. The age of mammals in Europe, Asia and North America. Mammals, Fossil; Paleontology. 12 THE AGE OF MAMMALS. The enlarged teeth are often so similar as to be very misleading in regard to relationship or affinity. As regards the elongation of the teeth the parallel with that of the feet is very close indeed, for we distinguish the following kinds of teeth: Brachyodont, primitive short-crowned teeth, with simple roots and simple cusps, and usually with simple conic, crescentic, or crested cusps, as of the pig, deer, and mastodon. Hypsodont, elongate grinding teeth, as of the ox, horse, and elep
. The age of mammals in Europe, Asia and North America. Mammals, Fossil; Paleontology. 12 THE AGE OF MAMMALS. The enlarged teeth are often so similar as to be very misleading in regard to relationship or affinity. As regards the elongation of the teeth the parallel with that of the feet is very close indeed, for we distinguish the following kinds of teeth: Brachyodont, primitive short-crowned teeth, with simple roots and simple cusps, and usually with simple conic, crescentic, or crested cusps, as of the pig, deer, and mastodon. Hypsodont, elongate grinding teeth, as of the ox, horse, and elephant. Just as the power of an herbivorous animal to move long distances or to take wide excursions in search of food or to move rapidly in escaping its enemies is brought about through changes in the number of digits, and in the form and proportions of the feet, so the power of an animal to live a long period of time and to assimilate the harder kinds of food is increased through changes of form and propor- tion in the teeth. The hypso- dont horse attains over thirty years of age; the hypsodont elephant lives about a hundred years. Elongate teeth may be far more highly perfected me- chanically and have more complicated crowns, consist- ing of three different dental tissues of three degrees of density, namely, enamel, den- tine, and cement, thus afford- ing three degrees of resistance, and always presenting a rough or uneven grinding surface. The passage from short- crowned to long-crowned teeth also marks the passage from browsing forms, living on softer kinds of food, to the grazing forms, living on the harder kinds of food, as well as from more short-lived animals to more long-lived animals. Here again we see that the elongation of the teeth like the elongation of the feet is eminently adaptive. For example, where physiographic changes reduce the softer herbage and increase the harder grasses, and separate the favorable feeding grounds as well as the drinking pools, the chang
Size: 2480px × 1008px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectpaleontology, bookyea
