R absent in their relatives that do exhibit paedomorphic features [36].PLOS

May 15, 2018

R absent in their relatives that do exhibit paedomorphic features [36].PLOS ONE | DOI:10.1371/journal.pone.0128333 June 17,58 /Skeletal Morphogenesis of Microbrachis and HyloplesionThe completion of postcranial development in early tetrapods such as Greererpeton, Eryops, and basal synapsids leads to relatively strongly developed limbs and girdles [36,51,57]. A mature humerus, for example, has a strongly developed deltopectoral qhw.v5i4.5120 crest, MGCD516 custom synthesis supinator processes, and capitellum (swollen, radial purchase Cycloheximide condyles). Those features are also evident in the welldeveloped humerus of Pantylus, one of the largest lepospondyls [1]. In the most mature H. longicostatum and M. pelikani, however, the supinator process is absent and the deltopectoral crest and radial condyle are developed only moderately. It may be the case that even more mature specimens of these two taxa have not yet been discovered. However, based on current data about the morphology of the humerus and other appendicular elements, and the relatively small size of adults, it is likely that the limbs of H. longicostatum and M. pelikani are paedomorphic relative to those of many basal tetrapods, stem amniotes, large temnospondyls, and large lepospondyls. Importantly, paedomorphosis may not affect all features of an element equally. In Greererpeton, for example, even though crests and tuberosities are strongly developed, adults do not exhibit humeral torsion greater than about 30?[36]. Torsion often increases with growth in temnospondyls and other early tetrapods, and in H. longicostatum and M. pelikani, in which adult torsion approaches 90? levels around 30?are observed only in the least mature specimens. A standard pnas.1408988111 feature of vertebral development in Greererpeton, temnospondyls, and stem amniotes, is the development of the centrum from multipartite elements and the appearance of the neural arches well before the centrum [36,51,58]. Contrary to that pattern, the early and synchronous appearance of the arches and centra in M. pelikani and H. longicostatum, as well as the unipartite centrum, is characteristic of lepospondyls [58]. In earlier growth stages the neural arch halves may initially be present as sutured, paired elements, but the centra always are a single entity. Although previously H. longicostatum was reported to exhibit ossification of the centra prior to the arches [59], no evidence for that pattern exists because even in the smallest individuals known, arches and centra are already ossified [16]. Despite the discovery of extremely small individuals of some lepospondyls taxa (e.g., CGH3), only Utaherpeton provides any evidence of incomplete vertebrae in basal lepospondyls [13]. In that taxon, an immature specimen has trunk centra that may not have been completely ossified dorsally, as well as potentially paired pleurocentra in the posterior tail. Additionally, although that juvenile has a bifurcated ilium, which is observed only in relatively mature M. pelikani and H. longicostatum individuals, the pubis is unossified. Carroll and Chorn [13] suggested a morphogenetic sequence of a fimbriated to smooth interclavicle in Utaherpeton, which differs from the situation in M. pelikani in which even the largest individuals display fimbriation. That change in Utaherpeton also is unanticipated considering that the interclavicle is dermal in origin and dermal bone does not usually show major morphogenetic changes ([36]; this study).Inconsistent MorphogenesisResults from earlier work on temnospondyls.R absent in their relatives that do exhibit paedomorphic features [36].PLOS ONE | DOI:10.1371/journal.pone.0128333 June 17,58 /Skeletal Morphogenesis of Microbrachis and HyloplesionThe completion of postcranial development in early tetrapods such as Greererpeton, Eryops, and basal synapsids leads to relatively strongly developed limbs and girdles [36,51,57]. A mature humerus, for example, has a strongly developed deltopectoral qhw.v5i4.5120 crest, supinator processes, and capitellum (swollen, radial condyles). Those features are also evident in the welldeveloped humerus of Pantylus, one of the largest lepospondyls [1]. In the most mature H. longicostatum and M. pelikani, however, the supinator process is absent and the deltopectoral crest and radial condyle are developed only moderately. It may be the case that even more mature specimens of these two taxa have not yet been discovered. However, based on current data about the morphology of the humerus and other appendicular elements, and the relatively small size of adults, it is likely that the limbs of H. longicostatum and M. pelikani are paedomorphic relative to those of many basal tetrapods, stem amniotes, large temnospondyls, and large lepospondyls. Importantly, paedomorphosis may not affect all features of an element equally. In Greererpeton, for example, even though crests and tuberosities are strongly developed, adults do not exhibit humeral torsion greater than about 30?[36]. Torsion often increases with growth in temnospondyls and other early tetrapods, and in H. longicostatum and M. pelikani, in which adult torsion approaches 90? levels around 30?are observed only in the least mature specimens. A standard pnas.1408988111 feature of vertebral development in Greererpeton, temnospondyls, and stem amniotes, is the development of the centrum from multipartite elements and the appearance of the neural arches well before the centrum [36,51,58]. Contrary to that pattern, the early and synchronous appearance of the arches and centra in M. pelikani and H. longicostatum, as well as the unipartite centrum, is characteristic of lepospondyls [58]. In earlier growth stages the neural arch halves may initially be present as sutured, paired elements, but the centra always are a single entity. Although previously H. longicostatum was reported to exhibit ossification of the centra prior to the arches [59], no evidence for that pattern exists because even in the smallest individuals known, arches and centra are already ossified [16]. Despite the discovery of extremely small individuals of some lepospondyls taxa (e.g., CGH3), only Utaherpeton provides any evidence of incomplete vertebrae in basal lepospondyls [13]. In that taxon, an immature specimen has trunk centra that may not have been completely ossified dorsally, as well as potentially paired pleurocentra in the posterior tail. Additionally, although that juvenile has a bifurcated ilium, which is observed only in relatively mature M. pelikani and H. longicostatum individuals, the pubis is unossified. Carroll and Chorn [13] suggested a morphogenetic sequence of a fimbriated to smooth interclavicle in Utaherpeton, which differs from the situation in M. pelikani in which even the largest individuals display fimbriation. That change in Utaherpeton also is unanticipated considering that the interclavicle is dermal in origin and dermal bone does not usually show major morphogenetic changes ([36]; this study).Inconsistent MorphogenesisResults from earlier work on temnospondyls.