Limits...
Micro-CT Study of Rhynchonkos stovalli (Lepospondyli, Recumbirostra), with Description of Two New Genera.

Szostakiwskyj M, Pardo JD, Anderson JS - PLoS ONE (2015)

Bottom Line: We revisit the homology of the supraoccipital, median anterior bone, and temporal bone of recumbirostrans, and discuss implications of alternate interpretations of the homology of these elements.Finally, we evaluate the characteristics previously used to unite Rhynchonkos stovalli with caecilians in light of these new data.These proposed similarities are more ambiguous than previous descriptions suggest, and result from the composite nature of previous descriptions, ambiguities in external morphology, and functional convergence between recumbirostrans and caecilians for head-first burrowing.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.

ABSTRACT
The Early Permian recumbirostran lepospondyl Rhynchonkos stovalli has been identified as a possible close relative of caecilians due to general similarities in skull shape as well as similar robustness of the braincase, a hypothesis that implies the polyphyly of extant lissamphibians. In order to better assess this phylogenetic hypothesis, we studied the morphology of the holotype and three specimens previously attributed to R. stovalli. With the use of micro-computed x-ray tomography (μCT) we are able to completely describe the external and internal cranial morphology of these specimens, dramatically revising our knowledge of R. stovalli and recognizing two new taxa, Aletrimyti gaskillae gen et sp. n. and Dvellacanus carrolli gen et sp. n. The braincases of R. stovalli, A. gaskillae, and D. carrolli are described in detail, demonstrating detailed braincase morphology and new information on the recumbirostran supraoccipital bone. All three taxa show fossorial adaptations in the braincase, sutural articulations of skull roof bones, and in the lower jaw, but variation in cranial morphology between these three taxa may reflect different modes of head-first burrowing behaviors and capabilities. We revisit the homology of the supraoccipital, median anterior bone, and temporal bone of recumbirostrans, and discuss implications of alternate interpretations of the homology of these elements. Finally, we evaluate the characteristics previously used to unite Rhynchonkos stovalli with caecilians in light of these new data. These proposed similarities are more ambiguous than previous descriptions suggest, and result from the composite nature of previous descriptions, ambiguities in external morphology, and functional convergence between recumbirostrans and caecilians for head-first burrowing.

No MeSH data available.


Related in: MedlinePlus

Isolated elements of the right otic capsule of Dvellecanus carrolli, gen. et sp. nov. (UCMP 202940).Scan (A) and interpretive line drawing (B) in ventromedial oblique view, with the anterior oriented to the left. Surrounding braincase elements have been removed to expose the otic capsule. Scale bar equals 1mm. Abbreviations: ant semi, groove for the anterior semicircular canal; cr inf, crista interfenestralis; fen vest, fenestra vestibuli; hor semi, groove for the horizontal semicircular canal; lag cr, lagenar crest; lag rec, lagenar recess; opi, opisthotic; pro, prootic; rec scala tymp, recessus scala tympani; V, fenestra prootica; X, foramen for the vagus nerve and jugular vein.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4465623&req=5

pone.0127307.g013: Isolated elements of the right otic capsule of Dvellecanus carrolli, gen. et sp. nov. (UCMP 202940).Scan (A) and interpretive line drawing (B) in ventromedial oblique view, with the anterior oriented to the left. Surrounding braincase elements have been removed to expose the otic capsule. Scale bar equals 1mm. Abbreviations: ant semi, groove for the anterior semicircular canal; cr inf, crista interfenestralis; fen vest, fenestra vestibuli; hor semi, groove for the horizontal semicircular canal; lag cr, lagenar crest; lag rec, lagenar recess; opi, opisthotic; pro, prootic; rec scala tymp, recessus scala tympani; V, fenestra prootica; X, foramen for the vagus nerve and jugular vein.

Mentions: The otic capsules are composed of a distinct anterior prootic and posterior opisthotic, with the opisthotic slightly larger than the prootic (Fig 13A and 13B). The otic capsules are large, spanning the length of the basal plate of the parasphenoid and together occupying over two-thirds the width of the skull. Only the opisthotic reaches the dermatocranium; the prootic is separated from the skull roof by the dorsal sinus. The only point of articulation between the otic capsule and the parasphenoid is a small contact at the anteroventral margin of the otic capsule. Posteriorly the otic capsule is firmly sutured to the occipital complex. The otic capsule is arched where it encloses the fenestra vestibuli. It has a ventrally deflected anterior surface that reaches the parasphenoid lateral to the pleurosphenoid and forms the lateral margin of the fenestra prootica. On the dorsal margin of the otic capsules is a medially oriented shelf that reaches the lateral processes of the supraoccipital. Ventral to this shelf is a space for the horizontal semicircular canal that spans the length of the otic capsules, and ventral to the semicircular canal is the fenestra vestibuli. In dorsal view the otic capsules are medially flat and laterally rounded.


Micro-CT Study of Rhynchonkos stovalli (Lepospondyli, Recumbirostra), with Description of Two New Genera.

Szostakiwskyj M, Pardo JD, Anderson JS - PLoS ONE (2015)

Isolated elements of the right otic capsule of Dvellecanus carrolli, gen. et sp. nov. (UCMP 202940).Scan (A) and interpretive line drawing (B) in ventromedial oblique view, with the anterior oriented to the left. Surrounding braincase elements have been removed to expose the otic capsule. Scale bar equals 1mm. Abbreviations: ant semi, groove for the anterior semicircular canal; cr inf, crista interfenestralis; fen vest, fenestra vestibuli; hor semi, groove for the horizontal semicircular canal; lag cr, lagenar crest; lag rec, lagenar recess; opi, opisthotic; pro, prootic; rec scala tymp, recessus scala tympani; V, fenestra prootica; X, foramen for the vagus nerve and jugular vein.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4465623&req=5

pone.0127307.g013: Isolated elements of the right otic capsule of Dvellecanus carrolli, gen. et sp. nov. (UCMP 202940).Scan (A) and interpretive line drawing (B) in ventromedial oblique view, with the anterior oriented to the left. Surrounding braincase elements have been removed to expose the otic capsule. Scale bar equals 1mm. Abbreviations: ant semi, groove for the anterior semicircular canal; cr inf, crista interfenestralis; fen vest, fenestra vestibuli; hor semi, groove for the horizontal semicircular canal; lag cr, lagenar crest; lag rec, lagenar recess; opi, opisthotic; pro, prootic; rec scala tymp, recessus scala tympani; V, fenestra prootica; X, foramen for the vagus nerve and jugular vein.
Mentions: The otic capsules are composed of a distinct anterior prootic and posterior opisthotic, with the opisthotic slightly larger than the prootic (Fig 13A and 13B). The otic capsules are large, spanning the length of the basal plate of the parasphenoid and together occupying over two-thirds the width of the skull. Only the opisthotic reaches the dermatocranium; the prootic is separated from the skull roof by the dorsal sinus. The only point of articulation between the otic capsule and the parasphenoid is a small contact at the anteroventral margin of the otic capsule. Posteriorly the otic capsule is firmly sutured to the occipital complex. The otic capsule is arched where it encloses the fenestra vestibuli. It has a ventrally deflected anterior surface that reaches the parasphenoid lateral to the pleurosphenoid and forms the lateral margin of the fenestra prootica. On the dorsal margin of the otic capsules is a medially oriented shelf that reaches the lateral processes of the supraoccipital. Ventral to this shelf is a space for the horizontal semicircular canal that spans the length of the otic capsules, and ventral to the semicircular canal is the fenestra vestibuli. In dorsal view the otic capsules are medially flat and laterally rounded.

Bottom Line: We revisit the homology of the supraoccipital, median anterior bone, and temporal bone of recumbirostrans, and discuss implications of alternate interpretations of the homology of these elements.Finally, we evaluate the characteristics previously used to unite Rhynchonkos stovalli with caecilians in light of these new data.These proposed similarities are more ambiguous than previous descriptions suggest, and result from the composite nature of previous descriptions, ambiguities in external morphology, and functional convergence between recumbirostrans and caecilians for head-first burrowing.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.

ABSTRACT
The Early Permian recumbirostran lepospondyl Rhynchonkos stovalli has been identified as a possible close relative of caecilians due to general similarities in skull shape as well as similar robustness of the braincase, a hypothesis that implies the polyphyly of extant lissamphibians. In order to better assess this phylogenetic hypothesis, we studied the morphology of the holotype and three specimens previously attributed to R. stovalli. With the use of micro-computed x-ray tomography (μCT) we are able to completely describe the external and internal cranial morphology of these specimens, dramatically revising our knowledge of R. stovalli and recognizing two new taxa, Aletrimyti gaskillae gen et sp. n. and Dvellacanus carrolli gen et sp. n. The braincases of R. stovalli, A. gaskillae, and D. carrolli are described in detail, demonstrating detailed braincase morphology and new information on the recumbirostran supraoccipital bone. All three taxa show fossorial adaptations in the braincase, sutural articulations of skull roof bones, and in the lower jaw, but variation in cranial morphology between these three taxa may reflect different modes of head-first burrowing behaviors and capabilities. We revisit the homology of the supraoccipital, median anterior bone, and temporal bone of recumbirostrans, and discuss implications of alternate interpretations of the homology of these elements. Finally, we evaluate the characteristics previously used to unite Rhynchonkos stovalli with caecilians in light of these new data. These proposed similarities are more ambiguous than previous descriptions suggest, and result from the composite nature of previous descriptions, ambiguities in external morphology, and functional convergence between recumbirostrans and caecilians for head-first burrowing.

No MeSH data available.


Related in: MedlinePlus