The development of complex tooth shape in reptiles.

Hana Dosedelova,Abigail S Tucker,Oldrich Zahradnicek,Marcela Buchtova

doi:10.3389/fphys.2014.00074

Abstract

Reptiles have a diverse array of tooth shapes, from simple unicuspid to complex multicuspid teeth, reflecting functional adaptation to a variety of diets and eating styles. In addition to cusps, often complex longitudinal labial and lingual enamel crests are widespread and contribute to the final shape of reptile teeth. The simplest shaped unicuspid teeth have been found in piscivorous or carnivorous ancestors of recent diapsid reptiles and they are also present in some extant carnivores such as crocodiles and snakes. However, the ancestral tooth shape for squamate reptiles is thought to be bicuspid, indicating an insectivorous diet. The development of bicuspid teeth in lizards has recently been published, indicating that the mechanisms used to create cusps and crests are very distinct from those that shape cusps in mammals. Here, we introduce the large variety of tooth shapes found in lizards and compare the morphology and development of bicuspid, tricuspid, and pentacuspid teeth, with the aim of understanding how such tooth shapes are generated. Next, we discuss whether the processes used to form such morphologies are conserved between divergent lizards and whether the underlying mechanisms share similarities with those of mammals. In particular, we will focus on the complex teeth of the chameleon, gecko, varanus, and anole lizards using SEM and histology to compare the tooth crown morphology and embryonic development.

Highlights

Teeth come in many shapes and sizes, this variation allowing animals to take advantage of very different food types, and influencing social behavior
The shape of the crowns ranged from the simple unicuspid teeth of the python (Figure 1A), to the highly complex teeth of the Nile monitor lizard, Varanus niloticus (Figure 1D)
The dentition of the juvenile of Varanus niloticus was composed of triconodont teeth with large lateral cusps (Figure 1D) prominent in the upper jaw attaching to the premaxillary bone

Summary

Introduction

Teeth come in many shapes and sizes, this variation allowing animals to take advantage of very different food types, and influencing social behavior. The enamel knot forms within the inner enamel epithelium and it signals to the surrounding tissue. The enamel knot itself does not proliferate, while the surrounding tissue does resulting in the folding of the inner dental epithelium. Single cuspid incisors only have one enamel knot, while multicuspid molars have additional secondary enamel knots (SEK) that further fold the inner enamel epithelium and create additional cusps. The position and time of induction of the SEK is central to the final tooth shape, by controlling the location and pattern of the final cusps in different species (Jernvall et al, 2000; Moustakas et al, 2011; Jernvall and Thesleff, 2012)

Methods

Results

Conclusion