Lesson 1Fossil Record
Put attention and take notes.
The fossil record helps paleontologists, archaeologists, and geologists place important events and species in the appropriate geologic era.
Study of the fossil record has provided important information for at least three different purposes:
1) The progressive changes observed within an animal group are used to describe the evolution of that group. In general, but not always, successive generations tend to change morphologically in a particular direction and these changes are often interpreted as better adaptation to a particular environment.
Fossils also provide the geologist a quick and easy way of assigning an age to the strata in which they occur. The precision with which this may be done in any particular case depends on the nature and abundance of the fauna: some fossil groups were deposited during much longer time intervals than others.
Fossil organisms, furthermore, may provide useful information about the climate and environment of the site where they were deposited and preserved. Certain species of coral, for example, require warm shallow water.
A fossil can preserve an entire organism or just part of one. Bones, shells, feathers, and leaves can all become fossils.
Fossils can be very large or very small. Microfossils are only visible with a microscope. Bacteria and pollen are microfossils. Macrofossils can be several meters long and weigh several tons. Macrofossils can be petrified trees or dinosaur bones.
Preserved remains become fossils if they reach an age of about 10,000 years. Fossils can come from the Archaeaean Eon (which began almost 4 billion years ago) all the way up to the Holocene Epoch (which continues today). The fossilized teeth of wooly mammoths are some of our most "recent" fossils. Some of the oldest fossils are those of ancient algae that lived in the ocean more than 3 billion years ago.
is one of the four geologic eons of Earth history, occurring 4,000 to 2,500 million years ago (4 to 2.5 billion years ago). During the Archean, the Earth's crust had cooled enough to allow the formation of continents and life started to form.
Fossils of ancient marine animals called ammonites have been unearthed in the highest mountain range in the world, the Himalayas in Nepal. This tells scientists that millions of years ago, the rocks that became the Himalayas were at the bottom of the ocean.
Fossils of an ancient giant shark, a megalodon, have been found in the landlocked U.S. state of Utah. This tells scientists that millions of years ago, the middle of North America was probably entirely underwater.
Steps to find a fossil
In order for a fossil to be useful in paleontology, we have to know it exists! Many fossils are discovered purely by accident, by individuals not looking for fossils at all. They are found by people digging foundations for buildings, or quarrying rocks, and then brought to the attention of scientists. However, for the most part paleontologists actively seek out new specimens. These might be elaborate expeditions, short day trips, or any scale in between. The team might be a few individuals, to a dozen, to many hundreds .
Step 1: Finding the Fossils (Prospecting)
While in the field, prospecting works by walking the hills of the badlands and looking for fragments of bones and teeth weathering out of the sediment. Normally you don't immediately find a bone sticking out of the ground: instead, one looks for a trail of fragments weathering out of the hillside, then trace them up to the layer in which they are coming. When a potential site is identified, it is surveyed using technology that produces three-dimensional maps and plans of potential fossil-bearing areas. Finds are plotted on virtual maps using a digital Geographical Information System (GIS). If you determine a layer in which fossils are preserved, you move from prospecting to excavating.
Step 2: Getting the Fossils Out of the Sediment (Excavating)
When you come across a layer with fossils, it is unlikely that it is the current surface of the ground. So some degree of removal of the sediment above the fossil layer has to be done. Depending on the geometry of the situation, this might involve geologic hammers, picks, shovels, pneumatic drills, jackhammers, backhoes, or (in the old days) dynamite.
Step 3: Jacketing & Return to the Museum
Smaller bones and teeth might be wrapped up with paper towels and/or foil, requiring no additional protection. These can be carried back to the field vehicle as is. But larger bones--or sets of bones still in articulation--require special care. A very standard technique in field paleontology is jacketing. At the end of a field season the specimens need to be shipped back to the museum in which they will be studied. By muscle power (or sledge or helicopter) the bags or bones and jackets are moved to the off-road vehicles, then driven back (or shipped via some other transport) to a lab.
Step 4: Preparation
After a fossil has been prepared and cleaned, it is studied in the laboratory.
There are many ways of examining fossils in detail. Significant fossils can be measured using callipers.
Binocular light microscopes are used to look at surface features of bones.
These can show cut marks or carnivore damage. A scanning electron microscope (SEM) is used for detailed, high magnification analysis, for example, to study microwear on teeth, yielding data on diet.
Step 5: Cataloging & Accessioning
Every specimen in a museum has to have a record; otherwise they are useless as data. So museums have catalogues listing each specimen, its identity, the site and formation it was from, who found it and when, etc. This process is called accessioning, and is the way a bone or tooth makes its way into the scientific record.
Step 6: Restoration & Mounting
The vast majority of fossils in any museum will mostly be in storage, and be worked on by researchers but not seen by the general public. But a number of skeletons and other specimens might be selected for public display. These are chosen for a number of reason: most importantly how impressive they might be and how they might be incorporated thematically into a larger exhibit.
Complete fossil skeletons are vanishing rare, however, especially for larger species. Broken bones need to be repaired, for instance, and missing bones need to be replaced. In the case of missing bones, they might be sculpted (or today, 3D printed) by mirror-imaging the same bone from the opposite side of the body. In other cases it might be replaced by the same bone from another individual (but care must be taken to make sure the proportions are appropriate for the main skeleton). Some museums make it clear (by color, for instance) which parts of a restored fossil are real, and which are filled in; in others, though, it is hard to tell.
Lesson about fossils
Alberto Aguilar
Created on March 8, 2021
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Transcript
Lesson 1Fossil Record
Put attention and take notes.
The fossil record helps paleontologists, archaeologists, and geologists place important events and species in the appropriate geologic era.
Study of the fossil record has provided important information for at least three different purposes:
1) The progressive changes observed within an animal group are used to describe the evolution of that group. In general, but not always, successive generations tend to change morphologically in a particular direction and these changes are often interpreted as better adaptation to a particular environment.
Fossils also provide the geologist a quick and easy way of assigning an age to the strata in which they occur. The precision with which this may be done in any particular case depends on the nature and abundance of the fauna: some fossil groups were deposited during much longer time intervals than others.
Fossil organisms, furthermore, may provide useful information about the climate and environment of the site where they were deposited and preserved. Certain species of coral, for example, require warm shallow water. A fossil can preserve an entire organism or just part of one. Bones, shells, feathers, and leaves can all become fossils.
Fossils can be very large or very small. Microfossils are only visible with a microscope. Bacteria and pollen are microfossils. Macrofossils can be several meters long and weigh several tons. Macrofossils can be petrified trees or dinosaur bones.
Preserved remains become fossils if they reach an age of about 10,000 years. Fossils can come from the Archaeaean Eon (which began almost 4 billion years ago) all the way up to the Holocene Epoch (which continues today). The fossilized teeth of wooly mammoths are some of our most "recent" fossils. Some of the oldest fossils are those of ancient algae that lived in the ocean more than 3 billion years ago.
is one of the four geologic eons of Earth history, occurring 4,000 to 2,500 million years ago (4 to 2.5 billion years ago). During the Archean, the Earth's crust had cooled enough to allow the formation of continents and life started to form.
Fossils of ancient marine animals called ammonites have been unearthed in the highest mountain range in the world, the Himalayas in Nepal. This tells scientists that millions of years ago, the rocks that became the Himalayas were at the bottom of the ocean.
Fossils of an ancient giant shark, a megalodon, have been found in the landlocked U.S. state of Utah. This tells scientists that millions of years ago, the middle of North America was probably entirely underwater.
Steps to find a fossil
In order for a fossil to be useful in paleontology, we have to know it exists! Many fossils are discovered purely by accident, by individuals not looking for fossils at all. They are found by people digging foundations for buildings, or quarrying rocks, and then brought to the attention of scientists. However, for the most part paleontologists actively seek out new specimens. These might be elaborate expeditions, short day trips, or any scale in between. The team might be a few individuals, to a dozen, to many hundreds .
Step 1: Finding the Fossils (Prospecting)
While in the field, prospecting works by walking the hills of the badlands and looking for fragments of bones and teeth weathering out of the sediment. Normally you don't immediately find a bone sticking out of the ground: instead, one looks for a trail of fragments weathering out of the hillside, then trace them up to the layer in which they are coming. When a potential site is identified, it is surveyed using technology that produces three-dimensional maps and plans of potential fossil-bearing areas. Finds are plotted on virtual maps using a digital Geographical Information System (GIS). If you determine a layer in which fossils are preserved, you move from prospecting to excavating.
Step 2: Getting the Fossils Out of the Sediment (Excavating)
When you come across a layer with fossils, it is unlikely that it is the current surface of the ground. So some degree of removal of the sediment above the fossil layer has to be done. Depending on the geometry of the situation, this might involve geologic hammers, picks, shovels, pneumatic drills, jackhammers, backhoes, or (in the old days) dynamite.
Step 3: Jacketing & Return to the Museum
Smaller bones and teeth might be wrapped up with paper towels and/or foil, requiring no additional protection. These can be carried back to the field vehicle as is. But larger bones--or sets of bones still in articulation--require special care. A very standard technique in field paleontology is jacketing. At the end of a field season the specimens need to be shipped back to the museum in which they will be studied. By muscle power (or sledge or helicopter) the bags or bones and jackets are moved to the off-road vehicles, then driven back (or shipped via some other transport) to a lab.
Step 4: Preparation
After a fossil has been prepared and cleaned, it is studied in the laboratory. There are many ways of examining fossils in detail. Significant fossils can be measured using callipers. Binocular light microscopes are used to look at surface features of bones. These can show cut marks or carnivore damage. A scanning electron microscope (SEM) is used for detailed, high magnification analysis, for example, to study microwear on teeth, yielding data on diet.
Step 5: Cataloging & Accessioning
Every specimen in a museum has to have a record; otherwise they are useless as data. So museums have catalogues listing each specimen, its identity, the site and formation it was from, who found it and when, etc. This process is called accessioning, and is the way a bone or tooth makes its way into the scientific record.
Step 6: Restoration & Mounting
The vast majority of fossils in any museum will mostly be in storage, and be worked on by researchers but not seen by the general public. But a number of skeletons and other specimens might be selected for public display. These are chosen for a number of reason: most importantly how impressive they might be and how they might be incorporated thematically into a larger exhibit. Complete fossil skeletons are vanishing rare, however, especially for larger species. Broken bones need to be repaired, for instance, and missing bones need to be replaced. In the case of missing bones, they might be sculpted (or today, 3D printed) by mirror-imaging the same bone from the opposite side of the body. In other cases it might be replaced by the same bone from another individual (but care must be taken to make sure the proportions are appropriate for the main skeleton). Some museums make it clear (by color, for instance) which parts of a restored fossil are real, and which are filled in; in others, though, it is hard to tell.