The study of chondrocrania has a long tradition with a focus on single specimens and stages. It revealed great interspecific diversity and a notion of intraspecific variation. As an embryonic structure, the chondrocranium is subject to major changes in ontogeny with resorption and ossification of different cartilaginous structures. The cupula nasi anterior is the anteriormost portion of the cartilaginous nasal capsule and is expected to mirror much of the animal's life history and lifestyle. Its diversity in mammals is reflected in the external nasal anatomy of newborns. Marsupials and placentals show marked differences, likely related to breathing and suckling behavior. We examined histological sections of five marsupial and three placentals species and traced the development of the cupula nasi anterior and the anterior nasal capsule. We found ontogenetic variation for nearly 50% of the 43 characters defined herein. By comparing to the literature and considering ontogenetic variation, we performed an analysis of character evolution in 70 mammalian species and reconstructed the nasal anatomy of the therian ancestor. At birth, marsupials have a complete but simple cupula nasi anterior, whereas placentals display a more diverse morphology due to reductions and variations of chondrocranial elements. The more compact nasal capsule in marsupials is related to a long and strong fixation to the mother’s teat after birth. Within marsupials and placentals, several derived characters distinguish major taxa, probably related to developmental and functional constraints. The reconstructed ancestral anatomy of the cupula nasi anterior supports the hypothesis that the therian ancestor was placental-like and that the marsupial lifestyle is more derived.

中文翻译：

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哺乳动物软骨颅的个体发育和系统发育：鼻杯前部和头部前部区域的相关结构

软骨颅的研究有着悠久的传统，重点是单一标本和阶段。它揭示了巨大的种间多样性和种内变异的概念。作为胚胎结构，软骨颅在个体发育过程中会发生重大变化，不同软骨结构会发生吸收和骨化。前鼻罩是软骨鼻囊的最前部，预计会反映动物的大部分生活史和生活方式。它在哺乳动物中的多样性反映在新生儿的外鼻解剖结构中。有袋动物和胎盘表现出明显的差异，可能与呼吸和哺乳行为有关。我们检查了五种有袋动物和三种胎盘动物的组织切片，并追踪了前鼻杯和前鼻囊的发育。我们发现本文定义的 43 个字符中近 50% 的个体发生变异。通过对比文献并考虑个体发育变异，我们对 70 种哺乳动物的特征进化进行了分析，并重建了兽类祖先的鼻部解剖结构。出生时，有袋动物具有完整但简单的鼻杯前部，而胎盘由于软骨颅成分的减少和变化而表现出更多样化的形态。有袋动物更紧凑的鼻囊与出生后对母亲乳头的长时间而牢固的固定有关。在有袋动物和胎盘动物中，几个衍生特征区分主要分类群，可能与发育和功能限制有关。