Background The pisiform and calcaneus are paralogous bones of the wrist and ankle and are the only carpal and tarsal, respectively, to develop from two ossification centers with an associated growth plate in mammals. Human pisiforms and calcanei have undergone drastic evolutionary changes since our last common ancestor with chimpanzees and bonobos. The human pisiform is truncated and has lost an ossification center with the associated growth plate, while the human calcaneus has expanded and retained two ossification centers and a growth plate. Mammalian pisiforms represent a wide range of morphologies but extremely short pisiforms are rare and ossification center loss is even rarer. This raises the question of whether the sole human pisiform ossification center is homologous to the primary center or the secondary center of other species. We performed an ontogenetic study of pisiform and calcaneus ossification patterns and timing in macaques, apes, and humans (n = 907) from museum skeletal collections to address this question. Results Human pisiforms ossify irregularly and lack characteristic features of other primates while they develop. Pisiform primary and secondary center ossification timing typically matches that of the calcaneus of non-human primates, while the human pisiform corresponds with calcaneal secondary center ossification. Finally, human pisiforms ossify at the same dental stages as pisiform and calcaneal secondary centers in other hominoids. Conclusions These data indicate that the human pisiform is homologous to the pisiform epiphysis of other species, and that humans have lost a primary ossification center and associated growth plate while retaining ossification timing of the secondary center. This represents an exceptional evolutionary event and demonstrates a profound developmental change in the human wrist that is unusual not only among primates, but among mammals.

中文翻译：

---

识别短人类豌豆形及其丢失的骨化中心的同源性。

背景豌豆骨和跟骨是腕部和踝部的旁系骨，并且分别是唯一的腕骨和跗骨，从哺乳动物的两个骨化中心发育而来，并具有相关的生长板。自从我们与黑猩猩和倭黑猩猩的最后一个共同祖先以来，人类豌豆形和跟骨经历了剧烈的进化变化。人豌豆骨被截断并失去了一个骨化中心和相关的生长板，而人跟骨扩大并保留了两个骨化中心和一个生长板。哺乳动物豌豆形代表了广泛的形态，但极短的豌豆形很少见，骨化中心损失更罕见。这就提出了一个问题，即唯一的人类豌豆骨化中心是否与其他物种的主要中心或次要中心同源。我们对博物馆骨骼收藏中的猕猴、猿和人类 (n = 907) 的豌豆骨和跟骨骨化模式和时间进行了个体发育研究，以解决这个问题。结果人类豌豆形骨化不规则，在发育过程中缺乏其他灵长类动物的特征。豌豆骨初级和次级中心骨化时间通常与非人类灵长类动物的跟骨相匹配，而人类豌豆骨对应于跟骨次级中心骨化。最后，人类豌豆形骨化的牙齿阶段与其他类人猿的豌豆形和跟骨次要中心相同。结论 这些数据表明，人类豌豆骨与其他物种的豌豆骨骺同源，并且人类已经失去了初级骨化中心和相关的生长板，同时保留了次级中心的骨化时间。这代表了一个特殊的进化事件，并展示了人类手腕的深刻发育变化，这不仅在灵长类动物中，而且在哺乳动物中都是不寻常的。