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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 tibia of H. longicostatum.A. Stage 1, CGH3; proximal toward top. B. Stage 2, St.152; proximal toward upper right. C. Stage 3, NHMW1898_X_23; proximal toward top. D. Stage 4, St.195; proximal toward upper right. E. Stage 5, RSM.1899.23.3; proximal toward upper left. Fem, femur; Fib, fibula; Int, intermedium; Tib, tibia; Tl, tibiale. Scale bars = 1mm.
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pone.0128333.g036: Ontogenetic changes in the tibia of H. longicostatum.A. Stage 1, CGH3; proximal toward top. B. Stage 2, St.152; proximal toward upper right. C. Stage 3, NHMW1898_X_23; proximal toward top. D. Stage 4, St.195; proximal toward upper right. E. Stage 5, RSM.1899.23.3; proximal toward upper left. Fem, femur; Fib, fibula; Int, intermedium; Tib, tibia; Tl, tibiale. Scale bars = 1mm.

Mentions: In the smallest known individual of H. longicostatum, the tibia is a block of bone with straight sides, unossified ends, and no identifiable features (Fig 36A). During the next stage of development, the proximal end of the tibia is greatly expanded (Fig 36B). Following that change, the intermedial facet of the tibia is developed as a medial slant at the distal end of the element (Fig 36C). Additionally, the head of tibia begins to slant medially. At the same stage of growth or soon after, the medial margin of the tibia becomes more concave, resulting in overall curvature (Fig 36D). In one large individual the facet for the tibiale is apparent as a lateral slant in the distal end of the tibia (Fig 36E).


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 tibia of H. longicostatum.A. Stage 1, CGH3; proximal toward top. B. Stage 2, St.152; proximal toward upper right. C. Stage 3, NHMW1898_X_23; proximal toward top. D. Stage 4, St.195; proximal toward upper right. E. Stage 5, RSM.1899.23.3; proximal toward upper left. Fem, femur; Fib, fibula; Int, intermedium; Tib, tibia; Tl, tibiale. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g036: Ontogenetic changes in the tibia of H. longicostatum.A. Stage 1, CGH3; proximal toward top. B. Stage 2, St.152; proximal toward upper right. C. Stage 3, NHMW1898_X_23; proximal toward top. D. Stage 4, St.195; proximal toward upper right. E. Stage 5, RSM.1899.23.3; proximal toward upper left. Fem, femur; Fib, fibula; Int, intermedium; Tib, tibia; Tl, tibiale. Scale bars = 1mm.
Mentions: In the smallest known individual of H. longicostatum, the tibia is a block of bone with straight sides, unossified ends, and no identifiable features (Fig 36A). During the next stage of development, the proximal end of the tibia is greatly expanded (Fig 36B). Following that change, the intermedial facet of the tibia is developed as a medial slant at the distal end of the element (Fig 36C). Additionally, the head of tibia begins to slant medially. At the same stage of growth or soon after, the medial margin of the tibia becomes more concave, resulting in overall curvature (Fig 36D). In one large individual the facet for the tibiale is apparent as a lateral slant in the distal end of the tibia (Fig 36E).

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