Department of Zoology, University of Cambridge, Downing St., Cambridge CB2 3EJ, UK.
Evol Dev. 2011 Sep-Oct;13(5):460-76. doi: 10.1111/j.1525-142X.2011.00503.x.
Previous analyses of how mammals vary in their ossification sequences have focused on monotremes, marsupials, and boreoeutherian placentals. Here, we focus on the sequence of cranial and postcranial ossification events during growth in the xenarthran skull and skeleton, including armadillos, anteaters, and sloths. We use two different methods to quantify sequence heterochrony: sequence analysis of variance (ANOVA) and event-paring/Parsimov. Our results indicate that Parsimov is conservative and does not detect clear heterochronic shifts between xenarthran and boreoeutherian placentals. Sequence-ANOVA performs better, but both methods exhibit sensitivity to the artifactual accumulation of ties. By controlling for ties and taking into account results that the methods have in common, our analysis suggests that xenarthrans significantly differ from other placentals by a late ossification of the sternum and an early ossification of the phalanges and pubis. We interpret these differences as showing that heterochrony plays a role in the skeletal development of xenarthrans, a change from previous studies that have emphasized the developmental homogeneity of the skeleton across placental mammals.
先前关于哺乳动物在骨化序列上的差异的分析主要集中在单孔目动物、有袋类和胎盘真兽类上。在这里，我们关注的是在食蚁兽、犰狳和树懒的头骨和骨骼生长过程中颅后骨化事件的顺序。我们使用两种不同的方法来量化序列异时性：序列方差分析（ANOVA）和事件配对/帕西莫夫法（Parsimov）。我们的结果表明，Parsimov 是保守的，并且在 Xenarthra 和胎盘真兽类之间没有检测到明显的异时性变化。序列 ANOVA 表现得更好，但这两种方法都对人为的平局积累敏感。通过控制平局并考虑到这些方法的共同结果，我们的分析表明，与其他胎盘动物相比，有袋动物的胸骨骨化较晚，指骨和耻骨骨化较早。我们将这些差异解释为表明异时性在 Xenarthra 的骨骼发育中发挥了作用，这与以前强调胎盘哺乳动物骨骼发育同质性的研究有所不同。
