Monday, 1 October 2012

Palaeontology is a Real Science Part 3: Using Geology to Understand Fossils

One of the most important things for palaeontologists to understand is geology. Being able to understand basic geological principles can help a palaeontologist in many ways. It can help determine the kind of sediments that the fossils are found in, which can tell us the environment the animal was living in, or how the animal died. 

Most fossils are found in marine sediments, as water preserves animals the best by quickly cutting off the oxygen supply to the animal which allows for better preservation. Marine sediments can be identified easily and there are several different kinds. Very quiet water from a lagoon or lake is typified by very fine sediments that usually take a long time to settle in a quiet lake. Rocks from this kind of environment often have fossils that are some of the best preserved, lying at the bottom of the lake, undisturbed. A great example of these types of sediments are in shales, and the Solnhofen limestone in Germany. Black shales are typical of anoxia (lack of oxygen) from quiet oceans or lakes. One example of that is the Burgess Shale, in Yoho National Park in BC. 
Marrella a typical Burgess Shale fossil (image from Wikimedia Commons user  PurpleHz)
The Solnhofen limestone in Germany is a type of Konservat-Lagerstaette from the Jurassic that is a lagoon deposit. It preserves some exceptional fossils of fish, crustaceans, insects, and even pterosaurs. The quiet, salty nature of the lagoon made oxygen rare and preservation potential very high. 
An example of an ophiuroid (also known as a brittle star) from the Solnhofen of Germany (image from Wikimedia Commons user UlrichStill) 
Sediments can also show when the fossils have been deposited by something like a river or floodplain. In the case of bone beds, they are often found jumbled up with bones all over the place, overlaying each other. Analysis of the sediments can reveal details about what caused the animals to die and fall apart to the point that they are found. In southern Alberta, there is a Centrosaurus bone bed. By analysing the sediments found along with the bones, it was determined that a herd had tried to cross a flooded river and had drowned. The bodies were swept down-river, while their bodies came apart in the river, separating their bones and eventually resulting in the bones settling together in a jumbled nature. The direction that the bones are facing can also tell us the direction of the stream or river that carried the bones. 
Photo from an Edmontosaurus bonebed showing jumbled nature of dinosaur bones in bone beds. Photo copyright of Liz Martin
Fossils in China are often found in sandstone, typical of animals buried in a sandstorm. These fossils are often preserved in 3-dimensions and show the animals caught in the sandstorm and in their natural positions. 

There are lots of other sedimentological and geological details that can be useful to palaeontologists to help understand the environment or even the cause of death for the animals. 

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