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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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Morpho-functional chewing grades and muroid phylogeny.This phylogeny is adapted from complementary results from the three most recent molecular phylogenies [13]–[15] and some palaeontological hypotheses [22]–[25]. The phylogenetic position of Platacanthomyidae has not been investigated yet with molecular data. We inferred the chewing grade of taxa whose direction of chewing has already been published or was measured in this study (See Table 4). B: grade B; C: grade C; D: grade D; O: grade O; M: grade M; †: fossil taxa. 1: Platacanthomyidae; 2: Spalacidae; 3: Calomyscidae; 4: Nesomyidae. 5: Muridae; 6: Cricetidae.
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pone-0003607-g005: Morpho-functional chewing grades and muroid phylogeny.This phylogeny is adapted from complementary results from the three most recent molecular phylogenies [13]–[15] and some palaeontological hypotheses [22]–[25]. The phylogenetic position of Platacanthomyidae has not been investigated yet with molecular data. We inferred the chewing grade of taxa whose direction of chewing has already been published or was measured in this study (See Table 4). B: grade B; C: grade C; D: grade D; O: grade O; M: grade M; †: fossil taxa. 1: Platacanthomyidae; 2: Spalacidae; 3: Calomyscidae; 4: Nesomyidae. 5: Muridae; 6: Cricetidae.

Mentions: Comparison of our results with molecular and palaeontological data relative to muroid phylogeny [13]–[15], [22]–[25] (Fig. 5) confirms that grade B is a primitive condition within Muroidea. It also reveals that the derived grades (C, M and D) were independently reached in several cases. Such results were to be expected because of the numerous cases of dental homoplasy observed in the course of muroid evolution revealed by a previous study combining dental characteristics and molecular data [14]. The emergence of grade D appears to be the most frequently achieved within the muroid radiation (at least 7 times) while grade C appeared at least 5 times and grade M at least 3 times (Fig. 5). Grade O up to now has only been recognized in one subfamily.


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)

Morpho-functional chewing grades and muroid phylogeny.This phylogeny is adapted from complementary results from the three most recent molecular phylogenies [13]–[15] and some palaeontological hypotheses [22]–[25]. The phylogenetic position of Platacanthomyidae has not been investigated yet with molecular data. We inferred the chewing grade of taxa whose direction of chewing has already been published or was measured in this study (See Table 4). B: grade B; C: grade C; D: grade D; O: grade O; M: grade M; †: fossil taxa. 1: Platacanthomyidae; 2: Spalacidae; 3: Calomyscidae; 4: Nesomyidae. 5: Muridae; 6: Cricetidae.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0003607-g005: Morpho-functional chewing grades and muroid phylogeny.This phylogeny is adapted from complementary results from the three most recent molecular phylogenies [13]–[15] and some palaeontological hypotheses [22]–[25]. The phylogenetic position of Platacanthomyidae has not been investigated yet with molecular data. We inferred the chewing grade of taxa whose direction of chewing has already been published or was measured in this study (See Table 4). B: grade B; C: grade C; D: grade D; O: grade O; M: grade M; †: fossil taxa. 1: Platacanthomyidae; 2: Spalacidae; 3: Calomyscidae; 4: Nesomyidae. 5: Muridae; 6: Cricetidae.
Mentions: Comparison of our results with molecular and palaeontological data relative to muroid phylogeny [13]–[15], [22]–[25] (Fig. 5) confirms that grade B is a primitive condition within Muroidea. It also reveals that the derived grades (C, M and D) were independently reached in several cases. Such results were to be expected because of the numerous cases of dental homoplasy observed in the course of muroid evolution revealed by a previous study combining dental characteristics and molecular data [14]. The emergence of grade D appears to be the most frequently achieved within the muroid radiation (at least 7 times) while grade C appeared at least 5 times and grade M at least 3 times (Fig. 5). Grade O up to now has only been recognized in one subfamily.

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