Ossification pattern of the unusual pisiform in two‐toed ( Choloepus ) and three‐toed sloths ( Bradypus )
Ossification pattern of the unusual pisiform in two‐toed ( Choloepus ) and three‐toed sloths ( Bradypus )
复制标题
二趾树懒 (Choloepus) 和三趾树懒 (Bradypus) 中不寻常的豌豆骨的骨化模式
DOI：
10.1002/ar.24832
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Reno, Philip L.
中科院分区：
文献类型：
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作者：
Gavazzi, Lia M.;Kjosness, Kelsey M.;Reno, Philip L.
两趾树懒（Choloepus sp.）和三趾树懒（Bradypus sp.）拥有短而圆的核状体，这在哺乳动物中是罕见的，与其他Xenarthra成员不同，如巨型食蚁兽（Myrmecophaga tridactyla），它们与大多数哺乳动物一样保留着细长的棒状核状体。利用照片、x线照片和微ct，我们评估了二趾树懒、三趾树懒和巨型食食兽的梨形骨化和旁系跗骨、跟骨的骨化模式，以确定树懒发生梨形骨化的过程，并将其与其他先前研究过的人类和猩猩的梨形骨化进行比较。现存的两种树懒都是通过失去次级骨化中心和基于异常多孔的软骨下表面的相关生长板的可能破坏来实现梨形复位的。这代表了哺乳动物中第三种独特的鱼状体减少机制，以及人类的初级骨化中心丢失和猩猩的两个骨化中心保留，可能缩短了生长期。考虑到二趾树懒和三趾树懒的梨形骨化模式和化石树懒中存在的梨形减少之间的显著相似性，现存树懒的梨形形态似乎并不代表最近对暂停运动的趋同适应，而是可能是在现存树懒和化石树懒辐射早期出现的Folivora祖先特征。
Two‐toed (Choloepus sp.) and three‐toed (Bradypus sp.) sloths possess short, rounded pisiforms that are rare among mammals and differ from other members of Xenarthra like the giant anteater (Myrmecophaga tridactyla) which retain elongated, rod‐like pisiforms in common with most mammals. Using photographs, radiographs, and μCT, we assessed ossification patterns in the pisiform and the paralogous tarsal, the calcaneus, for two‐toed sloths, three‐toed sloths, and giant anteaters to determine the process by which pisiform reduction occurs in sloths and compare it to other previously studied examples of pisiform reduction in humans and orangutans. Both extant sloth genera achieve pisiform reduction through the loss of a secondary ossification center and the likely disruption of the associated growth plate based on an unusually porous subchondral surface. This represents a third unique mechanism of pisiform reduction among mammals, along with primary ossification center loss in humans and retention of two ossification centers with likely reduced growth periods in orangutans. Given the remarkable similarities between two‐toed and three‐toed sloth pisiform ossification patterns and the presence of pisiform reduction in fossil sloths, extant sloth pisiform morphology does not appear to represent a recent convergent adaptation to suspensory locomotion, but instead is likely to be an ancestral trait of Folivora that emerged early in the radiation of extant and fossil sloths.