Cranial endocasts from a growth series of Monodelphis domestica (Didelphidae, Marsupialia): A study of individual and ontogenetic variation
Article first published online: 11 JUL 2007
Copyright © 2007 Wiley-Liss, Inc.
Journal of Morphology
Volume 268, Issue 10, pages 844–865, October 2007
How to Cite
Macrini, T. E., Rowe, T. and VandeBerg, J. L. (2007), Cranial endocasts from a growth series of Monodelphis domestica (Didelphidae, Marsupialia): A study of individual and ontogenetic variation. J. Morphol., 268: 844–865. doi: 10.1002/jmor.10556
- Issue published online: 12 SEP 2007
- Article first published online: 11 JUL 2007
- National Science Foundation. Grant Numbers: IIS 0208675, DEB 0309369
- Kalbfleisch/Lincoln Ellsworth Research Fellowship
- Helen C. Kleberg Foundation
- cranial endocast;
- intraspecific variation;
- computed tomography
Intraspecific variation (e.g., ontogenetic, individual, sexual dimorphic) is rarely examined among cranial endocasts (infillings of the braincase cavity) because of the difficulty in obtaining multiple specimens of a species, particularly fossil taxa. We extracted digital cranial endocasts from CT scans of a growth series of skulls of Monodelphis domestica, the gray short-tailed opossum, as a preliminary assessment of the amount of intraspecific variation in mammalian endocranial morphology. The goals of this study were 1) to provide an anatomical description to document developmental changes in endocranial morphology of M. domestica and 2) to examine ontogenetic and individual variation with respect to phylogenetic characters of endocranial cavities that are known to be variable between different mammalian taxa. In this study, “ontogenetic variation” refers to variation between specimens of different ages whereas “individual variation” (i.e., polymorphism) is restricted to variation between specimens of comparable age. Aside from size, changes in shape account for the greatest amount of morphological variation between the endocasts of different ages. Endocast length, width, and volume increase with age for the growth series. Relative olfactory bulb cast size increases with age in the growth series, but the relative size of the parafloccular casts shows a slight negative allometric trend through ontogeny. More than one-third of the phylogenetic characters of the endocranial cavity we examined showed some sort of variation (ontogenetic, individual, or both). This suggests that although endocasts are potentially informative for systematics, both ontogenetic and individual variation affect how endocranial characters are scored for phylogenetic analysis. Further studies such as this are necessary to determine the taxonomic extent of significant intraspecific variation of these endocranial characters. J. Morphol., 2007. © 2007 Wiley-Liss, Inc.