Hutchinson claims that I have not documented my methods for deriving mass estimates from nondigital, illustrative multi-view skeletal restorations, or even the scale of the volumetric models. The methodology has been described in a number of locations in greater detail than for any other similar efforts [1-5], including that the models are constructed at a femur length of 52.5 mm. For Tyrannosaurus that is close to the 1/24 scale that for similar sized World War II fighters results in large models. There is no reason to presume that at this large a scale that modeling accidents will result in substantial errors in the volume within the context of the particular skeletal restoration or volumetric model if the latter is carefully measured and assembled. For example, possible parallax in lateral view photographs can be searched for and if necessary corrected by use of direct measurements of the specimen. My lateral photograph of the front half of the Sue mount used to help restore the specimen records the same length ratio between the mandible and femur as the published measurements [6], as does the resulting skeletal restoration (see right column in figure link below), so it is not possible for substantial errors in the dimensions of the restoration to exist. Unless grave error has occurred in the skeletal restoration there is no cause to presume that the resulting model will be grossly deflated or inflated in proportional terms relative to the size of the actual individual – an error of 5% in the model will remain 5% for the specimen at full size.

Hutchinson seems to be under the misimpression that I assumed that the skeletal scans in Hutchinson et al. were presented at the same scale. What I did use was the length of the femur to determine the scale of each skeleton separately. The statements by Hutchinson concerning the accuracy of the skeletal scans as figured in the paper are rather odd and confusing. He indicates that the views are 'not perfectly orthographic' due to software issues, but claims that the 3D volumetric models are not likewise distorted. Even assuming this is correct, this means that viewers of the paper are left without proper documentation of the skeletal scans vis-à-vis the volumetric models. Such a failing cannot be charged concerning skeletal restorations such as mine that directly surround the skeleton with the restored soft tissue profile, leaving no ambiguity about the relationship between the two. In the future those presenting scanned skeletons and volumetric models based on the former would be well advised to publish accurate scans, and to imbed the skeleton within the volumetric model/s so that the skeleton-profile correspondence problem is eliminated. In any case, the Sue volumetric model in their figure 3 appears to retain the same under sizing of the skull relative to the femur that mars the skeleton in which the mandible is shorter than the femur rather than being longer as it should be. It is not possible to clarify the matter with the information on hand.

Other researchers restore the caudofemoralis as substantially larger than in my restorations, but even presuming this is correct the larger muscles add only a few percent of total mass, and the difference is well within the inherent margin of error. The very deep tail profiles utilized by Hutchinson et al. appear to offer a greater source of potential error, and negates their claim to have modeled the minimal plausible mass that requires that the soft tissues of the tail do not extend far above the neural spines or below the chevrons.

Hutchinson addresses the issue of how the gastralia series impacts body volume. The preserved arc of the series is not necessarily reliable because of the high possibility that the abdomen was inflated by bloating of the carcass. My restorations feature a hollow belly because of the near certainty that large predators – unlike herbivores whose bellies normally contain substantial amounts of forage – are gorge and fast animals whose bellies are slim when they are on the hunt and engaging in the locomotary activities that put the most load on their limbs. However, if the lateral thoracic air-sacs that line the sides of the trunk extended well caudal to the ribcage as some [7] but not all [8-9] researchers indicate, then it is possible that the belly never hollowed out. The latter possibility does not increase the mass of the animal since the larger volume consisted of air. At any rate the mass of the model will be dramatically affected only if the belly is restored as extremely bloated as if the subject had just gorged itself on a large carcass, doing that adds the prey to the mass of the predator.

Hutchinson contends that a caudal sweep of the ribs in tyrannosaurs is an assumption based on a presumption of minimal mass rather than anatomical fact. This posture has been well documented as standard for archosaurs and most other diapsids (2,3,5,10), being essentially universal in living crocodilians and birds, and the same in countless articulated fossil skeletons (as per Fig. 19 in [11], figs. 1,2,5 in [12]; fig. 1 in [13], Pls. 2-4,8,14B,15B,17-19 in [8], Pl. 24 in [14], figs. 14-1, 14-2 in [1]; occasional lack of caudal sweep is probably due to bloating of the carcass inflating its volume). So restoring Tyrannosaurus with the vertical or especially cranially swept ribs that will inflate the volume of the trunk is a markedly inferior hypothesis that lacks substantiation.

Hutchinson acknowledges that the inconsistencies in the skeletal mounts utilized in Hutchinson et al. reduces their cross comparability, reinforcing the argument that the much higher mass obtained for Sue over Stan is not demonstrated by their study. The contention that scans of skeletal mounts provide a better measure of the volume of fossil vertebrates than technical restorations is problematic because it is rare for fossils to be preserved without some degree of plastic distortion created by the pressure of overlying sediments. Correcting the distortions always involves some subjectivity whether it be digital or otherwise. The comment by Brochu concerning the distortion of the ribcage of Sue is particularly pertinent in this regard. Many fossil vertebrate specimens are literally flattened, precluding their being mounted. For these reasons nondigital technical restorations remain competitive with digital scans, neither of which can produce precise volumetric estimates for animals whose mass normally fluctuated in any case (up to a third in healthy adults over the course of a year [15,16]). To be blunt, there is so much slop in estimating masses that resorting to computers is not going to significantly improve the results, it is getting the proportions and anatomy consistently correct that is the most important whether doing so digitally or not, and there is little to choose between them.

Henderson [17] and Henderson and Snively [18] used my skeletal restoration of AMNH 5027 to generate computer mass estimates of 7200 to 10,200 kg, far above my sculpted model estimate of 5700 kg for the specimen. To test this issue I measured out enough modeling clay to represent the mass in ref. 18 and tried to apply it to my skeletal restoration. The effort was hopeless, I was only able to apply an additional 10% without bloating the 3-D model beyond reasonable bounds. That is not surprising because the problem lay elsewhere. A same scale comparison of my skeletal restoration with the models presented in refs. 17 & 18 solves the paradox, it is simply because the dimensions of 5027 somehow become increasingly inflated in the two papers (see left column in figure link below). I suspect that part of the initial inflation may have been due to a misunderstanding that my length measurement of 10.6 meters was along the curve of the vertebral series that was assumed to be between perpendiculars in ref. 17. How the length further expanded to 10% in ref 18 is a mystery. The differences in dimensions accounts for most but not all the difference in the mass estimates between refs. 3, 17 and 18, and the residual differences are minor and within plausible variation. The correspondence between the computer volume estimates and my plasticine models of my skeletal restorations in fact supports that the old fashioned analog method is not inferior to the digital.

Concerning the mass estimate of 12 tonnes for Tyrannosaurus in ref. 3, this was based on the assessment at the time that maxilla UCMP 118742 was exceptionally gigantic. Because it later proved to be no larger than those of other specimens such as Sue the claim of extra colossal Tyrannosaurus was withdrawn [4]. The implication by Celestist that I lowered the mass estimate for the taxon by being subjectively influenced by the femur circumference method is entirely errant I having long strongly criticized the unreliability of the equation [4]. Using the robustness of individual elements to estimate total mass is notoriously capricious because mass/ circumference-diameter values vary enormously between and within taxon. The citation by Celestist of the greater robustness of the elements of some Tyrannosaurus specimens as indicating greater total mass assumes that greater robustness of elements corresponds to a correspondingly greater total animal volume and therefore mass, but it is also possible and indeed probable that the differences record differing skeletal strength factors relative to mass (which could be the result of either sexual morphs or multiple gigantic species whose predatory behaviors were divergent). The only way to test the mass/strength alternatives is to restore the volume of the differing skeletons.

The figure link is at – http://gspauldino.com/rex...

All images to same scale, bar equals 2 m. Upper left GSP skeletals of AMNH 5027, immediately below Henderson 1999 volumetric model, further below Henderson & Snively (2004) volumetric model. Upper right GSP skeletals of Stan and Sue, immediately below solid extract profile of Sue with head and limbs removed to compare to same of the minimum Hutchinson et al. (2011) version of Sue (right column is from the figure in the initial comment).

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