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Elasmosaurus neck vertebrae count



From: Ben Creisler
bcreisler@gmail.com

New in PLoS ONE:


Sven Sachs, Benjamin P. Kear & Michael J. Everhart(2013)
Revised Vertebral Count in the “Longest-Necked Vertebrate”
Elasmosaurus platyurus Cope 1868, and Clarification of the
Cervical-Dorsal Transition in Plesiosauria.
PLoS ONE 8(8): e70877.
doi:10.1371/journal.pone.0070877
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0070877



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.