I’m starting 2015 at Valley of the Mastodon with an example of the blog’s namesake, a tooth from a mastodon.
This tooth is much smaller than the one I showed for Fossil Friday back in October, and represents a much younger animal. Like elephants, mastodons grow a total of six teeth in each quarter of their jaws (not including tusks), deciduous premolars 2-4 and molars 1-3. However, these teeth erupt sequentially as if they were on a conveyer belt, so there are never more than three teeth in the mouth at any one time.
The tooth is shown above in occlusal view, with the front of the tooth to the right. It seems to have been rolled around in a stream or otherwise eroded, as there is a fair amount of damage including missing roots. There is also a lot of wear on the tooth caused by chewing, so that the enamel ridges characteristic of mastodons have been worn down, leaving three oval enamel ridges on the occlusal surface of the tooth. The fact that there are three of these enamel ovals suggests that this was not the 2nd or 3rd premolar, as these teeth usually only have two enamel ridges. The tooth is also small, only about 7 cm long, and is about twice as long as it is wide, suggesting that it is the 4th premolar. Moreover, the enamel ridges are not perpendicular to the long axis of the tooth, suggesting that this is a lower premolar rather than an upper one.
Below is a labial view of the same tooth, showing the heavily worn crown and the damaged roots:
Because of the sequential tooth replacement in mastodons and elephants, the 4th premolar is only present in the mouth for a fairly short period of time. For modern elephants this tooth is only present from about 3 to 10 years of age. Assuming mastodonts grew at the same rate as elephants, this tooth probably represents a mastodon that was roughly 10 years old.