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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 pubis of M. pelikani.A. Stage 1, St.193; anterior up, medial to the right. Specimen is impression, but angle of lighting creates 3D effect. B. Stage 2, MB.Am.810; anterior to the right. Element from both sides present. C. Stage 3, CGH2098; anterior to the left. Element from both sides present. D. Stage 4, NHMW1983_32_67; isolated pelvis. Obturator foramen nearly closed. Fem, femur; Ili, ilium; Ish, ishium; Obf, obturator foramen; Pub, pubis. Scale bars = 1mm.
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pone.0128333.g023: Ontogenetic changes in the pubis of M. pelikani.A. Stage 1, St.193; anterior up, medial to the right. Specimen is impression, but angle of lighting creates 3D effect. B. Stage 2, MB.Am.810; anterior to the right. Element from both sides present. C. Stage 3, CGH2098; anterior to the left. Element from both sides present. D. Stage 4, NHMW1983_32_67; isolated pelvis. Obturator foramen nearly closed. Fem, femur; Ili, ilium; Ish, ishium; Obf, obturator foramen; Pub, pubis. Scale bars = 1mm.

Mentions: The pubis is one of the final elements to ossify during postcranial skeletal development of M. pelikani [16]. It first appears as an irregular, flat, subcircular bone (Fig 23A). Later in ontogeny a wide ring forms around the outer edge of the pubis, causing the center to appear depressed in small individuals (MB.Am.812-9). The thickened ring becomes proportionately narrower as the pubis increases in size and the center may instead be raised (Fig 23B). In more developmentally advanced specimens, the obturator foramen is first visible as a notch in the posteromedial margin of the pubis (Fig 23C). In one of the largest individuals, the pubis has nearly enclosed the obturator foramen (Fig 23D).


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 pubis of M. pelikani.A. Stage 1, St.193; anterior up, medial to the right. Specimen is impression, but angle of lighting creates 3D effect. B. Stage 2, MB.Am.810; anterior to the right. Element from both sides present. C. Stage 3, CGH2098; anterior to the left. Element from both sides present. D. Stage 4, NHMW1983_32_67; isolated pelvis. Obturator foramen nearly closed. Fem, femur; Ili, ilium; Ish, ishium; Obf, obturator foramen; Pub, pubis. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g023: Ontogenetic changes in the pubis of M. pelikani.A. Stage 1, St.193; anterior up, medial to the right. Specimen is impression, but angle of lighting creates 3D effect. B. Stage 2, MB.Am.810; anterior to the right. Element from both sides present. C. Stage 3, CGH2098; anterior to the left. Element from both sides present. D. Stage 4, NHMW1983_32_67; isolated pelvis. Obturator foramen nearly closed. Fem, femur; Ili, ilium; Ish, ishium; Obf, obturator foramen; Pub, pubis. Scale bars = 1mm.
Mentions: The pubis is one of the final elements to ossify during postcranial skeletal development of M. pelikani [16]. It first appears as an irregular, flat, subcircular bone (Fig 23A). Later in ontogeny a wide ring forms around the outer edge of the pubis, causing the center to appear depressed in small individuals (MB.Am.812-9). The thickened ring becomes proportionately narrower as the pubis increases in size and the center may instead be raised (Fig 23B). In more developmentally advanced specimens, the obturator foramen is first visible as a notch in the posteromedial margin of the pubis (Fig 23C). In one of the largest individuals, the pubis has nearly enclosed the obturator foramen (Fig 23D).

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