Many bones and implements of Paleolithic man (see above table) have been found mainly in river gravels and caves. The relative ages of Paleolithic human bones and implements are best determined by the associated fossil animals. Thus the most ancient truly human fossils are found directly associated with bones of very old types of elephants, rhinoceroses, and hippopotamuses which are definitely known to have lived during middle or early middle Glacial (Quaternary) time corresponding to early Paleolithic time. A very conservative estimate would make the age of such very old human remains at least 150,000 to 250,000 years because the Ice Age was at least 500,000 years long. In a later human stage there are many associations with extinct animals like an older type of mammoth, cave bear, cave hyena, and others of later Glacial time estimated at 50,000 to 150,000 years ago. Last of all was the latest Paleolithic stage corresponding to the close of the Ice Age, the human remains of which are found associated with reindeer and the latest mammoths which roamed in great numbers across Europe. This was probably not more than 30,000 to 50,000 years ago. Paleolithic man is so called because he fashioned stone weapons and implements. The structure of skull and skeleton shows him to have been a low-type savage, something over five feet high on the average, with a forward stooping carriage. The average Paleolithic brain was not greatly inferior in size to that of modern civilized man, but it was not so highly organized and occupied a thick skull with much lower forehead and heavy brow ridges. The bushmen of Australia and the recently extinct Tasmanians are the nearest modern resemblances. Many fine specimens of Paleolithic man have been found, especially in cave deposits. That he was an expert hunter is proved by the great accumulation of bones of now extinct animals found in and about his haunts or camps, bones representing at least 100,000 horses having been found around a single camp site! [Illustration: Fig. 68.--Comparison of skulls: a, Paleolithic (Neanderthal) man; b, modern man. (After Woodward, British Museum.)]