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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

Dermal ossifications of M. pelikani.A. Scleral ossicles of M3322 (National Museum Prague, (previously Narodini Museum), Prague, Czech Republic); arrow points to single ossicle. B. Palpebral bones and scleral ossicles; arrows points to palpebral bones. Scale bars = 1mm.
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pone.0128333.g002: Dermal ossifications of M. pelikani.A. Scleral ossicles of M3322 (National Museum Prague, (previously Narodini Museum), Prague, Czech Republic); arrow points to single ossicle. B. Palpebral bones and scleral ossicles; arrows points to palpebral bones. Scale bars = 1mm.

Mentions: Bony scleral ossicles and palpebral elements are present in M. pelikani. The scleral ossicles are fragile or weakly ossified because, even though they are present in individuals spanning the full size range known for M. pelikani, they are preserved only rarely [16]. The scleral ossicles are rectangular and form a ring inside the orbit [1]. I never observed a complete ring, but one specimen (M3322; National Museum Prague, (previously Narodini Museum), Prague, Czech Republic) possesses 11 ossicles in semi-articulation (Fig 2A). The ‘palpebral cup’ also was described by Carroll and Gaskill [1], although only from impressions, and the element was reported to be round and convex. In one individual (M3322), however, the palpebral is preserved in bone and shown to be a relatively robust element of oblong shape (Fig 2B), much more like the palpebrals described in other lepospondyls [1]. The palpebral exhibits sculpture similar to that of the dermal roofing elements (see below) and usually is found in a position dorsal to or overlying the scleral ossicles, suggesting that it forms within the eyelid, as in some living crocodilians and lizards. Clear preservation of the palpebral is even less common than for the scleral ossicles.


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

Olori JC - PLoS ONE (2015)

Dermal ossifications of M. pelikani.A. Scleral ossicles of M3322 (National Museum Prague, (previously Narodini Museum), Prague, Czech Republic); arrow points to single ossicle. B. Palpebral bones and scleral ossicles; arrows points to palpebral bones. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g002: Dermal ossifications of M. pelikani.A. Scleral ossicles of M3322 (National Museum Prague, (previously Narodini Museum), Prague, Czech Republic); arrow points to single ossicle. B. Palpebral bones and scleral ossicles; arrows points to palpebral bones. Scale bars = 1mm.
Mentions: Bony scleral ossicles and palpebral elements are present in M. pelikani. The scleral ossicles are fragile or weakly ossified because, even though they are present in individuals spanning the full size range known for M. pelikani, they are preserved only rarely [16]. The scleral ossicles are rectangular and form a ring inside the orbit [1]. I never observed a complete ring, but one specimen (M3322; National Museum Prague, (previously Narodini Museum), Prague, Czech Republic) possesses 11 ossicles in semi-articulation (Fig 2A). The ‘palpebral cup’ also was described by Carroll and Gaskill [1], although only from impressions, and the element was reported to be round and convex. In one individual (M3322), however, the palpebral is preserved in bone and shown to be a relatively robust element of oblong shape (Fig 2B), much more like the palpebrals described in other lepospondyls [1]. The palpebral exhibits sculpture similar to that of the dermal roofing elements (see below) and usually is found in a position dorsal to or overlying the scleral ossicles, suggesting that it forms within the eyelid, as in some living crocodilians and lizards. Clear preservation of the palpebral is even less common than for the scleral ossicles.

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