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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

Ontogenetic changes in the ulna of M. pelikani.A. Stage 1, NHMW1983_32_66; proximal toward left. B. Stage 2, R.2814; proximal toward bottom right. C. Stage 3, NHMW1894-2399; proximal toward top left. D. Stage 4, AMNH2557; proximal toward bottom right. Hum, humerus; Int, intermedium; Olc, olecranon process; Rad, radius; Uln, ulna. Scale bars = 1mm.
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pone.0128333.g020: Ontogenetic changes in the ulna of M. pelikani.A. Stage 1, NHMW1983_32_66; proximal toward left. B. Stage 2, R.2814; proximal toward bottom right. C. Stage 3, NHMW1894-2399; proximal toward top left. D. Stage 4, AMNH2557; proximal toward bottom right. Hum, humerus; Int, intermedium; Olc, olecranon process; Rad, radius; Uln, ulna. Scale bars = 1mm.

Mentions: Early in ontogeny, the ulna of M. pelikani also starts out undifferentiated, although the proximal end of the element is always at least slightly broader than the distal end (Fig 20A). As growth increases, the proximal end becomes much broader than the distal end (Fig 20B). Despite a contrary report [1], the olecranon process becomes ossified during ontogeny. Preliminary development of that process is manifest as a medial slant in the proximal surface of the ulna (Fig 20C). As the olecranon process becomes more developed, the rounded, high portion that articulates with the lateral surface of the humerus becomes distinct from the level surface of the proximal end of the ulna (Fig 20D). A well-developed intermedial facet does not appear to form in M. pelikani, but an ulnare facet may be partially developed in NHMW1894_2399, which also exhibits a partially developed olecranon process.


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

Olori JC - PLoS ONE (2015)

Ontogenetic changes in the ulna of M. pelikani.A. Stage 1, NHMW1983_32_66; proximal toward left. B. Stage 2, R.2814; proximal toward bottom right. C. Stage 3, NHMW1894-2399; proximal toward top left. D. Stage 4, AMNH2557; proximal toward bottom right. Hum, humerus; Int, intermedium; Olc, olecranon process; Rad, radius; Uln, ulna. Scale bars = 1mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0128333.g020: Ontogenetic changes in the ulna of M. pelikani.A. Stage 1, NHMW1983_32_66; proximal toward left. B. Stage 2, R.2814; proximal toward bottom right. C. Stage 3, NHMW1894-2399; proximal toward top left. D. Stage 4, AMNH2557; proximal toward bottom right. Hum, humerus; Int, intermedium; Olc, olecranon process; Rad, radius; Uln, ulna. Scale bars = 1mm.
Mentions: Early in ontogeny, the ulna of M. pelikani also starts out undifferentiated, although the proximal end of the element is always at least slightly broader than the distal end (Fig 20A). As growth increases, the proximal end becomes much broader than the distal end (Fig 20B). Despite a contrary report [1], the olecranon process becomes ossified during ontogeny. Preliminary development of that process is manifest as a medial slant in the proximal surface of the ulna (Fig 20C). As the olecranon process becomes more developed, the rounded, high portion that articulates with the lateral surface of the humerus becomes distinct from the level surface of the proximal end of the ulna (Fig 20D). A well-developed intermedial facet does not appear to form in M. pelikani, but an ulnare facet may be partially developed in NHMW1894_2399, which also exhibits a partially developed olecranon process.

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