title: Downsizing a giant: re-evaluating Dreadnoughtus body mass.
abstract: Estimates of body mass often represent the founding assumption on which biomechanical and macroevolutionary hypotheses are based. Recently, a scaling equation was applied to a newly discovered titanosaurian sauropod dinosaur (Dreadnoughtus), yielding a 59 300 kg body mass estimate for this animal. Herein, we use a modelling approach to examine the plausibility of this mass estimate for Dreadnoughtus. We find that 59 300 kg for Dreadnoughtus is highly implausible and demonstrate that masses above 40 000 kg require high body densities and expansions of soft tissue volume outside the skeleton several times greater than found in living quadrupedal mammals. Similar results from a small sample of other archosaurs suggests that lower-end mass estimates derived from scaling equations are most plausible for Dreadnoughtus, based on existing volumetric and density data from extant animals. Although volumetric models appear to more tightly constrain dinosaur body mass, there remains a clear need to further support these models with more exhaustive data from living animals. The relative and absolute discrepancies in mass predictions between volumetric models and scaling equations also indicate a need to systematically compare predictions across a wide size and taxonomic range to better inform studies of dinosaur body size.
authors.affiliation: Department of Musculoskeletal Biology, University of Liverpool, Duncan Building, Daulby Street, Liverpool L69 3GE, UK k.t.bates@liverpool.ac.uk.
authors.forename: Karl T
authors.initials: KT
authors.lastname: Bates
authors.affiliation: School of Natural Sciences and Psychology, Liverpool John Moores University, James Parsons Building, Bryon Street, Liverpool L3 3AF, UK.
authors.forename: Peter L
authors.identifier: http://orcid.org/0000-0003-1856-8377
authors.initials: PL
authors.lastname: Falkingham
authors.affiliation: Department of Musculoskeletal Biology, University of Liverpool, Duncan Building, Daulby Street, Liverpool L69 3GE, UK.
authors.forename: Sophie
authors.initials: S
authors.lastname: Macaulay
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester M13 9PL, UK.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Brassey
authors.affiliation: Department of Earth Science and Engineering, Imperial College, South Kensington, London SW7 2AZ, UK.
authors.forename: Susannah C R
authors.initials: SC
authors.lastname: Maidment
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001835:Body Weight; D025061:Dinosaurs / Q000502:physiology*; D005580:Fossils; D008954:Models, Biological
keywords: Dreadnoughtus; body mass; modelling; scaling equations