The study of Eurasian prehistory has always been closely associated with the study of horse domestication. Archaeozoologists use a variety of methods to establish if animals found in archaeological sites were domesticated.  One of the most commonly used indicators is to look for evidence of human management by herd culling, (for example slaughtering males before they mature).  This requires analyzing the age at death of animals found in sites. 

Horses have hypsodontic (meaning high-crowned) teeth that become shorter with age.  Horse diets are normally very abrasive because they eat fibrous grasses which include soil particles. Recent studies of grass wear on mammal teeth suggest that it is soil, not grass, that is responsible for most of the tooth wear in grazing mammals. In young horses the crowns (or the part of the teeth that includes enamel) are very long and the roots are short.  A normal horse diet will wear away 2-3mm of the crown every year.  As they are worn at the top, they continually erupt from the jaw, so the teeth get shorter as horses get older.

In previous studies of equids, the curve relating crown height to age was constructed using animals whose ages were estimated on the basis of eruption and tooth wear, in some cases using measurements taken from X-rays rather than directly from teeth. No one had constructed a crown height-and-age curve for horses using direct measurements on horse teeth from individuals of known age. For our bit wear study we had gathered mandibles from 36 domestic horses of known age, processed and documented by veterinary autopsy labs.  Veterinarian reports listing age, breed and usage were confirmed and elaborated in a subgroup of 13 horses whose owners chose to supply extra information. Their cooperation increased the accuracy of our age and usage data significantly. Molars from these 36 horses were measured directly for crown heights. We also collected 20 feral horse mandibles and directly measured their molars.   The crown heights curves are plotted below and all raw data is available in the linked Excell spreadsheet.

Using Crown Height Curves for Aging Archaeological Specimens:

Using crown height measurements to determine age is not as precise a method as we might hope for. Although correlations between age and crown height are very strong as indicated in the yellow legend of each graph above, crown height measurements taken from the right and left sides of an individual horse can vary by as much as 8mm. These are teeth of the exact same age, usage, temperament and environment.

P2 (25 horses)

P3 (24 horses)

P4 (24 horses)

M1 (30 horses)

M2 (25 horses)

M3 (23 horses)

Range (in cm)