The relationship between generation gland morphology and armour in Dragon Lizards ( Smaug ): a reassessment of ancestral states for the Cordylidae

To substantiate the claim of a relationship between generation gland morphology and degree of body armour in cordylid lizards, we studied the nine species in the genus Smaug. We predicted that well armoured species in this clade will have multi-layer generation glands, and lightly armoured species two-layer glands. Gland type was determined using standard histological techniques after sectioning a glandular patch of one adult male per species. A total of 133 specimens were examined for data on tail and occipital spine lengths (which were used as indicators of armour). We found that species with multi-layer generation glands (S. giganteus, S. breyeri, and S. vandami) have relatively long tail and occipital spines, while species with two-layer glands (S. mossambicus, S. regius, S. barbertonensis, S. warreni, and an undescribed species) have relatively short spines. Smaug depressus possesses both multi-layer and two-layer glands, and this variation was linked to regional variation in spine length. An ancestral state reconstruction for the Cordylidae showed that the two-layer state always results from the reduction of layers from a multi-layer precursor, and that reduction always culminates in two-layer glands and not in one-layer glands. This finding suggests that the one-layer state in the Ninurta-Chamaesaura-Pseudocordylus clade is most probably plesiomorphic, and therefore the ancestral state at the Cordylidae and Cordylinae nodes. Given the observed relationship between type of generation gland and body armour, this finding would suggest that the most recent common ancestor of the Cordylidae was lightly armoured.