Ponssa María Laura, Abdala Virginia
Área Herpetología, Unidad Ejecutora Lillo (UEL), CONICET-Fundación Miguel Lillo, San Miguel de Tucumán, Tucumán, Argentina.
Instituto de Biodiversidad Neotropical (IBN), UNT-CONICET. Cátedra de Biología General, Facultad de Ciencias Naturales e IML, UNT, Yerba Buena, Tucuman, Argentina.
PeerJ. 2020 Dec 18;8:e10595. doi: 10.7717/peerj.10595. eCollection 2020.
An integrative definition of sesamoid bones has been recently proposed, highlighting their relationship with tendons and ligaments, their genetic origin, the influence of epigenetic stimuli on their development, and their variable tissue composition. Sesamoid bones occur mainly associated with a large number of mobile joints in vertebrates, most commonly in the postcranium. Here, we present a survey of the distribution pattern of sesamoids in 256 taxa of Caudata and Gymnophiona and 24 taxa of temnospondyls and lepospondyls, based on dissections, high-resolution X-ray computed tomography from digital databases and literature data. These groups have a pivotal role in the interpretation of the evolution of sesamoids in Lissamphibia and tetrapods in general. Our main goals were: (1) to contribute to the knowledge of the comparative anatomy of sesamoids in Lissamphibia; (2) to assess the evolutionary history of selected sesamoids. We formally studied the evolution of the observed sesamoids by optimizing them in the most accepted phylogeny of the group. We identified only three bony or cartilaginous sesamoids in Caudata: the mandibular sesamoid, which is adjacent to the jaw articulation; one located on the mandibular symphysis; and one located in the posterior end of the maxilla. We did not observe any cartilaginous or osseous sesamoid in Gymnophiona. Mapping analyses of the sesamoid dataset of urodeles onto the phylogeny revealed that the very conspicuous sesamoid in the mandibular symphysis of and is an independent acquisition of these taxa. On the contrary, the sesamoid located between the maxilla and the lower jaw is a new synapomorphy that supports the node of and . The absence of a mandibular sesamoid is plesiomorphic to Caudata, whereas it is convergent in seven different families. The absence of postcranial sesamoids in salamanders might reveal a paedomorphic pattern that would be visible in their limb joints.
最近有人提出了籽骨的综合定义，强调了它们与肌腱和韧带的关系、它们的遗传起源、表观遗传刺激对其发育的影响以及它们可变的组织组成。籽骨主要出现在脊椎动物的大量活动关节中，最常见于颅后骨骼。在此，我们基于解剖、数字数据库中的高分辨率X射线计算机断层扫描以及文献数据，对256种有尾目和蚓螈目动物以及24种离片锥目和壳椎目动物的籽骨分布模式进行了调查。这些类群在解释有尾两栖类和一般四足动物籽骨的进化方面具有关键作用。我们的主要目标是：（1）增进对有尾两栖类籽骨比较解剖学的了解；（2）评估选定籽骨的进化历史。我们通过在该类群最被认可的系统发育树中对观察到的籽骨进行优化，正式研究了它们的进化。我们在有尾目中仅识别出三块骨性或软骨性籽骨：下颌籽骨，与颌关节相邻；一块位于下颌联合处；一块位于上颌后端。在蚓螈目中我们未观察到任何软骨性或骨性籽骨。将有尾目动物的籽骨数据集映射到系统发育树上的分析表明，在[具体物种1]和[具体物种2]下颌联合处非常明显的籽骨是这些类群的独立获得。相反，位于上颌和下颌之间的籽骨是一个新的共衍征，支持[具体物种3]和[具体物种4]的节点。下颌籽骨的缺失在有尾目中是祖征，而在七个不同科中是趋同的。蝾螈类颅后籽骨的缺失可能揭示了一种幼态延续模式，这种模式在它们的肢关节中可见。
