The last teeth seen in hard-shell turtles

The ancestors of turtles had teeth.
You can clearly see them in Elginia (Newton 1893; Fig. 1), Sclerosaurus (Meyer 1859) and even in the basalmost soft-shell turtle, Odontochelys (Li et al. 2008). What we’re missing is a set of teeth in the basalmost hard-shell turtle in the large reptile tree (LRT, 1050 taxa), Meiolania (Owen 1886, Gaffney 1983). So we go looking for them (Fig. 1). 

Figure 1. Palates of Elginia (from Newton 1893) and Meiolania (from Gaffney 1983). Although the drawing at lower right erases them, the photo at upper right seems to show some tiny teeth and tooth sockets.

Figure 1. Palates of Elginia (from Newton 1893) and Meiolania (from Gaffney 1983). Although the drawing at lower right erases them, the photo at upper right seems to show some tiny teeth and tooth sockets.

And there they are.
The jaw rims of Meioliania appear to have tiny, useless teeth. These were overlooked or avoided by Gaffney 1983 who eliminated those tiny bumps and holes in his drawing (Fig. 1). In the era before software generated cladograms, Gaffney did not consider Meiolania the basalmost hard-shell turtle, but in the modern era, the LRT does.

When you evolve from
teeth to no teeth sometimes the tetrapod pattern seems to be

  1. relatively few big teeth, then
  2. relatively many tiny teeth, then
  3. toothlessness

The same pattern seems to play out in ophthalmosaurs and ornithomimosaurs, but not birds and mysticetes.

References
Li C, Wu X-C, Rieppel O, Wang L-T and Zhao L-J 2008. An ancestral turtle from the Late Triassic of southwestern China. Nature 456: 497-501.
Meyer H von 1859. 
Sclerosaurus armatus aus dem bunten Sandestein von Rheinfelsen. Palaeontographica 7:35-40.
Newton ET 1893. On some new reptiles from the Elgin Sandstone: Philosophical Transactions of the Royal Society of London, series B 184:473-489.
Sues H-D and Reisz RR 2008. Anatomy and Phylogenetic Relationships of Sclerosaurus armatus (Amniota: Parareptilia) from the Buntsandstein (Triassic) of Europe. Journal of Vertebrate Paleontology 28(4):1031-1042. doi: 10.1671/0272-4634-28.4.1031 online

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