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A nomenclature for vertebral fossae in sauropods and other saurischian dinosaurs.

Wilson JA, D'Emic MD, Ikejiri T, Moacdieh EM, Whitlock JA - PLoS ONE (2011)

Bottom Line: We standardize the naming process by creating tripartite names from "primary landmarks," which form the zygodiapophyseal table, "secondary landmarks," which orient with respect to that table, and "tertiary landmarks," which further delineate a given fossa.The proposed nomenclatural system for lamina-bounded fossae adds clarity to descriptions of complex vertebrae and allows these structures to be sourced as character data for phylogenetic analyses.These anatomical terms denote potentially homologous pneumatic structures within Saurischia, but they could be applied to any vertebrate with vertebral laminae that enclose spaces, regardless of their developmental origin or phylogenetic distribution.

View Article: PubMed Central - PubMed

Affiliation: Museum of Paleontology and Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, United States of America. wilsonja@umich.edu

ABSTRACT

Background: The axial skeleton of extinct saurischian dinosaurs (i.e., theropods, sauropodomorphs), like living birds, was pneumatized by epithelial outpocketings of the respiratory system. Pneumatic signatures in the vertebral column of fossil saurischians include complex branching chambers within the bone (internal pneumaticity) and large chambers visible externally that are bounded by neural arch laminae (external pneumaticity). Although general aspects of internal pneumaticity are synapomorphic for saurischian subgroups, the individual internal pneumatic spaces cannot be homologized across species or even along the vertebral column, due to their variability and absence of topographical landmarks. External pneumatic structures, in contrast, are defined by ready topological landmarks (vertebral laminae), but no consistent nomenclatural system exists. This deficiency has fostered confusion and limited their use as character data in phylogenetic analysis.

Methodology/principal findings: We present a simple system for naming external neural arch fossae that parallels the one developed for the vertebral laminae that bound them. The nomenclatural system identifies fossae by pointing to reference landmarks (e.g., neural spine, centrum, costal articulations, zygapophyses). We standardize the naming process by creating tripartite names from "primary landmarks," which form the zygodiapophyseal table, "secondary landmarks," which orient with respect to that table, and "tertiary landmarks," which further delineate a given fossa.

Conclusions/significance: The proposed nomenclatural system for lamina-bounded fossae adds clarity to descriptions of complex vertebrae and allows these structures to be sourced as character data for phylogenetic analyses. These anatomical terms denote potentially homologous pneumatic structures within Saurischia, but they could be applied to any vertebrate with vertebral laminae that enclose spaces, regardless of their developmental origin or phylogenetic distribution.

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Vertebral fossae in the sauropod dinosaur Rapetosaurus krausei.Vertebral fossae in sauropods are hypothesized to be produced by pneumaticity, which is usually limited to the axial column, excluding the atlas, chevrons, and distal caudal vertebrae (bottom image). The middle photograph shows fossae in a cervical vertebra, which in the neural arch are bounded by vertebral laminae. The close-up photograph (top) shows the that bone texture within the fossa is often smooth, crenulated, and shiny, which is indicative of pneumatic bone. Silhouette reconstruction from [49]; cervical vertebra from [59]:fig. 10). Scale bar equals 1 m in silhouette; scale bars equal 3 cm in photographs. ©Copyright 2009 The Society of Vertebrate Paleontology. Reprinted and distributed with permission of the Society of Vertebrate Paleontology.
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pone-0017114-g001: Vertebral fossae in the sauropod dinosaur Rapetosaurus krausei.Vertebral fossae in sauropods are hypothesized to be produced by pneumaticity, which is usually limited to the axial column, excluding the atlas, chevrons, and distal caudal vertebrae (bottom image). The middle photograph shows fossae in a cervical vertebra, which in the neural arch are bounded by vertebral laminae. The close-up photograph (top) shows the that bone texture within the fossa is often smooth, crenulated, and shiny, which is indicative of pneumatic bone. Silhouette reconstruction from [49]; cervical vertebra from [59]:fig. 10). Scale bar equals 1 m in silhouette; scale bars equal 3 cm in photographs. ©Copyright 2009 The Society of Vertebrate Paleontology. Reprinted and distributed with permission of the Society of Vertebrate Paleontology.

Mentions: Among non-volant ornithodirans, axial pneumaticity is perhaps best developed in sauropod dinosaurs, in which pneumatic diverticulae leave their traces in postatlantal vertebrae and ribs, but apparently not chevrons (Fig. 1). Axial pneumaticity can take the form of deep and sometimes complex invasion of internal bone, or in the form of spaces enclosed by bony laminae connecting the processes projecting from the neural arch. The former, which we refer to as “internal pneumaticity,” displays variation that appears to characterize sauropod subgroups [7] and has important implications for sauropod paleobiology [8]. Internal pneumatic structures are typically not bounded by landmarks, however, and it is very difficult to homologize individual pneumatic spaces between vertebrae or between species. Neural arch fossae, on the other hand, are typically bounded by vertebral laminae and easily homologized within and between taxa. These structures display important phylogenetic variation that has not been extensively sampled thus far. We provide a practical nomenclature for lamina-bounded fossae that takes advantage of conventions and landmarks used in existing nomenclature for vertebral laminae [9]. The nomenclature for lamina-bounded fossae is designed to facilitate their use in comparative anatomy and phylogenetic analysis.


A nomenclature for vertebral fossae in sauropods and other saurischian dinosaurs.

Wilson JA, D'Emic MD, Ikejiri T, Moacdieh EM, Whitlock JA - PLoS ONE (2011)

Vertebral fossae in the sauropod dinosaur Rapetosaurus krausei.Vertebral fossae in sauropods are hypothesized to be produced by pneumaticity, which is usually limited to the axial column, excluding the atlas, chevrons, and distal caudal vertebrae (bottom image). The middle photograph shows fossae in a cervical vertebra, which in the neural arch are bounded by vertebral laminae. The close-up photograph (top) shows the that bone texture within the fossa is often smooth, crenulated, and shiny, which is indicative of pneumatic bone. Silhouette reconstruction from [49]; cervical vertebra from [59]:fig. 10). Scale bar equals 1 m in silhouette; scale bars equal 3 cm in photographs. ©Copyright 2009 The Society of Vertebrate Paleontology. Reprinted and distributed with permission of the Society of Vertebrate Paleontology.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3046170&req=5

pone-0017114-g001: Vertebral fossae in the sauropod dinosaur Rapetosaurus krausei.Vertebral fossae in sauropods are hypothesized to be produced by pneumaticity, which is usually limited to the axial column, excluding the atlas, chevrons, and distal caudal vertebrae (bottom image). The middle photograph shows fossae in a cervical vertebra, which in the neural arch are bounded by vertebral laminae. The close-up photograph (top) shows the that bone texture within the fossa is often smooth, crenulated, and shiny, which is indicative of pneumatic bone. Silhouette reconstruction from [49]; cervical vertebra from [59]:fig. 10). Scale bar equals 1 m in silhouette; scale bars equal 3 cm in photographs. ©Copyright 2009 The Society of Vertebrate Paleontology. Reprinted and distributed with permission of the Society of Vertebrate Paleontology.
Mentions: Among non-volant ornithodirans, axial pneumaticity is perhaps best developed in sauropod dinosaurs, in which pneumatic diverticulae leave their traces in postatlantal vertebrae and ribs, but apparently not chevrons (Fig. 1). Axial pneumaticity can take the form of deep and sometimes complex invasion of internal bone, or in the form of spaces enclosed by bony laminae connecting the processes projecting from the neural arch. The former, which we refer to as “internal pneumaticity,” displays variation that appears to characterize sauropod subgroups [7] and has important implications for sauropod paleobiology [8]. Internal pneumatic structures are typically not bounded by landmarks, however, and it is very difficult to homologize individual pneumatic spaces between vertebrae or between species. Neural arch fossae, on the other hand, are typically bounded by vertebral laminae and easily homologized within and between taxa. These structures display important phylogenetic variation that has not been extensively sampled thus far. We provide a practical nomenclature for lamina-bounded fossae that takes advantage of conventions and landmarks used in existing nomenclature for vertebral laminae [9]. The nomenclature for lamina-bounded fossae is designed to facilitate their use in comparative anatomy and phylogenetic analysis.

Bottom Line: We standardize the naming process by creating tripartite names from "primary landmarks," which form the zygodiapophyseal table, "secondary landmarks," which orient with respect to that table, and "tertiary landmarks," which further delineate a given fossa.The proposed nomenclatural system for lamina-bounded fossae adds clarity to descriptions of complex vertebrae and allows these structures to be sourced as character data for phylogenetic analyses.These anatomical terms denote potentially homologous pneumatic structures within Saurischia, but they could be applied to any vertebrate with vertebral laminae that enclose spaces, regardless of their developmental origin or phylogenetic distribution.

View Article: PubMed Central - PubMed

Affiliation: Museum of Paleontology and Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, United States of America. wilsonja@umich.edu

ABSTRACT

Background: The axial skeleton of extinct saurischian dinosaurs (i.e., theropods, sauropodomorphs), like living birds, was pneumatized by epithelial outpocketings of the respiratory system. Pneumatic signatures in the vertebral column of fossil saurischians include complex branching chambers within the bone (internal pneumaticity) and large chambers visible externally that are bounded by neural arch laminae (external pneumaticity). Although general aspects of internal pneumaticity are synapomorphic for saurischian subgroups, the individual internal pneumatic spaces cannot be homologized across species or even along the vertebral column, due to their variability and absence of topographical landmarks. External pneumatic structures, in contrast, are defined by ready topological landmarks (vertebral laminae), but no consistent nomenclatural system exists. This deficiency has fostered confusion and limited their use as character data in phylogenetic analysis.

Methodology/principal findings: We present a simple system for naming external neural arch fossae that parallels the one developed for the vertebral laminae that bound them. The nomenclatural system identifies fossae by pointing to reference landmarks (e.g., neural spine, centrum, costal articulations, zygapophyses). We standardize the naming process by creating tripartite names from "primary landmarks," which form the zygodiapophyseal table, "secondary landmarks," which orient with respect to that table, and "tertiary landmarks," which further delineate a given fossa.

Conclusions/significance: The proposed nomenclatural system for lamina-bounded fossae adds clarity to descriptions of complex vertebrae and allows these structures to be sourced as character data for phylogenetic analyses. These anatomical terms denote potentially homologous pneumatic structures within Saurischia, but they could be applied to any vertebrate with vertebral laminae that enclose spaces, regardless of their developmental origin or phylogenetic distribution.

Show MeSH
Related in: MedlinePlus