Date of Completion


Document Type

Honors College Thesis



Thesis Type

Honors College

First Advisor

Sara Helms Cahan


Didelphis, opossums, 3D Morphometrics, phylogeny, taxonomy, systematics


The 2D cranial morphometrics of the opossum genus Didelphis has been the topic of just a few studies over the past 20 years, most of which have focused on a selection of species within the genus. Only one paper has examined this genus in its entirety (Astúa, 2017), also with 2D morphometric methods. Here I present the first 3D morphometric study into Didelphis, and the second paper investigating the shape and size variation of this genus as a whole. Didelphis species have been separated historically on a basis of size differentiation, pelage morphology, and genomic methods, all of which support the validity of their currently-accepted evolutionary hypothesis (Dias, 2020; Lemos, 2002; Salazar, 2000). Opossums do not demonstrate the wide variety of cranial flexibility observed in other groups of clade Mammalia; their basic and generally unmodified body plan actually makes them a wonderful candidate for a living representative of the Mammalian MCRA. However, regardless of their general uniformity in shape, Didelphis craniums can be differentiated by size-independent shape differences. In this study, we employ novel 3D morphometric technologies to capture 3D surface data from n=58 Didelphis craniums, the landmark data from which is used to conduct statistical comparisons within the genus, as well as examining the extent of sexual dimorphism in each species. We are able to clearly delimitate each of the six Didelphis species with this 3D landmark data, and our shape change results correlate well with the previous 2D studies of this genus. Additionally, we recover significant size-independent shape changes within the white-eared opossum group, which have previously been separated morphologically only on a basis of size (Astúa, 2017; Lemos, 2002). Significant shape-based sexual dimorphism was recovered for all species except D. pernigra, although this result is likely attributed to small sample size as this species has been observed to demonstrate significant sexual dimorphism by past studies (Astúa, 2010). The evidence for size-based sexual dimorphism throughout the species of this genus is conflicting, with some research demonstrating significant differences (Cerquia, 2009) while others only recover shape differentiation between sexes (Salazar, 2002; Astúa, 2010). This study failed to recover significant size-based sexual dimorphism in any species, consistent with the results of Astúa et. al (2010).

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

Available for download on Wednesday, May 28, 2025