Pleurodeles waltl Michahelles 1830
Creators: name: Ishikawa, Kaoru
name: Taguchi, Yuki
name: Kobayashi, Ryomei
name: Anzai, Wataru
name: Hayashi, Toshinori
name: Tokita, Masayoshi
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Amphibia
Caudata
Salamandridae
Pleurodeles
Pleurodeles waltl

description: Pleurodeles waltl (Figs 3–5)   
 Smirnov et al. (2020) described cranial skeletogenesis of P. waltl and reported that ossification began soon after hatching. The results of Smirnov et al. (2020) and our results show a similar pattern of ossification. In the study by Smirnov et al. (2020), specimen body size was 5–7 mm at the hatching stage and 28–36 mm at the stage when metamorphosis occurs. However, in our study, these measurements were 8.5–9.2 mm and 48–54 mm, respectively. Given that the growth rate of salamanders is influenced strongly by external factors, such as temperature and food, this difference in the timing of ossification onset could be attributable to the different rearing environments (Stewart, 1956).   
In phases I–V, ossification has not yet started. In the skull, the sphenethmoid, otic capsule and exoccipital are observed as cartilaginous elements. In the mandible and pharynx, the Meckel’s cartilage, the first and second basibranchials, ceratohyal, hypohyal, the first and second hypobranchials and the first to fourth ceratobranchials are detected as cartilaginous elements.  
Ossification begins in phase VI. The premaxilla, vomer, prootic, squamosal, exoccipital, parasphenoid, dentary and angular begin to ossify. The palatine and pterygoid bones appear fused into a single bone.  
In phase VII, ossification of the skull progresses rapidly, and all bones except the nasal and orbitosphenoid begin to ossify. In the mandible, the coronoid is ossified from the medial side.  
In phase VIII, the nasal begins to ossify, meaning that all bones of the skull are ossified. In the hyobranchial skeleton, the second basibranchial starts to ossify.  
In phase IX, the posterolateral projection of the frontal and anteromedial projection of the squamosal are visible. The pterygoid is elongated in the anterior– posterior direction, forming a bony bar in the ventral side of the skull.  
In phases X and XI, the third to fourth ceratobranchials degenerate.  
In phases XII and XIII, the tips of the posterolateral projection of the frontal and the anteromedial projection of the squamosal fuse to form the frontosquamosal arch, a characteristic skull feature of the family Salamandridae. The maxilla is elongated posterolaterally and its posterior end is now bifurcated, possessing short lateral and medial projections. The bony bar formed by the formerly continuous anterior palatine and posterior pterygoid is now separated in the middle. In the mandible, the second basibranchial degenerates, and the previously cartilaginous ceratohyal, second ceratobranchial and second hypobranchial ossify.
description: Published as part of Ishikawa, Kaoru, Taguchi, Yuki, Kobayashi, Ryomei, Anzai, Wataru, Hayashi, Toshinori & Tokita, Masayoshi, 2022, Cranial skeletogenesis of one of the largest amphibians, Andrias japonicus, provides insight into ontogenetic adaptations for feeding in salamanders, pp. 299-314 in Zoological Journal of the Linnean Society 195 (1) on page 305, DOI: 10.1093/zoolinnean/zlab038, http://zenodo.org/record/6530541