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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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Primary landmarks, secondary landmarks, and the zygodiapophyseal table.Schematic diagrams of a cervical vertebra (left) and dorsal vertebra (right) in left lateral view (top) and anterior/posterior view (bottom). The zygodiapophyseal table (zgt) is formed by the primary landmarks (1°): the prezygapophysis (pr), postzygapophysis (po), and diapophysis (d). The zygodiapophyseal table is indicated by the double black lines highlighted in yellow. The neural spine (s) and centrum (c) are secondary landmarks (2°) that orient with respect to zygodiapophyseal table. In middle and posterior dorsal vertebrae, the parapophysis (pa) can act as either a primary or secondary landmark (see “Practical Application” for details). Diapophyseal fossae are in blue, and pre/postzygapophyseal fossae are in green.
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pone-0017114-g002: Primary landmarks, secondary landmarks, and the zygodiapophyseal table.Schematic diagrams of a cervical vertebra (left) and dorsal vertebra (right) in left lateral view (top) and anterior/posterior view (bottom). The zygodiapophyseal table (zgt) is formed by the primary landmarks (1°): the prezygapophysis (pr), postzygapophysis (po), and diapophysis (d). The zygodiapophyseal table is indicated by the double black lines highlighted in yellow. The neural spine (s) and centrum (c) are secondary landmarks (2°) that orient with respect to zygodiapophyseal table. In middle and posterior dorsal vertebrae, the parapophysis (pa) can act as either a primary or secondary landmark (see “Practical Application” for details). Diapophyseal fossae are in blue, and pre/postzygapophyseal fossae are in green.

Mentions: Historically, students of dinosaur vertebral anatomy have referred to fossae appearing above and below the zygapophyses and diapophysis (e.g., “infradiapophyseal fossa” [17]; Table 1). That is, these students used the plane, or “table”, formed by these processes to orient fossae [13]. For reasons discussed above, orientational descriptors and a single landmark are not always sufficient to point to a specific fossa, but we nonetheless adapt this historical practice to the proposed system. This we do by reference to one of three “primary landmarks” that define the zygodiapophyseal table and reference to a “secondary landmark” that orients with respect to it. The diapophyses (d), prezygapophyses (pr), and postzygapophyses (po) define the zygodiapophyseal table and are here arbitrarily referred to as “primary landmarks” because in our system they take primacy in the name for the fossa (e.g., a “diapophyseal fossa” or “df”). Because a given fossa may be bounded by two of the three primary landmarks, we arbitrarily define the diapophysis as the ‘primary’ primary landmark. As a rule of thumb, fossae visible in lateral view are typically diapophyseal fossae, whereas those visible in anterior or posterior views are prezygapophyseal or postzygapophyseal fossae, respectively (Fig. 2). The neural spine (s), centrum (c), and occasionally the parapophysis (pa) act as “secondary landmarks” that indicate the position of the fossa above or below the zygodiapophyseal plane (see “Practical Application”). Together, primary and secondary landmarks form a bipartite name. A diapophyseal fossa that is also bounded by the centrum is a “centrodiapophyseal fossa” or “cdf”; a postzygapophyseal fossa that is also bounded by the neural spine is a “spinopostzygapophyseal fossa” or “spof”. Bipartite names typically refer to a set of fossae, although there are cases when they can refer to a single fossa (see below). A “tertiary landmark” provides the final point of reference for a named fossa by discriminating within a set of fossae. The tertiary landmark is added to the front of any bipartite name to form a tripartite name (e.g., “prezygapophyseal centrodiapophyseal fossa” or “prcdf”). There are only three possible tertiary landmarks, the parapophysis (pa), prezygapophysis (pr), and postzygapophysis (po). The diapophysis, centrum and neural spine cannot act as tertiary landmarks because a landmark can only be used once to define a fossa (i.e., no “diapophyseal spinodiapophyseal fossa”). Any fossa bounded by the diapophysis would be a diapophyseal fossa, and any fossa bounded by the neural spine or centrum would have them already employed as secondary landmarks.


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)

Primary landmarks, secondary landmarks, and the zygodiapophyseal table.Schematic diagrams of a cervical vertebra (left) and dorsal vertebra (right) in left lateral view (top) and anterior/posterior view (bottom). The zygodiapophyseal table (zgt) is formed by the primary landmarks (1°): the prezygapophysis (pr), postzygapophysis (po), and diapophysis (d). The zygodiapophyseal table is indicated by the double black lines highlighted in yellow. The neural spine (s) and centrum (c) are secondary landmarks (2°) that orient with respect to zygodiapophyseal table. In middle and posterior dorsal vertebrae, the parapophysis (pa) can act as either a primary or secondary landmark (see “Practical Application” for details). Diapophyseal fossae are in blue, and pre/postzygapophyseal fossae are in green.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3046170&req=5

pone-0017114-g002: Primary landmarks, secondary landmarks, and the zygodiapophyseal table.Schematic diagrams of a cervical vertebra (left) and dorsal vertebra (right) in left lateral view (top) and anterior/posterior view (bottom). The zygodiapophyseal table (zgt) is formed by the primary landmarks (1°): the prezygapophysis (pr), postzygapophysis (po), and diapophysis (d). The zygodiapophyseal table is indicated by the double black lines highlighted in yellow. The neural spine (s) and centrum (c) are secondary landmarks (2°) that orient with respect to zygodiapophyseal table. In middle and posterior dorsal vertebrae, the parapophysis (pa) can act as either a primary or secondary landmark (see “Practical Application” for details). Diapophyseal fossae are in blue, and pre/postzygapophyseal fossae are in green.
Mentions: Historically, students of dinosaur vertebral anatomy have referred to fossae appearing above and below the zygapophyses and diapophysis (e.g., “infradiapophyseal fossa” [17]; Table 1). That is, these students used the plane, or “table”, formed by these processes to orient fossae [13]. For reasons discussed above, orientational descriptors and a single landmark are not always sufficient to point to a specific fossa, but we nonetheless adapt this historical practice to the proposed system. This we do by reference to one of three “primary landmarks” that define the zygodiapophyseal table and reference to a “secondary landmark” that orients with respect to it. The diapophyses (d), prezygapophyses (pr), and postzygapophyses (po) define the zygodiapophyseal table and are here arbitrarily referred to as “primary landmarks” because in our system they take primacy in the name for the fossa (e.g., a “diapophyseal fossa” or “df”). Because a given fossa may be bounded by two of the three primary landmarks, we arbitrarily define the diapophysis as the ‘primary’ primary landmark. As a rule of thumb, fossae visible in lateral view are typically diapophyseal fossae, whereas those visible in anterior or posterior views are prezygapophyseal or postzygapophyseal fossae, respectively (Fig. 2). The neural spine (s), centrum (c), and occasionally the parapophysis (pa) act as “secondary landmarks” that indicate the position of the fossa above or below the zygodiapophyseal plane (see “Practical Application”). Together, primary and secondary landmarks form a bipartite name. A diapophyseal fossa that is also bounded by the centrum is a “centrodiapophyseal fossa” or “cdf”; a postzygapophyseal fossa that is also bounded by the neural spine is a “spinopostzygapophyseal fossa” or “spof”. Bipartite names typically refer to a set of fossae, although there are cases when they can refer to a single fossa (see below). A “tertiary landmark” provides the final point of reference for a named fossa by discriminating within a set of fossae. The tertiary landmark is added to the front of any bipartite name to form a tripartite name (e.g., “prezygapophyseal centrodiapophyseal fossa” or “prcdf”). There are only three possible tertiary landmarks, the parapophysis (pa), prezygapophysis (pr), and postzygapophysis (po). The diapophysis, centrum and neural spine cannot act as tertiary landmarks because a landmark can only be used once to define a fossa (i.e., no “diapophyseal spinodiapophyseal fossa”). Any fossa bounded by the diapophysis would be a diapophyseal fossa, and any fossa bounded by the neural spine or centrum would have them already employed as secondary landmarks.

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