Macrini Thomas E, Rowe Timothy, Vandeberg John L
Department of Mammalogy, American Museum of Natural History, New York, New York 10024, USA.
J Morphol. 2007 Oct;268(10):844-65. doi: 10.1002/jmor.10556.
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.
由于获取同一物种的多个标本存在困难，尤其是化石类群，因此很少对颅腔模型（脑壳腔的填充物）进行种内变异（如个体发育、个体、两性异形）的研究。我们从灰色短尾负鼠（Monodelphis domestica）头骨生长系列的CT扫描中提取了数字化颅腔模型，作为对哺乳动物颅腔形态种内变异量的初步评估。本研究的目的是：1）提供解剖学描述，以记录家短尾负鼠颅腔形态的发育变化；2）研究颅腔系统发育特征的个体发育和个体变异，这些特征在不同哺乳动物类群之间是可变的。在本研究中，“个体发育变异”是指不同年龄标本之间的变异，而“个体变异”（即多态性）则仅限于可比年龄标本之间的变异。除了大小，形状的变化是不同年龄颅腔模型之间形态变异的最大组成部分。在生长系列中，颅腔模型的长度、宽度和体积随年龄增加。在生长系列中，相对嗅球模型大小随年龄增加，但副绒球模型的相对大小在个体发育过程中呈现轻微的负异速生长趋势。我们研究的颅腔系统发育特征中，超过三分之一表现出某种变异（个体发育、个体或两者兼有）。这表明，尽管颅腔模型对系统发育学可能具有信息价值，但个体发育和个体变异都会影响在系统发育分析中对颅腔特征的评分。需要进行更多这样的研究，以确定这些颅腔特征显著种内变异的分类学范围。
