A Histological Analysis of the Hadrosaurid Dental Battery

• Author / Creator

  Bramble, Katherine K

• The first histological study of an entire hadrosaurid dental battery provides a better understanding of this complex structure. The hadrosaurid dental battery is composed of interlocking, vertically stacked columns of teeth that form a complex grinding surface. The dental battery was previously considered to be a solid, cemented structure based on superficial examination of intact batteries and thin sections of isolated teeth. This first description of the dental battery using thin sections through the entire structure refutes the model of a single, fused mass of teeth. These thin sections confirm the presence of periodontal ligament connections between all teeth, underscoring its dynamic nature. The serial thin sections across an adult dental battery also revealed signs of gradual and possibly ontogenetic tooth migration. These signs include the extensive remodeling of the alveolar septa and the anteroposterior displacement of successive generations of teeth. The four most posterior tooth families migrated posteriorly whereas the remaining tooth families had a progressively more pronounced anterior trajectory. This migration is pronounced enough in some areas to cause extensive resorption of neighbouring teeth. Thin sections through a dental battery of a perinatal specimen reveal that all of the alveolar septa are angled anteriorly, which suggests that extensive and unidirectional tooth migration begins early in ontogeny and that any additional migration happens later in ontogeny. Although the mechanisms behind tooth migration in the hadrosaurid dental battery require further investigation, addition of tooth families during growth and opposition of forces during palinal mastication may have had a strong influence. Focusing on the individual hadrosaurid teeth shows that they exhibit a highly specialized arrangement of hard tissues to allow each tooth to be ground down completely. Histological thin sections of teeth from the hadrosaurid dentary and the mammalian ever-growing incisor reveal surprising similarities in morphology and hard tissue organization. These similarities include the shift of the cemento-enamel junction to form a cutting edge along the occlusal surface. Similar to modern rodents and lagomorphs, the wear of the softer dentine and cementum, continuous eruption, and plugging the pulp cavity allowed hadrosaurid teeth to form a continuously replenished wear surface. The mammalian ever-growing incisor thus serves as an unexpectedly accurate model for dentinogenesis in the hadrosaurid tooth. The mammalian ever-growing incisor is a valuable extant analogue for understanding the perceived complexity of the hadrosaurid tooth than previously proposed models. Using this model, a heterochronic shift in dental ontogeny was inferred between neonatal and adult hadrosaurids as dentinogenesis is inferred to function at a different rate in the adult hadrosaurid. A new subtype of primary dentine, crestal dentine, was also revealed during this study. Crestal dentine has an increased hardness based on its chemical composition and tubular structure, which allows it to functionally replace the enamel that is lost in older functional tooth generations of a tooth family.

• Subjects / Keywords

  • Mammalian ever-growing incisor
  • Hadrosauridae
  • Crestal dentine
  • Periodontal ligament
  • Tooth migration
  • Dental battery

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3ST7FB18

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.