Where did hind legs come from?

Summary

Thanks to newly discovered information about an ancient organism called the Tiktaalik roseae, scientists concluded that hind legs evolved from the fins of fish. This goes against the previously accepted hypothesis that hind legs developed in species after they moved onto land. The Tiktaalik is the one of the best examples of a transitional species between fish and land tetrapods that we have discovered. The organism looked like a cross between a fish and a crocodile. It was a long organism with scales and fins but also with elbows, shoulders, and partial wrists on its large forefins that allowed it to support itself on the seafloor. It wasn't until recently that a fossil containing the bottom half of a Tiktaalik was found, and that was where scientists found a pelvis that is very similar to the pelvis of a tetrapod. They were used by the animal to swim, and it gave Tiktaalik the ability to have a wider range of movements. This species gave us a new insight to how some common animal limbs came to be. 

Relevance

This article relates to our unit on evolution. We studied how various limbs evolved in species, and how we can use homologous structures to see how species are related.  With this new evidence discussed in the article, we can see where hind legs originally came from. The homologous structure, the pelvis, is similar in structure in both the Tiktaalik and many four legged animals, so we can conclude that many animals evolved from this ancient fish-tetrapod hybrid. This is a good article where we can see some of the methods of classification and evolution that we learned about in class actually being used in the real world. Also, the fact that this contradicts a previous hypothesis is good for us because we can see that we are often wrong, and that theories change over time as new evidence is discovered. 

Author: Rachel Reilly
Date Posted: January 13, 2014
Link: http://www.dailymail.co.uk/sciencetech/article-2538669/Did-hind-legs-evolve-FINS-375-million-year-old-fossil-rubbishes-theory-limbs-developed-vertebrates-lived-land.html