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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

Carpals, digits, and potential epiphyses in M. pelikani.A. Ossified intermedium in the manus of R.2814; proximal toward bottom right. B. Pes of AMNH2557; proximal toward top right. Arrow points to poorly ossified digit five. C. Crushed radius and ulna of CGH142. Note profusion of cell spaces that may indicate epiphysis. D. Femur of AMNH2557; proximal toward top right. Arrow points to line between shaft and potential epiphysis. D. Femur of MB.Am.840; proximal toward the left. Arrow points to line between shaft and potential epiphysis of well-developed femoral head. Fem, femur; Fib, fibula; Int, intermedium; Ish, ischium; Mc, metacarpals; Rad, radius; Uln, ulna; V, digit five. Scale bars = 1mm.
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pone.0128333.g027: Carpals, digits, and potential epiphyses in M. pelikani.A. Ossified intermedium in the manus of R.2814; proximal toward bottom right. B. Pes of AMNH2557; proximal toward top right. Arrow points to poorly ossified digit five. C. Crushed radius and ulna of CGH142. Note profusion of cell spaces that may indicate epiphysis. D. Femur of AMNH2557; proximal toward top right. Arrow points to line between shaft and potential epiphysis. D. Femur of MB.Am.840; proximal toward the left. Arrow points to line between shaft and potential epiphysis of well-developed femoral head. Fem, femur; Fib, fibula; Int, intermedium; Ish, ischium; Mc, metacarpals; Rad, radius; Uln, ulna; V, digit five. Scale bars = 1mm.

Mentions: In M. pelikani, a maximum of five ossified carpals was reported by Carroll and Gaskill [1]. The intermedium is the first carpal to ossify (Fig 27A). Based on one specimen (MB.Am.17) that possesses two carpals, the ulnare may be the second to ossify. However, precise identification is impossible because the wrist and partial digits are offset from the long bones. Specimen CGH3018, which exhibits five carpals, was reported to preserve the ulnare, intermedium, radiale, and two distal carpals [1]. In what appears to be ventral view, the carpals in M. pelikani have a small depression at the center of ossification.


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

Olori JC - PLoS ONE (2015)

Carpals, digits, and potential epiphyses in M. pelikani.A. Ossified intermedium in the manus of R.2814; proximal toward bottom right. B. Pes of AMNH2557; proximal toward top right. Arrow points to poorly ossified digit five. C. Crushed radius and ulna of CGH142. Note profusion of cell spaces that may indicate epiphysis. D. Femur of AMNH2557; proximal toward top right. Arrow points to line between shaft and potential epiphysis. D. Femur of MB.Am.840; proximal toward the left. Arrow points to line between shaft and potential epiphysis of well-developed femoral head. Fem, femur; Fib, fibula; Int, intermedium; Ish, ischium; Mc, metacarpals; Rad, radius; Uln, ulna; V, digit five. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4470922&req=5

pone.0128333.g027: Carpals, digits, and potential epiphyses in M. pelikani.A. Ossified intermedium in the manus of R.2814; proximal toward bottom right. B. Pes of AMNH2557; proximal toward top right. Arrow points to poorly ossified digit five. C. Crushed radius and ulna of CGH142. Note profusion of cell spaces that may indicate epiphysis. D. Femur of AMNH2557; proximal toward top right. Arrow points to line between shaft and potential epiphysis. D. Femur of MB.Am.840; proximal toward the left. Arrow points to line between shaft and potential epiphysis of well-developed femoral head. Fem, femur; Fib, fibula; Int, intermedium; Ish, ischium; Mc, metacarpals; Rad, radius; Uln, ulna; V, digit five. Scale bars = 1mm.
Mentions: In M. pelikani, a maximum of five ossified carpals was reported by Carroll and Gaskill [1]. The intermedium is the first carpal to ossify (Fig 27A). Based on one specimen (MB.Am.17) that possesses two carpals, the ulnare may be the second to ossify. However, precise identification is impossible because the wrist and partial digits are offset from the long bones. Specimen CGH3018, which exhibits five carpals, was reported to preserve the ulnare, intermedium, radiale, and two distal carpals [1]. In what appears to be ventral view, the carpals in M. pelikani have a small depression at the center of ossification.

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