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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 elements, M. pelikani.A. CGH727 (Narodini Museum, (now National Museum Prague), Prague, Czech Republic); isolated right palatine and ectopterygoid. Ventral view, anterior up, lateral to the right. B. CGH727; displaced right epipterygoid. Ventral view, anterior up. Specimen is impression, but the angle of the lighting causes a 3D effect. C. CGH251; ‘epipterygoid’ figured by Carroll and Gaskill [1]. Probably a circumorbital. D. M1689. Potential isolated epipterygoid. C?, circumorbital?; Ep, ectopterygoid; Epi, epipterygoid; Iv, interpterygoid vacuity; Pl, palatine; Ps, parasphenoid. Scale bars = 1mm.
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pone.0128333.g011: Palate elements, M. pelikani.A. CGH727 (Narodini Museum, (now National Museum Prague), Prague, Czech Republic); isolated right palatine and ectopterygoid. Ventral view, anterior up, lateral to the right. B. CGH727; displaced right epipterygoid. Ventral view, anterior up. Specimen is impression, but the angle of the lighting causes a 3D effect. C. CGH251; ‘epipterygoid’ figured by Carroll and Gaskill [1]. Probably a circumorbital. D. M1689. Potential isolated epipterygoid. C?, circumorbital?; Ep, ectopterygoid; Epi, epipterygoid; Iv, interpterygoid vacuity; Pl, palatine; Ps, parasphenoid. Scale bars = 1mm.

Mentions: Specimen CGH727 preserves a disarticulated palatine (Fig 11A). That element is relatively elongate and narrow, more similar to reconstructions by Carroll and Gaskill [1] than to those of Vallin and Laurin [9]. The vomerine (medial) process of the palatine is robust and projects relatively far medially. The largest denticles on the palatine are located at the base of the maxillary process, posterior to the smooth, U-shaped anterior edge that forms the posterior margin of the choana. Additionally, the disarticulated palatine appears to be in contact with an ectopterygoid, a much shorter and rounder bone. Both elements exhibit a straight lateral margin for contact with the maxilla. The base of an epipterygoid, with the dorsal stem broken and missing, appears to be preserved underneath the ectopterygoid.


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

Olori JC - PLoS ONE (2015)

Palate elements, M. pelikani.A. CGH727 (Narodini Museum, (now National Museum Prague), Prague, Czech Republic); isolated right palatine and ectopterygoid. Ventral view, anterior up, lateral to the right. B. CGH727; displaced right epipterygoid. Ventral view, anterior up. Specimen is impression, but the angle of the lighting causes a 3D effect. C. CGH251; ‘epipterygoid’ figured by Carroll and Gaskill [1]. Probably a circumorbital. D. M1689. Potential isolated epipterygoid. C?, circumorbital?; Ep, ectopterygoid; Epi, epipterygoid; Iv, interpterygoid vacuity; Pl, palatine; Ps, parasphenoid. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g011: Palate elements, M. pelikani.A. CGH727 (Narodini Museum, (now National Museum Prague), Prague, Czech Republic); isolated right palatine and ectopterygoid. Ventral view, anterior up, lateral to the right. B. CGH727; displaced right epipterygoid. Ventral view, anterior up. Specimen is impression, but the angle of the lighting causes a 3D effect. C. CGH251; ‘epipterygoid’ figured by Carroll and Gaskill [1]. Probably a circumorbital. D. M1689. Potential isolated epipterygoid. C?, circumorbital?; Ep, ectopterygoid; Epi, epipterygoid; Iv, interpterygoid vacuity; Pl, palatine; Ps, parasphenoid. Scale bars = 1mm.
Mentions: Specimen CGH727 preserves a disarticulated palatine (Fig 11A). That element is relatively elongate and narrow, more similar to reconstructions by Carroll and Gaskill [1] than to those of Vallin and Laurin [9]. The vomerine (medial) process of the palatine is robust and projects relatively far medially. The largest denticles on the palatine are located at the base of the maxillary process, posterior to the smooth, U-shaped anterior edge that forms the posterior margin of the choana. Additionally, the disarticulated palatine appears to be in contact with an ectopterygoid, a much shorter and rounder bone. Both elements exhibit a straight lateral margin for contact with the maxilla. The base of an epipterygoid, with the dorsal stem broken and missing, appears to be preserved underneath the ectopterygoid.

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