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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 ilium of M. pelikani.A. Stage 1, NHMW1894-2400; proximal toward top left. B. Stage 2, St.193; proximal toward bottom right. C. Stage 3, NHMW1983_32_3; proximal toward right. D. Stage 4, NHMW1894-2364; proximal toward top right. Act, acetabulum; Fem, femur; Ib, bifurcation; Ili, ilium; Ish, ishium; Pub, pubis. Scale bars = 1mm.
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pone.0128333.g021: Ontogenetic changes in the ilium of M. pelikani.A. Stage 1, NHMW1894-2400; proximal toward top left. B. Stage 2, St.193; proximal toward bottom right. C. Stage 3, NHMW1983_32_3; proximal toward right. D. Stage 4, NHMW1894-2364; proximal toward top right. Act, acetabulum; Fem, femur; Ib, bifurcation; Ili, ilium; Ish, ishium; Pub, pubis. Scale bars = 1mm.

Mentions: The ilium of M. pelikani forms relatively early in skeletal development [16]. At first, the ilium has a straight and relatively rectangular dorsal process (Fig 21A). The head is incompletely ossified and the acetabulum has not yet formed. The first major morphogenetic change is the development of the dorsal margin of the acetabulum along the ventrolateral margin of the iliac head (Fig 21B). In the next stage of development, the dorsal process of the ilium curves to assume a posterodorsal orientation at about the same time the acetabulum expands dorsally and becomes well-defined (Fig 21C). The posterior tip of the dorsal process is also less squared. Finally, during the latest stage of ilium development, the dorsal process bifurcates into two distinct, pointed processes and the head is greatly expanded for articulation with the rest of the pelvis (Fig 21D). However, even in the largest individuals, the ilium is not fused to the pubis, though it may be more firmly attached to the ischium.


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 ilium of M. pelikani.A. Stage 1, NHMW1894-2400; proximal toward top left. B. Stage 2, St.193; proximal toward bottom right. C. Stage 3, NHMW1983_32_3; proximal toward right. D. Stage 4, NHMW1894-2364; proximal toward top right. Act, acetabulum; Fem, femur; Ib, bifurcation; Ili, ilium; Ish, ishium; Pub, pubis. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g021: Ontogenetic changes in the ilium of M. pelikani.A. Stage 1, NHMW1894-2400; proximal toward top left. B. Stage 2, St.193; proximal toward bottom right. C. Stage 3, NHMW1983_32_3; proximal toward right. D. Stage 4, NHMW1894-2364; proximal toward top right. Act, acetabulum; Fem, femur; Ib, bifurcation; Ili, ilium; Ish, ishium; Pub, pubis. Scale bars = 1mm.
Mentions: The ilium of M. pelikani forms relatively early in skeletal development [16]. At first, the ilium has a straight and relatively rectangular dorsal process (Fig 21A). The head is incompletely ossified and the acetabulum has not yet formed. The first major morphogenetic change is the development of the dorsal margin of the acetabulum along the ventrolateral margin of the iliac head (Fig 21B). In the next stage of development, the dorsal process of the ilium curves to assume a posterodorsal orientation at about the same time the acetabulum expands dorsally and becomes well-defined (Fig 21C). The posterior tip of the dorsal process is also less squared. Finally, during the latest stage of ilium development, the dorsal process bifurcates into two distinct, pointed processes and the head is greatly expanded for articulation with the rest of the pelvis (Fig 21D). However, even in the largest individuals, the ilium is not fused to the pubis, though it may be more firmly attached to the ischium.

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