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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 femur of M. pelikani.A. Stage 1, NHMW1894-2400; proximal toward left. Note unfinished ends. B. Stage 2, NHMW1983_32_50; proximal toward bottom left. Note waisting of shaft. C. Stage 3, St.190; proximal toward bottom left. Impression of crushed element. D. Stage 4, MB.Am.810; proximal toward upper left. Internal trochanter is broken. E. Stage 5, AMNH2557; proximal toward upper right. F. Stage 6, MB.Am.840; Elements from both sides present, anterior is to the left. Femur toward top is ventral view, femur toward bottom is dorsal view. Adc, adductor crest; Dcd, distal condyles; Fem, femur; Fib, fibula; Fh, femoral head; Icf, intercondylar fossa; Ili, ilium; Ish, ischium; Itr, internal trochanter; Itrf, intertrochanteric fossa. Scale bars = 1mm.
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pone.0128333.g024: Ontogenetic changes in the femur of M. pelikani.A. Stage 1, NHMW1894-2400; proximal toward left. Note unfinished ends. B. Stage 2, NHMW1983_32_50; proximal toward bottom left. Note waisting of shaft. C. Stage 3, St.190; proximal toward bottom left. Impression of crushed element. D. Stage 4, MB.Am.810; proximal toward upper left. Internal trochanter is broken. E. Stage 5, AMNH2557; proximal toward upper right. F. Stage 6, MB.Am.840; Elements from both sides present, anterior is to the left. Femur toward top is ventral view, femur toward bottom is dorsal view. Adc, adductor crest; Dcd, distal condyles; Fem, femur; Fib, fibula; Fh, femoral head; Icf, intercondylar fossa; Ili, ilium; Ish, ischium; Itr, internal trochanter; Itrf, intertrochanteric fossa. Scale bars = 1mm.

Mentions: The femur of the most immature specimens of M. pelikani is a simple rectangle of bone, with little waisting to distinguish the shaft, and incompletely ossified proximal and distal ends (Table 2). The intertrochanteric fossa may be developing in some specimens at that stage of morphogenesis, but in general, features are poorly developed (Fig 24A). During the next stage of development, the intertrochanteric fossa is identifiable and the shaft becomes distinct from the ends of the femur (Fig 24B). With increased growth, the ends of the femur become rounded, and a small internal trochanter and adductor crest appear (Fig 24C). The shaft of the femur is still narrowing and the distal condyles are not differentiated. In specimens preserved in dorsal view, presence of the internal trochanter is evidenced by medial slanting of the femoral head and a small, angular inflection at the proximal-medial corner of the femur. The next set of morphogenetic changes include notable strengthening of the adductor crest and preliminary differentiation of the distal condyles, often signified by the presence of a small fossa between the tibial and fibular facets (Fig 24D). At about the same time, or shortly after, specimens preserved in dorsal view exhibit a small intercondylar fossa at the distal end of the femur (Fig 24E). Additionally, the distal condyles are rounded, have separated from one another, and frequently exhibit distinct patches of bone for articular facets (Fig 24F).


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 femur of M. pelikani.A. Stage 1, NHMW1894-2400; proximal toward left. Note unfinished ends. B. Stage 2, NHMW1983_32_50; proximal toward bottom left. Note waisting of shaft. C. Stage 3, St.190; proximal toward bottom left. Impression of crushed element. D. Stage 4, MB.Am.810; proximal toward upper left. Internal trochanter is broken. E. Stage 5, AMNH2557; proximal toward upper right. F. Stage 6, MB.Am.840; Elements from both sides present, anterior is to the left. Femur toward top is ventral view, femur toward bottom is dorsal view. Adc, adductor crest; Dcd, distal condyles; Fem, femur; Fib, fibula; Fh, femoral head; Icf, intercondylar fossa; Ili, ilium; Ish, ischium; Itr, internal trochanter; Itrf, intertrochanteric fossa. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4470922&req=5

pone.0128333.g024: Ontogenetic changes in the femur of M. pelikani.A. Stage 1, NHMW1894-2400; proximal toward left. Note unfinished ends. B. Stage 2, NHMW1983_32_50; proximal toward bottom left. Note waisting of shaft. C. Stage 3, St.190; proximal toward bottom left. Impression of crushed element. D. Stage 4, MB.Am.810; proximal toward upper left. Internal trochanter is broken. E. Stage 5, AMNH2557; proximal toward upper right. F. Stage 6, MB.Am.840; Elements from both sides present, anterior is to the left. Femur toward top is ventral view, femur toward bottom is dorsal view. Adc, adductor crest; Dcd, distal condyles; Fem, femur; Fib, fibula; Fh, femoral head; Icf, intercondylar fossa; Ili, ilium; Ish, ischium; Itr, internal trochanter; Itrf, intertrochanteric fossa. Scale bars = 1mm.
Mentions: The femur of the most immature specimens of M. pelikani is a simple rectangle of bone, with little waisting to distinguish the shaft, and incompletely ossified proximal and distal ends (Table 2). The intertrochanteric fossa may be developing in some specimens at that stage of morphogenesis, but in general, features are poorly developed (Fig 24A). During the next stage of development, the intertrochanteric fossa is identifiable and the shaft becomes distinct from the ends of the femur (Fig 24B). With increased growth, the ends of the femur become rounded, and a small internal trochanter and adductor crest appear (Fig 24C). The shaft of the femur is still narrowing and the distal condyles are not differentiated. In specimens preserved in dorsal view, presence of the internal trochanter is evidenced by medial slanting of the femoral head and a small, angular inflection at the proximal-medial corner of the femur. The next set of morphogenetic changes include notable strengthening of the adductor crest and preliminary differentiation of the distal condyles, often signified by the presence of a small fossa between the tibial and fibular facets (Fig 24D). At about the same time, or shortly after, specimens preserved in dorsal view exhibit a small intercondylar fossa at the distal end of the femur (Fig 24E). Additionally, the distal condyles are rounded, have separated from one another, and frequently exhibit distinct patches of bone for articular facets (Fig 24F).

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