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1. Tooth development and replacement in the Atlantic Cutlassfish, Trichiurus lepturus , with comparisons to other Scombroidei

   https://doi.org/10.1002/jmor.20919  

   Bemis, Katherine E. ; Burke, Samantha M. ; St. John, Carl A. ; Hilton, Eric J. ; Bemis, William E. ( December 2018 , Journal of Morphology)

   Atlantic Cutlassfish,Trichiurus lepturus, have large, barbed, premaxillary and dentary fangs, and sharp dagger‐shaped teeth in their oral jaws. Functional teeth firmly ankylose to the dentigerous bones. We used dry skeletons, histology, SEM, and micro‐CT scanning to study 92 specimens ofT. lepturusfrom the western North Atlantic to describe its dentition and tooth replacement. We identified three modes of intraosseous tooth replacement inT. lepturusdepending on the location of the tooth in the jaw. Mode 1 relates to replacement of premaxillary fangs, in which new tooth germs enter the lingual surface of the premaxilla, develop horizontally, and rotate into position. We suggest that growth of large fangs in the premaxilla is accommodated by this horizontal development. Mode 2 occurs for dentary fangs: new tooth germs enter the labial surface of the dentary, develop vertically, and erupt into position. Mode 3 describes replacement of lateral teeth, in which new tooth germs enter a trench along the crest of the dentigerous bone, develop vertically, and erupt into position. Such distinct modes of tooth replacement in a teleostean species are unknown. We compared modes of replacement inT. lepturusto 20 species of scombroids to explore the phylogenetic distribution of these three replacement modes. Alternate tooth replacement (in which new teeth erupt between two functional teeth), ankylosis, and intraosseous tooth development are plesiomorphic to Bluefish + other Scombroidei. Our study highlights the complexity and variability of intraosseous tooth replacement. Within tooth replacement systems, key variables include sites of formation of tooth germs, points of entry of tooth germs into dentigerous bones, coupling of tooth germ migration and bone erosion, whether teeth develop horizontally or immediately beneath the tooth to be replaced, and how tooth eruption and ankylosis occur. Developmentally different tooth replacement processes can yield remarkably similar dentitions.

    

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2. The moment of tooth: rate, fate and pattern of Pacific lingcod dentition revealed by pulse-chase

   https://doi.org/10.1098/rspb.2021.1436  

   Carr, E. M. ; Summers, A. P. ; Cohen, K. E. ( October 2021 , Proceedings of the Royal Society B: Biological Sciences)

   Tooth replacement rates of polyphyodont cartilaginous and bony fishes are hard to determine because of a lack of obvious patterning and maintaining specimens long enough to observe replacement. Pulse-chase is a fluorescent technique that differentially colours developing mineralized tissue. We present in situ tooth replacement rate and position data for the oral and pharyngeal detentions of Ophiodon elongatus (Pacific lingcod). We assessed over 10 000 teeth, in 20 fish, and found a daily replacement rate of about two teeth (3.6% of the dentition). The average tooth is in the dental battery for 27 days. The replacement was higher in the lower pharyngeal jaw (LPJ). We found no difference between replacement rates of feeding and non-feeding fish, suggesting feeding was not a driver of tooth replacement. Lingcod teeth have both a size and location fate; smaller teeth at one spot will not grow into larger teeth, even if a large tooth nearby is lost. We also found increased rates of replacement at the posterior of the LPJ relative to the anterior. We propose that lingcod teeth do not migrate in the jaw as they develop; their teeth are fated in size and location, erupting in their functional position. 

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3. Histology and μCT reveal the unique evolution and development of multiple tooth rows in the synapsid Endothiodon

   https://doi.org/10.1038/s41598-021-95993-6  

   Olroyd, Savannah L. ; LeBlanc, Aaron R. H. ; Araújo, Ricardo ; Angielczyk, Kenneth D. ; Duhamel, Aliénor ; Benoit, Julien ; Amaral, Marisa ( August 2021 , Scientific Reports)

   Several amniote lineages independently evolved multiple rows of marginal teeth in response to the challenge of processing high fiber plant matter. Multiple tooth rows develop via alterations to tooth replacement in captorhinid reptiles and ornithischian dinosaurs, but the specific changes that produce this morphology differ, reflecting differences in their modes of tooth attachment. To further understand the mechanisms by which multiple tooth rows can develop, we examined this feature inEndothiodon bathystoma, a member of the only synapsid clade (Anomodontia) to evolve a multi-rowed marginal dentition. We histologically sampledEndothiodonmandibles with and without multiple tooth rows as well as single-rowed maxillae. We also segmented functional and replacement teeth in µ-CT scanned mandibles and maxillae ofEndothiodonand several other anomodonts with ‘postcanine’ teeth to characterize tooth replacement in the clade. All anomodonts in our sample displayed a space around the tooth roots for a soft tissue attachment between tooth and jaw in life. Trails of alveolar bone indicate varying degrees of labial migration of teeth through ontogeny, often altering the spatial relationships of functional and replacement teeth in the upper and lower jaws. We present a model of multiple tooth row development inE. bathystomain which labial migration of functional teeth was extensive enough to prevent resorption and replacement by newer generations of teeth. This model represents another mechanism by which multiple tooth rows evolved in amniotes. The multiple tooth rows ofE. bathystomamay have provided more extensive contact between the teeth and a triturating surface on the palatine during chewing.

    

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4. Tooth eruption in the Early Cretaceous British mammal Triconodon and description of a new species

   https://doi.org/10.1002/spp2.1329  

   Jäger, Kai R. K. ; Cifelli, Richard L. ; Martin, Thomas ; Hautier, ed., Lionel ( August 2020 , Papers in Palaeontology)

   Triconodon mordax, from the lowest Cretaceous (Berriasian) part of the Purbeck Group, Dorset, is known by an ontogenetic series of specimens that document aspects of tooth eruption and replacement. Based on micro‐computed tomography of four specimens we refer one mandible to a new species,Triconodon averianovi, which differs fromT. mordaxin having a more slender, curved c; p4 notably low crowned with slender main cusp and smaller accessory cusps; and molars with weak cingula, m4 being notably smaller with weak cusps a and c.T. mordaxis variable in the number of mental foramina and posterior jaw morphology. Scans reveal an earlier developmental stage (p3 in early eruption) than previously recognized forTriconodon, and demonstrate sequential, anteroposterior replacement of premolars; it remains unclear whether p1–2 were replaced. Scans also support an earlier hypothesis that m4 erupted late in life. Onset of m4 mineralization is likely to have coincided with eruption of p3, followed by replacement of dp4 by p4 and eruption of c. The m4 developed within the lingual side of the coronoid process, well above the tooth row. It remained in position and was subsequently accommodated in the active tooth row through unusually prolonged and localized growth of the posterior part of the mandible. This pattern is seen in some later triconodontids and appears to be unique to the family.

    

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5. Dental Dynamics : A Fast New Tool for Quantifying Tooth and Jaw Biomechanics in 3D Slicer

   https://doi.org/10.1093/iob/obae015  

   Cohen, K_E ; Fitzpatrick, A_R ; Huie, J_M ( May 2024 , Integrative Organismal Biology)

   Teeth reveal how organisms interact with their environment. Biologists have long looked at the diverse form and function of teeth to study the evolution of feeding, fighting, and development. The exponential rise in the quantity and accessibility of computed tomography (CT) data has enabled morphologists to study teeth at finer resolutions and larger macroevolutionary scales. Measuring tooth function is no easy task, in fact, much of our mechanical understanding is derived from dental shape. Categorical descriptors of tooth shape such as morphological homodonty and heterodonty, overlook nuances in function by reducing tooth diversity for comparative analysis. The functional homodonty method quantitatively assesses the functional diversity of whole dentitions from tooth shape. This method uses tooth surface area and position to calculate the transmission of stress and estimates a threshold for functionally homodont teeth through bootstrapping and clustering techniques. However, some vertebrates have hundreds or thousands of teeth and measuring the shape and function of every individual tooth can be a painstaking task. Here, we present Dental Dynamics, a module for 3D Slicer that allows for the fast and precise quantification of dentitions and jaws. The tool automates the calculation of several tooth traits classically used to describe form and function (i.e., aspect ratio, mechanical advantage, force, etc.). To demonstrate the usefulness of our module we used Dental Dynamics to quantify 780 teeth across 20 salamanders that exhibit diverse ecologies. We coupled these data with the functional homodonty method to investigate the hypothesis that arboreal Aneides salamanders have novel tooth functions. Dental Dynamics provides a new and fast way to measure teeth and increases the accessibility of the functional homodonty method. We hope Dental Dynamics will encourage further theoretical and methodological development for quantifying and studying teeth.

    

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