. The age of mammals in Europe, Asia and North America. Mammals, Fossil; Paleontology. 222 THE AGE OF MAMMALS Among carnivores the archaic hyanodonts also appear for the last time, and are represented by rather highly varied forms, animals dis- similar in size, speed, and in the proportions of the skull, ranging from the diminutive H. mustelinus to the powerful H. horridus (Fig. 81), and including also species {H. leptocephalus) which exhibit in the closure of the posterior palate a backward extension of the respiratory tract which has been regarded (Scott) as evidence of aquatic adaptation,^
. The age of mammals in Europe, Asia and North America. Mammals, Fossil; Paleontology. 222 THE AGE OF MAMMALS Among carnivores the archaic hyanodonts also appear for the last time, and are represented by rather highly varied forms, animals dis- similar in size, speed, and in the proportions of the skull, ranging from the diminutive H. mustelinus to the powerful H. horridus (Fig. 81), and including also species {H. leptocephalus) which exhibit in the closure of the posterior palate a backward extension of the respiratory tract which has been regarded (Scott) as evidence of aquatic adaptation,^ but may be correlated with the extreme posterior position of the cutting or sectorial molars. At the same time the machserodont cats specialized into the fleet and slender-limbed, swift-moving Dinictis and the heavy-limbed Hoplophoneus (Fig. 87), which is transitional to the Eusmilus of the Upper. Fig. 109. -Skeleton of the Uligocene wolf, DapJuvnus. In the Carnegie , After Peterson. Oligocene. The canids ' also vary widely from the small civet-like Cyno- didis to powerful forms such as Daphoenus nebrascensis, which equaled the wolf (Canis lupus) in size. The Herbivora which formed the prey of these carnivores are included in six families of artiodactyls and six families of perissodactyls, these two orders at the time being nearly balanced both in numbers and differentia- tion. Of the artiodactyls the camelids (Poehrotherium), which are now of slender form, begin to take a prominent part in the Plains fauna. The hypertragulids, or primitive ruminants and deer, are still diminutive and hornless forms. The oreodonts are of intermediate size and now more sharply differentiated into three phyla, (1) the small brachycephalic Lep- tauchenia being added to (2) the typical cropping or grazing oreodonts and to (3) the forest-living Agriochoerus. Diminutive also are the leptochoerids. Of intermediate size are the anthracotheres, which include both the An- ' Scott, W.
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