Limits...
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 and braincase elements, M. pelikani.A. CGH253, parasphenoid; ventral view, anterior up. Note paired depressions on parasphenoid plate. Bone. B. M1689, isolated basioccipital; dorsal view, anterior to the left. Metal cast. C. CGH256, isolated basioccipital; dorsal view, anterior up. Bone. D. NHMW1983_32_66, ventral view of occipital-atlantal articulation; anterior up. Impression. At, atlas; Bo, basioccipital; Eo, exoccipital; Pp, postparietal. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4470922&req=5

pone.0128333.g012: Palate and braincase elements, M. pelikani.A. CGH253, parasphenoid; ventral view, anterior up. Note paired depressions on parasphenoid plate. Bone. B. M1689, isolated basioccipital; dorsal view, anterior to the left. Metal cast. C. CGH256, isolated basioccipital; dorsal view, anterior up. Bone. D. NHMW1983_32_66, ventral view of occipital-atlantal articulation; anterior up. Impression. At, atlas; Bo, basioccipital; Eo, exoccipital; Pp, postparietal. Scale bars = 1mm.

Mentions: When the parasphenoid is preserved in dorsal view, a pair of facets, open posteriorly, are present flanking either side of the midline (Fig 12A). Those facets likely facilitated articulation with the basioccipital. In a prior description of the parasphenoid, it was noted that in larger individuals, the element exhibits a bi-lobed posterior margin and a small posterolateral process [9]. I observed the bi-lobed morphology in all specimens in which the parasphenoid is preserved as bone and in most specimens in which only an impression remains. There is no clear association with size, except for a slight increase in the notch between lobes in larger individuals. Additionally, the short ‘posterolateral process’ described by Vallin and Laurin [9] appears to be an artifact of the broken lateral wing of the parasphenoid plate, which is a roughly triangular flange in all specimens that I examined.


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

Olori JC - PLoS ONE (2015)

Palate and braincase elements, M. pelikani.A. CGH253, parasphenoid; ventral view, anterior up. Note paired depressions on parasphenoid plate. Bone. B. M1689, isolated basioccipital; dorsal view, anterior to the left. Metal cast. C. CGH256, isolated basioccipital; dorsal view, anterior up. Bone. D. NHMW1983_32_66, ventral view of occipital-atlantal articulation; anterior up. Impression. At, atlas; Bo, basioccipital; Eo, exoccipital; Pp, postparietal. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g012: Palate and braincase elements, M. pelikani.A. CGH253, parasphenoid; ventral view, anterior up. Note paired depressions on parasphenoid plate. Bone. B. M1689, isolated basioccipital; dorsal view, anterior to the left. Metal cast. C. CGH256, isolated basioccipital; dorsal view, anterior up. Bone. D. NHMW1983_32_66, ventral view of occipital-atlantal articulation; anterior up. Impression. At, atlas; Bo, basioccipital; Eo, exoccipital; Pp, postparietal. Scale bars = 1mm.
Mentions: When the parasphenoid is preserved in dorsal view, a pair of facets, open posteriorly, are present flanking either side of the midline (Fig 12A). Those facets likely facilitated articulation with the basioccipital. In a prior description of the parasphenoid, it was noted that in larger individuals, the element exhibits a bi-lobed posterior margin and a small posterolateral process [9]. I observed the bi-lobed morphology in all specimens in which the parasphenoid is preserved as bone and in most specimens in which only an impression remains. There is no clear association with size, except for a slight increase in the notch between lobes in larger individuals. Additionally, the short ‘posterolateral process’ described by Vallin and Laurin [9] appears to be an artifact of the broken lateral wing of the parasphenoid plate, which is a roughly triangular flange in all specimens that I examined.

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