title: Neck length and mean arterial pressure in the sauropod dinosaurs.
abstract: How blood was able to reach the heads of the long-necked sauropod dinosaurs has long been a matter of debate and several hypotheses have been presented. For example, it has been proposed that sauropods had exceptionally large hearts, multiple 'normal' sized hearts spaced at regular intervals up the neck or held their necks horizontal, or that the siphon effect was in operation. By means of an experimental model, we demonstrate that the siphon principle is able to explain how blood was able to adequately perfuse the sauropod brain. The return venous circulation may have been protected from complete collapse by a structure akin to the vertebral venous plexus. We derive an equation relating neck height and mean arterial pressure, which indicates that with a mean arterial pressure similar to that of the giraffe, the maximum safe vertical distance between heart and head would have been about 12 m. A hypothesis is presented that the maximum neck length in the fossil record is due to the siphon height limit. The equation indicates that to migrate over high ground, sauropods would have had to either significantly increase their mean arterial pressure or keep their necks below a certain height dependent on altitude.
authors.affiliation: Biomedical Engineering and Medical Physics, School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD 4000, Australia sw.hughes@qut.edu.au.
authors.forename: Stephen
authors.initials: S
authors.lastname: Hughes
authors.affiliation: School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD 4000, Australia.
authors.forename: John
authors.initials: J
authors.lastname: Barry
authors.affiliation: Department of Neurosurgery, Royal Brisbane & Women's Hospital, Herston, Brisbane, QLD 4029, Australia.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Russell
authors.affiliation: CSIRO Education, EcoSciences Precinct, 41 Boggo Road, Dutton Park, QLD 4102, Australia.
authors.forename: Robert
authors.initials: R
authors.lastname: Bell
authors.affiliation: School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD 4000, Australia School of Postgraduate Studies, Paro College of Education, Royal University of Bhutan, Paro, Bhutan.
authors.forename: Som
authors.initials: S
authors.lastname: Gurung
mesh_terms: D000531:Altitude; D000818:Animals; D062186:Arterial Pressure / Q000502:physiology*; D001775:Blood Circulation; D003956:Dialysis; D025061:Dinosaurs / Q000033:anatomy & histology* / Q000502:physiology*; D008954:Models, Biological; D009333:Neck / Q000033:anatomy & histology*; D011312:Pressure; D014867:Water
chemical_list: D014867:Water
keywords: Circulation; Heart; Internal jugular vein; Siphon; Vertebral venous plexus