March 12, 2005

THE word “fossil” comes from Latin, which means “to dig up.” Originally, anything coming out of the ground as a result of digging was called fossil. Now, however, palaeontologists use the term specifically to denote the remains and impressions of ancient animals and plants that died millions of years ago but which are still preserved in rocks.

Earth is the sole planet in the solar system, which hosts life as we know it. Following its creation some 4.5 to 5 billion years ago, the planet remained devoid of animals and plants for a long time.

Animals are divided into two groups — vertebrates (those having backbones) and invertebrates (those lacking backbones). Therefore, two kinds of animal fossils are found in ancient rocks.

There are many ways in which the remains of animals and plants are preserved as fossils. In case of vertebrates, when a land animal dies its skeleton is usually scattered. The soft parts are eaten up by carnivores or disintegrate due to bacterial action. The best fossils are formed when the hard parts of a dead animal or plant fall into mud and get quickly covered over.

Over a period of many million years, the bones are hardened into well-preserved fossils. Traces of animals and plants, preserved in the form of footprints and structures, are indicative of fossils.

The remains of plants are also preserved in the form of fossils. Wood, the hard part, is preserved as a wood fossil or petrified wood. Soft parts like leaves are hardly fossilized, but are preserved as leaf prints (impressions) in the rocks. In the case of invertebrates, hard shells are preserved as fossils. Quick burial is a prerequisite for the fossilization of invertebrates.

Fossils take us way back into history, nay, pre-history. About three centuries ago, Greek and Roman scientists, found on land, some fossilized remains of sea creatures. They thought that land must have been submerged once.

Discoveries came on a regular basis throughout the 19th and 20th centuries in Europe, where the scientists found fossils of both marine and non-marine rocks. Since then, fossils representing most living groups have been collected from all over the world. This process continues to this day and thousands of fossils are being collected across the world every year.

Life on Earth through time is divided into several eras. The eras, from the oldest to the youngest, are: Archeozoic, Proterozoic, Paleozoic, Mesozoic and Cenozoic. The eras cover the time that Earth, and the life on it, took to form.

The remains of single-celled microscopic bacteria and traces of green algae have been found in three-billion-year-old rocks, which are among the oldest. During the Paleozoic era, the seas were full of life. Invertebrates, such as trilobites, echinoderms, corals, clam, brachiopods, ammonites, bivalves, pelecypods, graptolites and gastropods, have been preserved as fossils. Some of these were widely distributed on Earth but existed for a rather short period.

Fossils of these short-lived organisms are known as index fossils, which are used to determine the age of the rocks containing them. Invertebrates, like trilobites and graptolites, are examples of such fossils. This era is often referred to as “the age of trilobites.”

Although the vertebrates appeared one million years after invertebrates, some fossils have been found which reportedly belong to the Paleozoic era. Fossils of vertebrates, such as fish, appeared in the rocks of Ordovician and Silurian periods of the Paleozoic era. These fossils were fragmentary in nature.

However, truly representative fish fossils have been found that date back to the Devonian and later periods. Fossils of amphibians — creatures like frogs and toads who live both in water and on land — some reptiles (crawling animals like crocodiles) and some plants have also been found which date back to this era.

In case of Mesozoic, which follows the Paleozoic era (from 230 to 65 million years before present), fossils of invertebrates like ammonites, belemnites and oysters are common. Dinosaurs, the fearsome vertebrates, dominated the world during this era and their fossils have been discovered on all the continents. This era is called “the age of dinosaurs.”

Our era is Cenozoic, which began about 65 million years ago and is marked by the development of mammals into various types. The ancestors of most living mammals belong to this era. These include carnivores, ungulates, proboscidians, insectivores, rodents, whales and primates. Birds, reptiles and some invertebrates — such as mollusks, echinoderms and corals — are also represented. Because of the dominance of mammals, this era is called “the age of mammals.”

Fossils are found wherever the sedimentary, or layered, rocks are exposed. For the most part, collecting and identifying fossils is a difficult and tiring task. However, the best place to look for fossils is one where some have been found earlier. One can begin and expand his or her search outwards from that spot.

Since the invertebrates live in seas, which are suitable for burial and preservation, they are rather easy to find. Being small in size, complete fossilized remains of invertebrates can be found and one can collect a large number of fossils within a short period.

The fossils of vertebrates are commonly found in tar pits. Thousands of well-preserved sets of fossils representing horses, elephants and birds have been collected from the famous tar pit at Rancho la Brea in California. Animal and plant fossils can also be found in coalmines. Sometimes, the impressions of plants can easily be found there.

A few years ago a fossilized mammal known as Quettacyon, with well-preserved right upper jaw and teeth, was found in the 55-million-year-old Tariq Habib coal mine in Sor Range coalfield, near Quetta.

Fossils are collected both as a result of “surface collection” and excavation. Most major discoveries are, however, made through “surface collection.” The Olduvai Gorge in Tanzania, East Africa, is one of the most important sites in the world from where several hundred fossilized remains of vertebrates have been collected. A field museum has been established there for visitors.

A National Dinosaurs Monument in Utah, United States, houses the bones of dinosaurs of the Jurassic age. Well-preserved skeletons of rhinoceroses (horses, camels and other such animals) were found buried in 10-million-year-old volcanic ash in a park in Nebraska, USA. Palaeontologists uncovered the skeletons by brushing away the sediments. People visit these sites and see for themselves what animal life was like at these places millions of years ago.

Findings in Pakistan
Fossils, as stated above, are not confined to a few places but are found on all the continents. Pakistan is one of the few countries where fossils have been collected from rocks ranging in age from 600 to two million years. The Salt Range in Punjab is actually dominated by fossilized invertebrates.

Marine sedimentary rocks that are 600 to 70 million years old have also been exposed in the Salt Range. These rocks are highly fossiliferous and contain fossils of creatures such as brachiopods, bivalves, gastropods, corals, bryozoans, crinoids, nautiloids, ceratites, ammonoids, conodonts, ostracodes, foraminifers, echinoids, terebratula, cephalopods and trilobites. Bryozones, brachiopods, hyolith, crinoids, cephalopods and gastropods have been discovered in the Khyber Agency, southern Hazara and Nowshera areas.

Wulgai, Kingri, Drug and areas surrounding the Quetta valley have fossilized invertebrates — brachiopods, crinoids, fusulinids, belemnites, discocyclina and bivalves. In Sindh too, there are well-known sites from where fossils of invertebrates, vertebrates and wood have been collected. Gastropods, cephalopods, and bivalves have been found in Gaj Nai, Thana Bula Khan, and Hub Chowki. Vertebrates, especially mammals, are widely distributed in the Gaj Nai area. Vertebrates and wood have been found near Sehwan, Dadu District, too. Vertebrate and wood fossils are also common in: the Potowar Plateau, some areas of the Sulaiman Range (Punjab); the Bhittani-Marwat Range (NWFP); the Sor Range; and, the Bugti Hills (Balochistan). Some discoveries have been made near Mirpur, Azad Kashmir, as well.

Important and rare fossils — such as that of dinosaurs, primates, carnivores, artiodactyls, perissodactyls, rodents, whales and proboscideans have been collected by the Geological Survey of Pakistan. Fossils collected from Pakistan are on display at the Geological Survey of Pakistan Museum, Quetta, and the Pakistan Museum of Natural History, Islamabad.

The study of fossils is of fundamental importance in the advancement of knowledge. They are not only indicative of past life but also unveil the history of Earth and represent natural wealth. They are used to determine the ages of the rocks in which they are found.

Rocks containing similar fossils are generally of the same age. By studying them, scientists can piece together pictures of the world as it was millions of years ago. Some plants and animals grow only in warm climate, others in forests and so on. Through fossils, it is possible to understand ancient climates.

Fossils also give information about the different stages of evolution, besides their positions in the stratigraphic column. Then there are fossils with commercial importance. These are coal and oil, which are so valuable that without them the modern world could come to a grinding halt.

The writer is a former deputy director of the Geological Survey of Pakistan

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