Sometimes the fossils we recover are a little worse for wear. The remains may have deteriorated before burial, been damaged or deformed by sediment weight, structural forces, or groundwater after burial, weather out of the sediment and get eroded before discovery, or damaged during the act of discovery or excavation (I’ve collected numerous fossils that were “discovered” by bulldozers!). Sometimes it seems amazing that any fossils reach us at all. And yet, even these damaged specimens can be significant.
The rather amorphous lump above is actually a mastodon tooth from Diamond Valley Lake, seen in occlusal view (the chewing surface). If you don’t look at mastodon teeth on a regular basis, it might be a little difficult to recognize at first, because a lot of the enamel is missing. It’s much more recognizable in lateral view, although the damage to the crown is still obvious:
Even with the imperfect preservation, there’s quite a lot we can say about this tooth. The lophs (the enamel ridges on the crown) are nearly perpendicular to the long axis of the tooth, suggesting that this is an upper rather than a lower tooth. The curvature of the roots indicates that the anterior side of the tooth is on the left in the photo above. Upper mastodon teeth wear more rapidly along the inside edge (the lingual side) than along the outside edge (the labial side), so that makes this an upper left tooth. There are three lophs present so that limits the tooth to either the fourth premolar, the first molar, or the second molar (the second and third premolars only have two lophs each, while the third molar has four or sometimes five lophs). From P4 to M2 the teeth get progressively larger, and this tooth is pretty large. Combining all these observations, the tooth is the upper left second molar.
But wait, there’s more! Even though a lot of the enamel is missing, there’s enough to tell that the tooth was fairly heavily worn, so it had erupted before this animal died. But the crown wasn’t completely worn away; there are still grooves separating the lophs, at least on the labial side, so this tooth was probably still in use when the animal died. For example, Max’s 2nd molars, which are still in his jaws, are more worn than this one. That means the mastodon was a young adult when it died. This is supported by the long, intact root, indicating that the tooth had not been shed. Instead, this tooth was still in the mastodon’s skull when the animal died, and the skull was broken up at some point, probably before burial.
Finally, there is actually enough of this tooth preserved that we will be able to include this specimen in our study of mastodon tooth proportions, since we can get good crown length and width measurements.
Brett and I leave this morning on our museum tour to collect measurements on mastodon teeth from other areas, visiting at least five museums across the central U. S. during the next two weeks. I’ll be posting updates about our trip on this blog and on experiment.com/mastodons and Twitter (@AltonDooley), as well as on the museum’s Instagram and Facebook pages. Max’s alter ego is also accompanying us, and will be posting his own updates on his Twitter feed (@MaxMastodon).