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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

Vertebrae of H. longicostatum.A. Posteriormost presacral vertebrae of CGH3; anterior to the left, dorsal up; scale bar = 1mm. B. Caudal vertebrae of CGH3; anterior to the left, dorsal up; scale bar = 1mm. C. Posterior body of NHMW1898_X_23; Anterior toward top left; scale bar = 5 mm. Cn, centrum; Ha, haemal arch; Nap, neural arch pedicel; Nc, neural crest; Nr, neural arch.
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pone.0128333.g031: Vertebrae of H. longicostatum.A. Posteriormost presacral vertebrae of CGH3; anterior to the left, dorsal up; scale bar = 1mm. B. Caudal vertebrae of CGH3; anterior to the left, dorsal up; scale bar = 1mm. C. Posterior body of NHMW1898_X_23; Anterior toward top left; scale bar = 5 mm. Cn, centrum; Ha, haemal arch; Nap, neural arch pedicel; Nc, neural crest; Nr, neural arch.

Mentions: Unlike M. pelikani, which is relatively conservative in the number of presacral vertebrae present (see above), H. longicostatum is more variable, with about half the specimens studied possessing 30 and the other half possessing 31. One specimen (M1377) may have as many as 32 presacral vertebrae, but preservation is relatively poor and a definite count is not possible. Even more so than in M. pelikani, the vertebrae in the smallest individuals appear boxy and angular, with a centrum height nearly equal to centrum length (Fig 31A). Morphometric data for H. longicostatum support the visual observation that the relative height of the centrum decreases with growth [17]. The angle of the incline of the neural arch is usually 5–10 degrees, but in one individual it measures between 10–20 degrees. The transverse processes are directed anterolaterally, as in M. pelikani.


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

Olori JC - PLoS ONE (2015)

Vertebrae of H. longicostatum.A. Posteriormost presacral vertebrae of CGH3; anterior to the left, dorsal up; scale bar = 1mm. B. Caudal vertebrae of CGH3; anterior to the left, dorsal up; scale bar = 1mm. C. Posterior body of NHMW1898_X_23; Anterior toward top left; scale bar = 5 mm. Cn, centrum; Ha, haemal arch; Nap, neural arch pedicel; Nc, neural crest; Nr, neural arch.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4470922&req=5

pone.0128333.g031: Vertebrae of H. longicostatum.A. Posteriormost presacral vertebrae of CGH3; anterior to the left, dorsal up; scale bar = 1mm. B. Caudal vertebrae of CGH3; anterior to the left, dorsal up; scale bar = 1mm. C. Posterior body of NHMW1898_X_23; Anterior toward top left; scale bar = 5 mm. Cn, centrum; Ha, haemal arch; Nap, neural arch pedicel; Nc, neural crest; Nr, neural arch.
Mentions: Unlike M. pelikani, which is relatively conservative in the number of presacral vertebrae present (see above), H. longicostatum is more variable, with about half the specimens studied possessing 30 and the other half possessing 31. One specimen (M1377) may have as many as 32 presacral vertebrae, but preservation is relatively poor and a definite count is not possible. Even more so than in M. pelikani, the vertebrae in the smallest individuals appear boxy and angular, with a centrum height nearly equal to centrum length (Fig 31A). Morphometric data for H. longicostatum support the visual observation that the relative height of the centrum decreases with growth [17]. The angle of the incline of the neural arch is usually 5–10 degrees, but in one individual it measures between 10–20 degrees. The transverse processes are directed anterolaterally, as in M. pelikani.

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