Fossil Collecting 101



You might be a fossil if . . . .

Fossilization of a particular living organism in sedimentary deposits is a rare event. Yet, past life is so boundless in number that there exists, in fact, countless numbers of fossils buried in the earth. You might say that fossils are both common and rare at the same time. While they may be countless, finding fossils is generally not easy. Normally, a fossiliferous layer of sedimentary rock will lie between non-fossiliferous layers. In the former, the conditions enabling fossilization to occur existed, and in the latter, they did not. The gaps in between the fossiliferous layers constitute gaps in the fossil record that could be hundreds, thousands or even several millions of years.

There are numerous factors that influence whether a particular organism eventually becomes a fossil, some of which increase the probability and some of which decrease the probability of fossilization. Let your imagination roam, and consider that you are an organism in a population of like-kind organisms that existed some time between 4.5 billion years ago and much more recently.

You’ve probably heard jokes like: You might be a redneck if, your `huntin dawg' cost more than the truck you drive him around in, or if you have the local taxidermist's number on speed dial. Or, you might be an engineer if, you know vector calculus but you can't remember how to do long division, or, the salesperson at Circuit City can't answer any of your questions, or, you think that when people around you yawn, it's because they didn't get enough sleep. The section below looks at fossil formation in a similar stylistic manner.

You, or a close relative of yours at least, might be a fossil if:

  • You were lower on the food chain. - Organisms lower on the food chain are in greater abundance, have shorter life spans, high fecundity (make many offspring), and thus have a greater chance of appearing in the fossil record. Prey always far outnumbers predators, a balance of nature that always rules population ratios. Hence, Cambrian brachiopod or trilobite fossils that were prey far outnumber, for example, fossils of the soft-bodied terror of the Cambrian, the Anomalocaris that fed on them.
  • Similarly, you might be a fossil if, you were small and weak, rather than big and strong. – Size does matter, as predators always choose the smallest and weakest prey available to them. For example, big, carnivorous dinosaurs outnumbered the herbivores of the Mesozoic, and small fish have always outnumbered the big fish. Bigger animals live longer because they can, so nature makes fewer of them, and there will consequently be fewer fossils of them. Evolutionary adaptation requires that there are many of the small and weak so some can survive and pass along their genes. Populations of the small and weak left more fossils behind. There are some exceptions to this rule, such as: (1) maybe you were too small to tempt a larger predator to even bother; or, (2) your diminutive stature enabled you to hind more effectively (maybe you were a tiny mammal during the age of dinosaurs).
  • You might be a fossil if you were slow, lacked eyes, were attached to the sea floor and thus immobile, etc. Just like being small, being slow or immobile was not good, and evolution would have compensated by making more of you, and your family would have made more fossils. She or he who hesitates is lunch, so they say.
  • You might be a fossil if you lived in or near a marine or aquatic environment, as opposed to on land. – The likelihood of your fossilization was markedly higher in aquatic and marine environments than it is on land simply because there exists a minute yet finite possibility that before you are scavenged or rotted away, you may have settled to the bottom, and was quickly covered with muck or silt. If you were really lucky, the mucky bottom would have a paucity of aerobic bacteria to eat your remains; such anoxic (lacking oxygen) environments are the stuff of which the famous Lagerstatt fossil sites (for example, Green River, Solnhofen, Burgess Shale and Chengjiang) are made, but these are indeed rare.
  • You might be a fossil if you were crunchy rather than soft. - If you were a real softy, lacking bones and exoskeleton, there is almost no chance you left a trace of your life in the earth. This is why the fossil record is almost non-existent prior to the Cambrian some 550 million years ago. If you were soft, maybe you left a footprint if you were an arthropod with legs, or an impression if you were a jellyfish, but, your actual carcass if not gobbled whole, would have fallen victim to a myriad of bacteria, the predominant life form on the planet throughout all of geological history. However, if you were a post-Cambrian organism, and was crunchy, your crunchy part(s) might have left a trace of your past existence. If you were an invertebrate, you might have had an exoskeleton that was preserved because it was already fairly solid and partly mineralized. In fact, if you were a Paleozoic trilobite, you probably left a legacy before your final demise of many your calcareous exoskeletons that you periodically shed in order to grow. If, however, you were a dinosaur-age insect from the Mesozoic, or any time since then, your thin little chitin exoskeleton would have afforded your meager carcass scant protection from the ravages of nature, but at least your little exoskeleton had a better chance for fossilization than if you were a softy and lacked one.
  • You might be a fossil if you expired in water or fell in some water after you expired. – Regardless of where you lived, where you were exactly at the time of passing would make a huge difference in whether you would leave a trace of your existence. Unless you existed before the middle Cambrian, you surely would have expired in the sea In fact, if you existed prior to Devonian time when life adapted to living on land, your fossilization on land would be exceedingly rare, and even then only if you were washed into a tidal zone. Of course, you may have been washed ashore, or if you expired ashore, washed back out to sea. If you were any land-based organism throughout geological history, and expired near or in a river or stream, chances are good you would have ultimately been washed downstream, and your bones and crunchy parts hopelessly dispersed and further eaten. If you expired on an arid plain, your uneaten bones may have merely dried up and blew away before they could be buried; your teeth, however, had the best chance of surviving owing to their un-palatability and mineral constituency. If you died and fell in a lake, protected from currents and waves, and was buried in a mucky, anoxic bottom, your chances of becoming a fossil would be markedly enhanced.

Joking aside, it is really pretty hard for any given organism to become a fossil. Moreover, while such things as where you were of the food chain, how fast you were, your size, being soft or crunchy, etc., would have a bearing on the probability of becoming a fossils, but there are exceptions to all the above. Fossil formation can occur through a number of processes, each of which is chemically complex, and not completely understood. There is no realistic way to simulate in a laboratory the processes that take place over thousands to millions of years on and in the water and earth that results in the formation of a fossil.

The unlikelihood of fossilization results in large gaps in the fossil record. Creationists like to use these gaps to argue against evolution and promulgate supernatural views. Darwin particularly worried about the absence of Precambrian fossils that had not yet been discovered during his time. They have since been found, but not many, and they are found in very few localities, since Precambrian animals were simple, small and soft-bodied, and perhaps not very abundant, the Precambrian fossil record is indeed sparce.

For more, see fossil record across geologic time at Darwin's Dilemma.

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