The Scleral Ossicles of Sceloporine Iguanids: a Reexamination with Comments on Their Phylogenetic Significance

A reexamination of the scierai ossicles of sceloporine iguanids was undertaken after conflicting data sets were discovered in the literature. The scierai ossicles of certain other iguanids were also studied for comparative purposes. Sceloporines exhibit much greater variation in ossicle configuration than has previously been reported. This variation is often too great within genera and species to provide useful characters for inferring intergeneric relationships, although a few derived characters do suggest monophyletic groupings of genera. A large number of iguanids exhibit an ossicle arrangement in which there are 14 ossicles of approximately equal size in each eye; three positive and three negative ossicles occupy the same positions in the scierai rings of all these iguanids. This condition is thought to be either the direct or indirect precursor to all patterns of ossicle configuration seen in sceloporines. These patterns seem to have been derived from their presumed precursor by both reductions and losses of ossicles in the dorsal portion of the ring.