Last summer I posted about a partial horse skull from Diamond Valley Lake that still had its deciduous premolars in place. Of course, if that horse had lived a little longer the deciduous teeth would have fallen out and been replaced with permanent teeth, with the remnant of the shed tooth left behind.The large tooth shown above is a shed deciduous premolar, probably the upper left dP4. Besides Max, for scale there is also a modern human deciduous premolar (P2 instead of P4, since humans only have 2 premolars) courtesy of my son Tim.Horses eat abrasive food such as grasses, and their teeth take a beating. By the time the 4th deciduous premolar is shed at around 3 years of age, it is worn to a nub. This is more apparent in an oblique view of the same tooth: 
In the Diamond Valley Lake collections we only have a few shed deciduous horse teeth. Many animals don't live enough to shed their teeth, and if they do live that long, by the time the teeth are shed they're worn so thin that they aren't as likely to survive to become fossils as a more complete tooth.This tooth will be on display in the "Stories from Bones" exhibit, opening at Western Science Center on October 31.