Week 2 - Death and Fossilization Flashcards
what is taphonomy?
the study of all natural process that involve an organism after it dies, includes how it decays, if it’s scavenged, how it becomes fossilized and erodes
what are two mechanisms explaining how dino carcasses can be moved considerable distances from the original site of death
- predators or scavengers can move a carcass
- bloat and float
explain bloat-and-float
decay –> body swells with gasses –> carcass can float easily and can be transported by shallow and weakly flowing water
What are some taphonomic factors that can contribute to both the transportation and the disarticulation of a skeleton?
- partial consumption by carnivores
- rotten carcasses are easily torn apart and swept away by rivers or floods
- water currents can carry different portions of a skeleton to diff locations
- prolonged exposure to sunlight –> weakens and disintegrates bone
- partial burial –> lose exposed portions
- portions of skeletons may be trampled by animals or their mineral content leached away by plant roots
How can taphonomic factors modify a skeleton even when buried?
- weight of rock layers and sediment above a bone may flatten it
- plastic deformation - occurs when pressure causes the shape of a buried fossil to be changed such that, even when the fossil is removed, the fossil does not return to its original shape
Describe the processes that must occur for a fossil to be formed and discovered
death –> burial –> fossilization –> erosion –> excavation
Describe four different ways a body can be buried, which is the most common way?
- dies in its own burrow
- falls into a sinkhole
- bones are buried by a predator
- water washes sand or mud over a carcass (most common)
What conditions are best for fossilization?
- wet environments
- low elevations where sand and mud carried by water are able to build up
Where do we mostly find dino skeletons?
in ancient rivers, streams and lake deposits (fluvial deposits)
What deposits have the better chance of preserving soft tissues and why?
lacustrine deposits (lakes):
- little water movement in the lake to disrupt the skeleton
- sediments in lakes are very fine grained (easier to preserve impression of feathers in mud than sand)
Why is dino park a good place to find fossils?
- the region was once covered by massive glaciers: acted like giant bulldozers that removed the top layer of sediment. when they melted it created a lot of water to further erode the rock
- wind and rain continued to erode the rock
- sparse vegetation: plant roots help keep the top soil intact
Why don’t we usually find dinos in sediments representing ancient deserts?
there wasn’t enough sediment being deposited to preserve the skeleton
How is it possible to find dino in sediments representing ancient deserts?
- ancient oasis allowed desert animals to be buried
- sand dune could collapse on the living animal –> burial (occurs when dunes become wet and saturated as during a heavy rainstorm)
Describe the three different types of rocks, and which type best preserves fossils
- sedimentary = mineral and organic particles accumulate and become cemented or compacted together (best for preserving fossils)
- igneous = forms when magma/lava cools
- metamorphic = form when sedimentary or igneous rocks are changed by heat and pressure
What is sedimentology?
science of how rocks form
Why is it important to understand the environmental conditions that form different sedimentary rocks?
clues about the habitat of the organism
What minerals make up mudstone and shale, and what environment(s) produce this?
minerals = mud and slit
environments = lakes; therefore, large deposits of mudstone and shale = former lake bottoms
What minerals make up sandstone, and what environment(s) produce this?
mineral = sand
environments = beach, river channels, or ocean floor
What minerals make up coal, and what environment(s) produce this?
mineral = compressed remains of plants
environment = former swampy environ
What minerals make up limestone, and what environment(s) produce this?
mineral = accumulation of shells and exoskeletons of small marine invertebrates
environment = shallow marine environ
Why wouldn’t dino park be a good place to preserve fossils today?
very dry - sand and mud won’t accumulate
Describe dino park when the dinos lived
- wet and humid
- flat
- rivers and wetlands
What are four criteria to find dino bones?
- exposure
- rocks have to represent the right age (have to be from the Cretaceous)
- right environment represented (terrestrial)
- previous finds
What is a preservation style?
different ways that fossils form
What are the two different fossilization mechanisms?
- permineralization = empty internal spaces of a bone are filled with minerals (minerals are dissolved in water and then deposited as water soaks through the bone
- replacement = original bone gradually decays and minerals fill the space that the bone once occupied
Why can’t we find most dino fossils?
most dino fossils formed have been destroyed or are buried too deep for current excavation techniques to detect or reach
What are Badlands?
arid environments where vegetation is sparse, erosion rates are large, and where expanses of ancient sedimentary rocks are exposed
Why do paleontologists use geologic maps?
identify locations where there are exposures of sedimentary rocks that are the right age to contain dino fossils
What is the purpose of a specimen card mark?
identifies:
- where the fossil was found
- identification of the fossil
- age of the formation
What are some features of ideal dino skeletons? Why?
freshly and just barely exposed above ground
- fossils not exposed at all = undetectable
- fossily completely exposed for a long time = badly weathered
what is overburden?
rock and earth that covers a fossil specimen
What tools are used in overburden removal?
far proximity = shovels, pickaxes, jackhammers, and bulldozers
close proximity = hand picks and brushes
What are bonebeds?
accumulations of dino bones
Why do we map bones relative location to other bones?
- may help in putting a skeleton back together
- may give taphonomic clues
Describe how fossil bones are transported
- bone is wrapped in a layer of protective material
- 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
- plaster jackets are not open until they’ve reached the lab
- special glues are applied to fossils to strengthen them
What are taphonomic features common to dino bones and what do they indicate?
- disarticulation –> carnivores ate the carcass or the specimen was transported by water
- orientation of the fossils is important –> long bones aligned in the same direction indicate that the bones were transported by flowing water
- amount of abrasions on the bones –> how far the bones were transported by flowing water
- scratches –> possible tooth marks –> indicate that carnivores fed on the carcasses
