Lesson 2: Death and Fossilization Flashcards
What is Taphonomy?
The study of all natural processes that involve an organism after it dies - this includes how it decays, is scavenged by other organisms, becomes fossilized, and erodes.
Shortly after death, decay may cause a body to swell with putrid gasses, and this may cause the carcasses of even large animals to float easily and to be transported by shallow and weakly flowing water. This is called…?
Bloat-and-float.
What are some factors that can contribute to the disarticulation of a skeleton?
- Partial consumption by carnivores.
- Carcasses that have rotted for some time may be easily broken apart if swept away by rivers or flood waters.
- Water currents may also carry different portions of a skeleton to different locations, based on the weight and shape of the different bones.
- Prolonged exposure to sunlight gradually weakens and disintegrates bone. Skeletons that become only partially buried will eventually lose their exposed portions.
- Portions of skeletons may also be trampled by animals or have their mineral content leached away by the roots of plants.
What is Plastic deformation?
It occurs when pressure causes the shape of a buried fossil to be changed such that, even when the pressure is later removed, the fossil does not return to its original shape.
What are some ways a bone can be buried?
If an animal dies in its own burrow, if it falls into a sinkhole, or if it is buried by a predator. But, most often, burial occurs when water washes sand or mud over a carcass.
In what environments is fossilization most common?
Fossilization is more common in wet environments than in dry environments, where there is no water to help bury carcasses. Fossilization is also more common at low elevations, where sand and mud carried in by water are able to build up, than at high elevations, where sand and mud are often carried away by erosion before they can build up and ‘permanently’ bury and protect a carcass. For this reason, we most often find dinosaur skeletons in ancient river, stream, and lake deposits.
River and stream deposits are called…?
Fluvial deposits.
Animals that died and were preserved in lakes (lacustrine deposits) have a better chance of preserving soft tissues like hair or feathers in the fossil. Why?
This is because there is very little water movement in the lake to disrupt the skeleton, and the sediments laid down in lakes are very fine-grained – it’s easier to preserve impressions of feathers in mud than in sand.
Are dinosaur fossils ever found in deep water environments, like ancient oceans?
Even though there were no marine dinosaurs, we do sometimes find dinosaurs in ancient coastal environments (and, rarely, deeper-water environments), if the dinosaur was washed out to sea during a storm or tsunami.
We don’t often find dinosaurs in sediments representing ancient deserts (usually represented by aeolian, or wind-based, deposits), because there wasn’t enough sediment being deposited to preserve the skeleton. What is one amazing exception?
The ancient environment represented by the rocks in Mongolia. During the Cretaceous, it was a sand swept desert with a river that coursed through it, forming a large deltaic plain (huge oasis). Dinosaurs could be buried by the sediments that were deposited by the river. They could also be buried by sand dunes that suddenly collapsed onto the still living animal. This can happen when dunes suddenly become wet and saturated, as during a heavy rainstorm.
With only a few rare exceptions, all fossils are found in what type of rock?
Sedimentary rocks.
What are sedimentary rocks? Igneous rocks? Metamorphic rocks?
Sedimentary rocks are rocks that form when mineral and organic particles accumulate and become either cemented or compacted together.
Igneous rocks form when magma or lava cools.
Metamorphic rocks form when sedimentary or igneous rocks are changed by heat and pressure.
What is sedimentology?
The science of how sedimentary rocks form.
Understanding the environmental conditions that led to the formation of the particular sedimentary rocks that contain a fossil can…?
Give important clues about the habitat of the fossil organism.
Sedimentary rocks that form from mud and silt are called …? What do they indicate?
mudstone and shale. Lakes are places where large amounts of mud and silt accumulate, and large deposits of mudstone and shale often indicate a former lake bottom environment.
