The earliest tooth-like structures, known as proto-dental structures, reveal the deep evolutionary history of teeth. They are the product of a long evolutionary journey that began with simple, mineralized tissues in ancient marine creatures. These early developments set the stage for the diverse and specialized teeth seen across the animal kingdom today.
The Earliest Dental Structures
The first known structures resembling teeth belonged to conodonts, an extinct group of eel-like, jawless vertebrates that appeared over 500 million years ago. These structures, called conodont elements, were not true teeth set in jaws but formed a complex feeding apparatus within the animal’s mouth. This apparatus was composed of various shapes, including simple cones, comb-like bars, and broader platforms used for grasping and processing food.
These early dental elements were made of hydroxylapatite, a phosphatic mineral that is the primary component of modern tooth enamel and dentin, establishing a material link to present-day vertebrates. The discovery of rare fossils with preserved soft tissue revealed the conodont animal, showing an elongated body with large eyes and fins. This confirmed the phosphatic elements were part of a primitive vertebrate’s feeding mechanism, a foundational step before the evolution of jaws.
The Origin of Teeth from Skin
The “outside-in” hypothesis posits that teeth evolved from structures on the skin. Early jawless fish, living around 460 million years ago, were covered in protective, tooth-like scales known as dermal denticles or odontodes. These odontodes were composed of a dentin cone with a pulp cavity, covered by an enamel-like substance, and anchored to the skin by a bony base—structurally identical to a modern tooth. These scales provided defense and may have offered sensory or hydrodynamic advantages.
The transition from external armor to internal feeding tools is illustrated by modern sharks. A shark’s skin is covered in these placoid scales, and its mouth shows a seamless gradation from the dermal denticles on the skin to the rows of teeth within the jaw. This anatomical continuity supports the theory that odontodes around the mouth’s edge migrated into the oral cavity and were co-opted for feeding, becoming true teeth. The genes that regulate tooth development today are homologous to those involved in the formation of fish scales, solidifying this evolutionary connection.
Evolution into Modern Teeth
Once primitive, cone-shaped teeth became established inside the mouth, their evolution became intertwined with the development of jaws. The emergence of jaws in early vertebrates provided a framework for these structures, transforming them from simple grasping tools into more effective food-processing implements. This innovation offered a significant evolutionary advantage, allowing for a more diverse range of diets and hunting strategies. The attachment of teeth to jaws marked a significant shift in vertebrate evolution.
From these early stages, two major evolutionary paths emerged. In many fish and reptiles, teeth remained as simple, sharp cones that are continuously replaced throughout their lives, a condition known as polyphyodonty. In the lineage leading to mammals, teeth became more firmly anchored in sockets within the jaw, providing greater strength for chewing. This stability supported the evolution of more complex tooth shapes, or heterodonty, with different teeth in the mouth becoming specialized for different functions. This led to the familiar arrangement of incisors for cutting, canines for piercing, and premolars and molars for grinding and crushing, allowing mammals to exploit a wider variety of food sources efficiently and contributing to their success.