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Moya Meredith Smith - One of the best experts on this subject based on the ideXlab platform.
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Development and evolution of tooth renewal in neoselachian sharks as a model for transformation in chondrichthyan Dentitions.
Journal of anatomy, 2018Co-Authors: Moya Meredith Smith, Jürgen Kriwet, Charlie J. Underwood, Brett Clark, Zerina JohansonAbstract:A defining feature of Dentitions in modern sharks and rays is the regulated pattern order that generates multiple replacement teeth. These are arranged in labio-lingual files of replacement teeth that form in sequential time order both along the jaw and within successively initiated teeth in a deep dental lamina. Two distinct adult Dentitions have been described: alternate, in which timing of new teeth alternates between two adjacent files, each erupting separately, and the other arranged as single files, where teeth of each file are timed to erupt together, in some taxa facilitating similarly timed teeth to join to form a cutting blade. Both are dependent on spatiotemporally regulated formation of new teeth. The adult Angel shark Squatina (Squalomorphii) exemplifies a single file Dentition, but we obtained new data on the developmental order of teeth in the files of Squatina embryos, showing alternate timing of tooth initiation. This was based on micro-CT scans revealing that the earliest mineralised teeth at the jaw margin and their replacements in file pairs (odd and even jaw positions) alternate in their initiation timing. Along with Squatina, new observations from other squalomorphs such as Hexanchus and Chlamydoselachus, together with representatives of the sister group Galeomorphii, have established that the alternate tooth pattern (initiation time and replacement order) characterises the embryonic Dentition of extant sharks; however, this can change in adults. These character states were plotted onto a recent phylogeny, demonstrating that the Squalomorphii show considerable plasticity of dental development. We propose a developmental-evolutionary model to allow change from the alternate to a single file alignment of replacement teeth. This establishes new dental morphologies in adult sharks from inherited alternate order.
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RESEARCH ARTICLE Development and Evolution of Dentition Pattern and Tooth Order in the Skates And Rays (Batoidea; Chondrichthyes)
2016Co-Authors: Charlie J. Underwood, Gareth J Fraser, Brian Metscher, Liam J. Rasch, Zerina Johanson, Moya Meredith SmithAbstract:Shark and ray (elasmobranch) Dentitions are well known for their multiple generations of teeth, with isolated teeth being common in the fossil record. However, how the diverse den-titions characteristic of elasmobranchs form is still poorly understood. Data on the develop-ment and maintenance of the dental patterning in this major vertebrate group will allow comparisons to other morphologically diverse taxa, including the bony fishes, in order to identify shared pattern characters for the vertebrate Dentition as a whole. Data is especially lacking from the Batoidea (skates and rays), hence our objective is to compile data on em-bryonic and adult batoid tooth development contributing to ordering of the Dentition, from cleared and stained specimens and micro-CT scans, with 3D rendered models. We select-ed species (adult and embryonic) spanning phylogenetically significant batoid clades, such that our observations may raise questions about relationships within the batoids, particularly with respect to current molecular-based analyses. We include developmental data from em-bryos of recent model organisms Leucoraja erinacea and Raja clavata to evaluate the earli-est establishment of the Dentition. Characters of the batoid Dentition investigated includ
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Tooth addition in early ontogeny of rajid and rhinobatid batoids.
2015Co-Authors: Charlie J. Underwood, Gareth J Fraser, Monique Welten, Brian Metscher, Liam J. Rasch, Zerina Johanson, Moya Meredith SmithAbstract:A. Volume rendered Dentition of an embryo of Rhinobatos horkelli (BMNH 2015.1.25.13) showing on the upper jaw, the alternate positions of the first formed teeth across the entire width of the jaw. B-D, cleared, Alizarin Red stained preparation of an embryo of Raja clavata. The length of the R. clavata specimen is uncertain sue to it being dissected prior to mounting but is within a late stage of development prior to hatching. The first teeth are well mineralized (Alizarin positive for calcium), relative to the second tooth row (less strong Alizarin Red), in alternate positions. Two parasymphyseal teeth are present next to the jaw symphysis (S in B, C) in the upper first tooth row; in the lower jaw, a symphyseal tooth is present (S in D-F, H) in the first tooth row. B. Labial view of both jaws of the same specimen, showing the relative positions of the first row teeth of upper and lower jaws. C-D. Separated upper and lower jaws respectively. E, F. Cleared and stained lower and upper jaw Dentitions of Leucoraja erinacea, total length 107mm. F. Portion of the lower Dentition of Leucoraja erinacea showing alternate rows of teeth with progressive mineralization (degree of Alizarin Red uptake) in the successive tooth rows. G. Lower Dentition of Leucoraja erinacea in lingual view. H. Labial view of the lower Dentition of Leucoraja erinacea showing that the first tooth row of 10 positions contains a symphyseal tooth, as in that of Raja clavata. Symphysis marked by (S), false colour as in Fig. 6. Scale bars = 1 mm.
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Tooth addition in early ontogeny of batoids.
2015Co-Authors: Charlie J. Underwood, Gareth J Fraser, Monique Welten, Brian Metscher, Liam J. Rasch, Zerina Johanson, Moya Meredith SmithAbstract:A-E. Volume rendered, segmented, or false colour images of the early Dentitions of the torpediform Discopyge tschudii (A-C BMNH 2015.1.25.7, D-E BMNH 2015.1.25.8). A. Occlusal surface (labial), with density rendered transparent cartilage, lower jaw, segmented colour for teeth, first and second symphyseal teeth (S, for clarity all teeth in the rows are not shown). However, all tooth rows are shown in same specimen in Fig. 3B, and in false colour images D, E. B. Visceral surface of the same teeth shown in A, to show developing tooth roots. C. Volume rendered view of the upper and lower Dentitions of Discopyge tschudii, with the lower jaw cartilages digitally dissected to show the bases of the lower teeth. Note the abnormal symphyseal tooth with a labial expansion protruding between the first pair of parasymphyseal teeth. D. Volume rendered upper and lower jaws in labial view, with parasymphyseal pair of teeth (blue) in the apparent first row but subsequent, succeeding row with teeth in alternate positions does have a symphyseal tooth. E’ and E” are from D after rotation of image with lingual and labial views of the lower jaw to show progressive increase in tooth numbers in successive rows, (symphyseal tooth is red). F. Photomacrograph of the lower Dentition of an adult Discopyge tschudii (BMNH 2015.1.25.9) demonstrating the multitude of tooth files gained by gradual proximal addition of teeth during ontogeny (occlusal view). G, upper, H, lower, jaws of an embryo of Myliobatis sp. (BMNH 2015.1.25.11), volume rendered to show occlusal surface of the Dentition with the first formed pair of teeth as parasymphyseal (blue) in both jaws; the second row has a larger symphyseal tooth (red) and subsequent teeth in alternating rows of three and four teeth. I, J, volume rendered upper and lower Dentition of a neonate of Myliobatis sp. (BMNH 2015.1.25.12), occlusal surface showing the fixed number of teeth in each row (S+3) and the gradual enlargement of all through ontogeny (occlusal view). The ‘tongue and groove’ tooth locking is indicated by white arrows. K. Volume rendered jaws of I, J, showing mineralized crowns at occlusal surface compared with younger lingual teeth with less mineralization. False colour coding is used in the Dentitions A, B, D, E, G-J as in Fig. 4. All scale bars are 1mm.
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origin and evolution of gnathostome Dentitions a question of teeth and pharyngeal denticles in placoderms
Biological Reviews, 2005Co-Authors: Zerina Johanson, Moya Meredith SmithAbstract:The fossil group Placodermi is the most phylogenetically basal of the clade of jawed vertebrates but lacks a marginal Dentition comparable to that of the dentate Chondrichthyes, Acanthodii and Osteichthyes (crown-group Gnathostomata). The teeth of crown-group gnathostomes are part of an ordered Dentition replaced from, and patterned by, a dental lamina, exemplified by the elasmobranch model. A Dentition recognised by these criteria has been previously judged absent in placoderms, based on structural evidence such as absence of tooth whorls and typical vertebrate dentine. However, evidence for regulated tooth addition in a precise spatiotemporal order can be observed in placoderms, but significantly, only within the group Arthrodira. In these fossils, as in other jawed vertebrates with statodont, non-replacing Dentitions, new teeth are added at the ends of rows below the bite, but in line with biting edges of the Dentition. The pattern is different on each gnathal bone and probably arises from single odontogenic primordia on each, but tooth rows are arranged in a distinctive placoderm pattern. New teeth are made of regular dentine comparable to that of crown-gnathostomes, formed from a pulp cavity. This differs from semidentine previously described for placoderm gnathalia, a type present in the external dermal tubercles. The Arthrodira is a derived taxon within the Placodermi, hence origin of teeth in placoderms occurs late in the phylogeny and teeth are convergently derived, relative to those of other jawed vertebrates. More basal placoderm taxa adopted other strategies for providing biting surfaces and these vary substantially, but include addition of denticles to the growing gnathal plates, at the margins of pre-existing denticle patches. These alternative strategies and apparent absence of regular dentine have led to previous interpretations that teeth were entirely absent from the placoderm Dentition. A consensus view emerged that a Dentition, as developed within a dental lamina, is a synapomorphy characterising the clade of crown-group gnathostomes. Recent comparisons between sets of denticle whorls in the pharyngeal region of the jawless fish Loganellia scotica (Thelodonti) and those in sharks suggest homology of these denticle sets on gill arches. Although the placoderm pharyngeal region appears to lack denticles (placoderm gill arches are poorly known), the posterior wall of the pharyngeal cavity, formed by a bony flange termed the postbranchial lamina, is covered in rows of patterned denticle arrays. These arrays differ significantly, both in morphology and arrangement, from those of the denticles located externally on the head and trunkshield plates. Denticles in these arrays are homologous to denticles associated with the gill arches in other crown-gnathostomes, with pattern similarities for order and position of pharyngeal denticles. From their location in the pharynx these are inferred to be under the influence of a cell lineage from endoderm, rather than ectoderm. Tooth sets and tooth whorls in crown-group gnathostomes are suggested to derive from the pharyngeal denticle whorls, at least in sharks, with the patterning mechanisms co-opted to the oral cavity. A comparable co-option is suggested for the Placodermi.
Zerina Johanson - One of the best experts on this subject based on the ideXlab platform.
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Development and evolution of tooth renewal in neoselachian sharks as a model for transformation in chondrichthyan Dentitions.
Journal of anatomy, 2018Co-Authors: Moya Meredith Smith, Jürgen Kriwet, Charlie J. Underwood, Brett Clark, Zerina JohansonAbstract:A defining feature of Dentitions in modern sharks and rays is the regulated pattern order that generates multiple replacement teeth. These are arranged in labio-lingual files of replacement teeth that form in sequential time order both along the jaw and within successively initiated teeth in a deep dental lamina. Two distinct adult Dentitions have been described: alternate, in which timing of new teeth alternates between two adjacent files, each erupting separately, and the other arranged as single files, where teeth of each file are timed to erupt together, in some taxa facilitating similarly timed teeth to join to form a cutting blade. Both are dependent on spatiotemporally regulated formation of new teeth. The adult Angel shark Squatina (Squalomorphii) exemplifies a single file Dentition, but we obtained new data on the developmental order of teeth in the files of Squatina embryos, showing alternate timing of tooth initiation. This was based on micro-CT scans revealing that the earliest mineralised teeth at the jaw margin and their replacements in file pairs (odd and even jaw positions) alternate in their initiation timing. Along with Squatina, new observations from other squalomorphs such as Hexanchus and Chlamydoselachus, together with representatives of the sister group Galeomorphii, have established that the alternate tooth pattern (initiation time and replacement order) characterises the embryonic Dentition of extant sharks; however, this can change in adults. These character states were plotted onto a recent phylogeny, demonstrating that the Squalomorphii show considerable plasticity of dental development. We propose a developmental-evolutionary model to allow change from the alternate to a single file alignment of replacement teeth. This establishes new dental morphologies in adult sharks from inherited alternate order.
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RESEARCH ARTICLE Development and Evolution of Dentition Pattern and Tooth Order in the Skates And Rays (Batoidea; Chondrichthyes)
2016Co-Authors: Charlie J. Underwood, Gareth J Fraser, Brian Metscher, Liam J. Rasch, Zerina Johanson, Moya Meredith SmithAbstract:Shark and ray (elasmobranch) Dentitions are well known for their multiple generations of teeth, with isolated teeth being common in the fossil record. However, how the diverse den-titions characteristic of elasmobranchs form is still poorly understood. Data on the develop-ment and maintenance of the dental patterning in this major vertebrate group will allow comparisons to other morphologically diverse taxa, including the bony fishes, in order to identify shared pattern characters for the vertebrate Dentition as a whole. Data is especially lacking from the Batoidea (skates and rays), hence our objective is to compile data on em-bryonic and adult batoid tooth development contributing to ordering of the Dentition, from cleared and stained specimens and micro-CT scans, with 3D rendered models. We select-ed species (adult and embryonic) spanning phylogenetically significant batoid clades, such that our observations may raise questions about relationships within the batoids, particularly with respect to current molecular-based analyses. We include developmental data from em-bryos of recent model organisms Leucoraja erinacea and Raja clavata to evaluate the earli-est establishment of the Dentition. Characters of the batoid Dentition investigated includ
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Tooth addition in early ontogeny of rajid and rhinobatid batoids.
2015Co-Authors: Charlie J. Underwood, Gareth J Fraser, Monique Welten, Brian Metscher, Liam J. Rasch, Zerina Johanson, Moya Meredith SmithAbstract:A. Volume rendered Dentition of an embryo of Rhinobatos horkelli (BMNH 2015.1.25.13) showing on the upper jaw, the alternate positions of the first formed teeth across the entire width of the jaw. B-D, cleared, Alizarin Red stained preparation of an embryo of Raja clavata. The length of the R. clavata specimen is uncertain sue to it being dissected prior to mounting but is within a late stage of development prior to hatching. The first teeth are well mineralized (Alizarin positive for calcium), relative to the second tooth row (less strong Alizarin Red), in alternate positions. Two parasymphyseal teeth are present next to the jaw symphysis (S in B, C) in the upper first tooth row; in the lower jaw, a symphyseal tooth is present (S in D-F, H) in the first tooth row. B. Labial view of both jaws of the same specimen, showing the relative positions of the first row teeth of upper and lower jaws. C-D. Separated upper and lower jaws respectively. E, F. Cleared and stained lower and upper jaw Dentitions of Leucoraja erinacea, total length 107mm. F. Portion of the lower Dentition of Leucoraja erinacea showing alternate rows of teeth with progressive mineralization (degree of Alizarin Red uptake) in the successive tooth rows. G. Lower Dentition of Leucoraja erinacea in lingual view. H. Labial view of the lower Dentition of Leucoraja erinacea showing that the first tooth row of 10 positions contains a symphyseal tooth, as in that of Raja clavata. Symphysis marked by (S), false colour as in Fig. 6. Scale bars = 1 mm.
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Tooth addition in early ontogeny of batoids.
2015Co-Authors: Charlie J. Underwood, Gareth J Fraser, Monique Welten, Brian Metscher, Liam J. Rasch, Zerina Johanson, Moya Meredith SmithAbstract:A-E. Volume rendered, segmented, or false colour images of the early Dentitions of the torpediform Discopyge tschudii (A-C BMNH 2015.1.25.7, D-E BMNH 2015.1.25.8). A. Occlusal surface (labial), with density rendered transparent cartilage, lower jaw, segmented colour for teeth, first and second symphyseal teeth (S, for clarity all teeth in the rows are not shown). However, all tooth rows are shown in same specimen in Fig. 3B, and in false colour images D, E. B. Visceral surface of the same teeth shown in A, to show developing tooth roots. C. Volume rendered view of the upper and lower Dentitions of Discopyge tschudii, with the lower jaw cartilages digitally dissected to show the bases of the lower teeth. Note the abnormal symphyseal tooth with a labial expansion protruding between the first pair of parasymphyseal teeth. D. Volume rendered upper and lower jaws in labial view, with parasymphyseal pair of teeth (blue) in the apparent first row but subsequent, succeeding row with teeth in alternate positions does have a symphyseal tooth. E’ and E” are from D after rotation of image with lingual and labial views of the lower jaw to show progressive increase in tooth numbers in successive rows, (symphyseal tooth is red). F. Photomacrograph of the lower Dentition of an adult Discopyge tschudii (BMNH 2015.1.25.9) demonstrating the multitude of tooth files gained by gradual proximal addition of teeth during ontogeny (occlusal view). G, upper, H, lower, jaws of an embryo of Myliobatis sp. (BMNH 2015.1.25.11), volume rendered to show occlusal surface of the Dentition with the first formed pair of teeth as parasymphyseal (blue) in both jaws; the second row has a larger symphyseal tooth (red) and subsequent teeth in alternating rows of three and four teeth. I, J, volume rendered upper and lower Dentition of a neonate of Myliobatis sp. (BMNH 2015.1.25.12), occlusal surface showing the fixed number of teeth in each row (S+3) and the gradual enlargement of all through ontogeny (occlusal view). The ‘tongue and groove’ tooth locking is indicated by white arrows. K. Volume rendered jaws of I, J, showing mineralized crowns at occlusal surface compared with younger lingual teeth with less mineralization. False colour coding is used in the Dentitions A, B, D, E, G-J as in Fig. 4. All scale bars are 1mm.
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origin and evolution of gnathostome Dentitions a question of teeth and pharyngeal denticles in placoderms
Biological Reviews, 2005Co-Authors: Zerina Johanson, Moya Meredith SmithAbstract:The fossil group Placodermi is the most phylogenetically basal of the clade of jawed vertebrates but lacks a marginal Dentition comparable to that of the dentate Chondrichthyes, Acanthodii and Osteichthyes (crown-group Gnathostomata). The teeth of crown-group gnathostomes are part of an ordered Dentition replaced from, and patterned by, a dental lamina, exemplified by the elasmobranch model. A Dentition recognised by these criteria has been previously judged absent in placoderms, based on structural evidence such as absence of tooth whorls and typical vertebrate dentine. However, evidence for regulated tooth addition in a precise spatiotemporal order can be observed in placoderms, but significantly, only within the group Arthrodira. In these fossils, as in other jawed vertebrates with statodont, non-replacing Dentitions, new teeth are added at the ends of rows below the bite, but in line with biting edges of the Dentition. The pattern is different on each gnathal bone and probably arises from single odontogenic primordia on each, but tooth rows are arranged in a distinctive placoderm pattern. New teeth are made of regular dentine comparable to that of crown-gnathostomes, formed from a pulp cavity. This differs from semidentine previously described for placoderm gnathalia, a type present in the external dermal tubercles. The Arthrodira is a derived taxon within the Placodermi, hence origin of teeth in placoderms occurs late in the phylogeny and teeth are convergently derived, relative to those of other jawed vertebrates. More basal placoderm taxa adopted other strategies for providing biting surfaces and these vary substantially, but include addition of denticles to the growing gnathal plates, at the margins of pre-existing denticle patches. These alternative strategies and apparent absence of regular dentine have led to previous interpretations that teeth were entirely absent from the placoderm Dentition. A consensus view emerged that a Dentition, as developed within a dental lamina, is a synapomorphy characterising the clade of crown-group gnathostomes. Recent comparisons between sets of denticle whorls in the pharyngeal region of the jawless fish Loganellia scotica (Thelodonti) and those in sharks suggest homology of these denticle sets on gill arches. Although the placoderm pharyngeal region appears to lack denticles (placoderm gill arches are poorly known), the posterior wall of the pharyngeal cavity, formed by a bony flange termed the postbranchial lamina, is covered in rows of patterned denticle arrays. These arrays differ significantly, both in morphology and arrangement, from those of the denticles located externally on the head and trunkshield plates. Denticles in these arrays are homologous to denticles associated with the gill arches in other crown-gnathostomes, with pattern similarities for order and position of pharyngeal denticles. From their location in the pharynx these are inferred to be under the influence of a cell lineage from endoderm, rather than ectoderm. Tooth sets and tooth whorls in crown-group gnathostomes are suggested to derive from the pharyngeal denticle whorls, at least in sharks, with the patterning mechanisms co-opted to the oral cavity. A comparable co-option is suggested for the Placodermi.
L C Richards - One of the best experts on this subject based on the ideXlab platform.
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tooth wear and the design of the human Dentition a perspective from evolutionary medicine
American Journal of Physical Anthropology, 2003Co-Authors: Yousuke Kaifu, Kazutaka Kasai, G C Townsend, L C RichardsAbstract:Worn, flat occlusal surfaces and anterior edge-to-edge occlusion are ubiquitous among the denti- tions of prehistoric humans. The concept of attritional occlusion was proposed in the 1950s as a hypothesis to explain these characteristics. The main aspects of this hypothesis are: 1) the Dentitions of ancient populations in heavy-wear environments were continuously and dynam- ically changing owing to life-long attritional tooth reduc- tion and compensatory tooth migration, 2) all contempo- rary humans inherit these compensatory mechanisms, and recent reduction in wear severity has resulted in failure to develop attritional occlusion, and 3) this failure leads to an increased frequency of various dental problems in modern societies. Because of the potential significance of this concept, we review and synthesize relevant works and discuss attritional occlusion in the light of current knowledge. Available evidence, on balance, supports the first and second points of the hypothesis. As noted by many workers, the human Dentition is basically "de- signed" on the premise that extensive wear will occur, a conclusion that seems reasonable when one realizes that humans evolved in heavy-wear environments until rela- tively recently. Some dental problems in contemporary societies appear to reflect the disparity between the orig- inal design of our Dentition and our present environment, in which extensive wear no longer occurs, but this possi- bility still needs further investigation. Yrbk Phys An- thropol 46:47- 61, 2003. © 2003 Wiley-Liss, Inc. The Dentitions of prehistoric humans differ strik- ingly from those of contemporary people in terms of degree of tooth wear. Wear that was sufficiently severe to obliterate cusp morphology and flatten the occlusal surfaces of teeth was ubiquitous and normal in virtually every prehistoric society of the world (for reviews, see Brace, 1977; Molnar, 1972). Interprox- imal wear was also very severe compared with that observed in contemporary populations (Wolpoff, 1971) (Fig. 1). Relatively recent hunter-gatherer populations such as indigenous Australians and Es- kimo experienced considerable tooth wear before be- ing influenced by the Western way of life. A similar condition existed in the ancestors of present-day urban populations who consumed less refined and processed foods. Fossil remains of various extinct hominid species also show remarkable tooth wear,
Gareth J Fraser - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE Development and Evolution of Dentition Pattern and Tooth Order in the Skates And Rays (Batoidea; Chondrichthyes)
2016Co-Authors: Charlie J. Underwood, Gareth J Fraser, Brian Metscher, Liam J. Rasch, Zerina Johanson, Moya Meredith SmithAbstract:Shark and ray (elasmobranch) Dentitions are well known for their multiple generations of teeth, with isolated teeth being common in the fossil record. However, how the diverse den-titions characteristic of elasmobranchs form is still poorly understood. Data on the develop-ment and maintenance of the dental patterning in this major vertebrate group will allow comparisons to other morphologically diverse taxa, including the bony fishes, in order to identify shared pattern characters for the vertebrate Dentition as a whole. Data is especially lacking from the Batoidea (skates and rays), hence our objective is to compile data on em-bryonic and adult batoid tooth development contributing to ordering of the Dentition, from cleared and stained specimens and micro-CT scans, with 3D rendered models. We select-ed species (adult and embryonic) spanning phylogenetically significant batoid clades, such that our observations may raise questions about relationships within the batoids, particularly with respect to current molecular-based analyses. We include developmental data from em-bryos of recent model organisms Leucoraja erinacea and Raja clavata to evaluate the earli-est establishment of the Dentition. Characters of the batoid Dentition investigated includ
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Tooth addition in early ontogeny of rajid and rhinobatid batoids.
2015Co-Authors: Charlie J. Underwood, Gareth J Fraser, Monique Welten, Brian Metscher, Liam J. Rasch, Zerina Johanson, Moya Meredith SmithAbstract:A. Volume rendered Dentition of an embryo of Rhinobatos horkelli (BMNH 2015.1.25.13) showing on the upper jaw, the alternate positions of the first formed teeth across the entire width of the jaw. B-D, cleared, Alizarin Red stained preparation of an embryo of Raja clavata. The length of the R. clavata specimen is uncertain sue to it being dissected prior to mounting but is within a late stage of development prior to hatching. The first teeth are well mineralized (Alizarin positive for calcium), relative to the second tooth row (less strong Alizarin Red), in alternate positions. Two parasymphyseal teeth are present next to the jaw symphysis (S in B, C) in the upper first tooth row; in the lower jaw, a symphyseal tooth is present (S in D-F, H) in the first tooth row. B. Labial view of both jaws of the same specimen, showing the relative positions of the first row teeth of upper and lower jaws. C-D. Separated upper and lower jaws respectively. E, F. Cleared and stained lower and upper jaw Dentitions of Leucoraja erinacea, total length 107mm. F. Portion of the lower Dentition of Leucoraja erinacea showing alternate rows of teeth with progressive mineralization (degree of Alizarin Red uptake) in the successive tooth rows. G. Lower Dentition of Leucoraja erinacea in lingual view. H. Labial view of the lower Dentition of Leucoraja erinacea showing that the first tooth row of 10 positions contains a symphyseal tooth, as in that of Raja clavata. Symphysis marked by (S), false colour as in Fig. 6. Scale bars = 1 mm.
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Tooth addition in early ontogeny of batoids.
2015Co-Authors: Charlie J. Underwood, Gareth J Fraser, Monique Welten, Brian Metscher, Liam J. Rasch, Zerina Johanson, Moya Meredith SmithAbstract:A-E. Volume rendered, segmented, or false colour images of the early Dentitions of the torpediform Discopyge tschudii (A-C BMNH 2015.1.25.7, D-E BMNH 2015.1.25.8). A. Occlusal surface (labial), with density rendered transparent cartilage, lower jaw, segmented colour for teeth, first and second symphyseal teeth (S, for clarity all teeth in the rows are not shown). However, all tooth rows are shown in same specimen in Fig. 3B, and in false colour images D, E. B. Visceral surface of the same teeth shown in A, to show developing tooth roots. C. Volume rendered view of the upper and lower Dentitions of Discopyge tschudii, with the lower jaw cartilages digitally dissected to show the bases of the lower teeth. Note the abnormal symphyseal tooth with a labial expansion protruding between the first pair of parasymphyseal teeth. D. Volume rendered upper and lower jaws in labial view, with parasymphyseal pair of teeth (blue) in the apparent first row but subsequent, succeeding row with teeth in alternate positions does have a symphyseal tooth. E’ and E” are from D after rotation of image with lingual and labial views of the lower jaw to show progressive increase in tooth numbers in successive rows, (symphyseal tooth is red). F. Photomacrograph of the lower Dentition of an adult Discopyge tschudii (BMNH 2015.1.25.9) demonstrating the multitude of tooth files gained by gradual proximal addition of teeth during ontogeny (occlusal view). G, upper, H, lower, jaws of an embryo of Myliobatis sp. (BMNH 2015.1.25.11), volume rendered to show occlusal surface of the Dentition with the first formed pair of teeth as parasymphyseal (blue) in both jaws; the second row has a larger symphyseal tooth (red) and subsequent teeth in alternating rows of three and four teeth. I, J, volume rendered upper and lower Dentition of a neonate of Myliobatis sp. (BMNH 2015.1.25.12), occlusal surface showing the fixed number of teeth in each row (S+3) and the gradual enlargement of all through ontogeny (occlusal view). The ‘tongue and groove’ tooth locking is indicated by white arrows. K. Volume rendered jaws of I, J, showing mineralized crowns at occlusal surface compared with younger lingual teeth with less mineralization. False colour coding is used in the Dentitions A, B, D, E, G-J as in Fig. 4. All scale bars are 1mm.
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Common developmental pathways link tooth shape to regeneration
Developmental biology, 2013Co-Authors: Gareth J Fraser, Ryan Fredric Bloomquist, J. Todd StreelmanAbstract:In many non-mammalian vertebrates, adult Dentitions result from cyclical rounds of tooth regeneration wherein simple unicuspid teeth are replaced by more complex forms. Therefore and by contrast to mammalian models, the numerical majority of vertebrate teeth develop shape during the process of replacement. Here, we exploit the dental diversity of Lake Malawi cichlid fishes to ask how vertebrates generally replace their Dentition and in turn how this process acts to influence resulting tooth morphologies. First, we used immunohistochemistry to chart organogenesis of continually replacing cichlid teeth and discovered an epithelial down-growth that initiates the replacement cycle via a labial proliferation bias. Next, we identified sets of co-expressed genes from common pathways active during de novo, lifelong tooth replacement and tooth morphogenesis. Of note, we found two distinct epithelial cell populations, expressing markers of dental competence and cell potency, which may be responsible for tooth regeneration. Related gene sets were simultaneously active in putative signaling centers associated with the differentiation of replacement teeth with complex shapes. Finally, we manipulated targeted pathways (BMP, FGF, Hh, Notch, Wnt/β-catenin) in vivo with small molecules and demonstrated dose-dependent effects on both tooth replacement and tooth shape. Our data suggest that the processes of tooth regeneration and tooth shape morphogenesis are integrated via a common set of molecular signals. This linkage has subsequently been lost or decoupled in mammalian Dentitions where complex tooth shapes develop in first generation Dentitions that lack the capacity for lifelong replacement. Our dissection of the molecular mechanics of vertebrate tooth replacement coupled to complex shape pinpoints aspects of odontogenesis that might be re-evolved in the lab to solve problems in regenerative dentistry.
Yousuke Kaifu - One of the best experts on this subject based on the ideXlab platform.
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tooth wear and the design of the human Dentition a perspective from evolutionary medicine
American Journal of Physical Anthropology, 2003Co-Authors: Yousuke Kaifu, Kazutaka Kasai, G C Townsend, L C RichardsAbstract:Worn, flat occlusal surfaces and anterior edge-to-edge occlusion are ubiquitous among the denti- tions of prehistoric humans. The concept of attritional occlusion was proposed in the 1950s as a hypothesis to explain these characteristics. The main aspects of this hypothesis are: 1) the Dentitions of ancient populations in heavy-wear environments were continuously and dynam- ically changing owing to life-long attritional tooth reduc- tion and compensatory tooth migration, 2) all contempo- rary humans inherit these compensatory mechanisms, and recent reduction in wear severity has resulted in failure to develop attritional occlusion, and 3) this failure leads to an increased frequency of various dental problems in modern societies. Because of the potential significance of this concept, we review and synthesize relevant works and discuss attritional occlusion in the light of current knowledge. Available evidence, on balance, supports the first and second points of the hypothesis. As noted by many workers, the human Dentition is basically "de- signed" on the premise that extensive wear will occur, a conclusion that seems reasonable when one realizes that humans evolved in heavy-wear environments until rela- tively recently. Some dental problems in contemporary societies appear to reflect the disparity between the orig- inal design of our Dentition and our present environment, in which extensive wear no longer occurs, but this possi- bility still needs further investigation. Yrbk Phys An- thropol 46:47- 61, 2003. © 2003 Wiley-Liss, Inc. The Dentitions of prehistoric humans differ strik- ingly from those of contemporary people in terms of degree of tooth wear. Wear that was sufficiently severe to obliterate cusp morphology and flatten the occlusal surfaces of teeth was ubiquitous and normal in virtually every prehistoric society of the world (for reviews, see Brace, 1977; Molnar, 1972). Interprox- imal wear was also very severe compared with that observed in contemporary populations (Wolpoff, 1971) (Fig. 1). Relatively recent hunter-gatherer populations such as indigenous Australians and Es- kimo experienced considerable tooth wear before be- ing influenced by the Western way of life. A similar condition existed in the ancestors of present-day urban populations who consumed less refined and processed foods. Fossil remains of various extinct hominid species also show remarkable tooth wear,
