-cusped condition 

 have become the standard for the teeth, as pentadactyly has 

 long been for the feet, except that this is developed within 

 the mammalian stem, while our five fingers are a reptilian 

 legacy. Second, it springs from the recent thorough explora- 

 tion of the youngest jaws for evidences as to the primitive 

 form and succession of the teeth. This also supports the 

 reptile theory of tooth descent by proving, what has been in 

 considerable doubt, that the Pro-mammalia had a multiple suc- 

 cession of teeth like the reptiles, and that even some of the 

 modern mammals retain dim traces of four series of teeth. 



