Fossil – A thing of the past

(First of two parts)

Hey, have you ever wondered where your friend’s favorite t-shirt, watch or leather bag brand, Fossil, came from? Or when you stopped for a gas, have you noticed the "Fossil Fuels" sign at some gasoline stations? Well, the word fossil actually came from the Latin fossilis which means something dug up. Not a pretty picture, huh? The paleontologists or the experts studying fossils (and experts in fossil hunting and digging, too), say that any remains or traces that could serve as an evidence of life of an animal or a plant that once lived, can be called a fossil. They are very important inclusions in any type of rock – may it be sedimentary, igneous and in very rare cases, even in metamorphic rocks. Now, you may throw me this question, "How about the remains of Cro-Magnon man, cave paintings, potteries, and stone tools?" Can’t these things be considered fossils? The answer is yes. Cave paintings, potteries and tools were made by man and their mere presence indicates man’s earlier existence. The mold of a carabao and its calf under the lahar of the 1991 Mt. Pinatubo eruption is preserved, or if you bury the shell of the tahong you ate for dinner last night, they will be modified and could become true fossils after thousands or millions of years. One qualification for something to be called a fossil is that it must give us some hint of the size, shape, form and structure of the life form that once lived. The organism, however, doesn’t have to be extinct.

Generally, there are two types of fossils. First are those formed by the body or by some parts of the organism like the footprints or the burrows left by ancient worms and crabs. The second are those which include the body itself – it be only the teeth or scales. Furthermore, they can be altered or unaltered. One perfect example of an unaltered fossil is the frozen mammoth or extinct hairy elephant found in Siberia and Alaska. The amazing thing is you can still find its blood fresh, their eyes, skin and flesh intact, and most of all, even tell what it ate on its last dinner as if it only died yesterday.

On the other hand, altered remains are less spectacular than the mammoth fossil. This group includes the bones of the first mammal discovered in the Philippines, the Stegodon mindanensis. This fossil found in Tanay, Rizal in 1887 is considered to be the ancestor of elephants. Actually, there are two species of elephants, Elephas beyeri and Elephas cf. namadicus, and one species of rhinoceros, Rhinoceros philippinensis, that once resided in our archipelago. There are also four species of stegodons: Stegodon cf. trigonocephalus, Stegodon luzonensis, Stegodon cf. sinensis and Stegodon mindanensis.

These fossils have survived the tests of time – physical and chemical weathering. The latter could be the filling up of pore spaces by minerals and/or the replacement of the original components of the bone (or wood) by minerals from circulating solutions. The petrified wood (or turned-into-stone wood) looks just like ordinary wood but it is heavier and more compact and its texture more polished. The fibers and cellulose of the original tree were gradually replaced by silica or calcite, retaining its form but not its composition.

Another type of fossil are the impressions produced by organisms. Under the right conditions, they can serve as molds that may be filled by sediments which would later harden. If they are split, the impression (mold) and the cast (figure produced) can give the features (size, shape, markings, etc.) of the organism. On the other hand, leaves and delicate animals (e.g. jellyfish and worms) can be preserved when they leave a thin carbon film.

Another Philippine fossil example is the first and oldest coral called Gshelia sp. found in a clast near the base of the Late Tertiary Punso Conglomerate found by Easton and Melendres in 1963. This coral is approximately 290 million years (my) old!

Since 1959, several discoveries were done in the Philippines starting in the Puerto Galera area in northern Mindoro. Most of these remains are very tiny marine protozoans, ranging from only 1 mm to 5 cm. Examples are the deep marine foraminifera (Orbitolina and Globorotalia velascoensis — 65.5 my) and algae (Distichoplax biserialis— 65.5 my). In 1966, another significant discovery is the 250-million-year-old rice grain-like foraminifera called fusulinids (Neoschwagerina and Paraschwagerina) by Andal. Hayami, in 1968, also described the Jurassic or ~160-million-year-old mollusks, while Shuto worked on gastropods obtained from Iloilo.

It is good to note that only a fraction of the total number of organisms that lived in the past is written on the fossil record. Some buried plants and animals were completely destroyed by scavengers or decomposed by bacteria. The sediments where they were originally laid down could be disturbed and eroded again hindering preservation. That’s the reason why rapid burial is needed. Another necessary condition is for the organism to possess hard parts. (To be concluded)

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Marietta M. de Leon obtained her Ph.D. in Geology from the University of the Philippines. She is currently an associate professor at the National Institute of Geological Sciences, College of Science, University of the Philippines, Diliman. Her fields of specialization include Micropaleontology (Foraminifera and Calcareous Nannofossils) and Biostratigraphy, mainly with application to petroleum exploration. Send queries or comments on this article to [email protected] or [email protected].