Although amniotes (reptiles, including birds, and mammals) are capable of replacing certain tissues, complete appendage regeneration is rare. Perhaps the most striking example is the lizard tail. Tail loss initiates a spontaneous epimorphic (blastema‐mediated) regenerative program, resulting in a fully functional but structurally non‐identical replacement. Here we review lizard tail regeneration with a particular focus on the blastema. In many lizards, the original tail has evolved a series of fracture planes, anatomical modifications that permit the tail to be self‐detached or autotomized. Following tail loss, the wound site is covered by a specialized wound epithelium under which the blastema develops. An outgrowth of the spinal cord, the ependymal tube, plays a key role in governing growth (and likely patterning) of the regenerate tail. In some species (e.g., geckos), the blastema forms as an apical aggregation of proliferating cells, similar to that of urodeles and teleosts. For other species (e.g., anoles) the identification of a proliferative blastema is less obvious, suggesting an unexpected diversity in regenerative mechanisms among tail‐regenerating lizards.

Although often overlooked, the integument of many vertebrates is reinforced by skeletal elements. In anurans these calcified structures include osteoderms, bone‐rich elements, and the lamina calcarea, a calcified, acellular layer that lacks collagen. We investigated the histology of anuran integument with a special focus on taxa developing skeletal elements. When present, the lamina calcarea forms a thin but discrete horizon at the interface between the superficial and deep dermis. This layer is rich in glycosaminoglycans (GAG) and is structurally unlike bone and cartilage. In contrast, anuran osteoderms are composed of cellular bone with limited GAG. A partial ontogenetic series of the tree frog Phyllomedusa bicolor provides the first details of anuran osteoderms development. In P. bicolor osteoderm development begins as a cluster of small calcified centres localized over the head. With continued body growth, osteoderms become larger in size and become distributed across the dorsal and ventral surfaces of the body, and across the limbs. The leaf litter frog Brachytarsophyrys cariensis is unusual in developing both osteoderms (on the dorsal body surface) and a lamina calcarea (on the ventral body surface). Our data shows that anuran integument has the ability to form skeletal elements and suggests that these elements arose in multiple anuran lineages.Grant Funding Source: NSERC

Many lizards are able to voluntarily self‐detach (autotomize) a portion of the tail and then regenerate a functional replacement. Autotomy occurs at an intravertebral fracture plane and ruptures all the major tissue types of the tail, resulting in an open wound with various tissues exposed. The objectives of this study were to investigate the anatomy and histology of tail loss and wound healing in the leopard gecko, Eublepharis macularius. Microcomputed tomography and serial histology reveals the structure of the fracture plane and associated tissues, including a persistent notochord and sphincter muscles of the caudal artery. Following tail loss the remaining skin collapses over the wound site, the spinal cord is retracted into the original tail stump, and a clot is formed. Epithelial cells adjacent to the wound site begin to proliferate and migrate deep to the clot. Once the wound epithelium completely spans the wound site the clot drops off to reveal the developing blastema. Unlike most invasive wounds, fibrous scar tissue is not formed. Ongoing studies of wound healing studies in Eublepharis provide an important complement for ongoing regenerative research by expanding the comparative framework.