SOUTH AFRICAN FOSSIL REPTILES 339 



eroding exposed surfaces and filling up the hollows. Jutting out from the 

 plains are the kopjes and mountains. These are preserved through being 

 protected by sheets of igneous rock. In the plains, owing to the fact that 

 almost the whole surface is covered with wind-blown dust, it is impossible 

 to see any fossils except where the ground has been washed by a flood. On 

 the sides of the hills in many places the shale is denuded of vegetation and 

 exposed, and it is on these exposed slopes that most fossils are obtained. 

 Unfortunately if a slope is steep it is extremely difficult to excavate any 

 specimen even if discovered, the best localities being gentle slopes and the 

 beds of rivers. 



The distribution of fossils is very uneven. In some places one may travel 

 and search over every slope of shale for forty miles without seeing a scrap of 

 bone; in other places, sometimes in a small area of a few hundred square 

 feet, a large number of specimens may be obtained. Bones are usually seen 

 readily because their color is lighter than the shale. To many of the Dutch 

 farmers and to members of their families, we are indebted for some of our 

 best specimens, and even the Hottentot goatherds are often useful in spot- 

 ting specimens while out on the hills watching their flocks. 



The oldest animals we meet with in the Karroo formation in any number 

 are of middle Permian age, shall we say of the year 18,000,000 b. c. These 

 are of especial interest from the resemblance they bear to the American 

 Permian reptiles from Texas and New Mexico. One of the largest and 

 best-known animals is called Pareiasaurus. It is a large-limbed reptile, 

 about nine feet in length and standing about three and one-half feet in 

 height. In many points of its organization it shows affinities with the 

 American reptile Diadectes, of which a mounted skeleton is to be seen in 

 the American Museum. Another group of animals contemporaneous with 

 Pareiasaurus is the reptilian group of Dinocephalians. These also were 

 large reptiles with very powerful limbs. Although herbivorous and having 

 no remarkable specialization of the spines of the vertebrae, they are never- 

 theless fairly closely allied to the very remarkable American fin-backed 

 Pelycosaurs, of which skeletons are to be seen in the American Museum. 



One of the most striking peculiarities of the Karroo reptiles is that al- 

 most all agree with Pareiasaurus and the Dinocephalians in having power- 

 fully developed limbs. How these have been evolved is a matter of doubt 

 but there can be little question that it was this strengthening and lengthen- 

 ing of the limbs that started the evolution which ultimately resulted in the 

 formation of the warm-blooded mammals. 



The best-known and in some respects the most remarkable of the Karroo 

 reptiles, belong to a group named by Owen, the Anomodonts, from their hav- 

 ing horny beaks like the turtles or birds with in addition in many forms a pair 

 of large walrus-like tusks. The first specimen was discovered as far back as 

 1844 and was called Dicynodon but although many skulls have been dis- 



