The Cephalic Osteoderms of Varanus komodoensis as Revealed by High‐Resolution X‐Ray Computed Tomography

Abstract

Osteoderms constitute a morphological system that plays an important role in squamate systematics. However, their study and visualization have always been difficult due to their isolated occurrence in the skin, among the first organs to be removed during the skeletonization process. High‐resolution X‐ray computed tomography (HRXCT) offers a nondestructive means of visualizing osteoderms both in their natural relationship to each other and to the underlying cranial bones. Although it is often stated that Varanus komodoensis has a “chain mail” of osteoderms, this morphological system was never described in this taxon. Further, given its size, it might be expected that V. komodoensis would present the extreme of osteoderm development in extant varanids, a group that tends to have weakly developed osteoderms or none at all. Indeed, our HRXCT scan of a 19‐year‐old captive individual reveals an elaborate mesh of cephalic osteoderms that are incredibly numerous and morphologically diverse. We describe this skeletal system and compare it to the cephalic osteoderms in other varanoids. Anat Rec, 302:1675–1680, 2019. © 2019 American Association for Anatomy

Cranial anatomy of the Galápagos marine iguana Amblyrhynchus cristatus (Squamata: Iguanidae)

“…The difference about integumentary structures between Amblyrhynchus and C. subcristatus seems to be similar to what has been described for Heloderma suspectum and Varanus komodoensis in terms of relationship with the underlying bones (Maisano et al, 2019). While both H. suspectum and V. komodoensis have cephalic osteoderms, only in H. suspectum do they fuse to the underlying bones; in V. komodoensis the osteoderms are never fused to the cranial bones.…”

Cranial Structure of Varanus komodoensis as Revealed by Computed-Tomographic Imaging

“…Several causes have been reported to explain the low resolution of soft tissue structures showed in our study [1,15], such as the small volume of these species, the impossibility of reducing the field of view of the CT scanner, and the presence of bones embedded within the skin. These bones, called cephalic osteoderms, vary in shape and complexity and serve primarily as a defensive anatomical system to protect individuals during aggressive confrontations with other specimens [11]. To avoid this low resolution, some investigations reported the use of micro-CT scanners [17], although this equipment is not usually available in veterinary clinics [15].…”

“…Since 1996, the Komodo dragon (Varanus komodoensis) is listed as vulnerable by the Red List of the World Conservation Union [4]. To our knowledge, the anatomy of different species of reptiles has already been thoroughly described by radiology and CT [1,[5][6][7][8][9][10], but only sparse numbers of these studies reported comprehensive descriptions of computed tomographic features of the head [1,5,6,[9][10][11][12]. To date, not one of these reports investigates to what extent structures of the varanid head could be visualized and identified in low-resolution clinical CT-image data.…”

The multiscale hierarchical structure of Heloderma suspectum osteoderms and their mechanical properties

“…Osteoderms are particularly common and diverse in lizards [5], where their shapes, range from compound plates, and scales [5,32] to needles [33]. They also vary in size from centimeters to millimeters [26,34], but size is not always correlated with body length and it is not uncommon for small lizards to present large osteoderms [35].…”