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Figure 1. Idealized expressions of double tooth pathologies of stylized mammalian incisor teeth in lingual view.Illustrations of mammalian incisor teeth showing no pathology, gemination, twinning, fusion, and concrescence. Note that there is a spectrum of manifestations of these pathologies and that gemination, fusion, and concrescence can overlap in morphology depending on their stage of development.
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Figure 2. Anatomical abbreviations.All linear measurements used for analysis of the external morphology of the specimens. (A) (NSCM 33639: O. megalodon; lingual view) NH, Neck Height; RH, Root Height; RL, Root Length; LIPL, Lingual Pathology Length; LLCL, Left Lateral Crown Length in Lingual View; and RLCL, Right Lateral Crown Length in Lingual View. (B) (NCSM 33639; O. megalodon labial view) CH, Crown Height; MICL, Mid-Crown Length; BCL, Basal Crown Length; and LAPL, Labial Pathology Length; LLSD, Left Lateral Serration Density; and RLSD, Right Lateral Serration Density. (C) (NCSM 33639; O. megalodon; lateral view) MCW, Mid-Crown Width; BCW, Basal Crown Width; and RW, Root Width. (D) (NCSM 33640; C. leucas; lingual view) MECL, Mesial Crown Length; DCL, Distal Crown Length; MC, Mesiocentral Serration Density; and DC, Distocentral Serration Density.
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Figure 3. External morphology of Otodus megalodon teeth.Pathological O. megalodon tooth NCSM 33639 in (A) lingual, (B) labial, and (C) occlusal views. (D) Enlarged view of the pathology and serrations. Non-pathological O. megalodon tooth NCSM 9545 in (E) lingual, (F) labial, and (G) occlusal views. (H) Enlarged view of the lack of pathology and serrations. Non-pathological O. megalodon tooth NCSM 14984 in (I) lingual, (J) labial, and (K) occlusal views. (L) Enlarged view of the normal apex and serrations of non-pathological O. megalodon tooth NCSM 14984. Scale bar equals 5 cm for views A–C, E–G, & I–K and 1 cm for view D, H, & L.
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Figure 4. Internal morphology of Otodus megalodon teeth.3-D model (A–C) and nano-CT scan slice (D) of pathological O. megalodon tooth NCSM 33639 showing internal structures, primarily the lack of a pulp cavity, six ascending canals (highlighted in blue), and secondary canals (highlighted in yellow) in (A) labiolingual, (B) mesiodistal, and (C and D) occlusal views. 3-D model (E–G) and Nano-CT scan slice (H) of non-pathological O. megalodon tooth NCSM 9545 showing internal structures, primarily the lack of a pulp cavity, three ascending canals (blue), and secondary canals (yellow) in (E) labiolingual, (F) mesiodistal, and (G and H) occlusal views. Scale bar equals 5 cm for views A–H. NCSM 14984 not depicted due to COVID-19 restrictions not allowing for Nano-CT scanning. The dashed line on A and E corresponds to where the slices shown in D and H were taken, respectively.
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Figure 5. External morphology of Carcharhinus leucas teeth.Pathological C. leucas tooth NCSM 33640 in (A) lingual, (B) labial, and (C) occlusal views. (D) Enlarged view of the pathology and serrations. Pathological C. leucas tooth NCSM 33641 in (E) lingual, (F) labial, and (G) occlusal views. (H) Enlarged view of the pathology and serrations. Non-pathological C. leucas tooth NCSM 34038 in (I) lingual, (J) labial, and (K) occlusal views. (L) Enlarged view of the normal apex and serrations. For views A, F, and J, the mesial side of the tooth is on the left and the distal is on the right, it is the inverse for views B, E, and I. Scale bar equals 1 cm for views A–C, E–G, and I–K and 0.5 cm for views D, H, and L.
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Figure 6. Internal morphology of Carcharhinus leucas teeth.3-D model (A–C) and Nano-CT scan slice (D) of pathological C. leucas tooth NCSM 33640 showing internal structures, primarily the presence of a singular, bifurcating pulp cavity in (A) labiolingual, (B) mesiodistal, and (C and D) occlusal views. (E–G) (NCSM 33641) 3-D model (E–G) and Nano-CT scan slice (H) of pathological C. leucas tooth NCSM 33641 showing internal structures, primarily the presence of a singular, bifurcating pulp cavity in (E) labiolingual, (F) mesiodistal, and (G and H) occlusal views. A total of 3-D model (I–K) and Nano-CT scan slice (L) of non-pathological C. leucas tooth NCSM 34038 showing internal structures, primarily the presence of a singular pulp cavity in (I) labiolingual, (J) mesiodistal, and (K and L) occlusal views. Scale bar equals 1 cm for views A–L. The dashed lines on A, E, and I correspond to where the slices shown in D, H, and L were taken, respectively.
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Figure 7. Simplified Chondrichthyes composite phylogeny highlighting the published distribution of dental pathologies.Main branching structure of selachians including the pattern of divergence among Chlamydoselachidae, Heterodontidae, Carcharhinidae, Mitsukurinidae, Odontospididae, the relationships among Carcharhiniformes, and the placement of Carcharodon in Lamnidae follows Vélez-Zuazo & Agnarsson (2011). Extinct taxa from Otodontidae, Cretoxyrhinidae, Anacoracidae, and Archaeolamnidae were not included in the molecular analyses that form the backbone of this phylogeny. We have therefore grafted them unresolved within Lamniformes but outside Lamnidae (following Shimada et al., 2017; Siverson & Lindgren, 2005; Rozefelds, 1993; respectively and Cappetta, 2012) relative to the relationships of Mitsukurinidae, Odontospididae, and Lamnidae hypothesized by Vélez-Zuazo & Agnarsson (2011) and Sorenson, Santini & Alfaro (2014). Cretomanta is placed unresolved within Batoidae following Underwood & Cumbaa, 2010. Leonodus is hypothesized to belong to a clade representing a sister group to all other chondrichthyans (Antarctilamna-Wellerous; Ginter, 2004). Batoidea silhouette adapted from art by Piotr Siedlecki from FreeIMG: https://www.freeimg.net/photo/1471979/manta-ray-sting-silhouette. Selachii silhouettes adapted from art by Faceone911 Glass on toppng: https://toppng.com/free-image/shark-silhouette-PNG-free-PNG-Images_49350. Carcharhinidae and Heterodontus silhouettes adapted from art by Francois Libert and John Turnbull, respectively. Lamniformes silhouette from wikimedia commons. Chlamydoselachus silhouette adapted from art by Tambja on wikimedia commons. Leonodus based on Antarctilamna art by DiBgd from Wikimedia Commons. Silhouettes representing tooth deformation and abnormal tooth row from Becker, Chamberlain & Stoffer (2000) and Gudger (1937). All Silhouettes fall under creative commons fair use. Image sources: [Blacktip Reef Shark, female - Carcharhinus melanopterus] (https://www.flickr.com/photos/zsispeo/36123502541), [CC BY-NC-SA 2.0] (https://creativecommons.org/licenses/by-nc-sa/2.0/)- [Port Jackson shark (juvenile) - Heterodontus portusjacksoni] (https://www.flickr.com/photos/johnwturnbull/15026942705), [CC BY-NC-SA 2.0] (https://creativecommons.org/licenses/by-nc-sa/2.0/)- [File:Megalodon-Carcharodon-Scale-Chart-SVG] (https://commons.wikimedia.org/wiki/File:Megalodon-Carcharodon-Scale-Chart-SVG.svg), [CC BY-SA 4.0] (https://creativecommons.org/licenses/by-sa/4.0/deed.en)- [File:Chlamydoselachus ang.JPG] (https://commons.wikimedia.org/wiki/File:Chlamydoselachus_ang.JPG), [CC BY-SA 3.0] (https://creativecommons.org/licenses/by-sa/3.0/deed.en)- [File:Antarctilamna speciesDB15.jpg] (https://commons.wikimedia.org/wiki/File:Antarctilamna_speciesDB15.jpg), [CC BY-SA 4.0] (https://creativecommons.org/licenses/by-sa/4.0/deed.en).
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