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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 radius of M. pelikani.A. Stage 1, NHMW1894-2504; proximal toward upper right. B. Stage 2, CGH267; proximal toward upper left. C. Stage 3, St.207; proximal toward upper right. Intf, intermedial facet; Rad, radius; Uln, ulna. Scale bars = 1 mm.
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pone.0128333.g019: Ontogenetic changes in the radius of M. pelikani.A. Stage 1, NHMW1894-2504; proximal toward upper right. B. Stage 2, CGH267; proximal toward upper left. C. Stage 3, St.207; proximal toward upper right. Intf, intermedial facet; Rad, radius; Uln, ulna. Scale bars = 1 mm.

Mentions: The ossified radius of M. pelikani first appears as a featureless, rectangular bone with no processes and flat, indistinct proximal and distal ends (Fig 19A). The first morphogenetic change to occur is the development of a distinctly waisted shaft with expanded proximal and distal ends (Fig 19B). Throughout ontogeny, the distal end of the radius is equal to or broader than the proximal end. The ends of the radius also become rounded (convex). During the next stage of morphogenesis, the medial surface of the distal end slants inward to form the intermedial facet (Fig 19C). The radiale facet is not well developed in any specimens, though St.207 and NHMW1894_2399 may show preliminary differentiation of that region.


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 radius of M. pelikani.A. Stage 1, NHMW1894-2504; proximal toward upper right. B. Stage 2, CGH267; proximal toward upper left. C. Stage 3, St.207; proximal toward upper right. Intf, intermedial facet; Rad, radius; Uln, ulna. Scale bars = 1 mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g019: Ontogenetic changes in the radius of M. pelikani.A. Stage 1, NHMW1894-2504; proximal toward upper right. B. Stage 2, CGH267; proximal toward upper left. C. Stage 3, St.207; proximal toward upper right. Intf, intermedial facet; Rad, radius; Uln, ulna. Scale bars = 1 mm.
Mentions: The ossified radius of M. pelikani first appears as a featureless, rectangular bone with no processes and flat, indistinct proximal and distal ends (Fig 19A). The first morphogenetic change to occur is the development of a distinctly waisted shaft with expanded proximal and distal ends (Fig 19B). Throughout ontogeny, the distal end of the radius is equal to or broader than the proximal end. The ends of the radius also become rounded (convex). During the next stage of morphogenesis, the medial surface of the distal end slants inward to form the intermedial facet (Fig 19C). The radiale facet is not well developed in any specimens, though St.207 and NHMW1894_2399 may show preliminary differentiation of that region.

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