In many vertebrate animals that run or leap, the metatarsals and/or metacarpals of the distal limb are fused into a single larger element, likely to resist fracture due to high ground‐reaction forces during locomotion. Although metapodial fusion evolved independently in modern birds, ungulates, and jerboas, the developmental basis has only been explored in chickens, which diverged from the mammalian lineage approximately 300 million years ago. Here, we use a bipedal rodent, the lesser Egyptian jerboa (Jaculus jaculus), to understand the cellular processes of metatarsal fusion in a mammal, and we revisit the developing chicken to assess similarities and differences in the localization of osteoblast and osteoclast activities. In both species, adjacent metatarsals align along flat surfaces, osteoblasts cross the periosteal membrane to unite the three elements in a single circumference, and osteoclasts resorb bone at the interfaces leaving a single marrow cavity. However, the pattern of osteoclast activity differs in each species; osteoclasts are highly localized to resorb bone at the interfaces of neighboring jerboa metatarsals and are distributed throughout the endosteum of chicken metatarsals. Each species, therefore, provides an opportunity to understand mechanisms that pattern osteoblast and osteoclast activities to alter bone shape during development and evolution.

中文翻译：

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j骨和鸡的osteo骨融合融合是由成骨细胞和破骨细胞活动模式的相似性和差异性介导的。

在许多奔跑或跳跃的脊椎动物中，远端肢骨的meta骨和/或掌骨被融合为一个较大的元件，可能在运动过程中由于高地面反应力而抵抗断裂。尽管脚掌融合在现代鸟类，有蹄类动物和哈雷博斯中独立发展，但仅在大约3亿年前与哺乳动物血统不同的鸡中研究了发育基础。在这里，我们使用两足动物啮齿动物，即较小的埃及Egyptian（Jaculus jaculus）），以了解哺乳动物meta骨融合的细胞过程，然后我们重新审视发育中的鸡，以评估成骨细胞和破骨细胞活性定位的异同。在这两个物种中，相邻的meta骨沿着平坦的表面对齐，成骨细胞穿过骨膜，在一个圆周上将这三个元素结合在一起，破骨细胞在界面处吸收骨骼，从而留下单个骨髓腔。但是，破骨细胞活性的模式在每个物种中都不同。破骨细胞高度局限在相邻的j骨meta骨界面处吸收骨质，并分布在整个鸡meta骨内膜中。因此，每个物种