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Abstract:
Madagascar's endemic ground-dwelling leaf chameleons (Brookesiinae:
Brookesia Gray, 1865 + Palleon Glaw, et al., Salamandra, 2013, 49, pp.
237-238) form the sister taxon to all other chameleons (i.e., the
Chamaeleoninae). They possess a limited ability of color change, a
rather dull coloration, and a nonprehensile tail assisting locomotion in
the leaf litter on the forest floor. Most Brookesia species can readily
be recognized by peculiar spiky dorsolateral projections ("Ruckensage"),
which are caused by an aberrant vertebral structure and might function
as body armor to prevent predation. In addition to a pronounced
Ruckensage, the Antsingy leaf chameleon Brookesia perarmata (Angel,
1933) exhibits conspicuous, acuminate tubercle scales on the lateral
flanks and extremities, thereby considerably enhancing the overall
armored appearance. Such structures are exceptional within the
Chamaeleonidae and despite an appreciable interest in the integument of
chameleons in general, the morphology of these integumentary elements
remains shrouded in mystery. Using various conventional and petrographic
histological approaches combined with mu CT-imaging, we reveal that the
tubercle scales consist of osseous, multicusped cores that are embedded
within the dermis. Based on this, they consequently can be interpreted
as osteoderms, which to the best of our knowledge is the first record of
such for the entire Chamaeleonidae and only the second one for the
entire clade Iguania. The combination of certain aspects of tissue
composition (especially the presence of large, interconnected, and
marrow-filled cavities) together with the precise location within the
dermis (being completely enveloped by the stratum superficiale),
however, discriminate the osteoderms of B. perarmata from those known
for all other lepidosaurs.
