Reptile Anatomy and Physiology is an important part of Herpetology and captive care!
Reptile Teeth
In Zoology, record keeping is an important part of the science. This industry branches off into many biological sections including Animal Anatomy and Physiology, which studies how an animal works functionally. These include bodily functions and details like eyes, organs, and teeth! It is common to use teeth as a way to classify animals, including Reptiles. In this article, we simplify and describe the common types of Reptile teeth. (For detailed research, visit Google Scholar and use the search engine for scholarly journals.)
Barry Berkovitz, Peter Shellis, in The Teeth of Non-Mammalian Vertebrates, 2017
Three types of reptile teeth: (left to right) Thecodont teeth, Pleurodont teeth, and Acrodont teeth
This type of classification sheds light into the lives of animals as they currently are and also historically and evolutionarily. Understanding teeth and their development helps us better understand animals for conservation, husbandry, and record keeping purposes. The more we understand species specific details, the better we can preserve and appreciate them!
In regards to teeth, specific teeth formations allowed animals, including humans and reptiles, to adapt to specific and opportunistic diets. This has helped reptiles survive in the wild while allowing us to attempt to recreate the most naturalistic conditions in captivity (diet).
There are many different types of teeth in Vertebrates, and this is a key characteristic when comparing reptiles to mammals. Reptile teeth are more uniform than mammals, who have specialized, different teeth designed for chewing. Reptile teeth shape are still species specific, but there are generalities — like all vertebrate teeth have a crown and a root. Few exceptions do exist such as turtles and tortoises, who are the only toothless reptiles. Instead, they have sharp beaks that help them eat a variety of herbivorous, omnivorous, and carnivorous diets. The only reptiles that currently exist (many exceptions exist in fossils and extinct species,) that do not have uniform teeth are the Crocodilians and venomous snakes.
In reptiles, three teeth types, or “dental formations” are the most common. The Acrodont, Pleurodont, and Thecodont teeth. The ability to regrow teeth in vertebrates is called polyphyodonty, and is typical in non-mammalian vertebrates like reptiles. The genetic understanding for this regeneration is poorly understood. The major differences when comparing animal teeth are the shape, placement, and whether or not they shed. In reptiles, the shape of the teeth are species specific and typically uniform, but there are exceptions such as the Venomous Snakes, Chelonians, and Crocodilians. Like mammals, reptile teeth are made of enamel, dentin, cementum, and pulp. Enamel is the outside portion of the tooth that keeps it strong, dentin is underneath the enamel, and cementum is like the “cement” that anchors the tooth to the jaw bone. Cementum surrounds and protects the pulp, which is made of nerves and blood vessels. Each type of tooth has a different attachment design and strength described below.
Acrodont teeth
Acrodont Teeth are the weakest, and do not have a firm attachment inside the jaw. Instead, they are actually fused to the jaw bone itself. This tooth formation is seen in lizards like chameleons, uromastyces, frilled dragons, and bearded dragons. Lizards have both Acrodont and Pleurodont teeth.
Because Acrodont teeth are superficially attached to the jaw and aren’t deep in the bone, they can be easily broken with enough force. This should be kept in mind when feeding and handling reptiles with this tooth formation. Acrodont teeth are also more susceptible to bacterial and fungal infections, like mouth rot. Acrodont teeth have short roots and firm attachment, according to a Journal on vertebrate feeding published by Science Direct. Acrodont teeth are typically pointy to help chew food. Acrodont teeth are not replaced, but new teeth can grow in as the old are worn down. This does not happen frequently as adults. Some lizards have a mixture of Acrodont and Pleurodont teeth in their mouths, showing rare heterodonty (different teeth shape and sizes) in reptiles. Common diets of reptiles with acrodont teeth include a variety of invertebrates, greens, and small mammals!
Barry Berkovitz, Peter Shellis, in The: Teeth of Non-Mammalian Vertebrates, 2017
(a) Acrodont dentition in the Frilled Dragon (b) Pleurodont dentition in a Spiny Tail Iguana. You can see the attachments to the bone differ!
Pleurodont teeth
Pleurodont teeth are common in many lizard species including all iguana subspecies, varanid monitors, and geckos. Pleurodont teeth are superficially attached like Acrodont teeth, but the Pleurodont teeth are anchored on the inside of the actual jaw. This makes them have stronger roots, but weaker attachment since they are not fused to the bone. Pleurodont teeth can continuously grow back within the same space of the original tooth. This space continuously absorbs and reforms as the new teeth grow in. Keep in mind that teeth are living tissue! The shape of Pleurodont teeth are species specific and can be very unique, like the round and flattened pleurodont teeth seen in the caiman lizard. Their teeth are very specialized to crush mollusks like snails and clams. The two methods of pleurodont teeth regeneration are called the “iguanid” and “varanid” methods, according to one scholarly journal. The “iguanid” method teeth grow into the same place as the original tooth whereas the “varanid” method grows posterior (behind) the original tooth. The growth patterns of these teeth vary. The Pleurodont teeth are also seen in the only venomous lizard group, Heloderma, which has been said to help enhance venom introduction. According to one source, “snake dentition has been described as Pleurodont, however snake teeth have more recently been debated as ‘modified Thecodont’ because each tooth is fused to the rim of a shallow socket.”
Image courtesy of Andrew Gilpin
Macro shot of Gargoyle Gecko (Rhacodactylus auriculatus) acrodont teeth fused to the bone.
BARRY BERKOVITZ, PETER SHELLIS, IN THE: TEETH OF NON-MAMMALIAN VERTEBRATES, 2017
Pleurodont dentition model of the European Green Lizard showing normal regrowth and development. You can see the ‘iguanid’ regrowth pattern of Pleurodont lizards in this model.
Thecodont teeth
Thecodont teeth are the rarest in Reptiles and Crocodilians are the only true reptiles with Thecodont dentition. Crocodilian teeth are continuously replaced, which is vital to their apex predator lifestyles and carnivorous diets. They are often consuming large prey and engaging in violent territorial battles. Strong teeth help them do just that! This cycle is continuous throughout a Crocodilians life. As they age, dental replacement slows down. Thecodont teeth are the strongest because they are placed inside sockets carved deepest within the jaw bone. Whereas most reptile teeth are uniform, Thecodont Crocodilian teeth are not, meaning they have different shapes and sizes depending on the placement within the mouth. This gives them extra tissue and muscle holding their teeth in place for crushing power and sturdiness. Compared to other animals, crocodiles have incredibly strong pressure and force, according to a scholarly article published in the Journal of Structural Biology. Snakes are classified under “modified thecodont” according to some studies, because they have specially designed teeth to hold prey instead of chewing it. The teeth are sharp and anchored within pockets in the jaw, typically angled in the front to secure prey. According to the previously mentioned study, “the arrangement and number of (snake) teeth varies. Some species have almost no teeth and others have many, highly developed teeth.” Venomous snakes have extremely specialized dentition with fangs, which are used to deliver venom. There are three types of fangs in venomous snakes include the: Proteroglyphous (fixed fangs), Opisthoglyphous (rear fanged), and Solenoglyphous (foldable and front fanged).
Research has reported that, “in general, reptile teeth have not been as thoroughly investigated as the teeth of other large animals.” It seems that lab analysis on species specific reptile teeth is lacking, and more research into the details of Reptile Anatomy and Physiology can help advance captive husbandry and Herpetology!
Sources
https://www.nature.com/articles/ijos201336
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/pleurodont
https://cdn.ymaws.com/members.arav.org/resource/resmgr/Files/Proceedings_2002/2002_49.pdf
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/acrodont
http://www.animalplanet.com/pets/other-pets/oralcavity/
https://lafeber.com/vet/understanding-reptile-dental-anatomy-clinical-applications/#Snakes
https://www.sciencedirect.com/science/article/pii/S0012160608001942
