Age determination of the Mongolian wild ass (Equus hemionus Pallas, 1775) by the dentition patterns and annual lines in the tooth cementum

Abstract

Based on 440 skulls recently collected from two areas of the wild ass population in Mongolia, the time course of tooth eruption and replacement was investigated. The dentition pattern allows identification of age up to five years. We also conclude that annual lines in the tooth cementum can be used to determine the age in years for wild asses older than five years after longitudinal tooth sections were made with a lowspeed precision saw. The first upper incisor proved to be most suitable for age determination, although the starting time of cement deposition is different between the labial and lingual sides of the tooth. The accurate age of the wild ass can be determined from the number of annual lines and the time before the first formation of the cementum at the respective side of the tooth.

Morphological Approach to Genetic Variability of the Asiatic Wild Ass (Equus hemionus) Using Non-metric Skull Characters

“…A total of 440 skulls of Asiatic wild ass were collected from carcasses in the Gobi region of Mongolia since 2001 by researchers of the National University of Mongolia (NUM) and Halle University (Stubbe et al, 2005;Lkhagvasuren et al, 2013). All of the skulls were found as dried carcasses; at least 41% were hunted illegally based on cut marks and bullet holes although the true number of poached animals was probably higher (Lkhagvasuren et al, submitted).…”

“…Furthermore fewer skulls are from the Dzungarian Gobi (n = 61) mainly collected in 2010 (Lkhagvasuren et al, 2013). The geographical location of the sample areas is shown in Fig.…”

“…The sequence of tooth eruption and replacement shows the age up to fi ve years (Ansorge et al, 2007;Lkhagvasuren et al, 2013). For older animals, longitudinal root sections of the fi rst upper incisor produce incremental annual cementum lines allowing the exact age determination in years (Ansorge, 1995;Ansorge et al, 2007;Lkhagvasuren et al, 2013). After age determination all skulls were divided in fi ve age groups to evaluate the potential dependence of non-metric character expression on normal growth.…”

“…To avoid including sex dependent non-metric characters, the sex of Asiatic wild asses was determined by the presence of canines in males, being mostly absent or rudimentary in females (Lkhagvasuren et al, 2013).…”

“…The Asiatic wild ass has lost about 50% of its distribution range in Mongolia during the last 70 years (Stubbe et al, 2012), and population size has decreased severely due to habitat fragmentation and loss, confl icts with livestock for pasture and water access, and poaching (Kaczensky et al, 2011;Stubbe et al, 2007). Therefore, many investigations on the species in diff erent parts of Mongolia were conducted, including studies on social structure Neumann-Denzau & Denzau, 2007), population characteristics (Reading et al, 2001;Lkhagvasuren, 2007;Tsendjav & Purevsuren, 2007;Ransom et al, 2012), habitat fragmentation and loss (Kaczensky et al, 2011;Ito et al, 2013), reproduction and mortality Stubbe et al, 2012), age determination (Ansorge et al, 2007;Lkhagvasuren et al, 2013), as well as population structure and mortality (Lkhagvasuren et al, submitted). Nevertheless, for a more comprehensive evaluation of the population status of the Asiatic wild ass in Mongolia, there is still a need for more insight into the population genetics of the species.…”