Glossary

Cheek teeth are the teeth located posterior to the canines in the dental arcade, positioned along the inner surface of the cheeks. In mammals, the term collectively refers to the premolars and molars—teeth characterised by complex occlusal surfaces bearing cusps, ridges, and basins specialised for grinding, shearing, and crushing food. Premolars are distinguished from molars ontogenetically: premolars are replaced once during diphyodont development (having deciduous precursors), whereas molars erupt only as permanent teeth. In non-mammalian vertebrates, the term is applied more broadly to any posterior jaw teeth that perform analogous food-processing functions. Cheek teeth attained their most elaborate development in herbivorous ornithischian dinosaurs. Hadrosaurids (duck-billed dinosaurs) evolved dental batteries containing up to approximately 300 teeth per jaw ramus stacked in 60 tooth positions, forming a constantly replenished grinding surface for processing tough plant fibre. Ceratopsians such as Triceratops independently evolved dental batteries with a distinct slicing function, their cheek teeth composed of five different dental tissue layers that self-sharpened through differential wear to create blade-like cutting edges. The morphology of cheek teeth is tightly correlated with diet across vertebrate lineages. In palaeontology, cheek tooth form, occlusal wear patterns, and dental microwear provide primary evidence for reconstructing the dietary ecology and feeding behaviour of extinct animals, making cheek teeth among the most informative anatomical structures in the vertebrate fossil record.

Dentition refers to the complete set of teeth in an organism and, more broadly, to the characteristic arrangement, number, morphology, and mode of attachment of those teeth within the jaws. In vertebrate biology and paleontology, dentition encompasses several descriptive axes: uniformity of tooth shape (homodont versus heterodont), the number of tooth generations produced over a lifetime (monophyodont, diphyodont, or polyphyodont), the manner of implantation in the jawbone (acrodont, pleurodont, or thecodont), crown height (brachydont, hypsodont, or hypselodont), and the detailed cusp pattern of individual teeth (e.g., tribosphenic, bunodont, selenodont, lophodont, secodont). Each of these parameters reflects functional demands imposed by diet, feeding mechanics, and ecological niche. In paleontology, dentition is among the most diagnostically valuable features of the skeleton because enamel—the hardest tissue in the vertebrate body—resists taphonomic destruction, ensuring that teeth are frequently the most abundant and best-preserved fossils. The morphology of a dentition allows researchers to reconstruct trophic ecology, infer bite mechanics, estimate body size, and resolve phylogenetic relationships. In dinosaurs specifically, dentition ranges from the ziphodont (blade-like, serrated) teeth of predatory theropods to the elaborate dental batteries of hadrosaurs containing up to 300 interlocking teeth per jaw ramus, and the peg-shaped, rapidly replaced teeth of diplodocoid sauropods. By analyzing incremental growth lines (lines of von Ebner) in tooth dentine, paleontologists can also determine tooth formation times and replacement rates, thereby adding a temporal dimension to dietary and ecological inferences. As a result, dentition serves as one of the most important single lines of evidence for understanding vertebrate evolution, ecology, and adaptation across both living and extinct taxa.

A **toothless beak** is a cranial feeding structure in which the jaw bones are entirely devoid of teeth (edentulous) and are instead covered by a keratinous sheath known as a rhamphotheca. The rhamphotheca envelops both the outer (rostral) and part of the inner (oral) surfaces of the jawbones, functionally replacing teeth for food acquisition and manipulation. Within theropod dinosaurs alone, fully edentulous beaks evolved independently at least seven times, appearing in lineages such as Oviraptorosauria, Ornithomimosauria, Therizinosauria, Ceratosauria (notably Limusaurus), and multiple clades of Mesozoic birds. Ornithischian dinosaurs, including ceratopsians and hadrosaurs, also possessed beaks, though typically in combination with posterior dentition. Biomechanical analyses using finite element modeling have demonstrated that keratinous beaks reduce stress and strain in the rostral skull, enhancing structural stability during feeding. The repeated convergent evolution of toothless beaks across Dinosauria reflects a complex interplay of selective pressures, including dietary shifts toward herbivory or omnivory, weight reduction, enhanced cranial stability, and possibly shorter incubation periods linked to the elimination of embryonic tooth development.