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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

Lateral lines of M. pelikani.Arrows point to pits and grooves. A. Pits and grooves on paired frontals of NHMW1894-2399 (Naturhistorisches Museum, Vienna, Austria); Impression of dorsal view, anterior up, grooves lateral. B. Pits on premaxilla of CGH3018 (Narodini Museum, (now National Museum Prague), Prague, Czech Republic); Impression of anterior view (3D caused by lighting), teeth denote ventral surface, medial down. C. Pits on maxilla and dentary of NHMW1983_32_49; Impression of lateral view (3D caused by lighting), anterior to the right, dorsal up. D. Groove on articular of CGH5; lateral view of bone, anterior to the right, dorsal up. Scale bars = 1mm.
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pone.0128333.g004: Lateral lines of M. pelikani.Arrows point to pits and grooves. A. Pits and grooves on paired frontals of NHMW1894-2399 (Naturhistorisches Museum, Vienna, Austria); Impression of dorsal view, anterior up, grooves lateral. B. Pits on premaxilla of CGH3018 (Narodini Museum, (now National Museum Prague), Prague, Czech Republic); Impression of anterior view (3D caused by lighting), teeth denote ventral surface, medial down. C. Pits on maxilla and dentary of NHMW1983_32_49; Impression of lateral view (3D caused by lighting), anterior to the right, dorsal up. D. Groove on articular of CGH5; lateral view of bone, anterior to the right, dorsal up. Scale bars = 1mm.

Mentions: Traces of lateral lines were present in all specimens of M. pelikani examined, suggesting that the system is retained throughout ontogeny. However, previous descriptions of the lateral lines as a clear ‘lyre pattern’ resembling that of temnospondyls [1] are exaggerated. Especially in the larger individuals in which sculpture patterns are rough, evidence for lateral lines may occur only as pits rather than deep grooves. In a few cases, even the pits are visible only along the lateral edge of the frontal where that bone contacts the prefrontal and postfrontal. Usually, however, as described by Carroll and Gaskill [1], the pits are contained within a shallow groove and are present on the lacrimal, frontal, prefrontal, postfrontal, jugal, postorbital, articular, and dentary. In addition, I observed well developed clusters and lines of small foramina along the premaxilla and maxilla, respectively, which are probably sensory canals and possibly connected to the lateral line system, although Carroll and Gaskill [1] suggested that these bones did not contain lateral line receptors. I did not observe any pits or grooves on the quadratojugal or squamosal, although such structures were reported previously [1]. Therefore, it appears that the lateral line system was restricted to a ring around the orbit and continued for a short distance posteriorly along the medial margin of the jugal, the lateral surface of the dentary and articular, and as small sensory pits along the maxilla and premaxilla (Fig 4).


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

Olori JC - PLoS ONE (2015)

Lateral lines of M. pelikani.Arrows point to pits and grooves. A. Pits and grooves on paired frontals of NHMW1894-2399 (Naturhistorisches Museum, Vienna, Austria); Impression of dorsal view, anterior up, grooves lateral. B. Pits on premaxilla of CGH3018 (Narodini Museum, (now National Museum Prague), Prague, Czech Republic); Impression of anterior view (3D caused by lighting), teeth denote ventral surface, medial down. C. Pits on maxilla and dentary of NHMW1983_32_49; Impression of lateral view (3D caused by lighting), anterior to the right, dorsal up. D. Groove on articular of CGH5; lateral view of bone, anterior to the right, dorsal up. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g004: Lateral lines of M. pelikani.Arrows point to pits and grooves. A. Pits and grooves on paired frontals of NHMW1894-2399 (Naturhistorisches Museum, Vienna, Austria); Impression of dorsal view, anterior up, grooves lateral. B. Pits on premaxilla of CGH3018 (Narodini Museum, (now National Museum Prague), Prague, Czech Republic); Impression of anterior view (3D caused by lighting), teeth denote ventral surface, medial down. C. Pits on maxilla and dentary of NHMW1983_32_49; Impression of lateral view (3D caused by lighting), anterior to the right, dorsal up. D. Groove on articular of CGH5; lateral view of bone, anterior to the right, dorsal up. Scale bars = 1mm.
Mentions: Traces of lateral lines were present in all specimens of M. pelikani examined, suggesting that the system is retained throughout ontogeny. However, previous descriptions of the lateral lines as a clear ‘lyre pattern’ resembling that of temnospondyls [1] are exaggerated. Especially in the larger individuals in which sculpture patterns are rough, evidence for lateral lines may occur only as pits rather than deep grooves. In a few cases, even the pits are visible only along the lateral edge of the frontal where that bone contacts the prefrontal and postfrontal. Usually, however, as described by Carroll and Gaskill [1], the pits are contained within a shallow groove and are present on the lacrimal, frontal, prefrontal, postfrontal, jugal, postorbital, articular, and dentary. In addition, I observed well developed clusters and lines of small foramina along the premaxilla and maxilla, respectively, which are probably sensory canals and possibly connected to the lateral line system, although Carroll and Gaskill [1] suggested that these bones did not contain lateral line receptors. I did not observe any pits or grooves on the quadratojugal or squamosal, although such structures were reported previously [1]. Therefore, it appears that the lateral line system was restricted to a ring around the orbit and continued for a short distance posteriorly along the medial margin of the jugal, the lateral surface of the dentary and articular, and as small sensory pits along the maxilla and premaxilla (Fig 4).

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