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Revised vertebral count in the "longest-necked vertebrate" Elasmosaurus platyurus Cope 1868, and clarification of the cervical-dorsal transition in Plesiosauria.

Sachs S, Kear BP, Everhart MJ - PLoS ONE (2013)

Bottom Line: Accurately determining the number of vertebral centra vis-à-vis the maximum length of the neck in plesiosaurians has significant implications for phylogenetic character designations, as well as the inconsistent terminology applied to some osteological structures.This morphology is unambiguously distinguishable from standard cervicals, in which the functional rib facet is borne exclusively on the centrum, and dorsals in which the rib articulation is situated above the neurocentral suture and functionally borne only by the transverse process of the neural arch.Given these easily distinguishable definitions, the maximum number of neck vertebrae preserved in E. platyurus is 72; this is only three vertebrae shorter than the recently described Albertonectes, which together with E. platyurus constitute the "longest necked" animals ever to have lived.

View Article: PubMed Central - PubMed

Affiliation: Engelskirchen, Germany. Sachs.Pal@gmx.de

ABSTRACT
Elasmosaurid plesiosaurians are renowned for their immensely long necks, and indeed, possessed the highest number of cervical vertebrae for any known vertebrate. Historically, the largest count has been attributed to the iconic Elasmosaurus platyurus from the Late Cretaceous of Kansas, but estimates for the total neck series in this taxon have varied between published reports. Accurately determining the number of vertebral centra vis-à-vis the maximum length of the neck in plesiosaurians has significant implications for phylogenetic character designations, as well as the inconsistent terminology applied to some osteological structures. With these issues in mind, we reassessed the holotype of E. platyurus as a model for standardizing the debated cervical-dorsal transition in plesiosaurians, and during this procedure, documented a "lost" cervical centrum. Our revision also advocates retention of the term "pectorals" to describe the usually three or more distinctive vertebrae close to the cranial margin of the forelimb girdle that bear a functional rib facet transected by the neurocentral suture, and thus conjointly formed by both the parapophysis on the centrum body and diapophysis from the neural arch (irrespective of rib length). This morphology is unambiguously distinguishable from standard cervicals, in which the functional rib facet is borne exclusively on the centrum, and dorsals in which the rib articulation is situated above the neurocentral suture and functionally borne only by the transverse process of the neural arch. Given these easily distinguishable definitions, the maximum number of neck vertebrae preserved in E. platyurus is 72; this is only three vertebrae shorter than the recently described Albertonectes, which together with E. platyurus constitute the "longest necked" animals ever to have lived.

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Pectoral series.A. Elasmosaurus platyurus (ANSP 10081) and B. Seeleyosaurus guilelmiimperatoris (Museum für Naturkunde Berlin, MB.R.1992). Not to scale. Abbreviations.crf = conjoint rib facet, dap = diapophysis, fd = first dorsal, fp = first pectoral, lc = last cervical, pap = parapophysis, rf = single rib facet, rtp = single rib facet on transverse process.
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pone-0070877-g003: Pectoral series.A. Elasmosaurus platyurus (ANSP 10081) and B. Seeleyosaurus guilelmiimperatoris (Museum für Naturkunde Berlin, MB.R.1992). Not to scale. Abbreviations.crf = conjoint rib facet, dap = diapophysis, fd = first dorsal, fp = first pectoral, lc = last cervical, pap = parapophysis, rf = single rib facet, rtp = single rib facet on transverse process.

Mentions: To counter these seemingly random redefinitions, together with what we feel is the off-handed disregard of a long-standing, morphologically accurate expression to describe a phylogenetically meaningful trait, we propose the reinstatement of “pectoral” into standard terminological usage as the most correct and convenient solution. Carpenter’s [12] original critique that the term is “pointless and disadvantageous” because it has not been applied to lepidosaurians is superfluous, since Plesiosauria is both independently divergent and unanimously monophyletic [26], [28], [29], [34], [53], [54], thus manifesting its own suite of uniquely derived features with recognizable intermediate conditions in ancestral lineages (e.g. nothosaurians and pistosauroids [49], [51], [52], [55]). The acquisition and evolutionary modification of a discrete pectoral series within the presacral vertebral column is therefore demonstrably evident (see Fig. 3), and essentially not contested, whereas the problem of practical definition relative to the cervical-dorsal transition is. Carpenter’s ([12]: p. 150) literal designations of the last cervical as “the vertebra in which the rib facet (formed by the combined diapophysis and parapophysis) extends across the centrum-neural-arch boundary” and is located “near the base of the of the neural canal”, and the first dorsal as “the vertebra in which the rib facet overlies the neural arch-centrum suture”, are both inadequate and counterintuitive because multiple consecutive vertebrae within the pectoral series could fit these definitions (e.g. the cervical terminus could be interpreted as part of the cranial dorsal region, or the first dorsal mistakenly construed as a cervical based on the rib facet “overlying” the neurocentral suture). The recommended use of the neural canal base as a proxy landmark for the fully fused vertebral sutures in osteologically mature individuals [12] is also problematic, since the neurocentral contact can extend well below the pedicle and even overly the cervical ribs as thin “lappets” in some taxa (e.g. Hauffiosaurus[29], [58]). Additionally, we question the use of pectoral girdle positioning as a determinant of vertebral placement [34] because there is no way of unambiguously establishing whether the appendicular elements are preserved in life position. Finally, Kubo et al. [20] advocated the presence of “long ribs” (presumably equating to the “dorsalised” category of Benson and Druckenmiller [34]) to distinguish the first dorsal, but this is subjective for disarticulated remains in which comparative rib proportions must be assumed (if they can be reconstructed at all: e.g. ANSP 10081 does not preserve complete ribs [1], [21]).


Revised vertebral count in the "longest-necked vertebrate" Elasmosaurus platyurus Cope 1868, and clarification of the cervical-dorsal transition in Plesiosauria.

Sachs S, Kear BP, Everhart MJ - PLoS ONE (2013)

Pectoral series.A. Elasmosaurus platyurus (ANSP 10081) and B. Seeleyosaurus guilelmiimperatoris (Museum für Naturkunde Berlin, MB.R.1992). Not to scale. Abbreviations.crf = conjoint rib facet, dap = diapophysis, fd = first dorsal, fp = first pectoral, lc = last cervical, pap = parapophysis, rf = single rib facet, rtp = single rib facet on transverse process.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3733804&req=5

pone-0070877-g003: Pectoral series.A. Elasmosaurus platyurus (ANSP 10081) and B. Seeleyosaurus guilelmiimperatoris (Museum für Naturkunde Berlin, MB.R.1992). Not to scale. Abbreviations.crf = conjoint rib facet, dap = diapophysis, fd = first dorsal, fp = first pectoral, lc = last cervical, pap = parapophysis, rf = single rib facet, rtp = single rib facet on transverse process.
Mentions: To counter these seemingly random redefinitions, together with what we feel is the off-handed disregard of a long-standing, morphologically accurate expression to describe a phylogenetically meaningful trait, we propose the reinstatement of “pectoral” into standard terminological usage as the most correct and convenient solution. Carpenter’s [12] original critique that the term is “pointless and disadvantageous” because it has not been applied to lepidosaurians is superfluous, since Plesiosauria is both independently divergent and unanimously monophyletic [26], [28], [29], [34], [53], [54], thus manifesting its own suite of uniquely derived features with recognizable intermediate conditions in ancestral lineages (e.g. nothosaurians and pistosauroids [49], [51], [52], [55]). The acquisition and evolutionary modification of a discrete pectoral series within the presacral vertebral column is therefore demonstrably evident (see Fig. 3), and essentially not contested, whereas the problem of practical definition relative to the cervical-dorsal transition is. Carpenter’s ([12]: p. 150) literal designations of the last cervical as “the vertebra in which the rib facet (formed by the combined diapophysis and parapophysis) extends across the centrum-neural-arch boundary” and is located “near the base of the of the neural canal”, and the first dorsal as “the vertebra in which the rib facet overlies the neural arch-centrum suture”, are both inadequate and counterintuitive because multiple consecutive vertebrae within the pectoral series could fit these definitions (e.g. the cervical terminus could be interpreted as part of the cranial dorsal region, or the first dorsal mistakenly construed as a cervical based on the rib facet “overlying” the neurocentral suture). The recommended use of the neural canal base as a proxy landmark for the fully fused vertebral sutures in osteologically mature individuals [12] is also problematic, since the neurocentral contact can extend well below the pedicle and even overly the cervical ribs as thin “lappets” in some taxa (e.g. Hauffiosaurus[29], [58]). Additionally, we question the use of pectoral girdle positioning as a determinant of vertebral placement [34] because there is no way of unambiguously establishing whether the appendicular elements are preserved in life position. Finally, Kubo et al. [20] advocated the presence of “long ribs” (presumably equating to the “dorsalised” category of Benson and Druckenmiller [34]) to distinguish the first dorsal, but this is subjective for disarticulated remains in which comparative rib proportions must be assumed (if they can be reconstructed at all: e.g. ANSP 10081 does not preserve complete ribs [1], [21]).

Bottom Line: Accurately determining the number of vertebral centra vis-à-vis the maximum length of the neck in plesiosaurians has significant implications for phylogenetic character designations, as well as the inconsistent terminology applied to some osteological structures.This morphology is unambiguously distinguishable from standard cervicals, in which the functional rib facet is borne exclusively on the centrum, and dorsals in which the rib articulation is situated above the neurocentral suture and functionally borne only by the transverse process of the neural arch.Given these easily distinguishable definitions, the maximum number of neck vertebrae preserved in E. platyurus is 72; this is only three vertebrae shorter than the recently described Albertonectes, which together with E. platyurus constitute the "longest necked" animals ever to have lived.

View Article: PubMed Central - PubMed

Affiliation: Engelskirchen, Germany. Sachs.Pal@gmx.de

ABSTRACT
Elasmosaurid plesiosaurians are renowned for their immensely long necks, and indeed, possessed the highest number of cervical vertebrae for any known vertebrate. Historically, the largest count has been attributed to the iconic Elasmosaurus platyurus from the Late Cretaceous of Kansas, but estimates for the total neck series in this taxon have varied between published reports. Accurately determining the number of vertebral centra vis-à-vis the maximum length of the neck in plesiosaurians has significant implications for phylogenetic character designations, as well as the inconsistent terminology applied to some osteological structures. With these issues in mind, we reassessed the holotype of E. platyurus as a model for standardizing the debated cervical-dorsal transition in plesiosaurians, and during this procedure, documented a "lost" cervical centrum. Our revision also advocates retention of the term "pectorals" to describe the usually three or more distinctive vertebrae close to the cranial margin of the forelimb girdle that bear a functional rib facet transected by the neurocentral suture, and thus conjointly formed by both the parapophysis on the centrum body and diapophysis from the neural arch (irrespective of rib length). This morphology is unambiguously distinguishable from standard cervicals, in which the functional rib facet is borne exclusively on the centrum, and dorsals in which the rib articulation is situated above the neurocentral suture and functionally borne only by the transverse process of the neural arch. Given these easily distinguishable definitions, the maximum number of neck vertebrae preserved in E. platyurus is 72; this is only three vertebrae shorter than the recently described Albertonectes, which together with E. platyurus constitute the "longest necked" animals ever to have lived.

Show MeSH
Related in: MedlinePlus