Cranial endocasts from a growth series of Monodelphis domestica (Didelphidae, Marsupialia)

A study of individual and ontogenetic variation

Thomas E. Macrini, Timothy Rowe, John L. VandeBerg

Research output: Contribution to journalArticle

43 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Pages (from-to)844-865
Number of pages22
JournalJournal of Morphology
Volume268
Issue number10
DOIs
StatePublished - Oct 2007
Externally publishedYes

Fingerprint

Monodelphis
Monodelphis domestica
Didelphidae
Opossums
Marsupialia
Metatheria
Growth
Olfactory Bulb
phylogeny
Skull
olfactory bulb
opossums
computed tomography
skull
polymorphism
ontogeny
fossils
taxonomy
intraspecific variation

Keywords

  • Computed tomography
  • Cranial endocast
  • Intraspecific variation
  • Opossum
  • Polymorphism

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • Developmental Biology
  • Anatomy

Cite this

Cranial endocasts from a growth series of Monodelphis domestica (Didelphidae, Marsupialia) : A study of individual and ontogenetic variation. / Macrini, Thomas E.; Rowe, Timothy; VandeBerg, John L.

In: Journal of Morphology, Vol. 268, No. 10, 10.2007, p. 844-865.

Research output: Contribution to journalArticle

@article{7e7dd8e0090d43e1ac35a61ca0d2d1ad,
title = "Cranial endocasts from a growth series of Monodelphis domestica (Didelphidae, Marsupialia): A study of individual and ontogenetic variation",
abstract = "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.",
keywords = "Computed tomography, Cranial endocast, Intraspecific variation, Opossum, Polymorphism",
author = "Macrini, {Thomas E.} and Timothy Rowe and VandeBerg, {John L.}",
year = "2007",
month = "10",
doi = "10.1002/jmor.10556",
language = "English (US)",
volume = "268",
pages = "844--865",
journal = "Journal of Morphology",
issn = "0362-2525",
publisher = "John Wiley and Sons Inc.",
number = "10",

}

TY - JOUR

T1 - Cranial endocasts from a growth series of Monodelphis domestica (Didelphidae, Marsupialia)

T2 - A study of individual and ontogenetic variation

AU - Macrini, Thomas E.

AU - Rowe, Timothy

AU - VandeBerg, John L.

PY - 2007/10

Y1 - 2007/10

N2 - 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.

AB - 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.

KW - Computed tomography

KW - Cranial endocast

KW - Intraspecific variation

KW - Opossum

KW - Polymorphism

UR - http://www.scopus.com/inward/record.url?scp=34848813811&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=34848813811&partnerID=8YFLogxK

U2 - 10.1002/jmor.10556

DO - 10.1002/jmor.10556

M3 - Article

VL - 268

SP - 844

EP - 865

JO - Journal of Morphology

JF - Journal of Morphology

SN - 0362-2525

IS - 10

ER -