In the afterword, Tiktaalik's habitat is described in greater detail. Did Tiktaalik survive in an arctic habitat, or do the fossils of other organisms show a different past? What was the climate like 375 million years ago? Make a prediction at what could have eradicated Tiktaalik based on climate shifts nearly 400 million years ago. Use information from previous chapters and describe how the characteristics of this "fish" fit the habitat/climate it lived in.
Eryk Fundakowski
The Tiktaalik fossil was first found in the Arctic Circle on Ellesmere Island. Now, this may make it seem like the Tiktaalik lived in the Arctic with a very cold and treacherous climate, however, this is not the case. The Tiktaalik fossil was a “tropical fossil inside [an] Arctic rock” (208). This means that something had to be different when the Tiktaalik was around 375 million years ago. Two things that have changed from then until now are that the “climate today is different from that 375 million years ago and the rocks that are in Ellesmere Island today were once very close to the equator” (208). Back then, the temperatures were much warmer overall so there was no ice covering the north and south poles. Also, the continents were arranged very differently 375 million years ago. This means that the island the Tiktaalik fossil was found on wasn’t located where it is now (80⁰ north latitude). It was situated mostly in the southern hemisphere near the equator. So, the temperature would have been warmer and it would have had a more tropical climate which means the Tiktaalik did not live in the arctic.
ReplyDeleteSince the Tiktaalik lived in shallow waters, it had to be able to walk around. This was made possible because even though it had fins like a fish, inside these fins there were “bones that correspond to the upper arm, the forearm, even parts of the wrist…This [was] a fish with shoulder, elbow, and wrist joints” (23). Also, the Tiktaalik did not have an operculum and, therefore, had a “true neck”. This neck allowed the Tiktaalik to move its head independently of its body and helped the fish to be able to support itself on land and in shallow waters. In general, the Tiktaalik’s size and shape shows that it was fitted for living in an environment “that probably encouraged the fish to venture into shallow water or even make forays onto land in search of food or shelter from predators” (http://english.peopledaily.com.cn/200604/06/eng20060406_256349.html). Also, the skeleton indicated that the “fish” could support itself under the force of gravity (Jenkins). Overall, the Tiktaalik was very well fitted for the environment and habitat in which it lived.
Sources:
http://tiktaalik.uchicago.edu/arcticgeo.html
http://english.peopledaily.com.cn/200604/06/eng20060406_256349.html
Danielle Webb (dwebb456@gmail.com)
I agree with Danielle that the warmer climates and certain physical characteristics (such as the independently mobile neck and shoulder/elbow wrist joints) of Tiktaalik would give it certain selective advantages to navigating shallow marine waters and eventually making that transition to land habitats as compared to other primitive organisms. However, I would like to elaborate that bone structure around the ears of Tiktaalik’s cephalized head parts also majorly contributed to its ability to thrive in its environment; On page 206 in the afterword, Neil Shubin says “the underside of the skull also shows just how intermediate Tiktaalik is in other ways. The stapes, a bone in our middle ear that we use to hear is originally a bone in the gill arch series of the fish” (Shubin 206, Afterword). With regards to discussion of the differences between hearing mechanisms in human and fish, previous research has concluded that the bones in human ears that are essential to hearing probably evolved from early primitive fish gills like the ones found in 370-million-year-old fossil fish Panderichthys and Eusthenopteron, specifically a small earlobe bone called the hyomandibula which obstructed their gill openings (Source 1). Since Tiktaalik is often accredited to being the missing gap being the evolutionary structures of Panderitchys and the tetrapod Acanthostega (from which human features also evolved from), Tiktaalik most likely possessed similar gill bone structures to Pandericthys but benefited from having less gill obstruction and much tinier bones in the ear “from its primitive condition as a large bone supporting the skull in sharks and bony fish”, which made transition to land environments easier (Shubin 206). Some evolutionary advantages to these ear bones include improved hearing in a new air-concentrated medium for Tiktaalik when it arrived on terrestrial shores and less weight stressed on its head than other primitive fish with larger, more developed cephalization.
ReplyDeleteSimiliarly, Danielle was correct in pointing out that Tiktaalik needed to have bones supporting the arm and forearm structures in order to move around efficiently in shallow waters, but I wanted to add that Tiktaalik also possessed overlapping (‘imbricate’) ribs and a pectoral girdle (connects the upper limb to the axial skeleton around the clavicle area and pectoral muscles in the chest) that may have given it an ability to lift the front part of its body by its fins; the combination of this advantage to mobility and the structures Danielle mentioned definitely helped Tiktaalik become successful in its changed environment (Source 3). To relate Tiktaalik to other organisms making the transition from marine to terrestrial environments, arthropods were considered to be pre-adapted to life on land due to their hard exoskeletons, lighter bodies and slim, strong legs that could support them against the pull of gravity (Source 4). While Tiktaalik may not have possessed an outer protective layer as strong as an arthropods’, the small size and ability of limbs to fully mobilize the rest of the body were also characteristics befitting it to its environment.
ReplyDeleteSources:
1. http://www.livescience.com/558-human-ears-evolved-ancient-fish-gills.html
2. Neil Shubin
3. http://www.earthhistory.org.uk/technical-issues/tiktaalik-roseae
4. http://sci.waikato.ac.nz/evolution/AnimalEvolution.shtml#Colonisation
Christine Lin
choco_cat11@comcast.net
This comment has been removed by the author.
ReplyDeleteFrom the information above, you get a great idea of what the habitat of the Tiktaalik was back when it existed. It use to live somewhere along the equator back when it was around, but after millions of years, tectonic plates moved around and displaced many of these fossils into regions where you would have never guessed it would be found. "The idea that continents can move was proposed by Wegener in 1915 on the basis of fossil evidence, the way in which coastlines seemed to fit together, and other features, but it was not widely accepted at the time." http://www.visionlearning.com/library/module_viewer.php?mid=65. The earliest idea of tectonic plates was originally founded by the scattering of similar fossils found in different parts of the world. Finding the age of rocks based on the presence of naturally occurring long-lived radioactive isotopes of several elements in certain minerals and rocks. http://wiki.answers.com/Q/How_do_scientists_measure_rock_age. In Subin's book, he refers to finding the right rocks too look at based off geographical sights as well as rock ages. He was looking for rocks that fit the proper conditions to find the perfect organism that liked fish to land animals, therefore, the tiktaalik was born. It lived in a shallow environment, more of a riverbank or beach, lived in a very tropical environment around the equator, and moved along the floor of the ocean rather than swimming.
ReplyDeleteTiktalik was in between a fish and an amphibian in terms of bone structure and genes. It had scales and webbing on its fins, however it had a flat head, a neck, and multiple bones that comprise the arm of the organism. These legs that were formed were very powerful and were able to lift up the Tiktalik to simulate a 'push-up'. But as Christine mentioned above, it wasn't strong enough to resist the force of gravity for long periods of time. And as Christine also mentioned, it didn't have a very strong outer protective layer, so it couldn't last very long in an ocean where there is a competitive arm's race over teeth vs bones. In the ocean, Neil Shubin described it as literally a “fish-eat-fish world,” and the only way to survive would to be to “get big, get armor, or get out of the water”(Shubin 41). It is obvious that Tiktalik chose the last one.
The reason why Tiktalik didn't survive in the ocean too long was because it didn't have the required characteristics to survive. Each creature started out the same way, but based on the conditions it was required to face, it had to adapt over generations to overcome the obstacles found there. For the Tiktalik, it was saying in the water too long, so over time, it evolved into arthropods which could survive on land. And as time moved on, natural selection picked ones that moved to the land and killed off the ones that stayed in the water (the original Tiktaliks). This led to their "extinction."
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