Anomalies in the vertebral column and ilio-sacral articulation of some anuran amphibians


We present accounts of vertebral anomalies in 17 individuals representing 13 species of anuran amphibians. These cases were detected while perusing a larger survey on the skeleton of frogs, for which μCT scans of a broad range of species were collected and evaluated. Our data and reports from the literature suggest that malformations, asymmetries, and irregularities, if present, appear to be particularly prevalent in the posterior region of the axial skeleton in frogs. Anomalies at the trunk-tail boundary, i.e., at the sacrum and neighbouring segments, were relatively common. Malformations at the trunk-tail boundary often include sacralization of pre- and postsacral elements with asymmetrically or symmetrically developed diapophyses, fusion with the posteriormost presacral vertebra, occurrence of postsacral vertebrae, unusual transverse processes at the proximal end of the urostyle, formation of additional zygapophyses, or fusion of elements that normally articulate. Vertebral fusion in the anterior vertebral column (Presacral Vertebrae I+II) has been reported both in evolutionary context and in cases of individual developmental anomalies. Malformations in the middle section of the vertebral column, such as the case of Epidalea calamita reported herein, are rare.
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