The Wonders of Human Teeth (or why i should really start remembering to wear my retainer more often)

One human organ is both exceptionally well-preserved in the fossil record and has the potential to provide us with endless information about our evolutionary history. This organ is our teeth!  They also offer an explanation as to how humans secured their position at the  “top of the food chain.” One reason why humans have successfully been able to exploit such a wide diet is the precision and efficiency with which our distinctly mammalian teeth work. In a process known as occlusion, the many bumps and ridges in our molars fit together perfectly, breaking down various types of food in an extremely efficient manner. Additionally, our incisors, front teeth, work something like reptilian teeth, cutting into food like blades. The efficiency of our molars, coupled with the diverse functions of our differentiated teeth, allows mammals like humans to consume an exceptionally diverse array of foods, part of the key to our ability to occupy lots of niches and therefore nearly all the habitats on earth.



But how did we get such complicated teeth? If humans evolved originally from fish and more recently from reptiles, how have teeth changed since these forms. Fossilized reptilian teeth from around 300 million years ago show that they were much more incisor-like, all flat and sharp and used for slicing. These teeth did not fit together in any specific pattern and were replaced throughout the animals’ lives. When mammals appeared in the fossil record about 200 million years ago, teeth changed completely, fulfilling the above-described pattern on a much more developed jaw.
Yet what connects these two vastly different forms? Much of our evolutionary
understanding is based on transitional forms found in the fossil record. These are species that, while they do not fulfill the direct link of evolution between two extant species, they can be seen as the likely common ancestor of two seemingly unrelated species or groups. And, unsurprisingly, an understanding of teeth was used to identify a transitional form that links reptiles and mammals. Tritheledont fossils, found in South Africa and Nova Scotia, were reptiles with mammalian teeth. Tritheledont teeth were held to the jaw by a single root (an unequivocally reptilian characteristic), yet they contain bumps and ridges whose wear patterns prove that tritheledonts used tooth-to-tooth occlusion to process food efficiently. Following the appearance of tritheledonts in the fossil record, mammalian teeth begin to evolve and we see the first sets of differentiated teeth within the same mouth about 150 million years ago. From here on out, mammalian development exploded because foodswere able to be used and processed so many different ways.
    Now I sure understand a lot better why my orthodontist subjected me to TWO full rounds of braces in my awkward adolescence! He just wanted to make sure my teeth were occluding correctly so I could reap the full benefits of my efficient mammalian teeth!

-Hannah

Sources:
       "Occlusion - Definition and More from the Free Merriam-Webster Dictionary." Dictionary and Thesaurus - Merriam-Webster Online. Web. 24 Jan. 2012. <http://www.merriam-webster.com/dictionary/occlusion>.
       Shubin, Neil H., A.W. Crompton, Hans-Dieter Sues, and Paul E. Olsen. "New Fossil Evidence on the Sister-Group of Mammals and Early Mesozoic Faunal Distributions." Science 251.4997 (1991): 1063-065. JSTOR. Web. 24 Jan. 2012. <http://www.jstor.org.ezproxy.rice.edu/stable/2875224?>.
       Shubin, Neil. Your Inner Fish: A Journey into the 3.5-billion-year History of the Human Body. New York: Pantheon, 2008. Print.