Cranial sutures, both open and closed, support a myriad of skull functions, including redistributing strain, accommodating brain expansion, supporting cranial bone growth, and protecting the brain. Thus, variation in the degree, timing, and pattern of suture fusion has functional implications. Using a comparative ontogenetic framework across Mammalia, we quantified degree and pattern of suture fusion through ontogeny for 22 mammalian species (N = 165). Suture closure was scored on a discrete scale for 31 cranial sutures and used to calculate closure scores for individual sutures and specimens. Ancestral state estimations found the degree of ancestral marsupial fusion to be more derived, differing from both the ancestral placental and ancestral therian. The average placental pattern followed the Krogman pattern of suture fusion (cranial vault, cranial base, circum-meatal, palatal, facial, and cranio-facial), whereas marsupials showed a distinct pattern. We propose a new pattern of suture fusion for marsupials: vault, cranio-facial, facial, circum-meatal, palate, cranial base. Delayed fusion of the marsupial cranial base is hypothesized here to support prolonged postnatal growth of the marsupial brain. Collectively, our study has identified a clear marsupial-placental dichotomy in the degree, timing, and pattern of suture fusion, with implications for understanding skull function and ontogeny.

中文翻译：

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有袋动物和胎盘哺乳动物颅缝融合的不同模式


颅缝，无论是开放式还是闭合式，都支持多种颅骨功能，包括重新分配应变、适应大脑扩张、支持颅骨生长和保护大脑。因此，缝线融合的程度、时间和模式的变化具有功能意义。使用哺乳动物的比较个体发育框架，我们通过 22 种哺乳动物物种的个体发育（N = 165）量化了缝合线融合的程度和模式。对 31 条颅缝线的缝合线闭合情况进行离散评分，并用于计算单个缝合线和标本的闭合分数。祖先状态估计发现祖先有袋动物的融合程度更加衍生，与祖先胎盘类和祖先兽类不同。平均胎盘模式遵循克罗格曼缝线融合模式（颅顶、颅底、环肉、腭、面部和颅面），而有袋动物则表现出独特的模式。我们提出了一种有袋动物缝合融合的新模式：穹窿、颅面、面部、环肉、腭、颅底。这里假设有袋动物颅底融合延迟，以支持有袋动物大脑出生后的长期生长。总的来说，我们的研究在缝线融合的程度、时间和模式上确定了有袋动物-胎盘的明显二分法，这对理解头骨功能和个体发育具有重要意义。