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As rays in a number of species grow, they increase the number of teeth in their jaws through a process called file splitting. The below pictures and text are from elasmo.com: “In the accompanying image of the Roughtail Stingray, the fifth upper left file is in the process of splitting. The oldest tooth (at the labial margin) has a normal design. The following tooth is laterally expanded and by the third row, a second cusp is clearly visible. It is possible that these teeth still share a common root. In row five, there are now two teeth occupying the old (now expanded) file 5 position.” I’ve seen a number of examples of file splitting ray teeth in the fossil ray teeth that I collect and I thought that I would post a few examples. I just recently found an example of a file splitting tooth (3 mm) from an Archaeomanta melenhorsti ray from the Eocene of Virginia. In this specimen you can see two distinct crowns but the crowns haven’t fully separated yet (there is also a bit of pyrite between the crowns) and two root lobes but they haven’t completely separated yet either. Here is an example of a file splitting tooth (2.5 mm) from a Coupatezia woutersi ray from the Eocene of Virginia. In this specimen you can see two distinct crowns but the crowns haven’t fully separated yet and there is only a shared single set of root lobes. Here is an example of a file splitting tooth (4.5 mm) from a Dasyatis sp. ray from the Miocene of Florida. In this specimen you can see two completely separated crowns but the root lobes have not fully separated yet. If you have any examples of ray file splitting teeth in your collection, please take some pictures and add them to this post. Marco Sr.