From just basic observation, all three have the common trait of scales. However from the surface one might believe that the fish and the sea turtle are most related, since they have much in common. They both spend a majority (if not all) of their lives in the sea, have scales, and have limbs for locomotion in water (fins and flippers), while a snake has only scales.
But just because two species share this trait does not mean they are closely related; maybe distantly so, but they are actually analogous in comparison. Both fish and sea turtles have scales for protection, and sometimes for camouflage, but that's essentially where the similarities end. If we go far enough back in evolution, all animals evolved from fish, so their common ancestor is more than likely another fish than a reptile. This common ancestor probably did share this analogous trait, given that even ancient fish would need to protect themselves from the elements and other predators, so when fish evolved into tetrapods, then to amphibians, and even later still reptiles, this is an evolutionarily beneficial quality they passed down through the generations, disappearing in the amphibian stage and reappearing in the reptiles that followed.
For snakes and sea turtles however, the connection is much more closely related, given that they are both reptiles and thus came from a common genetic relationship. The composition of their scales differs in that the scales of a snake have a sort of waxy layer that allows snakes to be away from water, whereas the scales on the shells of turtles are much drier in comparison. Also, scales for a snake are constructed as part of its skin, much like a fish, while turtles have scutes, which are much more like plates on its shell. And while sea turtles are equipped from the structure of their shells to live most of their lives underwater, most snakes cannot do the same. Both snakes and sea turtles have seemingly more in common with the scales of fish than with each other, but they are homologous nonetheless.
Citations and Resources
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Reptile and Amphibian Evolution. Reptile and Amphibian Evolution.
University of Michigan Museum of Zoology, accessed 03 July 2014. http://www.michellecaldwell.com/linkfiles/scaredcricket/articles/other/evolution.html.
Hall, Brook
Ellen
2002
Animal Sciences: Scales, Feathers, and Hair. Encyclopedia.com.
HighBeam Research, accessed July 2014.
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T., Pooja Sehgal, Nikhilesh Jasuja, and Rupal Bansal.
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Amphibian vs. Reptile. Diffen.com. Diffen LLC, accessed 03 July
2014. http://www.diffen.com/difference/Amphibian_vs_Reptile#Evolution_of_Reptiles_and_Amphibians.
Strauss, Bob
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The Evolution of Vertebrates, in 10 (Not So Easy) Steps. About.com
Dinosaurs. About.com, accessed 03 July 2014. http://dinosaurs.about.com/od/otherprehistoriclife/tp/Vertebrate-Animal-Evolution.htm.
Trimarchi, Maria
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Can a Turtle Outgrow Its Shell? HowStuffWorks.com. InfoSpace LLC, accessed
03 July 2014.
Very interesting comparison!
ReplyDeleteIt wasn't required to set up a triple comparison as was done in the guidelines but it doesn't create a visual that makes the homologous vs. the analogous traits more apparent. I actually found that, though visual comparison alone, I thought the fish and the snake were more closely related because of the flexibilitiy and skin-like texture, with sea turtle being the stand out. Well done with your explanantions on function and ancestry.
Hi there!
ReplyDeleteI really enjoyed reading your post, it was very eyeopening and interesting! I never wold have guessed that sea turtles and snakes were closely related. I thought it was really interesting that snakes have a waxy layer on their scales to keep the water away, whereas turtles scales are much dryer in comparison! Before reading your post I would have guessed that turtles and fish were much more similar than snakes and turtles. I definitely learned something new today!