It seems that most of the mastodon remains from Diamond Valley Lake are from adult or nearly adult animals, although there are exceptions representing younger animals. Then we have the example shown here, from an almost ridiculously cute baby mastodon.
This tooth is the upper right second premolar (dP2), the very first upper tooth to erupt in mastodons. It’s shown above in occlusal view, with the front of the tooth to the left. Mastodon teeth have distinctive transverse ridges of enamel (they’re what make tooth look “bumpy”), and the number of ridges differs by tooth position. Typically the second and third premolars each have two ridges, the fourth premolar and first two molars each have three, and the third molar has five. The two ridges in this tooth make it either a second or third premolar, but its size gives away its position; this tooth is only 31 mm long! This puts it squarely in the size range of dP2 specimens from Florida described by Green and Hulbert (2005), which ranged from 27.6 to 36.4 mm. To get an idea of just how tiny this tooth is, here it is beside a mastodon third molar:
Here’s a labial (side) view of the premolar:
This tooth was discovered near the West Dam in December 1997. It turns out that some other baby mastodon teeth were found at the same site three days earlier. While they have separate numbers in the collection, it’s very likely that these teeth all came from one animal. The additional material includes the left maxilla fragment below, shown in labial view with the front toward the left:
Here’s the same fragment in occlusal view, again with the front toward the left:
The larger, complete tooth is the fourth premolar (note the three transverse enamel ridges). In front of it is the posterior ridge of the third premolar.
The fragmentary right fourth premolar was also collected (occlusal view, anterior to the right):
If all these pieces came from one individual (which I think is very likely), we have almost the entire upper left premolar series, lacking only the front half of the third premolar, as well as part of one right premolar.
So I called this a baby mastodon, but how young was it? We can estimate the age if we assume that mastodon growth rates and tooth eruption times were similar to those of modern elephants. Mastodonts and elephants are only distantly related, so undoubtedly this introduces some uncertainty, but given their similar sizes and tooth replacement patterns it should produce a reasonable estimate.
A key feature to look at is the amount of wear on each tooth. The fourth premolars and the preserved part of the third premolar show no wear at all. But in the second premolar, while the enamel ridges are mostly intact, there is a little wear at the tips (this is most clearly visible in the occlusal view at the top). In African elephants, the second premolar begins to wear when the elephant is about 2 months old, and by the age of 2 years the tooth has worn down and fallen out. Given the light wear present on this tooth, this mastodon was likely no more than 4 to 6 months old!
Reference: Green, J. L. And R. C. Hulbert, Jr. 2005. The deciduous premolars of Mammut americanum (Mammalia, Proboscidea). Journal of Vertebrate Paleontology 25:702-715.