Squamate egg tooth development revisited using three‐dimensional reconstructions of brown anole (Anolis sagrei, Squamata, Dactyloidae) dentition

Abstract

The egg tooth is a hatching adaptation, characteristic of all squamates. In brown anole embryos, the first tooth that starts differentiating is the egg tooth. It develops from a single tooth germ and, similar to the regular dentition of all the other vertebrates, the differentiating egg tooth of the brown anole passes through classic morphological and developmental stages named according to the shape of the dental epithelium: epithelial thickening, dental lamina, tooth bud, cap and bell stages. The differentiating egg tooth consists of three parts: the enamel organ, hard tissues and dental pulp. Shortly before hatching, the egg tooth connects with the premaxilla. Attachment tissue of the egg tooth does not undergo mineralization, which makes it different from the other teeth of most squamates. After hatching, odontoclasts are involved in resorption of the egg tooth's remains. This study shows that the brown anole egg tooth does not completely conform to previous reports describing iguanomorph egg teeth and reveals a need to investigate its development in the context of squamate phylogeny.

Embryonic skull development in the gecko,Tarentola annularis(Squamata: Gekkota: Phyllodactylidae)

“…2019; Hermyt et al . 2020), but this can arise in different ways. In snakes, a single egg tooth can arise from the fusion of paired adjacent tooth germs during early embryonic stages (Fons et al .…”

“…2019), but in lizards, a median egg tooth can result from the degeneration of one of an original pair of egg teeth or from a single median tooth germ (De Beer, 1949; Hermyt et al . 2020). The egg tooth or teeth are lost a few days post hatching, and replaced by adult premaxillary teeth (Trauth, 1988).…”

Do all geckos hatch in the same way? Histological and 3D studies of egg tooth morphogenesis in the geckos Eublepharis macularius Blyth 1854 and Lepidodactylus lugubris Duméril & Bibron 1836

“…It is known that all the egg teeth in unidentates are located in the midline of the frontal part of the palate (Fons et al, 2019;Hermyt et al, 2020Hermyt et al, , 2017Smith et al, 1953). They have varying spatial orientation, which in some cases can change in the course of embryonic development.…”

“…However, these fibers and long axes of cells located among them are oriented in the leftright axis. In previously investigated unidentates they are oriented in the dorsoventral axis (Hermyt et al, 2020(Hermyt et al, , 2017. It is possible that differences, both in terms of attachment and fiber orientation, result from different positions of gekkotan egg teeth, and different premaxilla shape.…”

“…Leopard gecko egg teeth have similar shape and curvature as previously described egg teeth of unidentates. They differ from them in terms of spatial orientation, attachment tissue, and localization on the premaxilla (Fons et al, 2019;Hermyt et al, 2020Hermyt et al, , 2017Smith et al, 1953). Egg teeth of mourning geckos are distinct from other teeth and even from egg teeth of other squamate species in having a vessel; D, dentin; DL, dental lamina; DP, dental pulp; EO, enamel organ; ET, egg tooth; NC, nasal capsule; OB, odontoblasts; PMX, premaxilla; SR, stellate reticulum caudoventrally oriented cusps at their tip which might be connected with different hardness of their eggshell.…”