Sesamoids in Caudata and Gymnophiona (Lissamphibia): absences and evidence

Abstract

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 Necturus beyeri and Amphiuma tridactylum 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 Hydromantes platycephalus and Karsenia coreana. 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.

A new species of the genus Tylototriton (Urodela, Salamandridae) from western Thailand

“…The left and right dentaries touch each other antero-medially on the lower jaw. At the antero-medial ends, some expansions are developed posteriorly in the dorsal view, while in the anterior view this expansion slightly develops in the ventral direction (e.g., Villa et al 2014 ; Parra Olea et al 2020 ; Ponssa and Abdala 2020 ). This expansion is prominently present in the UPWS population (Fig.…”

Ontogeny of the meniscus in the anuran Xenopus laevis

“…The particular lack of differentiation of the knee joint structures, including the meniscus and the associated ligaments, could be related to the fusion of the tibia and fibula in the tibia‐fibula long bone anurans. The meniscus seems to be absent in the salamanders, which also lack patella sesamoid (Cosden et al, 2011; Soren, 1985), exhibiting a highly simple knee joint (Ponssa & Abdala, 2020). Interestingly, a meniscus has been described in the acetabulum of salamanders (Canillas et al, 2011).…”

Figure 2 from: Pomchote P, Peerachidacho P, Hernandez A, Sapewisut P, Khonsue W, Thammachoti P, Nishikawa K (2021) A new species of the genus Tylototriton (Urodela, Salamandridae) from western Thailand. ZooKeys 1072: 83-105. https://doi.org/10.3897/zookeys.1072.75320

“…The left and right dentaries touch each other antero-medially on the lower jaw. At the antero-medial ends, some expansions are developed posteriorly in the dorsal view, while in the anterior view this expansion slightly develops in the ventral direction (e.g., Villa et al 2014;Parra Olea et al 2020;Ponssa and Abdala 2020). This expansion is prominently present in the UPWS population (Fig.…”