SPEAKER 1: The word fossil comes from a Latin root meaning something that's dug out of the Earth. And indeed, most fossils are dug out of the Earth in various stratigraphic sections. But technically, a fossil refers to the remains of any organism that was once alive. So technically, we could think of a corpse as a fossil, or a mummy, or a frozen body in ice in the tundra of Siberia. Impressions, tracks-- these are all examples of fossils.
But the fossils of keenest interest to us are those that we call rocky fossils or petrifications. Now what happens in this process is that once bones are buried in their deposits, they begin to lose their organic content. And the proteins, and the collagens, and things that make up live bone are lost and are replaced by minerals. And these minerals are often phosphates, and calcites, and carbonates. If you pick up a bone of a fresh cow, it's very light compared to picking up the bone of a fossilized cow, because the fossilized bone will be much heavier, having lost its organic contents and picked up mineral content.
This is one of the stories relating to fossils. The other is what actually happens to the fossils. Now when you think of an animal that has been downed by a predator, let's say, lying on the ground, and it begins to disintegrate. Predators will come and remove parts. Insects will work on the body. But there will be other changes-- erosional changes, weathering changes, changes in temperature. Vegetation can interfere with the integrity of the skeleton.
So in time, you're going to have most often a fragmentary representation of the given dead organism. And when this occurs, the elements of the skeleton may be widely scattered. This, in part, explains why so many fossils are fragmentary, because the whole animal is no longer intact. However, if you have very rapid burial and you have burial in a biostratigraphic context that is not disturbed, you may have more complete specimens. And indeed, in the human skeletal record, as with dinosaurs and mammoths, we have sometimes very complete skeletons.
The nature of the fossil evidence then is that every fossil has a kind of history once it becomes a fossil, once the individual is dead and the remains are there. And the discovery of what has happened to the remains, interestingly enough, is the core of another science. And this science is called taphonomy.
And taphonomists are those that are interested in the life history of fossils. They want to know what happened to the bone after its initial deposition. What kinds of predators got to it, which may be represented by marks on the teeth. They also want to know something about the chemical changes taking place in the bone. Perhaps DNA can be recovered, in which case certain other kinds of information are available. These are the concerns of taphonomists and, consequently, of human paleontologists, because when we find a skeleton and describe it, apart from its variations in size and shape, we also want to know about the history of its deposition in its geological context.
It's the hard parts of the organism that are preserved. And teeth are much harder materials than bone, so it's hardly surprising that, in the fossil record, we find a great number of teeth. And from these, again, many conclusions can be reached about the nature of the animal, the age of its death, its taphonomic history, its species, and other kinds of information that are critical in reconstructing a picture of the ancient past.
Well, where do we find fossils? You want to find a fossil. Where would you look? The chance of finding fossils via serendipity is, of course, always possible. And many great discoveries have been made that way, people being in the right place at the right time and with sharp eyes and looking on the ground or in the cliff of the deposit, being able to pull out and recognize a fossil specimen. However, a systematic surveying of an area where you know that fossils of a particular geological period may be is always the most reliable and profitable procedure.
The way that I've done this with my students when I've been working on a palaeontological site is to walk a grid across the area, have a little collecting bag in everybody's hand, and looking to see what is on the surface. After you've crisscrossed the survey, you come back and you dump the contents of the bag out and you see what you have. And some of it will be very uninteresting. Coke bottle caps, somebody's lighter. But among these things you may find some teeth, some fragments of bone, and other clues that indicate this is a profitable place to look, to survey further, and perhaps to excavate.
Satellite pictures have been very, very helpful in showing areas that look promising for excavation. You certainly don't want to spend your time and your effort excavating in a geological period or epoch where you're not going to have the animals you're looking for. So when we look for human fossils, we're looking in those that we assume are in Pleiocene, or Pleistocene, or Holocene geological deposits. If we're looking for some of the earlier apes ancestral to us, well, we would look in Miocene or Oligocene deposits. So knowing where to look is extremely important in having success.
Now once you are at a site where you feel that there is reason to pursue further excavations, yes, you may dig some holes in the ground. And again, you will find all kinds of other organisms that may be human. But those are important because they tell you something about the paleo environment, the ancient ecology, climate, temperature change, geological events, and other things that took place when those people were living whose fossils you have found.
The great thing about the surveys is that they help you to cover ground in a systematic way. And it's really quite unusual for someone just by chance to come upon fossils. You have to have a trained eye also. A certain amount of cleaning of the fossil material takes place at the site. But if you can bring out large blocks of material, and crate them and carefully transport them to the research laboratory, there you can meticulously excavate every bone and tooth, parts of the skeleton that are preserved, and classify these and put them into their collections.
And in the case of fossils, human or otherwise, these become very valuable possessions in museums. They are parts of the acquisition of the museum. Casts may be made of some of these for teaching purposes, but the ultimate specimens themselves are found only in certain institutions, namely the institutions where there has been sponsorship for the paleontological excavation.
There's a myth that human fossils are very few. Well, at one time, that was true. It's not true today. We have thousands of examples of human fossils from different parts of the world. And while Africa has been predominant in recent years of yielding its human fossil record, we also find these in other parts of the world as well. And much of the success of increasing the human fossil record is based upon systematic organization and the discovery of key finds that turn people on, with great enthusiasm, to research those areas more thoroughly.
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Since the time of separation of the evolutionary lines of apes and humans about 5 million years ago, some fossil specimens of the skeletal remains of our earliest ancestors have been preserved and discovered. Putting together the pieces of the puzzle of human biological history is the task of paleontologists, geologists and anthropologists.
In this room we explore how these scientists can reconstruct the past from their studies of the geological contexts in which fossils are found, the dating of the specimens, their comparative anatomy with extinct and living species of our taxonomic order, the Primates, and the lifeways and behavior patterns of the first members of the human family within the Primates.
By looking at reproductions and pictures of this fossil record, including representations of pre-human Primate species, we learn about our prehistoric beginnings among those populations of first two million years of our evolution, as identified as Ardipithecus, Australopithecus and the earliest members assigned to our own genus- Homo habilis and Homo rudolfensis.
This video is part 3 of 13 in the Human Paleontology series.