Matt Kim
(matthewkim0803@gmail.com)
Friday, April 1, 2011
Fossil Finding
On page 9 of your inner fish, there is a great diagram titled "pattern at the zoo." Furthermore, Shubin says that "every rock sitting on the ground has a story to tell" (11). Discuss the evolutionary changes we see from fish like animals to humans using the diagram, campbell, and any outside resources. Further explain how this evolution affects the fossils we see and where we find these fossils. How did Shubin use this background knowledge when looking for fossils that showed evidence of the change from water to land animals. What challenges do scientists face when searching for these fossils?
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ReplyDeleteOn page 9, Shubin’s diagram that he calls the “pattern at the zoo,” which outlines the evolutionary changes from fishlike animals to humans. This brief description of the evolutionary changes we see is juxtaposed with where we would find fossils of these certain types of animals. The fishlike organism is at the bottom (beginning) of the evolutionary pattern and labeled “Everything with heads” (9). In class, the two classes of vertebrates that we labeled “everything with heads” would be class Chondrichthyes (cartilaginous fishes) and class Osteichthyes (bony fishes). Some descriptive details about class Chondrichthyes are the following: they have cartilage skeletons and jaws, they breathe using gills derived from the pharyngeal slits, they possess a lateral line system in which they can sense changes in water pressure, and they must continuously swim to pass water over their gills for oxygen and carbon dioxide exchange and because if they stop swimming, they are more dense than water so they’ll sink. Some example organisms of class Chondrichthyes are sharks and rays. Some descriptive details about class Osteichthyes are the following: they have bone skeletons, operculum movement allows the fish to breathe while stationary, they have swim bladders that help control the buoyancy and density of the fish, and they also possess a lateral line system to sense changes in water pressure. Some example organisms of class Osteichthyes are tuna and salmon (YUM!).
ReplyDeleteThe next pattern we see at the zoo is “Everything with heads and limbs” (9). These would be the first amphibians (8). From class, we know that amphibians belong to class Amphibia, the class of the oldest tetrapods. Some descriptive details about class Amphibia are the following: they have damp skin used in gas exchange, they have shell-less eggs, and some undergo metamorphosis in which there are two complete different stages in the organisms life (the larval stage and the adult stage). Some example organisms from class Amphibia are frogs and salamanders.
The next patterns we see in at the zoo (which are not included in Shubin’s diagram) are class Reptilia (reptiles) and class Aves (birds). Some descriptive details about class Reptilia are the following: their eggs are amniotic, they breathe using lungs, and they are ectothermic. Some example organisms of class Reptilia are turtles and snakes. Some descriptive details about class Aves are the following: thy have wings, feathers, and a four-chambered heart. Some example organisms of class Aves are pigeons and robins.
Finally, we reach class Mammalia, which Shubin defines as “Everything with heads, limbs, hair, and breasts” (9) and then “Everything with heads, limbs, hair, and breasts that walks on two legs” (9). In Shubin’s descriptions, he uses placental mammals and humans as the examples from class Mammalia. Some examples of placental mammals are humans, mice, dogs, and wolves. Key details about class Mammalia are that they have hair, large brains, and specialized teeth.
(con't)
ReplyDeleteSo all of the above has mainly described the differences and changes we see among the different classes of animals as they have evolved from fishlike organisms to mammals. The significance of these changes with respect to fossil finding is that the earliest evolved animals (the fishlike organisms, class Chondrichthyes, and class Osteichthyes) would be found in the most ancient rock. As scientists look at younger and younger rock, they start seeing the earliest amphibians, reptiles, birds, and then mammals.
When Shubin was looking for the fossil record of an organism that would be labeled “fish with hands” on the evolutionary table he provides, the organism would have to be between fossil records of “Everything with heads” and “Everything with heads and limbs.” They had to find a very specific type of rock that would be from the period that existed between the last records of the earliest evolved fish and the first records of the earliest evolved amphibians. So after doing research, they would have to look for rock that would be around 375 million years old. Some challenges scientist face when looking for fossils is they have to first find rock from the right time period, they may face extreme weather conditions, and they need the money to pay for their trips. Fortunately for Shubin, after a few trips his team was able to prevail.
(Bobby Muttilainen, rmuttilainen@gmail.com)
Bobby nailed upon every class we have learned about. However, the main question still remains, what challenges do the scientists face in finding fossils that show the evolution from fish to land animals? For one thing, fossils are very hard to find and take a lot of patience. Out of a whole 100 square miles, many paleontologists don’t find a single fossil. Although scientists contain technology to locate where fossils can be based on weather conditions thousands of years ago, fossils are very hard to find. Fossils, usually found in sedimentary rock, are very hard to find. Sedimentary rock is found everywhere as it is “formed in three main ways—by the deposition of the weathered remains of other rocks (known as clastic sedimentary rocks); by the deposition of the results of biogenic activity; and by precipitation from solution.” (http://www.graniteland.com/infos/home/sedimentary-rock). It is also very tough to find fossils because they are not always along the surface. Many times, fossils are covered in layers of debris that blew over or floated over that ended up covering the fossil and causing layers and layers of debris to pile up. On land, wind can push sand, dirt, and other debris over the fossil which can accumulate to great lengths that the fossil has been covered by layers of dirt. In water, current along the ocean floor can push sand and other debris over fossils to create layers and layers of dirt. Thus, external weather conditions play a major role in the preservation and finding of the fossils. Also, fossils can also erode. With weather conditions such as tornados, hail, and hurricanes, dirt can be eroded from the ground and will cause the fossil to disintegrate. Other factors such as acid rain and wind can also cause the erosion of the fossils that formed. “Areas where fossils can be found are usually where these rocks, clays, etc. are exposed” (http://www.premdesign.com/fosfaq.html). Although the best spot to find fossils is where rocks lay exposed, erosion can still cause the fossils to disintegrate and fade away. Thus, time is also an enemy to fossils. As time moves along, wear and tear of fossils can occur because of natural external conditions.
ReplyDelete(cont.)
ReplyDeleteThe type of fossilization most humans are aware of is carbonization. This is when carbon is the only thing preserved from a dead structure. From this carbon, imprints are made into rocks, “sometimes with great detail” (http://www.fossils-facts-and-finds.com/how_are_fossils_formed.html). These are also some of the hardest fossils to come across because these are the fossils that are usually covered by layers of debris and dirt. However, upon coming across these fossils, many observances can be made. Structures the organism contain on the outside can be seen imprinted and sometimes, if the fossils are very intricate, inner organs can sometimes be seen as well, all depending on the timing of the fossil. Thus, based on these intricate fossils, scientists such as Shubin can make distinctions to show relationships between two organisms. It is through the well-defined fossils that help scientists show relationship. That is also a reason fossil finding is hard, however. To show resemblances within two different species, scientists must obtain fossils that contain intricate designs. This goes back to patience and time being a worst enemy. Finding these fossils may take years. As bobby said, money is also an issue. If it takes years to find the perfect fossil, not all crews have the right amount of money to perform the expedition. Many crews nowadays take grants from many companies when going on expeditions in order to obtain more money. More money is theoretically “buying more time” because it allows scientists to stay on the field longer. Fossils are generally hard to find. Scientists have a lot of trouble find the perfect fossil to analyze and make conclusions to.
Sources:
http://www.fossils-facts-and-finds.com/how_are_fossils_formed.html
http://www.premdesign.com/fosfaq.html
http://www.graniteland.com/infos/home/sedimentary-rock
Shreeraj Patel
shreeraj.patel1@gmail.com