Morphometric Variation in Thirteen-Lined Ground Squirrels, Spermophilus Tridecemlineatus, From West Texas‪.‬

ABSTRACT. -- Univariate and multivariate statistical tests were used to assess individual and secondary sexual morphological variation in a sample of 99 Spermophilus tridecemlineatus from northwestern Texas. Based on multiple analysis of variance results, variation in standard morphological measurements (condylobasal length, zygomatic breadth, mastoid breadth, and depth of skull) of adults was independent of age group, but dependent on sex. Discriminant function analysis correctly assigned 95% of the individuals to the correct sex when both cranial and external measurements were used, whereas 86% of the individuals were assigned correctly to sex based on cranial measurements only. Principal components analysis confirmed the presence of two distinct groups based on sex; a combination of four cranial and five external measurements accounted for 95% of the variation between sexes. Consequently, sexes should be analyzed separately when addressing systematic questions in this taxon from this area. Key words: Spermophilus tridecemlineatus; 13-lined ground squirrel; cranial variation; Texas. **********