Three‐Dimensional Geometric Morphometric Analysis of Treeshrew (Scandentia) Lower Molars: Insight into Dental Variation and Systematics

Abstract

Scandentia (treeshrews) is an order of small‐bodied Indomalayan mammals generally agreed to be a member of Euarchonta with Primates and Dermoptera (colugos). However, intraordinal relationships among treeshrews are less well understood. Although recent studies have begun to clarify treeshrew taxonomy using morphological and molecular datasets, previous analysis of treeshrew dentition has yielded little clarity in terms of species‐level relationships within the order. However, these studies made use of character‐based methods, scoring traits across the dental arcade, which depend on there being clear differences among taxa that can be encapsulated in coding schemes. Geometric morphometrics has the potential to capture subtler shape variation, so it may be better for examining similarities among closely related taxa whose teeth have a similar bauplan. We used three‐dimensional geometric morphometrics on a sample of treeshrew lower second molars and compared the patterns of variation to the results of previous studies. We captured 19 landmarks on a sample of 43 specimens representing 15 species. Using specimen‐based principal components analysis and between‐group principal component analysis, the two treeshrew families (Tupaiidae and Ptilocercidae) were well separated in morphospace. Moreover, several treeshrew species plot in morphospace according to the clades established in previous molecular work, with closely related species plotting closer to one another than to more distantly related species, suggesting that dental morphology can be useful when studying relationships among treeshrews. As most extinct treeshrews are known only from teeth, understanding morphological patterns in treeshrew molars is important for future work on the evolutionary history of Scandentia. Anat Rec, 302:1154–1168, 2019. © 2019 Wiley Periodicals, Inc.

Using three-dimensional geometric morphometric and dental topographic analyses to infer the systematics and paleoecology of fossil treeshrews (Mammalia, Scandentia)

“…kylin overlaps with the tupaiids and plots near, though not among, the specimens of extant Ptilocercus lowii. Selig et al (2019a) found that PC1 mainly distinguished among various species of Tupaia and does not distinguish among the treeshrew genera or families. They found that taxa with lower values on PC1 plot in negative morphospace and are largely characterized by a narrower crown, a mesially shifted paraconid, and a protoconid that is taller and wider toward the cervix relative to taxa that plot in positive morphospace.…”

“…2). These landmarks are the same as those collected by Selig et al (2019a); a closely related set of landmarks was assessed in an error study by Cooke (2011) and found to be highly repeatable. As the hypoconid of Pr.…”

“…Given that the buccal margin of the hypoconid shifts lingually toward the cusp tip, we are confident in the placement of this landmark at the widest point of the hypoconid on this specimen, even though the cusp tip is missing. We used the same landmark coordinates for the extant taxa as those collected by Selig et al (2019a) with the addition of single specimens of P. lowii (YPM MAM 10179) and D. murina (Schlegel and Müller, 1843) (UAM:Mamm:103000). Landmark coordinates were analyzed in PAST 3.14 (Hammer et al, 2001), which was used for all statistical analyses.…”

“…The cropped surfaces were simplified to 10,000 faces and smoothed 100 iterations with the lambda set at 0.6 to remove noise irrelevant to the morphology of the meshes (Bunn et al, 2011; Pampush et al, 2016a; Prufrock et al, 2016a, b; Winchester, 2016a; Spradley et al, 2017; López-Torres et al, 2018). These protocols have been adapted for the analysis of dental topography; however, geometric morphometric landmarks can still be successfully and accurately placed on the resulting meshes (see Selig et al, 2019a).…”

“…Overall, they found that dental topography is useful for examining patterns of variation within the dietary morphospace of Scandentia. Although the GMA (Selig et al, 2019a) and DTA (Selig et al, 2019b) examined the morphology of the m2 in extensively overlapping samples of treeshrews, the differences in the methodology used in each analysis provided Table S1 for more details. 1, Tupaiidae (Jacobs, 1980); 2, Tupaia sivalicus Luckett and Jacobs, 1980); 3, Tupaia sp.…”