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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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Configuration of vertebral laminae and fossae associated with the parapophysis in presacral vertebrae.Left, a cervical or anterior dorsal vertebra, in which the parapophysis is positioned on the centrum. Two laminae extend ventrally from the diapophysis (acdl, pcdl), helping to bound three fossae (prcdf, cdf, pocdf). Center, a simple mid- or posterior dorsal vertebra in which the parapophysis has risen onto the neural arch and is connected to the diapophysis and anterior centrum via two complementary laminae (ppdl, acpl). The configuration of fossae and their nomenclature, however, remains the same: the three fossae are still bounded by the zygapophyses, diapophysis, and centrum. Right, a complex mid- or posterior dorsal vertebra in which the parapophysis has risen onto the neural arch and four, rather than two, laminae extend from it (ppdl, acpl, pcpl, prpl). The addition of two laminae bisects the fossae between the diapophysis and centrum (cdf) and between the diapophysis, centrum, and prezygapophysis (prcdf). Four fossae are created, two of which require special naming (noted by asterisks). The fossa between the parapophysis and centrum does not contact the zygodiapophyseal table and thus lacks a primary landmark; in this case the parapophysis is enlisted as a primary landmark (cpaf). The fossa between the diapophysis, parapophysis, and prezygapophysis is not bounded by a secondary landmark (i.e., neural spine or centrum), and the parapophysis is enlisted as a secondary landmark (prpadf).
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pone-0017114-g005: Configuration of vertebral laminae and fossae associated with the parapophysis in presacral vertebrae.Left, a cervical or anterior dorsal vertebra, in which the parapophysis is positioned on the centrum. Two laminae extend ventrally from the diapophysis (acdl, pcdl), helping to bound three fossae (prcdf, cdf, pocdf). Center, a simple mid- or posterior dorsal vertebra in which the parapophysis has risen onto the neural arch and is connected to the diapophysis and anterior centrum via two complementary laminae (ppdl, acpl). The configuration of fossae and their nomenclature, however, remains the same: the three fossae are still bounded by the zygapophyses, diapophysis, and centrum. Right, a complex mid- or posterior dorsal vertebra in which the parapophysis has risen onto the neural arch and four, rather than two, laminae extend from it (ppdl, acpl, pcpl, prpl). The addition of two laminae bisects the fossae between the diapophysis and centrum (cdf) and between the diapophysis, centrum, and prezygapophysis (prcdf). Four fossae are created, two of which require special naming (noted by asterisks). The fossa between the parapophysis and centrum does not contact the zygodiapophyseal table and thus lacks a primary landmark; in this case the parapophysis is enlisted as a primary landmark (cpaf). The fossa between the diapophysis, parapophysis, and prezygapophysis is not bounded by a secondary landmark (i.e., neural spine or centrum), and the parapophysis is enlisted as a secondary landmark (prpadf).

Mentions: These six bipartite names and six tripartite names serve to identify the vast majority of neural arch fossae, but fossae associated with the parapophysis require further explication (Fig. 4). In cervical and anterior dorsal vertebrae, the parapophysis is situated on the centrum and there are only two laminae emanating ventrally from the diapophysis: the anterior and posterior centrodiapophyseal laminae (acdl, pcdl). Together with centrozygapophyseal laminae (cprl, cpol) and zygodiapophyseal laminae (prdl, podl), the acdl and pcdl bound three fossae, the prcdf, cdf, and pocdf (Fig. 5). In middle and posterior dorsal vertebrae, the parapophysis migrates onto the neural arch in the path of the acdl, essentially breaking it into complementary laminae known as the parapodiapophyseal lamina (ppdl) and the anterior centroparapophyseal lamina (acpl). On its own, this change in laminar configuration does not alter the configuration of the two fossae associated with the the diapophysis, centrum, and prezygapophysis (Fig. 5). However, in most cases the parapophysis develops its own laminae that connect to the prezygapophysis (i.e., the prpl) and to the centrum (i.e., the pcpl) and subdivide the prcdf and cdf, respectively (Fig. 5). Of the four resultant fossae, two do not fit into the system of 12 bipartite and tripartite fossae described above: one does not contact the zygodiapophyseal table (and thus the primary landmarks), and the other contacts the zygodiapophyseal table but does not contact a secondary landmark. To accommodate this special case, we allow the parapophysis to act as a primary landmark (-paf) in the former case and a secondary landmark (-padf) in the latter case (Fig. 4). Two bipartite fossae (cpaf, padf) and one tripartite fossa (prpadf), constructed using the parapophysis as primary and secondary landmarks, are recognized here. This yields a total of eight bipartite and seven tripartite names that describe all vertebral fossae of sauropods with the exception of the special cases that we describe below.


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)

Configuration of vertebral laminae and fossae associated with the parapophysis in presacral vertebrae.Left, a cervical or anterior dorsal vertebra, in which the parapophysis is positioned on the centrum. Two laminae extend ventrally from the diapophysis (acdl, pcdl), helping to bound three fossae (prcdf, cdf, pocdf). Center, a simple mid- or posterior dorsal vertebra in which the parapophysis has risen onto the neural arch and is connected to the diapophysis and anterior centrum via two complementary laminae (ppdl, acpl). The configuration of fossae and their nomenclature, however, remains the same: the three fossae are still bounded by the zygapophyses, diapophysis, and centrum. Right, a complex mid- or posterior dorsal vertebra in which the parapophysis has risen onto the neural arch and four, rather than two, laminae extend from it (ppdl, acpl, pcpl, prpl). The addition of two laminae bisects the fossae between the diapophysis and centrum (cdf) and between the diapophysis, centrum, and prezygapophysis (prcdf). Four fossae are created, two of which require special naming (noted by asterisks). The fossa between the parapophysis and centrum does not contact the zygodiapophyseal table and thus lacks a primary landmark; in this case the parapophysis is enlisted as a primary landmark (cpaf). The fossa between the diapophysis, parapophysis, and prezygapophysis is not bounded by a secondary landmark (i.e., neural spine or centrum), and the parapophysis is enlisted as a secondary landmark (prpadf).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3046170&req=5

pone-0017114-g005: Configuration of vertebral laminae and fossae associated with the parapophysis in presacral vertebrae.Left, a cervical or anterior dorsal vertebra, in which the parapophysis is positioned on the centrum. Two laminae extend ventrally from the diapophysis (acdl, pcdl), helping to bound three fossae (prcdf, cdf, pocdf). Center, a simple mid- or posterior dorsal vertebra in which the parapophysis has risen onto the neural arch and is connected to the diapophysis and anterior centrum via two complementary laminae (ppdl, acpl). The configuration of fossae and their nomenclature, however, remains the same: the three fossae are still bounded by the zygapophyses, diapophysis, and centrum. Right, a complex mid- or posterior dorsal vertebra in which the parapophysis has risen onto the neural arch and four, rather than two, laminae extend from it (ppdl, acpl, pcpl, prpl). The addition of two laminae bisects the fossae between the diapophysis and centrum (cdf) and between the diapophysis, centrum, and prezygapophysis (prcdf). Four fossae are created, two of which require special naming (noted by asterisks). The fossa between the parapophysis and centrum does not contact the zygodiapophyseal table and thus lacks a primary landmark; in this case the parapophysis is enlisted as a primary landmark (cpaf). The fossa between the diapophysis, parapophysis, and prezygapophysis is not bounded by a secondary landmark (i.e., neural spine or centrum), and the parapophysis is enlisted as a secondary landmark (prpadf).
Mentions: These six bipartite names and six tripartite names serve to identify the vast majority of neural arch fossae, but fossae associated with the parapophysis require further explication (Fig. 4). In cervical and anterior dorsal vertebrae, the parapophysis is situated on the centrum and there are only two laminae emanating ventrally from the diapophysis: the anterior and posterior centrodiapophyseal laminae (acdl, pcdl). Together with centrozygapophyseal laminae (cprl, cpol) and zygodiapophyseal laminae (prdl, podl), the acdl and pcdl bound three fossae, the prcdf, cdf, and pocdf (Fig. 5). In middle and posterior dorsal vertebrae, the parapophysis migrates onto the neural arch in the path of the acdl, essentially breaking it into complementary laminae known as the parapodiapophyseal lamina (ppdl) and the anterior centroparapophyseal lamina (acpl). On its own, this change in laminar configuration does not alter the configuration of the two fossae associated with the the diapophysis, centrum, and prezygapophysis (Fig. 5). However, in most cases the parapophysis develops its own laminae that connect to the prezygapophysis (i.e., the prpl) and to the centrum (i.e., the pcpl) and subdivide the prcdf and cdf, respectively (Fig. 5). Of the four resultant fossae, two do not fit into the system of 12 bipartite and tripartite fossae described above: one does not contact the zygodiapophyseal table (and thus the primary landmarks), and the other contacts the zygodiapophyseal table but does not contact a secondary landmark. To accommodate this special case, we allow the parapophysis to act as a primary landmark (-paf) in the former case and a secondary landmark (-padf) in the latter case (Fig. 4). Two bipartite fossae (cpaf, padf) and one tripartite fossa (prpadf), constructed using the parapophysis as primary and secondary landmarks, are recognized here. This yields a total of eight bipartite and seven tripartite names that describe all vertebral fossae of sauropods with the exception of the special cases that we describe below.

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