676 MAMMALS 



modern orders Carnivora and Pinnipedia (seals) are fairly direct de- 

 scendants. From pre-creodonts, there diverged a line which produced 

 the artiodactyl 'ungulates'* (peccaries, pigs, hippopotami, tylopods 

 [camels etc.], deer, antelopes, cattle). 



The Lipotyphla (hedgehogs, tenrecs, otter-shrews, shrews, moles, 

 golden moles etc.) comprise the larger of the two groups of living 

 insectivores. From this stock diverged the smaller branch called the 

 Menotyphla, the living members of which comprise the tree-shrews and 

 elephant-shrews. Along the way, the Menotyphla gave off a branch 

 which bifurcated into the Dermoptera (taguans or 'flying lemurs'' — 

 Galeopithecus and Galeopterus) and the Chiroptera (bats). The order 

 Primates also branched off from menotyphlous stock, close to the tree- 

 shrews ; and the latter, like the higher primates, have secondarily become 

 diurnal — perhaps the most primitive placentals to have done so. 



From a second of the groups of Mesozoic insectivore-like forms, the ro- 

 dents and lagomorphs arose. In their highest specializations, the rodents 

 have risen above some other groups whose origins were not as ancient. 



A third assemblage of Mesozoic forms gave rise to the modern Xen- 

 arthra, comprising the sloths, armadillos, and ant-bears. To these Amer- 

 ican forms the African pangolins or 'scaly ant-eaters', the Nomarthra 

 may be closely related. The Xenarthra and Nomarthra, if they are thus 

 related, form a natural order, the Edentata; otherwise the Nomarthra, 

 deserve ordinal rank. To the 'edentates' in a former, looser sense, the 

 Tubulidentata (now considered quite unrelated) were once assigned. 



The Tubulidentata, represented today only by the aard-varks iOryc- 

 teropus spp.), the hyracoid-proboscidean-sirenian bouquet, and the peris- 

 sodactyl ungulates (horses, zebras, tapirs, rhinoceroses) are all deriv- 

 atives of pro-ungulates which flourished in Cretaceous time and radiated 

 from still a fourth branch of the Mesozoic radiation of insectivore- 

 derivatives. 



The Eye as a Whole — In so diversified a group of vertebrates — in 

 contrast to the birds — the eye naturally exhibits a profuse adaptive 



*The mammalogical reader will have noticed that throughout this book the old term 'un- 

 gulate' has been employed. It embraces several orders which are of course widely separated 

 in modern classification: the Artiodactyla (even-toed) and the Perissodactyla (odd-toed 

 hoofed forms), the Hyracoidea (hyraxes) and their close relatives the Proboscidea (ele- 

 phants). (The Sirenia, though never classed as 'ungulates', are connected with the base of 

 the elephant branch). The nowadays artificial term 'ungulate' has seemed here a conven- 

 ient word-saver, for the orders embraced by it have eyes which are much alike. From 

 comparative ophthalmological evidence, no one would be led to believe that the artiodactyl 

 and perissodactyl lines of descent have actually been separate since almost the inception 

 of the Placentalia. 



