HOW DO WE KNOW WHAT LIVED MILLIONS OF YEARS AGO?
Paleontology, fossils, the messy science of deep time reconstruction.
The earth was so full of organisms that humans can hardly imagine a million or so years ago, when dinosaurs, ancient sea monsters, and huge creatures roamed the land and sea that are now gone.
But how do we really get to know about that?
There were obviously no cameras. No pictures. No writings. Nobody was there to write down what events happened. Rather, scientists turn to the far older evidence that is preserved within the rocks.
The science of paleontology starts there!
THE FOSSIL RECORD
A fossil is not just an old bone. Tokens that we call fossils indeed refer to bones, teeth, shells, and wood. They also refer to very less common but equally important fossil materials: for example, animal tracks, the burrows made by invertebrates, eggs, preserved impressions of skins, and coprolites which are fossilised dung. Each fossil leaves a little whisper about the creature that came before it.
What a tooth says is only one little bit of an animal's diet. A footprint says something more - how it was moving. You can find some information about how a dinosaur was caring for its baby from the fact you have got a nest. A coprolite tells you directly something about what the animal has been eating recently before its death. Each individual bit of information, though, looks as small as a trifle at the first glance. However, when the whole set is pieced together with such pieces of information then the bigger picture starts to emerge.
MORE THAN JUST BONES
Most of the times if a layperson thinks about what a paleontologist does, he imagines that the scientist dusts off a dinosaur skeleton with great care. Well, indeed, sometimes that's just how it goes. The skeleton, however, is but only one aspect of the picture.
By way of their skeletons and bones, we can know the way in which such animals' bodies were arranged and the way in which they walked, ran or climbed. Teeth are the first place to look to identify the feeding habits of an animal. Eye placement can show whether it was the predator or prey. Even the rocks around a fossil are important - the sediment layers of these rocks can help pinpoint the time of fossilization or the environment. Sometimes, a few fossil finds together can reconstruct one whole prehistoric ecological system instead of just a single organism.
So, paleontology is certainly not limited to the mere excavating of fossils. What it really is, is the science of reading and interpreting fossil evidence.
READING THE EVIDENCE
Come with me for a second. You have just discovered a single tooth of a dinosaur, which doesn't look like a very big discovery at the first glance. Nonetheless, its form, the curvature, and microscopic structures will tell a long story. Sharp, tooth-like edges will be indicative of a predatory dinosaur. The flat part that is meant for chewing a bit of plant will have been used on a dinosaur eating plant.
This same thinking goes for the case of footprints. From a trackway it may be determined an animal's direction of movement, length of its stride, or a mere estimate of how much it moved per hour. Several footprints of different kinds that came together might be a sign that the dinosaurs lived as a kind of family or social group.
Mystery time starts here! The paleontologist is no longer just a person who handles fossils. The scientist collects clues, the paleontologist compares it with existing knowledge then formulates the best hypothesis possible regarding what happened at that time and place.
FROM FOSSIL TO RECONSTRUCTION
One of paleontology's great feats is reconstructing an animal using only bits and pieces of its former self! Besides, fossils hardly ever show us perfect bones. Bones are lost, crushed, bent or just missing. Soft tissue such as muscles, skin or internal organs seldom get preserved in the fossils.
What is the method used by researchers to imagine an extinct creature? They look for similarities in the fossils and other examples. They analyze modern animals. They use anatomy and biomechanics information. The rocks surrounding the fossil give them an idea about its history. Gradually, all those clues allow more precise reconstructions.
However, it's very important to understand: At best, the reconstruction is still an educated guess from the available data rather than a literal photograph of the past. This is the reason why paleontologists keep modifying their reconstructions.
A newly-found and complete dinosaur might be sufficient to destroy the old ideas. A missing or newly identified bone would provide a radically different understanding about an extinct animal's posture or body shape that will not conform to previous assumptions. New data can come from a research study that reveals completely new details about a dinosaur such as diet, mating, or other types of behavioral characteristics. Scientists are only able to revise our knowledge through continuous research supported by new discoveries.
WHAT WE STILL DON'T KNOW
Despite the many things that paleontology has taught us, there is still a vast amount of the unknown. The fossil record is discontinuous. Very peculiar conditions are required for fossilization which is a fact that makes the vast majority of the living creatures to have left behind no record at all. It is very difficult to fossilize soft-bodied organisms. There might have been complete species that have died out without leaving a fossil which is not enough for us to discover them.
Not only that, even if we do find the fossil, it may still be difficult to figure out what was going on. Have this creature lived alone or have been part of a group? Has it been a killer, or a scavenger eating from carcasses? Did it take care of its young? Did it have any kind of covering over its skin? For instance, was it scaled skin, a hairy animal, or feathered? Or maybe it was even an animal that did not leave skins? And how would this creature send messages to its groupmates? Did it vocalize in some strange way that cannot be detected easily by human eyes? Or maybe they were silent and used non-vocal communication methods?
This is another example, when scientists discover a piece of bone and through various tests determine the presence of melanosomes inside it, then they could be able to know the color of the fossil animal if those melanosomes still retained their original structure. It is true that sometimes the evidence is very compelling but more often, scientists are just throwing out their views because of a lack of enough data. There is no consensus on these issues at the present moment. To be candid, these things being uncertain are really what make palaeontology so exciting.
THE PAST IS STILL BEING WRITTEN
Every fossil found is an evidence of a story that began a million to a billion years ago. One tooth. A trace preserved in stone. A piece of a dinosaur's nest fossil buried under layers of sedimentary rock from the past. Or it has got so many stories for us. A leg bone of some creature that has just been unearthed where no one expected its presence!
Every finding provides us with an additional puzzle piece to fit the story together. We will probably never figure out the full details of that past world. Still, as time goes and with each fossil brought out and every new technique invented, our image of it becomes progressively more accurate and detailed. The past is lost already. It is still speaking out, however. That is how we interpret what the evidence is trying to tell us.
It will take us a lot of work to come up with our version of what happened.