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

PONSSA, MARÍA LAURA; ABDALA V

PeerJ

PeerJ

Lugar: London; Año: 2020

An integrative definition of sesamoid bones has been recently proposed, highlightingtheir relationship with tendons and ligaments, their genetic origin, the influence ofepigenetic stimuli on their development, and their variable tissue composition.Sesamoid bones occur mainly associated with a large number of mobile joints invertebrates, most commonly in the postcranium. Here, we present a survey of thedistribution pattern of sesamoids in 256 taxa of Caudata and Gymnophiona and24 taxa of temnospondyls and lepospondyls, based on dissections, high-resolutionX-ray computed tomography from digital databases and literature data. These groupshave a pivotal role in the interpretation of the evolution of sesamoids in Lissamphibiaand tetrapods in general. Our main goals were: (1) to contribute to the knowledgeof the comparative anatomy of sesamoids in Lissamphibia; (2) to assess theevolutionary history of selected sesamoids. We formally studied the evolution ofthe observed sesamoids by optimizing them in the most accepted phylogeny of thegroup. We identified only three bony or cartilaginous sesamoids in Caudata: themandibular sesamoid, which is adjacent to the jaw articulation; one located on themandibular symphysis; and one located in the posterior end of the maxilla. We didnot observe any cartilaginous or osseous sesamoid in Gymnophiona. Mappinganalyses of the sesamoid dataset of urodeles onto the phylogeny revealed that thevery conspicuous sesamoid in the mandibular symphysis of Necturus beyeri andAmphiuma tridactylum is an independent acquisition of these taxa. On the contrary,the sesamoid located between the maxilla and the lower jaw is a new synapomorphythat supports the node of Hydromantes platycephalus and Karsenia coreana.The absence of a mandibular sesamoid is plesiomorphic to Caudata, whereas itis convergent in seven different families. The absence of postcranial sesamoids insalamanders might reveal a paedomorphic pattern that would be visible in their limbjoints.