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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

Lower jaw, M. pelikani.A. Sagittal section of mandible displaying natural cast of mandibular canal; NHMW1983_32_67; anterior to the left, dorsal up. B. Ventral view of palate and lower jaw; CGH727; anterior to the left, lateral up. Specimen is impression, but angle of light creates 3D effect. Den, dentary; Psp, postsplenial; Sp, splenial. Scale bars = 1 mm.
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pone.0128333.g014: Lower jaw, M. pelikani.A. Sagittal section of mandible displaying natural cast of mandibular canal; NHMW1983_32_67; anterior to the left, dorsal up. B. Ventral view of palate and lower jaw; CGH727; anterior to the left, lateral up. Specimen is impression, but angle of light creates 3D effect. Den, dentary; Psp, postsplenial; Sp, splenial. Scale bars = 1 mm.

Mentions: There are no significant ontogenetic changes in the morphology of the lower jaw. One specimen, NHMW1983_32_67, suffered damage to the lower jaw in such a manner as to reveal a natural cast of the mandibular canal and tooth roots (Fig 14A). In the endocast of the mandible, narrow passages connect the mandibular canal space not only to the tooth roots, but also to lateral openings in the dentary, which were probably innervated and possibly part of the lateral line system. The range in the maximum number of dentary teeth that I recorded for M. pelikani is 22–31, an increase from the maximum of 29 reported by Carroll and Gaskill [1]. Similar to the pattern observed in the maxilla, the middle teeth of the dentary, usually teeth 13–21, are largest.


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

Olori JC - PLoS ONE (2015)

Lower jaw, M. pelikani.A. Sagittal section of mandible displaying natural cast of mandibular canal; NHMW1983_32_67; anterior to the left, dorsal up. B. Ventral view of palate and lower jaw; CGH727; anterior to the left, lateral up. Specimen is impression, but angle of light creates 3D effect. Den, dentary; Psp, postsplenial; Sp, splenial. Scale bars = 1 mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g014: Lower jaw, M. pelikani.A. Sagittal section of mandible displaying natural cast of mandibular canal; NHMW1983_32_67; anterior to the left, dorsal up. B. Ventral view of palate and lower jaw; CGH727; anterior to the left, lateral up. Specimen is impression, but angle of light creates 3D effect. Den, dentary; Psp, postsplenial; Sp, splenial. Scale bars = 1 mm.
Mentions: There are no significant ontogenetic changes in the morphology of the lower jaw. One specimen, NHMW1983_32_67, suffered damage to the lower jaw in such a manner as to reveal a natural cast of the mandibular canal and tooth roots (Fig 14A). In the endocast of the mandible, narrow passages connect the mandibular canal space not only to the tooth roots, but also to lateral openings in the dentary, which were probably innervated and possibly part of the lateral line system. The range in the maximum number of dentary teeth that I recorded for M. pelikani is 22–31, an increase from the maximum of 29 reported by Carroll and Gaskill [1]. Similar to the pattern observed in the maxilla, the middle teeth of the dentary, usually teeth 13–21, are largest.

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