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Mosaic convergence of rodent dentitions.

Lazzari V, Charles C, Tafforeau P, Vianey-Liaud M, Aguilar JP, Jaeger JJ, Michaux J, Viriot L - PLoS ONE (2008)

Bottom Line: Based on an abundant fossil record and on a well resolved phylogeny, our results show that the most derived functional condition associates longitudinal chewing and non interlocking of cusps.In the second type however, flattening is subsequent to rotation of the chewing movement which can be associated with certain changes in cusp morphology.Because convergent pathways imply distinct ontogenetic trajectories, new Evo/Devo comparative studies on cusp morphogenesis are necessary.

View Article: PubMed Central - PubMed

Affiliation: Institut des Sciences de l'Evolution, CNRS UMR 5554, Université de Montpellier 2, Montpellier, France.

ABSTRACT

Background: Understanding mechanisms responsible for changes in tooth morphology in the course of evolution is an area of investigation common to both paleontology and developmental biology. Detailed analyses of molar tooth crown shape have shown frequent homoplasia in mammalian evolution, which requires accurate investigation of the evolutionary pathways provided by the fossil record. The necessity of preservation of an effective occlusion has been hypothesized to functionally constrain crown morphological changes and to also facilitate convergent evolution. The Muroidea superfamily constitutes a relevant model for the study of molar crown diversification because it encompasses one third of the extant mammalian biodiversity.

Methodology/principal findings: Combined microwear and 3D-topographic analyses performed on fossil and extant muroid molars allow for a first quantification of the relationships between changes in crown morphology and functionality of occlusion. Based on an abundant fossil record and on a well resolved phylogeny, our results show that the most derived functional condition associates longitudinal chewing and non interlocking of cusps. This condition has been reached at least 7 times within muroids via two main types of evolutionary pathways each respecting functional continuity. In the first type, the flattening of tooth crown which induces the removal of cusp interlocking occurs before the rotation of the chewing movement. In the second type however, flattening is subsequent to rotation of the chewing movement which can be associated with certain changes in cusp morphology.

Conclusion/significance: The reverse orders of the changes involved in these different pathways reveal a mosaic evolution of mammalian dentition in which direction of chewing and crown shape seem to be partly decoupled. Either can change in respect to strong functional constraints affecting occlusion which thereby limit the number of the possible pathways. Because convergent pathways imply distinct ontogenetic trajectories, new Evo/Devo comparative studies on cusp morphogenesis are necessary.

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Related in: MedlinePlus

Discrimination of the masticatory grades in Muroidea (27 taxa).PCA performed on morpho-functional parameters CD, K, O and H. PC1 (63% of variance) is strongly supported by the direction of chewing (CD) and by the average orientation of main cusps lowest slopes (O). PC2 (33% of variance) is strongly supported by crown flattening (K). The green area indicates grade B, red area grade M and blue area grade D. Grades C and O are situated in intermediary positions. Cricetine dental plans are shown by circles, intermediary plans are indicated by pentagons and murine plans are represented by squares. Full points indicate cusp interlocking (discontinuous wear facets), while empty points indicate no cusp interlocking (continuous wear facets).
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pone-0003607-g004: Discrimination of the masticatory grades in Muroidea (27 taxa).PCA performed on morpho-functional parameters CD, K, O and H. PC1 (63% of variance) is strongly supported by the direction of chewing (CD) and by the average orientation of main cusps lowest slopes (O). PC2 (33% of variance) is strongly supported by crown flattening (K). The green area indicates grade B, red area grade M and blue area grade D. Grades C and O are situated in intermediary positions. Cricetine dental plans are shown by circles, intermediary plans are indicated by pentagons and murine plans are represented by squares. Full points indicate cusp interlocking (discontinuous wear facets), while empty points indicate no cusp interlocking (continuous wear facets).

Mentions: A principal component analysis (Fig. 4) was performed on the linear correlation matrix of CD, K, O, and H (Table 3). PC1 is strongly supported by CD and O, while PC2 is mainly related to K. The PCA shows that three main morpho-functional groups are distinguished among Muroidea (Fig. 4): i) a group corresponding to grade B with cuspidate crowns, oblique orientation of lowest cusp slope, and oblique chewing movements,; ii) a group corresponding to grade D with flattened crowns, longitudinal orientation of lowest cusp slope, and propalinal chewing movement; iii) a group corresponding to grade M with cuspidate crowns, longitudinal orientation of cusp lowest slopes, and propalinal chewing movements. Two taxa show intermediary situations. Rotundomys displays a flattened crown and an oblique chewing direction which corresponds to a grade C. Myocricetodon ouedi has a cuspidate crown, shows an oblique orientation of lowest cusp slope, and exhibits an occlusion characterized by cusp interlocking with propalinal movements which corresponds to a grade O.


Mosaic convergence of rodent dentitions.

Lazzari V, Charles C, Tafforeau P, Vianey-Liaud M, Aguilar JP, Jaeger JJ, Michaux J, Viriot L - PLoS ONE (2008)

Discrimination of the masticatory grades in Muroidea (27 taxa).PCA performed on morpho-functional parameters CD, K, O and H. PC1 (63% of variance) is strongly supported by the direction of chewing (CD) and by the average orientation of main cusps lowest slopes (O). PC2 (33% of variance) is strongly supported by crown flattening (K). The green area indicates grade B, red area grade M and blue area grade D. Grades C and O are situated in intermediary positions. Cricetine dental plans are shown by circles, intermediary plans are indicated by pentagons and murine plans are represented by squares. Full points indicate cusp interlocking (discontinuous wear facets), while empty points indicate no cusp interlocking (continuous wear facets).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2572836&req=5

pone-0003607-g004: Discrimination of the masticatory grades in Muroidea (27 taxa).PCA performed on morpho-functional parameters CD, K, O and H. PC1 (63% of variance) is strongly supported by the direction of chewing (CD) and by the average orientation of main cusps lowest slopes (O). PC2 (33% of variance) is strongly supported by crown flattening (K). The green area indicates grade B, red area grade M and blue area grade D. Grades C and O are situated in intermediary positions. Cricetine dental plans are shown by circles, intermediary plans are indicated by pentagons and murine plans are represented by squares. Full points indicate cusp interlocking (discontinuous wear facets), while empty points indicate no cusp interlocking (continuous wear facets).
Mentions: A principal component analysis (Fig. 4) was performed on the linear correlation matrix of CD, K, O, and H (Table 3). PC1 is strongly supported by CD and O, while PC2 is mainly related to K. The PCA shows that three main morpho-functional groups are distinguished among Muroidea (Fig. 4): i) a group corresponding to grade B with cuspidate crowns, oblique orientation of lowest cusp slope, and oblique chewing movements,; ii) a group corresponding to grade D with flattened crowns, longitudinal orientation of lowest cusp slope, and propalinal chewing movement; iii) a group corresponding to grade M with cuspidate crowns, longitudinal orientation of cusp lowest slopes, and propalinal chewing movements. Two taxa show intermediary situations. Rotundomys displays a flattened crown and an oblique chewing direction which corresponds to a grade C. Myocricetodon ouedi has a cuspidate crown, shows an oblique orientation of lowest cusp slope, and exhibits an occlusion characterized by cusp interlocking with propalinal movements which corresponds to a grade O.

Bottom Line: Based on an abundant fossil record and on a well resolved phylogeny, our results show that the most derived functional condition associates longitudinal chewing and non interlocking of cusps.In the second type however, flattening is subsequent to rotation of the chewing movement which can be associated with certain changes in cusp morphology.Because convergent pathways imply distinct ontogenetic trajectories, new Evo/Devo comparative studies on cusp morphogenesis are necessary.

View Article: PubMed Central - PubMed

Affiliation: Institut des Sciences de l'Evolution, CNRS UMR 5554, Université de Montpellier 2, Montpellier, France.

ABSTRACT

Background: Understanding mechanisms responsible for changes in tooth morphology in the course of evolution is an area of investigation common to both paleontology and developmental biology. Detailed analyses of molar tooth crown shape have shown frequent homoplasia in mammalian evolution, which requires accurate investigation of the evolutionary pathways provided by the fossil record. The necessity of preservation of an effective occlusion has been hypothesized to functionally constrain crown morphological changes and to also facilitate convergent evolution. The Muroidea superfamily constitutes a relevant model for the study of molar crown diversification because it encompasses one third of the extant mammalian biodiversity.

Methodology/principal findings: Combined microwear and 3D-topographic analyses performed on fossil and extant muroid molars allow for a first quantification of the relationships between changes in crown morphology and functionality of occlusion. Based on an abundant fossil record and on a well resolved phylogeny, our results show that the most derived functional condition associates longitudinal chewing and non interlocking of cusps. This condition has been reached at least 7 times within muroids via two main types of evolutionary pathways each respecting functional continuity. In the first type, the flattening of tooth crown which induces the removal of cusp interlocking occurs before the rotation of the chewing movement. In the second type however, flattening is subsequent to rotation of the chewing movement which can be associated with certain changes in cusp morphology.

Conclusion/significance: The reverse orders of the changes involved in these different pathways reveal a mosaic evolution of mammalian dentition in which direction of chewing and crown shape seem to be partly decoupled. Either can change in respect to strong functional constraints affecting occlusion which thereby limit the number of the possible pathways. Because convergent pathways imply distinct ontogenetic trajectories, new Evo/Devo comparative studies on cusp morphogenesis are necessary.

Show MeSH
Related in: MedlinePlus