EVOLUTION OF THE VERTEBPwATA. 



343 



A postglcnoid process ; mandibular condyle transverse ; limbs not volant ; no 

 scapholunar bone;* hemispheres small, smooth 12. Bunotheria.\ 



A postgleuoid process ; limbs not volant, with a scapholunar bone ; hemispheres 

 larger, convoluted 13. Carnivora. 



Paleontology has cleared up the phylogeny of most of these 

 orders, but some of them remain as yet unexplained. This is the 

 case with the Cetacea, the Sirenia, and the Taxeopoda. The 

 last-named order and the Marsupialia can be supposed with much 

 probability to have come off from the Monotremata, but there is 

 as yet no j)aleontological evidence to sustain the hypothesis. Xo 

 progress has been made in unraveling the phylogeny of the Ceta- 

 cea and Sirenia. The facts and hypotheses as to the phylogeny 

 of the Mammalia may be represented in the following diagram : 



Diplarthra Hyracoidea Insectivora Rodentia Chiroptera 



Proboscidea \ Anthropoidea / Edentata 



Arablypoda 



Sirenia 

 Cetacea 



Quadrumana, 



Tilled 

 Taeniodonta 



Carnivora 



onta 

 Creodonta 



Condylartlira 



I 

 Marsupialia pt.| 



I 

 Monotremata 



Marsupialia pt. 



It will be readily seen from the above diagram that the dis- 

 covery of the Condylarthra was an important event in the history 

 of our knowledge of this subject. This suborder of the Lower 

 Eocene epoch stands to the placental Mammalia in the same rela- 

 tion as the Theromorphous order does to the reptilian orders. It 

 generalizes the characteristics of them all, and is apparently the 

 parent stock of all, excepting, perhaps, the Cetacea. The dis- 

 covery of the extinct Bunotherian suborders united together in- 

 separably the clawed orders, excepting the bats ; while the extinct 

 order Amblypoda is the ancestor of the most specialized of the 

 Ungulates, the odd- and even-toed Diplarthra. 



The characters of the skeleton of the order Monotremata show 

 that it is nearest of kin to the Eeptilia, and many subordinate 



* Except Erinaceus. 



f With the suborders Insectivora, Creodonta, Taeniodonta, and Tillodonta. 



t This was inadvertently omitted in the original. (Ed. 1886.) 



