Ashwell K W S
Department of Anatomy, School of Medical Sciences, The University of NSW, Sydney, NSW, Australia.
Brain Behav Evol. 2008;71(3):181-99. doi: 10.1159/000114406. Epub 2008 Jan 30.
Encephalization of Australian marsupials was analyzed using the endocranial volume (ECV) of 52 species of Dasyuromorphia and Notoryctemorphia, 14 species of Peramelemorphia and 116 species of Diprotodontia from Australia and New Guinea and compared with 16 species of Ameridelphian marsupials and 3 species of native and recently introduced Australian eutherian carnivores (dingo, feral cat and feral fox). Linear regression analysis of the relationship between ECV and body weight for marsupials revealed that allometric parameters for these groups are different from those previously derived for samples of (mainly eutherian) mammals, with higher slopes for Dasyuromorphia and Diprotodontia and lower slopes for Ameridelphians and Peramelemorphia. Absolute ECV for small Australian and New Guinea marsupial carnivores (Antechinus and Sminthopsis) were found to be comparable to eutherians of similar body weight, but large marsupial carnivores such as the Tasmanian devil and thylacine had substantially smaller ECVs than eutherian carnivores of similar body weight. Similarly, members of some superfamilies within Diprotodontia (Burramyoidea, Petauroidea, Tarsipedoidea) had ECVs comparable to prosimians, whereas bandicoots, bilbies and many macropods were found to be poorly encephalized. When both encephalization quotient (EQ) and residuals from regression analysis were used to compare relative ECV of extinct/threatened species with common species there were no significant differences for any of the orders of Australian marsupials, suggesting that encephalization is not a major factor in the current extinction crisis for Australian marsupials. Similarly there were no consistent differences in relative ECV between marsupials from New Guinea and associated islands compared to Australia or between arid and non-arid Australian regions for any of the marsupial orders. The results indicate that marsupials are not uniformly poorly encephalized and that small marsupial carnivores and some members of Diprotodontia are of comparable encephalization to eutherians of similar body weight. In particular, honey possums and some gliders show an encephalization level comparable to prosimians, perhaps reflecting convergence in adaptation to similar arboreal niches.
利用来自澳大利亚和新几内亚的52种袋鼬目和袋食虫目、14种袋狸目以及116种双门齿目的颅内容积（ECV），对澳大利亚有袋类动物的脑化进行了分析，并与16种美洲有袋类动物以及3种澳大利亚本土和近期引入的真兽亚纲食肉动物（澳洲野犬、野猫和狐狸）进行了比较。有袋类动物的ECV与体重之间关系的线性回归分析表明，这些类群的异速生长参数与之前从（主要是真兽亚纲）哺乳动物样本中得出的参数不同，袋鼬目和双门齿目的斜率较高，而美洲有袋类和袋狸目的斜率较低。发现澳大利亚和新几内亚小型有袋类食肉动物（狭足袋鼩属和小袋鼩属）的绝对ECV与体重相似的真兽亚纲动物相当，但像袋獾和袋狼这样的大型有袋类食肉动物的ECV比体重相似的真兽亚纲食肉动物小得多。同样，双门齿目内的一些超科（袋貂超科、袋鼯超科、跗猴超科）成员的ECV与原猴亚目动物相当，而袋狸、兔耳袋狸和许多袋鼠的脑化程度较低。当使用脑化商（EQ）和回归分析的残差来比较灭绝/濒危物种与常见物种的相对ECV时，澳大利亚有袋类动物的任何目都没有显著差异，这表明脑化不是澳大利亚有袋类动物当前灭绝危机的主要因素。同样，与澳大利亚相比，来自新几内亚及相关岛屿的有袋类动物之间，或者澳大利亚干旱和非干旱地区的任何有袋类目之间，相对ECV也没有一致的差异。结果表明，有袋类动物的脑化程度并非都很低，小型有袋类食肉动物和双门齿目的一些成员的脑化程度与体重相似的真兽亚纲动物相当。特别是，蜜袋鼯和一些滑翔类动物的脑化水平与原猴亚目动物相当，这可能反映了在适应相似树栖生态位方面的趋同现象。
