Re: [DMG] Dinosaur body size and shape evolution (free pdf)

[Gregory Paul]

My profile-skeletals produce "low" masses because they are based on the most appropriate models for the particular types. For example for the big dinosaur herbivores it is big mammalian herbivores. Which are shrink wrapped when in a lean-healthy conditions. As per assorted rhino species in which the ribs are normally visible --

https://www.worldwildlife.org/species/white-rhino

https://www.ifaw.org/journal/rhino-faq

https://en.wikipedia.org/wiki/Black_rhinoceros#/media/File:Black_Rhino_at_Working_with_Wildlife.jpg

https://all-new-animals.fandom.com/wiki/Indian_Rhinoceros?file=IndianRhinoceros.jpg

https://www.savetherhino.org/asia/indonesia/a-story-of-hope-an-extremely-rare-sumatran-rhino-has-been-born

Not much extraneous fat on those babies. The soft tissues outside the ribs are not thick in big mammals, although many like elephants do not show the individual ribs. Also visible are the neural spines, edges of some pelvic elements, etc. The vast majority of the mass of herbivores is in the plant material processing belly, which I always shows as very rotund and capacious (unlike Ely Gish who was forced to show hollow bellies under those peculiar starvation condition instructions of Dale Russell). Nor are the limbs bulging with enormous muscles. The skeleton defines the volume, which defines the mass. Using armored aquatic crocs to try to restore dinomasses is incorrect excpet maybe for ankylosaurs. 

As for sauropod necks, using birds is incorrect because they are too small, even the ratites. The only suitable living large animal model is giraffes. Their necks are crazy narrow, with each cervical bulge easily visible in front view (this is not apparent from the side because the mottled cameo hides it) --

https://www.imeche.org/news/news-article/engineering-insight-into-giraffe-necks-and-hedgehog-'shock-absorbers

https://www.istockphoto.com/photo/giraffe-isolated-on-white-background-gm1282345357-380106074?searchscope=image%2Cfilm

Talk about shrink wrapping. 

The same would have been true of sauropods. As I have been pointing out for decades the trachea and esophagus were set between the lower cervical ribs, and soft tissues below the ribs would have just added unneeded mass to the neck, so the common presence of soft tissues below the neck ribs in restorations is not anatomically logical. On the other hand the work Asier and a colleague and I in The Anatomical Record indicate that sauropod necks were not as air-filled as assumed -- and dinosaur SGs in general were higher. Ratite necks may be more appropriate for similar sized slender necked dinosaurs such as ornithomimids. I have despite searching not seen a proper dissection of a ratite neck musculature. There are some X-rays online, but they are confusing and may show postmortem distortions. And ratite trachea may be loose and flop around on the neck.

Predator's trunks are shrink wrapped because they are lean mean killing machines that cannot be burdened with lots of unneeded soft tissues. On lions the ribs and/or the lower edge of the thin latissimus dorsi humerus retractor muscle that is spread over much of the ribcage can be seen. 

https://www.britannica.com/animal/lion

https://www.krugerpark.co.za/africa_lion.html

Ladling lots of flesh onto dinosaurs is going back to the cereal box dinosaurs -- and the damn brachiosaur in JP. 

Dempsey et al. cite my 1997 Dinofest article which ironically was not peer reviewed. For an updated explanation they did not cite of how to realistically restore dinosaurs, sauropods especially, check out my Annals of the Carnegie Museum paper (it was done before the upward revision of the SGs) -- 

http://www.gspauldino.com/Titanomass.pdf

For up to date lists of my dinomass estimates see the latest Princeton Guides and the restored specimens lists on their websites. 

GSPaul

On Friday, May 9, 2025 at 11:08:13 AM EDT, Ben Creisler <bcre...@gmail.com> wrote:

Ben Creisler

bcre...@gmail.com

A new paper:

Free pdf:

Matthew Dempsey, Samuel R. R. Cross, Susannah C. R. Maidment, John R. Hutchinson, Karl T. Bates (2025)
New perspectives on body size and shape evolution in dinosaurs
Biological Review (advance online publication)
doi: https://doi.org/10.1111/brv.70026
https://onlinelibrary.wiley.com/doi/10.1111/brv.70026

Free pdf:
https://onlinelibrary.wiley.com/doi/epdf/10.1111/brv.70026


Diversity in the body shapes and sizes of dinosaurs was foundational to their widespread success during the Mesozoic era. The ability to quantify body size and form reliably is therefore critical to the study of dinosaur biology and evolution. Body mass estimates for any given fossil animal are, in theory, most informative when derived from volumetric models that account for the three-dimensional shapes of the entire body. In addition to providing estimates of total body mass, volumetric approaches can be used to determine the inertial properties of specific body segments and the overall distribution of mass throughout the body, each of which are essential for the modelling and interpretation of form–function relationships and their associations with ecology. However, the determination of body volumes in fossil taxa is often subjective, and may be sensitive to varied artistic inference. This highlights the need for an approach to body mass estimation in which body segment volumes are systematically constrained by quantitative scaling relationships between the hard tissues that fossilise and the soft tissues only observable in extant taxa. To this end, we used recently published skeletal to soft tissue volumetric scaling factors derived from CT data of extant sauropsids to estimate body segment mass properties from skeletal models of 52 non-avian dinosaurs representing the majority of major clades and body plans. The body masses estimated by this study range from less than 200 g in the tiny avialan Yixianornis to over 60 tonnes in the giant sauropod Patagotitan, which is currently the largest dinosaur known from mostly complete skeletal remains. From our models, we infer that many previous reconstructions of soft tissue envelopes may be too small, and that many dinosaurs were therefore heavier than previous estimates. Our models generally overlap with the range of body mass estimates derived from limb bone shaft dimensions, but with considerable quantitative variability among major clades. This suggests that different taxa either differed in skeletal to soft tissue volume ratios, or that their limb bone dimensions varied relative to body mass, perhaps related to differences in locomotor dynamics and postural evolution. Our models also allowed us to investigate variation in mass distribution and body proportions across different dinosaurs from a perspective grounded in extant anatomical data, framing long-standing hypotheses about their form, function, and behaviour in a quantitative context. For example, reconstructed disparity in whole-body centres of mass reflects a broad array of postures in different dinosaur clades, while the lack of strong positive allometry in the dimensions of the weight-bearing limb segments relative to total body mass corroborates previous studies suggesting an overall decrease in dinosaur locomotor performance as body size increased.

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[Michael Habib]

> On May 27, 2025, at 8:04 AM, 'Gregory Paul' via Dinosaur Mailing Group <DinosaurMa...@googlegroups.com> wrote:
>
> Nor are the limbs bulging with enormous muscles. The skeleton defines the volume, which defines the mass.

I’d say the limbs of large mammals have rather large, bulging limb muscles. Consider a giraffe skeleton in lateral view:
https://svpow.com/wp-content/uploads/2020/05/giraffe-limbs-labeled.jpg

versus the external appearance in lateral view:
https://www.smithsonianmag.com/science-nature/cardiovascular-secrets-giraffes-180977785/

The scapular muscles are so large that they are bulging well out of plane places where the underlying bone is concave. And of course, the thighs are just huge.

At the same time, I feel like your reconstructions accurately represent these sorts of features, so perhaps you meant that line regarding muscles a bit differently from how I’m reading it. Are you referring to massive bulging out into the lateral space? Certainly not a ton of that.

> The same would have been true of sauropods. As I have been pointing out for decades the trachea and esophagus were set between the lower cervical ribs, and soft tissues below the ribs would have just added unneeded mass to the neck, so the common presence of soft tissues below the neck ribs in restorations is not anatomically logical.

I’ve been thinking about this a bit, and I think it’s worth a bit of a dive. The cervical “ribs” are, of course, mostly ossified tendons of the hypaxial muscles (they are fused into the true rib, which is quite short, even in things with very long ossified tendons). That gives us the most ventral extent of the *dorsal* compartment. But the esophagus and trachea, along with the carotid vasculature, are in the ventral compartment. This will, as in all tetrapods, be suspended ventral (anterior in humans) to the dorsal compartment (aka the axial skeleton and intrinsic muscles of the spine).

Now, the dorsal compartment in the cervical spine of sauropods is, of course, wrapped around some of the ventral compartment, forming the deep “inverted U” shape in the cervical vertebrae. I can imagine that this might completely enclose the ventral compartment in taxa with the deepest ventral concavities, but there is a fair bit that needs to be in there (the carotids will more dorsal, with esophagus and then trachea below them), and I’m not sure what would keep those tissues from hanging at least partially below the margin of the cervical tendons, unless there was some kind of retinaculum at the base - which is an interesting prospect. It seems more likely, though, that normal compartmental fascia would simply be thickened, with the ventral compartment suspended between and slightly below the ribs/tendons, leading to a small “V” of tissue below the margin of the hypaxial muscles.

Anyway… just some idle thoughts. I’m curious to get your take.

Cheers,

—Mike Habib

[Gregory Paul]

In prosauropods (sauropodomorphs excluding sauropods, is that allowed in the Phylocode?) and some sauropods the ventral edge of the cervical ribs is too high relative to the ventral surface of the centra for the assorted tubes and vessels etc to not be partly below the former. But in most sauropods there is a lot of room between the ventral portions of the cervical ribs and it looks to me -- and Asier L -- like everything could be between those, with nothing projecting below them. This is most extreme in apatosaurines and Euhelopus. 

What I am particularly objecting to is using long bird necks to restore the musculature of those of sauropods. The only good analog in that size class are giraffe necks, which are very narrow. And I am tired of folks calling me restorations shrink wrapped when they are obviously patterned after big mammals and birds when appropriate. I can imagine the screaming if I showed the rib contours of ceratopsids or hadrosaurs, when that is normal with rhinos. 

GSPaul

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[Tim Williams]

Gregory Paul wrote:

> In prosauropods (sauropodomorphs excluding sauropods, is that allowed in the Phylocode?)

No.  But does it matter?

[Eric Snively]

Mike wrote:
... I can imagine that this might completely enclose the ventral compartment in taxa with the deepest ventral concavities, but there is a fair bit that needs to be in there (the carotids will more dorsal, with esophagus and then trachea below them)

Agreed that the cervical ribs would enclose most of the ventral compartment. The trachea and esophagus (when and where full) would be prominent ventrally, but probably not the carotids. Along most of the neck the caritids in birds (confusingly called "internal carotids") are pretty deep, in a wide groove between crista carotica on either side and dorsal to the m. longus colli ventrais muscles (and m. flexor colli cranially). Some birds have just one carotid vessel in that groove, fed by common carotids posterielry and spltting into cerebral and external carotids anteirorly.. In crocs there's also a single, medial common carotid along most of the neck, according to Jayc Sedlmayr.

Greg wrote:

The only good analog in that size class are giraffe necks, which are very narrow.

Certainly for the "bulk" of neck muscles in sauropods. The necks worked "remotely" through long tendons. The big ventro- and lateroflexors in sauropods, as in birds, were probably deep in the thorax: bellies of m. longus colli ventralis sending those long tendons to the cervical ribs. The neck dorsiflexors were also from the anterior part of the thorax and base of the neck, running by long tendons to epipophyses. Takanobo Tsuihiji and Cary Woodruff showed that ligaments would reduce necessary muscular work for holding up and lateroflexing the neck.

[Gregory Paul]

An advantage of having the ventral neck tissues blood vessels included between the cervical ribs instead of hanging below them is that it would have afforded them some protection against attack.

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[Russell Engelman]

> My profile-skeletals produce "low" masses because they are based on the most appropriate models for the particular types. For example for the big dinosaur herbivores it is big mammalian herbivores. Which are shrink wrapped when in a lean-healthy conditions. As per assorted rhino species in which the ribs are normally visible --

If that is the case, I would think that would be pretty easily demonstrable by showing these larger animals have a lower body fat contribution than typical sized animals. Which it kind of makes sense that they would simply because larger animals tend to have proportionally more massive skeletons for their size, both on land and in the ocean. I didn't do a very deep search into this but it does look like elephants are reported to have a slightly lower body fat composition than humans.

Though I don't know if that comparison is wild elephants relative to relatively fat westerners. One of my advisors works with people living in conditions roughly comparable to the Neolithic in Africa, and they pointed out that for these people is actually typical to see the outlines of flat bones such as the zygomatic arches or ribs. These people aren't living in famine conditions but they do live a fairly hand to mouth existence, and so maybe even pre-Bronze Age humans in a "natural state" would look a lot leaner and bonier then we are expecting. Of course, one has to wonder if that is due to living conditions as well. I've seen it pointed out that most living cultures that are still living as hunter-gatherers or Neolithic level farmers are living on what constitutes fairly marginal land for humans, and thus would be expected to have a lot less caloric surplus. Early humans living in prime habitat (savanna, chaparal, temperate forest) might be expected to be a bit plumper.

I didn't do an extremely deep literature dive into this question but I found this article which seems to kind of support what's being said (Heidegger et al. 2016). This article looks at body condition in Indian rhinoceroses for use in zoo health and considers the "ideal" condition to be one where the ribs are slightly visible. If the ribs are not visible the animal is considered at least somewhat overweight.

However, for asian elephants the ribs are never visible unless the animal is severely emaciated, even in wild individuals, though the outlines of the scapula and pelvis are at least slightly visible. This also appears to be the case for African elephants (Morfield et al. 2014), again with wild individuals included in this study. In tapir as well all but the most extreme protruberances of bone are not visible in healthy individuals (Pérez-Flores et al. 2016). Another paper says visible ribs are not normal for black rhinos, and implies what look like ribs in healthy individuals of Indian rhinos are just skin folds (Reuter and Adcock 1998). Median body condition values for cape buffalo suggest the ribs should be slightly visible (Ezenwa et al. 2009), but looking at pictures of wild cape buffalo the ribs are barely visible and I wonder if this is another skin fold thing. Indeed it almost looks like one is seeing the individual intercostal muscles rather than the actual ribs. That's kind of what I'm noticing with these other studies: normal animals have broad-scale muscle blocks outlines (i.e., the shoulder, the hip), but not necessarily individual bones.

I wonder if looking at birds without feathers such as in Katrina van Grouw's The Unfeathered Bird might give a better idea as to how bony dinosaurs would be expected to be. Although it's possible birds might be overtly bony because of weight constraints for flight and because they have feathers to deal with any thermoregulation issues. Overly obese dinosaurs would be unlikely even in high productivity conditions simply because sauropsids tend to store weight in their tail before they do anywhere else, in contrast to mammals where it usually goes straight to the belly.

Ezenwa, Vanessa O., Anna E. Jolles, and Michael P. O’Brien. "A reliable body condition scoring technique for estimating condition in African buffalo." African Journal of Ecology 47.4 (2009): 476-481.

Heidegger EM, von Houwald F, Steck B, Clauss M. Body condition scoring system for greater one-horned rhino (Rhinoceros unicornis): Development and application. Zoo Biol. 2016 Sep;35(5):432-443. doi: 10.1002/zoo.21307. Epub 2016 Jun 20. PMID: 27322390.

Morfeld, Kari A., et al. "Development of a body condition scoring index for female African elephants validated by ultrasound measurements of subcutaneous fat." PloS one 9.4 (2014): e93802.

Pérez-Flores J, Calmé S, Reyna-Hurtado R. Scoring Body Condition in Wild Baird's Tapir (Tapirus bairdii) Using Camera Traps and Opportunistic Photographic Material. Tropical Conservation Science. 2016;9(4). doi:10.1177/1940082916676128

Reuter, H. O., and K. Adcock. "Standardised body condition scoring system for black rhinoceros (Diceros bicornis)." Pachyderm 26 (1998): 116-121.

Wijeyamohan, S., Treiber, K., Schmitt, D. and Santiapillai, C. (2015), A visual system for scoring body condition of Asian elephants (Elephas maximus). Zoo Biology, 34: 53-59. https://doi.org/10.1002/zoo.21181