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Downsizing a giant: re-evaluating Dreadnoughtus body mass.

Bates KT, Falkingham PL, Macaulay S, Brassey C, Maidment SC - Biol. Lett. (2015)

Bottom Line: Estimates of body mass often represent the founding assumption on which biomechanical and macroevolutionary hypotheses are based.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Musculoskeletal Biology, University of Liverpool, Duncan Building, Daulby Street, Liverpool L69 3GE, UK k.t.bates@liverpool.ac.uk.

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.

No MeSH data available.


Comparison of skeletal proportions and convex hull volumes for Apatosaurus (top), Dreadnoughtus (middle) and Giraffatitan (bottom) in (a) dorsal and (b) lateral views. Comparison of mass predictions from the models in this study to masses derived from the scaling equation [2], with (c) model mass and density calculated using reconstructed zero-density respiratory structures, and (d) density artificially set to 800 kg m−3 [7]. The positive error bar on our maximal models represents the mass predicted by expanding convex hull volumes by the highest exponent (×1.91) for mammals [5] and archosaurs to date. The ‘PPE’ error bars on scaling equation outputs represent the average ‘per cent prediction error’, whereas ‘95PI’ error bars represent the ‘95% prediction interval’.
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RSBL20150215F2: Comparison of skeletal proportions and convex hull volumes for Apatosaurus (top), Dreadnoughtus (middle) and Giraffatitan (bottom) in (a) dorsal and (b) lateral views. Comparison of mass predictions from the models in this study to masses derived from the scaling equation [2], with (c) model mass and density calculated using reconstructed zero-density respiratory structures, and (d) density artificially set to 800 kg m−3 [7]. The positive error bar on our maximal models represents the mass predicted by expanding convex hull volumes by the highest exponent (×1.91) for mammals [5] and archosaurs to date. The ‘PPE’ error bars on scaling equation outputs represent the average ‘per cent prediction error’, whereas ‘95PI’ error bars represent the ‘95% prediction interval’.

Mentions: The convex hull volume reconstruction of Dreadnoughtus results in a total body volume of 26.910 m3 (figure 1a and table 1). Expanding this minimum convex hull volume by 21% raises the whole-body volume to 32.534 m3 (figure 1b), while the volume of our maximal model is 43.016 m3 (figure 1c). Deducting the volume of our reconstructed respiratory structures from each of these models yields total body masses of 22 117, 27 741 and 38 225 kg for the three model iterations. These data and data from equivalent models of Apatosaurus and Giraffatitan (figure 2a,b) are shown in table 1, while the data from extant taxa are tabulated in the electronic supplementary material (tables S1–S6, and figures S8 and S9). Convex hull volumes are available in the electronic supplementary material.Table 1.


Downsizing a giant: re-evaluating Dreadnoughtus body mass.

Bates KT, Falkingham PL, Macaulay S, Brassey C, Maidment SC - Biol. Lett. (2015)

Comparison of skeletal proportions and convex hull volumes for Apatosaurus (top), Dreadnoughtus (middle) and Giraffatitan (bottom) in (a) dorsal and (b) lateral views. Comparison of mass predictions from the models in this study to masses derived from the scaling equation [2], with (c) model mass and density calculated using reconstructed zero-density respiratory structures, and (d) density artificially set to 800 kg m−3 [7]. The positive error bar on our maximal models represents the mass predicted by expanding convex hull volumes by the highest exponent (×1.91) for mammals [5] and archosaurs to date. The ‘PPE’ error bars on scaling equation outputs represent the average ‘per cent prediction error’, whereas ‘95PI’ error bars represent the ‘95% prediction interval’.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4528471&req=5

RSBL20150215F2: Comparison of skeletal proportions and convex hull volumes for Apatosaurus (top), Dreadnoughtus (middle) and Giraffatitan (bottom) in (a) dorsal and (b) lateral views. Comparison of mass predictions from the models in this study to masses derived from the scaling equation [2], with (c) model mass and density calculated using reconstructed zero-density respiratory structures, and (d) density artificially set to 800 kg m−3 [7]. The positive error bar on our maximal models represents the mass predicted by expanding convex hull volumes by the highest exponent (×1.91) for mammals [5] and archosaurs to date. The ‘PPE’ error bars on scaling equation outputs represent the average ‘per cent prediction error’, whereas ‘95PI’ error bars represent the ‘95% prediction interval’.
Mentions: The convex hull volume reconstruction of Dreadnoughtus results in a total body volume of 26.910 m3 (figure 1a and table 1). Expanding this minimum convex hull volume by 21% raises the whole-body volume to 32.534 m3 (figure 1b), while the volume of our maximal model is 43.016 m3 (figure 1c). Deducting the volume of our reconstructed respiratory structures from each of these models yields total body masses of 22 117, 27 741 and 38 225 kg for the three model iterations. These data and data from equivalent models of Apatosaurus and Giraffatitan (figure 2a,b) are shown in table 1, while the data from extant taxa are tabulated in the electronic supplementary material (tables S1–S6, and figures S8 and S9). Convex hull volumes are available in the electronic supplementary material.Table 1.

Bottom Line: Estimates of body mass often represent the founding assumption on which biomechanical and macroevolutionary hypotheses are based.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Musculoskeletal Biology, University of Liverpool, Duncan Building, Daulby Street, Liverpool L69 3GE, UK k.t.bates@liverpool.ac.uk.

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.

No MeSH data available.