Taxonomic identification using geometric morphometric approach and limited data: an example using the upper molars of two sympatric species of Calomys (Cricetidae: Rodentia)

Abstract

ABSTRACT. The taxonomic identification of micromammals might be complicated when the study material is fragmented, as it is the case with pellets and fossil material. On the other hand, tooth morphology generally provides accurate information for species identification. Teeth preserve notably well, retaining their original morphology, unlike skulls and mandibles, which can get crushed or have missing parts. Here, we explored a geometric morphometrics approach (GM) to identify fragmented specimens of two sympatric Calomys Waterhouse, 1837 species -Calomys tener (Winge, 1888) and Calomys expulsus (Lund, 1841) -using the morphology of intact molars as the basis for identification. Furthermore, we included some specimens of uncertain taxonomic identification to test their affinities and the utility of the shape of the molar to identify incomplete specimens. We evaluated the variations in the shape of the first upper molar (M1) among 46 owl pellets specimens of Calomys, including C. expulsus (n = 15), C. tener (n = 15), and unidentified specimens treated as Calomys sp. (n = 16) through GM analysis using 17 landmarks. The data was explored using PCA, PERMANOVA, and Discriminant analyses over the Procrustes residuals matrix were applied to evaluate inter-and intraspecific shape differences. Also, we evaluated whether allometric shape differences could impact the data, but found no evidence of a correlation between size and shape. Our results support that shape differences in the M1 are effective for discriminating between C. tener and C. expulsus. Moreover, the unidentified specimens do not represent a third shape but could be identified with confidence either as C. tener or C. expulsus. Our results show that even with fragmentary materials, GM is a feasible and useful tool for exploring inter-specific shape differences and assisting in taxonomic identification as a complement to traditional qualitative description of diagnostic features in poorly preserved specimens.

On the Misidentification of Species: Sampling Error in Primates and Other Mammals Using Geometric Morphometrics in More Than 4000 Individuals

“…Indeed, the whole field of virtual anthropology originated from the use of a mix of geometric morphometrics and 3D imaging techniques, with extensive applications to reconstruct and compare fragmentary material to produce results unachievable with traditional non-quantitative methods (e.g., Hublin et al, 2009Hublin et al, , 2017. More generally, in recent years, taxonomists have turned increasingly frequently to geometric morphometrics to assign living or fossil specimens to species-level taxa using clustering methods, discriminant functions or other morphometric analyses, with variable accuracy depending on the variability and overlap of the morphologies of the species in question as well as the morphometric sample available to the researcher (e.g., Polly and Head 2004;McGuire 2011;Boroni et al, 2017;Fang et al, 2018).…”

Morphological Variation in the Skull of Nephelomys meridensis (Rodentia, Cricetidae): Evidence for Cryptic Species in Andean Populations from Northern South America

“…Rivas and Péfaur (1999a) explored the geographic variation in skulls of specimens of the genus Nephelomys from Venezuela using multivariate analyses; their results supported the differentiation of the populations from Yacambú National Park and Mérida. Our results using geometric morphometrics demonstrate the validity of this tool for taxonomic studies and for the identification or detection of cryptic species (Cordeiro-Estrela et al 2006Astúa et al 2015;Boroni et al 2017).…”

“…The use of geometric morphometrics on bony structures (mainly skulls) of cricetid rodents has increased lately as a means to examine intra-and interspecific morphological variation, and to identify and diagnose cryptic species within the group (Cordeiro-Estrela et al 2006García and Sánchez-González 2013;Astúa et al 2015;Boroni et al 2017;García et al 2018). Geometric morphometrics is a biologically based statistical analysis method that decomposes variations in size and shape in a two-or three-dimensional space (Bookstein 1991).…”

Call me by my name: unravelling the taxonomy of the gulper shark genus Centrophorus in the Mediterranean Sea through an integrated taxonomic approach

“…We integrated traditional morphometric analyses with geometric morphometry to investigate in-depth the morphological variation in the Mediterranean samples of Centrophorus. Landmarks-based techniques, being based on shape instead of linear measurements, allow us to highlight different sources of phenotypic variation among species (Schmieder et al, 2015;Guillaud et al, 2016;Wilke et al, 2016;Boroni et al, 2017;Ibáñez & Jawad, 2018).…”