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
How could a dead dinosaur’s body have been moved from the area where it originally died?
predators and scavengers may carry a carcass to their dens or some other more secure feeding area
the bloat-and-float phenomenon
What is the bloat-and-float phenomenon?
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
What are the many taphonomic 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 disarticulation?
A skeleton that is separated into its various components
What is plastic deformation?
occurs when pressure causes the shape of of a buried fossil to be changed such that, even when pressure is later removed, the fossil does not return to it’s original shape
it is an important process to understand and be mindful of
otherwise, plastically deformed fossils may be incorrectly assumed to display their true original shapes
How can a bone become buried?
burial can occur if an animal dies in its own burrow, if it galls into a sinkhole, or if it, or one of its bones, is buried by a predator
most often, burial occurs when water washes sand or mud over a carcass
In what types of locations is fossilization most common?
more common in wet environments than in dry environments, where there is no water to help bury the carcass
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 bury a carcass
therefore, most often dinosaur skeletons are found in ancient river, stream, and lake deposits
What are fluvial deposits?
river and stream deposits
What do animals preserved in lakes have a better chance of?
they have a better chance of preserving soft tissues like hair and feathers in the fossil
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
What are lacustrine deposits?
lake deposits
Why don’t we find dinosaurs in sediments representing ancient deserts?
because there wasn’t enough sediment being deposited to preserve the skeleton
How were fossils able to form in the rocky regions of Mongolia?
during the Cretaceous much of what is now Mongolia was a sand swept desert, but it was not all dry
a river also coursed through the desert and the river formed a large deltaic plain that created a huge oasis
in this deltaic plain, many desert animals, including large dinosaurs, had a chance to be buried by the sediments that were deposited by the river
How can sand dunes create fossils?
sand dunes suddenly collapsed onto the still living animal
this can happen when dunes suddenly become wet and saturated, as during a heavy rainstorm
What are sedimentary rocks?
rocks that form when mineral and organic particles accumulate and become either cemented or compacted together
What are igneous rocks?
form when magma or lava cools
What are metamorphic rocks?
form when sedimentary or igneous rocks are changed by heat and pressure
What is sedimentology?
is the science of how sedimentary rocks form
different kinds of sedimentary rocks form in different environments
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
What is mudstone and shale?
sedimentary rocks that form from mud and silt
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
What is sandstone?
sedimentary rocks that form from sand
sandstone can indicate a former beach, river channel, or ocean floor environment
What is coal?
a special kind of sedimentary rock that forms from the compressed remains of plants
coal indicates a former swampy environment
What is limestone?
usually formed from the accumulations of shells and exoskeletons of small marine invertebrates
always indicates a former shallow marine environment
What are preservation styles?
the different ways that fossils form
most dinosaur bone fossils form through either permineralization or replacement
What is permineralization?
occurs when the empty internal spaces of a bone are filled with minerals
these minerals are first dissolved in water and are then deposited in the empty bone spaces as water soaks through the bone
What is replacement?
occurs when the original bone gradually decays and minerals fill the space that the bone once occupied
Why might a fossil not be discovered by a paleontologist?
most of the dinosaur fossils that ever formed have ether been destroyed (they have been melted or metamorphosed by geologic processes deep within the earth r have eroded away to dust on the earth’s surface)
they remain buried too deep for current excavation technology to detect or to reach
What are Badlands?
Badlands, such as those throughout the Canadian and American west, are arid environments where vegetation is sparse, where erosion rates are high, and where large expanses of ancient sedimentary rocks are exposed
Badlands are among the best places to hunt for fossils
What is the ideal dinosaur skeleton?
the ideal dinosaur skeleton is one that is freshly, and only just barely, exposed above ground
fossils that are not exposed at all are simply not detectable, and fossils that are completely exposed, and have been for a long time, may be badly weathered
What is overburden?
the rock and earth that covers a fossil specimen and that must be removed before the full extent of the specimen can be judged
overburden removal usually involves large indelicate tools like shovels, pickaxes, and occasionally ven jackhammers and bulldozers
What are bonebeds?
accumulations of the bones of many dinosaurs
How is a fossil bone protected in transport?
the bone is wrapped in a layer of protective material and is then covered by strips of burlap that have been soaked in plaster
once the plaster hardens, it forms a strong and rigid jacket around the fossil
these plaster jackets are not opened until they have reached the laboratory
What are some clues that help paleontologists understand what happened to a dinosaur after it died?
disarticulation of a skeleton may occur as carnivores eat the carcass, or because the specimen was transported by water
in a bonebed, the orientation of the fossils is important
the amount of abrasion on the bones can give a relative sense of how far the bones may have been transported by flowing water
scratches on the bones can be tooth marks, which indicate that carnivores fed on the carcass
Why is the orientation of fossils important in the bonebed?
long bones (like the femur or humerus) that are aligned in the same direction indicate that the bones were transported by water, and tell us the direction the water was flowing
