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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 H. longicostatum.A. Stage 1, CGH3; proximal toward top. B. Stage 2, St.152; proximal toward upper right. C. Stage 3, CGH3028; proximal toward upper left. D. Stage 4, NHMW1898_X_23; proximal toward top. E. Stage 5, RSM.1899.32.3; proximal toward upper left. Fem, femur; Fib, fibula; Fl, fibulare; Int, intermedium; Intf, intermedial facet; Tib, tibia. Scale bars = 1mm.
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pone.0128333.g037: Ontogenetic changes in the fibula of H. longicostatum.A. Stage 1, CGH3; proximal toward top. B. Stage 2, St.152; proximal toward upper right. C. Stage 3, CGH3028; proximal toward upper left. D. Stage 4, NHMW1898_X_23; proximal toward top. E. Stage 5, RSM.1899.32.3; proximal toward upper left. Fem, femur; Fib, fibula; Fl, fibulare; Int, intermedium; Intf, intermedial facet; Tib, tibia. Scale bars = 1mm.

Mentions: The least well-developed fibula that I observed is a narrow column of bone with flat, unfinished ends (Fig 37A). The first morphogenetic change in the fibula is the expansion of the distal end of the element (Fig 37B). As in M. pelikani, expansion is asymmetric, so that the medial surface of the distal end projects further. Shortly thereafter, the fibula exhibits moderate curvature caused mainly by the medial margin of the shaft becoming concave (Fig 37C). In the next stage of development the distal end of the fibula slants medially to produce the intermedial facet (Fig 37D). Late in ontogeny a distinct facet for the fibulare is visible and the bone is more strongly curved overall (Fig 37E).


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 H. longicostatum.A. Stage 1, CGH3; proximal toward top. B. Stage 2, St.152; proximal toward upper right. C. Stage 3, CGH3028; proximal toward upper left. D. Stage 4, NHMW1898_X_23; proximal toward top. E. Stage 5, RSM.1899.32.3; proximal toward upper left. Fem, femur; Fib, fibula; Fl, fibulare; 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.g037: Ontogenetic changes in the fibula of H. longicostatum.A. Stage 1, CGH3; proximal toward top. B. Stage 2, St.152; proximal toward upper right. C. Stage 3, CGH3028; proximal toward upper left. D. Stage 4, NHMW1898_X_23; proximal toward top. E. Stage 5, RSM.1899.32.3; proximal toward upper left. Fem, femur; Fib, fibula; Fl, fibulare; Int, intermedium; Intf, intermedial facet; Tib, tibia. Scale bars = 1mm.
Mentions: The least well-developed fibula that I observed is a narrow column of bone with flat, unfinished ends (Fig 37A). The first morphogenetic change in the fibula is the expansion of the distal end of the element (Fig 37B). As in M. pelikani, expansion is asymmetric, so that the medial surface of the distal end projects further. Shortly thereafter, the fibula exhibits moderate curvature caused mainly by the medial margin of the shaft becoming concave (Fig 37C). In the next stage of development the distal end of the fibula slants medially to produce the intermedial facet (Fig 37D). Late in ontogeny a distinct facet for the fibulare is visible and the bone is more strongly curved overall (Fig 37E).

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