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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

Palate of H. longicostatum.A. Anterior palate of RSM.1899.32.3; anterior up, ventral view, impression. B. Isolated pterygoid of M4885; Anterior up, lateral to the left, dorsal view, bone. C. Palate of NHMW1899_IX_8; anterior up, ventral view, latex cast. D. Isolated epipterygoid of M4885; bone. Bpt, basipterygoid process of pterygoid; Ct, cultriform process of the parasphenoid; Den, dentary; Epi, epipterygoid; Iv, interpterygoid vacuity; Ppt, palatine process of pterygoid; Pl, palatine; Ps, parasphenoid; Pt, pterygoid; Qpt, quadrate ramus of the pterygoid; Vo, vomer. Scale bars = 1mm.
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pone.0128333.g030: Palate of H. longicostatum.A. Anterior palate of RSM.1899.32.3; anterior up, ventral view, impression. B. Isolated pterygoid of M4885; Anterior up, lateral to the left, dorsal view, bone. C. Palate of NHMW1899_IX_8; anterior up, ventral view, latex cast. D. Isolated epipterygoid of M4885; bone. Bpt, basipterygoid process of pterygoid; Ct, cultriform process of the parasphenoid; Den, dentary; Epi, epipterygoid; Iv, interpterygoid vacuity; Ppt, palatine process of pterygoid; Pl, palatine; Ps, parasphenoid; Pt, pterygoid; Qpt, quadrate ramus of the pterygoid; Vo, vomer. Scale bars = 1mm.

Mentions: My interpretation of the anterior palate does not agree with previously published descriptions [1]. The vomers do not have an extensive posterior, midline extension as was reconstructed ([1] reference figure 89). Much of that prior reconstruction was based on a single specimen, RSM.1899.32.3 (Royal Scottish Museum, Edinburgh, United Kingdom). The smooth structure interpreted as the complete vomer actually is a space in the palate, partially formed by separation of the vomers (Fig 30A). The matrix-filled space is continuous with the interpterygoid vacuities, which also were filled with fine sediment.


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

Olori JC - PLoS ONE (2015)

Palate of H. longicostatum.A. Anterior palate of RSM.1899.32.3; anterior up, ventral view, impression. B. Isolated pterygoid of M4885; Anterior up, lateral to the left, dorsal view, bone. C. Palate of NHMW1899_IX_8; anterior up, ventral view, latex cast. D. Isolated epipterygoid of M4885; bone. Bpt, basipterygoid process of pterygoid; Ct, cultriform process of the parasphenoid; Den, dentary; Epi, epipterygoid; Iv, interpterygoid vacuity; Ppt, palatine process of pterygoid; Pl, palatine; Ps, parasphenoid; Pt, pterygoid; Qpt, quadrate ramus of the pterygoid; Vo, vomer. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g030: Palate of H. longicostatum.A. Anterior palate of RSM.1899.32.3; anterior up, ventral view, impression. B. Isolated pterygoid of M4885; Anterior up, lateral to the left, dorsal view, bone. C. Palate of NHMW1899_IX_8; anterior up, ventral view, latex cast. D. Isolated epipterygoid of M4885; bone. Bpt, basipterygoid process of pterygoid; Ct, cultriform process of the parasphenoid; Den, dentary; Epi, epipterygoid; Iv, interpterygoid vacuity; Ppt, palatine process of pterygoid; Pl, palatine; Ps, parasphenoid; Pt, pterygoid; Qpt, quadrate ramus of the pterygoid; Vo, vomer. Scale bars = 1mm.
Mentions: My interpretation of the anterior palate does not agree with previously published descriptions [1]. The vomers do not have an extensive posterior, midline extension as was reconstructed ([1] reference figure 89). Much of that prior reconstruction was based on a single specimen, RSM.1899.32.3 (Royal Scottish Museum, Edinburgh, United Kingdom). The smooth structure interpreted as the complete vomer actually is a space in the palate, partially formed by separation of the vomers (Fig 30A). The matrix-filled space is continuous with the interpterygoid vacuities, which also were filled with fine sediment.

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