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Skeletal Morphogenesis of Microbrachis and Hyloplesion (Tetrapoda: Lepospondyli), and Implications for the Developmental Patterns of Extinct, Early Tetrapods.

Olori JC - PLoS ONE (2015)

Bottom Line: However, early and rapid ossification of the postcranial skeleton, including a well-developed pubis and ossified epipodials, suggests that neither taxon metamorphosed nor were they neotenic in the sense of branchiosaurids and salamanders.Overall patterns of postcranial ossification may indicate postaxial dominance in limb and digit formation, but also more developmental variation in early tetrapods than has been appreciated.The phylogenetic position and developmental patterns of M. pelikani and H. longicostatum are congruent with the hypothesis that early tetrapods lacked metamorphosis ancestrally and that stem-amniotes exhibited derived features of development, such as rapid and complete ossification of the skeleton, potentially prior to the evolution of the amniotic egg.

View Article: PubMed Central - PubMed

Affiliation: Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas, United States of America.

ABSTRACT
The ontogeny of extant amphibians often is used as a model for that of extinct early tetrapods, despite evidence for a spectrum of developmental modes in temnospondyls and a paucity of ontogenetic data for lepospondyls. I describe the skeletal morphogenesis of the extinct lepospondyls Microbrachis pelikani and Hyloplesion longicostatum using the largest samples examined for either taxon. Nearly all known specimens were re-examined, allowing for substantial anatomical revisions that affect the scoring of characters commonly used in phylogenetic analyses of early tetrapods. The palate of H. longicostatum is re-interpreted and suggested to be more similar to that of M. pelikani, especially in the nature of the contact between the pterygoids. Both taxa possess lateral lines, and M. pelikani additionally exhibits branchial plates. However, early and rapid ossification of the postcranial skeleton, including a well-developed pubis and ossified epipodials, suggests that neither taxon metamorphosed nor were they neotenic in the sense of branchiosaurids and salamanders. Morphogenetic patterns in the foot suggest that digit 5 was developmentally delayed and the final digit to ossify in M. pelikani and H. longicostatum. Overall patterns of postcranial ossification may indicate postaxial dominance in limb and digit formation, but also more developmental variation in early tetrapods than has been appreciated. The phylogenetic position and developmental patterns of M. pelikani and H. longicostatum are congruent with the hypothesis that early tetrapods lacked metamorphosis ancestrally and that stem-amniotes exhibited derived features of development, such as rapid and complete ossification of the skeleton, potentially prior to the evolution of the amniotic egg.

No MeSH data available.


Related in: MedlinePlus

Ontogenetic changes in the fibula of M. pelikani.A. Stage 1, NHMW1898-2400; proximal toward upper left. B. Stage 2, NHMW1898_X_33; proximal toward upper right. C. Stage 3, AMNH2557; D. Stage 4, NHMW1983_32_67; proximal toward top. Fem, femur; Fib, fibula; Int, intermedium; Intf, intermedial facet; Tib, tibia. Scale bars = 1mm.
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pone.0128333.g026: Ontogenetic changes in the fibula of M. pelikani.A. Stage 1, NHMW1898-2400; proximal toward upper left. B. Stage 2, NHMW1898_X_33; proximal toward upper right. C. Stage 3, AMNH2557; D. Stage 4, NHMW1983_32_67; proximal toward top. Fem, femur; Fib, fibula; Int, intermedium; Intf, intermedial facet; Tib, tibia. Scale bars = 1mm.

Mentions: After initial ossification, the fibula and tibia nearly are indistinguishable. At that early point in ontogeny the ends of the fibula are approximately equal in breadth (Fig 26A). The first ontogenetic change is a marked expansion of the distal end of the fibula (Fig 26B). The expansion is asymmetric so that later in ontogeny the medial surface projects farther than the lateral surface. Shortly after expansion of the distal end, the fibula starts to appear curved, although only weakly. The intermedial facet, manifested as a medial slant in the distal end of the fibula, is the next feature to appear (Fig 26C). The facet is developed before ossification of the intermedium. In the most mature specimens, the fibula exhibits strong curvature, and both the proximal and distal ends are slanted (Fig 26D). I did not observe a distinct facet for the fibulare, although one specimen (CGH2098) may exhibit preliminary differentiation.


Skeletal Morphogenesis of Microbrachis and Hyloplesion (Tetrapoda: Lepospondyli), and Implications for the Developmental Patterns of Extinct, Early Tetrapods.

Olori JC - PLoS ONE (2015)

Ontogenetic changes in the fibula of M. pelikani.A. Stage 1, NHMW1898-2400; proximal toward upper left. B. Stage 2, NHMW1898_X_33; proximal toward upper right. C. Stage 3, AMNH2557; D. Stage 4, NHMW1983_32_67; proximal toward top. Fem, femur; Fib, fibula; Int, intermedium; Intf, intermedial facet; Tib, tibia. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4470922&req=5

pone.0128333.g026: Ontogenetic changes in the fibula of M. pelikani.A. Stage 1, NHMW1898-2400; proximal toward upper left. B. Stage 2, NHMW1898_X_33; proximal toward upper right. C. Stage 3, AMNH2557; D. Stage 4, NHMW1983_32_67; proximal toward top. Fem, femur; Fib, fibula; Int, intermedium; Intf, intermedial facet; Tib, tibia. Scale bars = 1mm.
Mentions: After initial ossification, the fibula and tibia nearly are indistinguishable. At that early point in ontogeny the ends of the fibula are approximately equal in breadth (Fig 26A). The first ontogenetic change is a marked expansion of the distal end of the fibula (Fig 26B). The expansion is asymmetric so that later in ontogeny the medial surface projects farther than the lateral surface. Shortly after expansion of the distal end, the fibula starts to appear curved, although only weakly. The intermedial facet, manifested as a medial slant in the distal end of the fibula, is the next feature to appear (Fig 26C). The facet is developed before ossification of the intermedium. In the most mature specimens, the fibula exhibits strong curvature, and both the proximal and distal ends are slanted (Fig 26D). I did not observe a distinct facet for the fibulare, although one specimen (CGH2098) may exhibit preliminary differentiation.

Bottom Line: However, early and rapid ossification of the postcranial skeleton, including a well-developed pubis and ossified epipodials, suggests that neither taxon metamorphosed nor were they neotenic in the sense of branchiosaurids and salamanders.Overall patterns of postcranial ossification may indicate postaxial dominance in limb and digit formation, but also more developmental variation in early tetrapods than has been appreciated.The phylogenetic position and developmental patterns of M. pelikani and H. longicostatum are congruent with the hypothesis that early tetrapods lacked metamorphosis ancestrally and that stem-amniotes exhibited derived features of development, such as rapid and complete ossification of the skeleton, potentially prior to the evolution of the amniotic egg.

View Article: PubMed Central - PubMed

Affiliation: Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas, United States of America.

ABSTRACT
The ontogeny of extant amphibians often is used as a model for that of extinct early tetrapods, despite evidence for a spectrum of developmental modes in temnospondyls and a paucity of ontogenetic data for lepospondyls. I describe the skeletal morphogenesis of the extinct lepospondyls Microbrachis pelikani and Hyloplesion longicostatum using the largest samples examined for either taxon. Nearly all known specimens were re-examined, allowing for substantial anatomical revisions that affect the scoring of characters commonly used in phylogenetic analyses of early tetrapods. The palate of H. longicostatum is re-interpreted and suggested to be more similar to that of M. pelikani, especially in the nature of the contact between the pterygoids. Both taxa possess lateral lines, and M. pelikani additionally exhibits branchial plates. However, early and rapid ossification of the postcranial skeleton, including a well-developed pubis and ossified epipodials, suggests that neither taxon metamorphosed nor were they neotenic in the sense of branchiosaurids and salamanders. Morphogenetic patterns in the foot suggest that digit 5 was developmentally delayed and the final digit to ossify in M. pelikani and H. longicostatum. Overall patterns of postcranial ossification may indicate postaxial dominance in limb and digit formation, but also more developmental variation in early tetrapods than has been appreciated. The phylogenetic position and developmental patterns of M. pelikani and H. longicostatum are congruent with the hypothesis that early tetrapods lacked metamorphosis ancestrally and that stem-amniotes exhibited derived features of development, such as rapid and complete ossification of the skeleton, potentially prior to the evolution of the amniotic egg.

No MeSH data available.


Related in: MedlinePlus