Dinosaur Herds Dinosaur fossils have been known for over a century and yet little is known about their daily life when they were alive. Paleontologists, however, argue that discoveries made since the late 1970's indicate that some, if not many, dinosaurs might have been social organisms. Fossil beds of duck-billed dinosaurs not only revealed scooped-out, mud-filled nests with as many as fifteen offspring, but also showed that the nests were closely spaced, strongly suggesting communal nesting grounds, as are seen in birds. Within the nests were offspring of varying ages, suggestive of parental care. Dinosaur footprints are also used to infer that many species grouped together in herds, some of whichmayhave migrated long distances in what are known as trackways. Trackways preserve the footprints of a number of individuals in mud, which was later fossilized. These trackways show dozens of animals traveling in the same direction at roughly the same speed. Such trackways have been found for Eubontes (a Jurassic dinosaur), Triceratops, Iguanodon, and others. The final piece of evidence that paleontologists use to infer herding in dinosaurs is the presence of horns and superfluous appendages. Observations of extant herding species indicate that males most often display horns, tusks, or other features that are used in male dominance fights over sexually receptive females within the herd. Paleontologists use these modern-day rituals to hypothesize that dinosaursmayhave used their horns in a similar fashion.
Tool Use and Culture The genus Homo was the first to leave clear evidence of toolmaking. Pebble tools of Homo erectus were described by Louis Leakey, and he named the collection of artifacts "Oldowan" culture, from the Olduvai Gorge where some of his most famous excavations were done. On the basis of his collection of African fossils dated to between one million and two million years ago, Leakey proposed a new species, Homo habilis, which would be intermediate between Homo erectus and Homo sapiens, but there were too few fossils from this critical period to make the sequence clear. In any case, the simple pebble tools of the earliest members of the human genus were gradually supplanted by somewhat more sophisticated implements made by chipping both sides, along with a growing preference for flint over softer stones. There are many more examples of flint tools than there are of actual bones of human ancestors from this period. The techniques used for making these tools were evidently handed down from generation to generation, and the patterns were quite conservative, so tools from a given culture can be identified wherever they are found. The tools and artifacts of the later members of Homo erectus are known as the Acheulian culture. The most characteristic tool of this culture is the hand axe, used for chopping, cutting, scraping, and possibly even as a weapon. The species to which modern humans belong first appeared between 200,000 and 300,000 years ago. In 1856, when the first example of Homo sapiens was discovered, it was named Neanderthal man because the skeleton was found in a cave by the Neander Valley near Dusseldorf, Germany. Neanderthals were a robust species with a somewhat larger brain than modern humans. They wandered widely, leaving their remains over much of Europe, Asia, and Africa. The name Mousterian culture was coined to describe their artifacts, which were much more sophisticated than Acheulian tools. Finally, perhaps as recently as fifty thousand years ago, Neanderthals were replaced by fully modern humans. The two groups can be separated into the subspecies Homo sapiens neanderthalensis and Homo sapiens sapiens. At about the same time the Neanderthals disappeared, the Mousterian artifacts were replaced by much more complex and widely varied implements of the Aurignacian culture. The explosion of cultural innovation-including cave paintings, carvings, and other artistic and technological inventions- had a remarkable effect on life. The first fossils of the sapiens subspecies were found in a limestone cliff atCro-Magnon in southern France in 1868. They and numerous later finds from the same period were given the name Cro- Magnon man, and from the very beginning, they were recognized as being fully modern in form.
