I'm in Chicago this week for the National Science Teachers' Association meeting, in part so that my wife Brett and I can demonstrate teaching kits that we're developing based on the WSC collections (I'll have more about those in a future post). One of these teaching kits involves fossil bison, including the specimen featured in today's Fossil Friday. This is a partial right lower jaw from a bison, seen above in lateral (side) view. Below is the same specimen from above (dorsal view):
While most of this jaw is missing, it does preserve the tooth sockets ("alveolae"), even though only a single tooth is preserved. That tooth is the last molar, m3, and it's pretty unusual in occlusal view:
The tooth is almost completely worn away. None of the usual complex enamel patterns that we see in bison teeth are present, because the enamel is mostly gone, except for a few patches on the edges of the tooth. Modern bison live to about 15 years in the wild, and this one had to be getting up there.But there's actually more to look at here. It's not that unusual to have a jaw fragment with only one tooth preserved; once a jaw is broken it's easy for the teeth to fall out. But if we look at the empty tooth sockets in this jaw, we can see that's not what happened here:
These sockets actually have bone covering the openings. That means that the teeth fell out before the animal died, and the sockets healed over! This bison was shockingly old; it had actually lived long enough for every tooth except the last one wear all the way down to the roots and fall out, with the sockets healing over. Even the last tooth was close to falling out when the animal died.It's tough to estimate the age of such an old animal, but this had to be a particularly elderly individual, and has resulted in us nicknaming it "Methuselah".