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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

Palpebral bone and lateral lines in H. longicostatum.Arrows point to lateral line grooves and pits. A. Dorsal view of orbit of NHMW1898_X_23, showing palpebral bone and scleral ossicle impressions; anterior up, lateral to the right. Note lateral line groove on anterior edge of postorbital and crescentic shape of postfrontal. B. Dorsal view of jugal of CGH2028; anterior to the left, lateral up. C. Lateral view of maxilla of CGH3028; anterior to the left, dorsal up. D. Partial left orbital region of CGH16; dorsal view, anterior up, lateral to the left. Fr, frontal; Ju, jugal; Mx, maxilla; Pa, parietal; Pb, palpebral bone; Pof, postfrontal; Scl, scleral ossicles. Scale bars = 1mm.
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pone.0128333.g028: Palpebral bone and lateral lines in H. longicostatum.Arrows point to lateral line grooves and pits. A. Dorsal view of orbit of NHMW1898_X_23, showing palpebral bone and scleral ossicle impressions; anterior up, lateral to the right. Note lateral line groove on anterior edge of postorbital and crescentic shape of postfrontal. B. Dorsal view of jugal of CGH2028; anterior to the left, lateral up. C. Lateral view of maxilla of CGH3028; anterior to the left, dorsal up. D. Partial left orbital region of CGH16; dorsal view, anterior up, lateral to the left. Fr, frontal; Ju, jugal; Mx, maxilla; Pa, parietal; Pb, palpebral bone; Pof, postfrontal; Scl, scleral ossicles. Scale bars = 1mm.

Mentions: The same two scale types described for M. pelikani also are found in H. longicostatum. However, the heavy ridge is not as strongly developed in the latter. No specimens of H. longicostatum have branchial plates, although they were reported in a specimen (now lost) collected from Třemošomá, Czech Republic [55]. Additionally, except for sporadic pitting and fine striae, H. longicostatum lacks sculpture on the dermal roofing elements. Sclerotic plates are present, but a palpebral cup was not identified previously in H. longicostatum. One specimen that I examined, NHMW1898_X_23, has an oval structure preserved within the orbit, but because of poor preservation it is unclear if the structure is a palpebral or a palatal fragment. However, two other specimens have impressions within the orbit that strongly resemble the palpebral impressions preserved in M. pelikani (Fig 28A). Hyloplesion longicostatum previously was reported to lack lateral lines [1], but I observed lateral line canal grooves on the maxillary (anterior) process of the jugal, the prefrontal (anterior) process of the postfrontal, the anterior edge of the postorbital, the lateral margin of the frontal, and the lateral surface of the maxilla (Fig 28A–28D). Moreover, as in M. pelikani, there are distinct pores located on the premaxilla, maxilla, and dentary, which also may connect to the lateral line system.


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

Olori JC - PLoS ONE (2015)

Palpebral bone and lateral lines in H. longicostatum.Arrows point to lateral line grooves and pits. A. Dorsal view of orbit of NHMW1898_X_23, showing palpebral bone and scleral ossicle impressions; anterior up, lateral to the right. Note lateral line groove on anterior edge of postorbital and crescentic shape of postfrontal. B. Dorsal view of jugal of CGH2028; anterior to the left, lateral up. C. Lateral view of maxilla of CGH3028; anterior to the left, dorsal up. D. Partial left orbital region of CGH16; dorsal view, anterior up, lateral to the left. Fr, frontal; Ju, jugal; Mx, maxilla; Pa, parietal; Pb, palpebral bone; Pof, postfrontal; Scl, scleral ossicles. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g028: Palpebral bone and lateral lines in H. longicostatum.Arrows point to lateral line grooves and pits. A. Dorsal view of orbit of NHMW1898_X_23, showing palpebral bone and scleral ossicle impressions; anterior up, lateral to the right. Note lateral line groove on anterior edge of postorbital and crescentic shape of postfrontal. B. Dorsal view of jugal of CGH2028; anterior to the left, lateral up. C. Lateral view of maxilla of CGH3028; anterior to the left, dorsal up. D. Partial left orbital region of CGH16; dorsal view, anterior up, lateral to the left. Fr, frontal; Ju, jugal; Mx, maxilla; Pa, parietal; Pb, palpebral bone; Pof, postfrontal; Scl, scleral ossicles. Scale bars = 1mm.
Mentions: The same two scale types described for M. pelikani also are found in H. longicostatum. However, the heavy ridge is not as strongly developed in the latter. No specimens of H. longicostatum have branchial plates, although they were reported in a specimen (now lost) collected from Třemošomá, Czech Republic [55]. Additionally, except for sporadic pitting and fine striae, H. longicostatum lacks sculpture on the dermal roofing elements. Sclerotic plates are present, but a palpebral cup was not identified previously in H. longicostatum. One specimen that I examined, NHMW1898_X_23, has an oval structure preserved within the orbit, but because of poor preservation it is unclear if the structure is a palpebral or a palatal fragment. However, two other specimens have impressions within the orbit that strongly resemble the palpebral impressions preserved in M. pelikani (Fig 28A). Hyloplesion longicostatum previously was reported to lack lateral lines [1], but I observed lateral line canal grooves on the maxillary (anterior) process of the jugal, the prefrontal (anterior) process of the postfrontal, the anterior edge of the postorbital, the lateral margin of the frontal, and the lateral surface of the maxilla (Fig 28A–28D). Moreover, as in M. pelikani, there are distinct pores located on the premaxilla, maxilla, and dentary, which also may connect to the lateral line system.

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