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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

Vertebral elements, M. pelikani.A. St.193, vertebra showing tall neural arch pedicel; anterior to the right, dorsal up. B. AMNH2557 (American Museum of Natural History, New York, New York), dorsal view of neural arch showing anterolaterally directed transverse processes; anterior up. C. M3322, sagittal section through centrum; anterior to the left. D. St.207, anterior section through vertebrae. E. CGH256, medial view of neural arch half; anterior to left, dorsal up. Cn, centrum; Cp, capitulum of rib; Ivc, intervertebral cartilage region; Nap, neural arch pedicel; Nc, neural crest; Poz, postzygopophysis; Prz, prezygapophysis; Tvp, transverse process. Scale bars = 1mm.
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pone.0128333.g015: Vertebral elements, M. pelikani.A. St.193, vertebra showing tall neural arch pedicel; anterior to the right, dorsal up. B. AMNH2557 (American Museum of Natural History, New York, New York), dorsal view of neural arch showing anterolaterally directed transverse processes; anterior up. C. M3322, sagittal section through centrum; anterior to the left. D. St.207, anterior section through vertebrae. E. CGH256, medial view of neural arch half; anterior to left, dorsal up. Cn, centrum; Cp, capitulum of rib; Ivc, intervertebral cartilage region; Nap, neural arch pedicel; Nc, neural crest; Poz, postzygopophysis; Prz, prezygapophysis; Tvp, transverse process. Scale bars = 1mm.

Mentions: No uncinate processes were present on the ribs of any M. pelikani, contra reports by Carroll and Gaskill [1]; prior descriptions are otherwise accurate. Changes over ontogeny were not observed, but in most cases the heads of the ribs were obscured either by matrix or their articulation with the vertebrae. Nearly all complete specimens of M. pelikani that I examined possess 38 presacral vertebrae. Only four specimens show variation by possession of 39 presacral vertebrae, although counts were difficult in those individuals. The large number of vertebrae is diagnostic for M. pelikani relative to other ‘microsaurian’ lepospondyls present in Nýřany, such as H. longicostatum (see below), Sparodus, Ricnodon, and Crinodon. The angle of the incline of the neural arch is usually between 5 and 15 degrees, although it may reach 20 degrees in some individuals. In smaller specimens, the arches are relatively high, with a narrow neural arch pedicel (Fig 15A). The base is relatively wider in larger specimens, but the pedicels do not exceed the anterior two-thirds of the centrum in length. The location of the contact was mistakenly described as on the posterior portion of the centrum, but was figured accurately by Carroll and Gaskill ([1] reference figure 81A,D). The transverse processes of M. pelikani are deflected anterolaterally (Fig 15B), as in most other ‘microsaurian’ lepospondyls [1], but unlike the condition in many other tetrapods.


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

Olori JC - PLoS ONE (2015)

Vertebral elements, M. pelikani.A. St.193, vertebra showing tall neural arch pedicel; anterior to the right, dorsal up. B. AMNH2557 (American Museum of Natural History, New York, New York), dorsal view of neural arch showing anterolaterally directed transverse processes; anterior up. C. M3322, sagittal section through centrum; anterior to the left. D. St.207, anterior section through vertebrae. E. CGH256, medial view of neural arch half; anterior to left, dorsal up. Cn, centrum; Cp, capitulum of rib; Ivc, intervertebral cartilage region; Nap, neural arch pedicel; Nc, neural crest; Poz, postzygopophysis; Prz, prezygapophysis; Tvp, transverse process. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g015: Vertebral elements, M. pelikani.A. St.193, vertebra showing tall neural arch pedicel; anterior to the right, dorsal up. B. AMNH2557 (American Museum of Natural History, New York, New York), dorsal view of neural arch showing anterolaterally directed transverse processes; anterior up. C. M3322, sagittal section through centrum; anterior to the left. D. St.207, anterior section through vertebrae. E. CGH256, medial view of neural arch half; anterior to left, dorsal up. Cn, centrum; Cp, capitulum of rib; Ivc, intervertebral cartilage region; Nap, neural arch pedicel; Nc, neural crest; Poz, postzygopophysis; Prz, prezygapophysis; Tvp, transverse process. Scale bars = 1mm.
Mentions: No uncinate processes were present on the ribs of any M. pelikani, contra reports by Carroll and Gaskill [1]; prior descriptions are otherwise accurate. Changes over ontogeny were not observed, but in most cases the heads of the ribs were obscured either by matrix or their articulation with the vertebrae. Nearly all complete specimens of M. pelikani that I examined possess 38 presacral vertebrae. Only four specimens show variation by possession of 39 presacral vertebrae, although counts were difficult in those individuals. The large number of vertebrae is diagnostic for M. pelikani relative to other ‘microsaurian’ lepospondyls present in Nýřany, such as H. longicostatum (see below), Sparodus, Ricnodon, and Crinodon. The angle of the incline of the neural arch is usually between 5 and 15 degrees, although it may reach 20 degrees in some individuals. In smaller specimens, the arches are relatively high, with a narrow neural arch pedicel (Fig 15A). The base is relatively wider in larger specimens, but the pedicels do not exceed the anterior two-thirds of the centrum in length. The location of the contact was mistakenly described as on the posterior portion of the centrum, but was figured accurately by Carroll and Gaskill ([1] reference figure 81A,D). The transverse processes of M. pelikani are deflected anterolaterally (Fig 15B), as in most other ‘microsaurian’ lepospondyls [1], but unlike the condition in many other tetrapods.

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