Estimating the size and shape of extinct animals (free pdf)

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

A new paper:

Free pdf:

Joel H. Gayford, Russell K. Engelman, Phillip C. Sternes, Wayne M. Itano, Mohamad Bazzi, Alberto Collareta, Rodolfo Salas-Gismondi, Kenshu Shimada
Cautionary tales on the use of proxies to estimate body size and form of extinct animals
Ecology and Evolution 14(9): e70218
doi: https://doi.org/10.1002/ece3.70218
https://onlinelibrary.wiley.com/doi/10.1002/ece3.70218

Free pdf:
https://onlinelibrary.wiley.com/doi/epdf/10.1002/ece3.70218


Body size is of fundamental importance to our understanding of extinct organisms. Physiology, ecology and life history are all strongly influenced by body size and shape, which ultimately determine how a species interacts with its environment. Reconstruction of body size and form in extinct animals provides insight into the dynamics underlying community composition and faunal turnover in past ecosystems and broad macroevolutionary trends. Many extinct animals are known only from incomplete remains, necessitating the use of anatomical proxies to reconstruct body size and form. Numerous limitations affecting the appropriateness of these proxies are often overlooked, leading to controversy and downstream inaccuracies in studies for which reconstructions represent key input data. In this perspective, we discuss four prominent case studies (Dunkleosteus, Helicoprion, Megalodon and Perucetus) in which proxy taxa have been used to estimate body size and shape from fragmentary remains. We synthesise the results of these and other studies to discuss nuances affecting the validity of taxon selection when reconstructing extinct organisms, as well as mitigation measures that can ensure the selection of the most appropriate proxy. We argue that these precautionary measures are necessary to maximise the robustness of reconstructions in extinct taxa for better evolutionary and ecological inferences.

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Blog:

My Big Fat Dimensional Wedding
Andre Cau on overestimating the size of prehistoric critters (in Italian)

https://theropoda.blogspot.com/2024/09/il-mio-grosso-grasso-matrimonio.html

[Russell Engelman]

The supplementary information is worth checking out too, if you haven't seen it. We review body size controversies in the literature and find there's been quite a systematic problem with size overestimates. Something like 50+ independent cases resulting in size overestimates, and that's treating all azdarchids, mosasaurs, South American caimanines, abelisauroids, etc., as one group. And the disparities in size estimates were often quite large. We didn't look super hard to find every last example, especially for dinosaurs, we were just trying to do a brief survey to show how widespread this problem is. So there may be a lot more out there. By contrast, I think we identify like 5 cases where the original size turned out to be underestimated: two mega-marsupials, Jaekelopterus (maybe, as other factors raise questions about that estimate), Metriorhynchidae, and megalodon (again, maybe, depending on how one interprets Sternes et al. 2024).

[Gregory Paul]

The paper Asier Larramendi and I have resubmitted for review addresses some of the issue raised by this paper regarding Perucetus. Including getting a mass of only ~60 t for the Biannucci et al. skeletal way below their 85-340 t range, and 35-40 t for our multi-view restoration based on the proportions of dense boned basilosaurs. 

Another reason megalodon was not tunniform is that nothing that big ever is, the largest such being orcas of 6 t. Tunniform ichthyosaurs are even smaller. 

GSPaul

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[mkir...@gmail.com]

Very informative paper.  I was interested in the statement:  

Indeed, the fragmentary nature of remains used to reconstruct the body size and form of many extinct taxa can substantially increase error. Fragmentary remains are often first used to estimate the size of some larger or complete morphological structure (e.g., skull), which is in turn used to approximate total length. These cascading assumptions result in the propagation of error at each stage of reconstruction (Molnar & Vasconcellos, 2016), further complicating downstream ecological, evolutionary and bio-mechanical interpretations. (p. 10)

The paper makes a good argument that social pressures influence media statements.

Several factors may also make researchers reluctant to publish modest size estimates of extinct taxa. Researchers may be reluctant to downsize spectacular charismatic megafauna for fear that it will reduce public interest in their research area or burn bridges in the academic community, which could have downstream consequences for collaborations, funding acquisition or even the outcome of peer review. They may also fear museums may restrict access to specimens or otherwise respond poorly to research downsizing their flagship taxon. Furthermore, one must be aware of backlash from the ever-growing fan communities of prehistoric organisms (such as Dunkleosteus, O. megalodon and theropod dinosaurs) on the internet, who may feel strongly about the perceived appearance of their favourite organisms. None of these concerns are hypotheticals, and all have happened at one point or another to many palaeobiologists who study well-known, iconic fossil taxa, including some of those mentioned in the present study. (pp. 11-12)

 I was dismayed that some estimates come from Planet Dinosaur and Walking With Monsters!. I quickly checked to make sure that the Dinosaur Mailing List was not a culprit!

[Nick Gardner]

I'll openly admit I (unknowingly) made errors in our 2012 paper. I am glad to see this paper out there, and I appreciate the way it was discussed in the supplementary information. I was contacted by one of the authors prior to submission and we had a very productive conversation about how this could be potentially done better in the future. The long story short is we need a lot more people out there measuring complete (or as complete as possible) skeletons of living and fossil skeletons using multiple proxies for then extrapolating size as well as accounting for phylogeny in those estimations/extrapolations. If you're relying on estimating the size of one body region from a proxy, then using that estimate to estimate the total body size (length or mass), the opportunities for overestimation just compound dramatically. Now if only I had the funding to go measure the possibly hundreds of crocodylians in East Coast museums. :)

[Gregory Paul]

The Gayford et al paper does not consider what is along with the Perucetus disaster the biggest -- pun intended -- scandal in over sizing extinct beasts. The recent estimates that Triassic ichthyosaurs were reaching 40-80 tonnes, including in Science. My skeletals in the Princeton Field Guide to Mesozoic Sea Reptiles leave no doubt that the biggest known sea reptiles did not exceed 20 tonnes (and that the 21 m length estimate for "S." sikanniensis was a boo-boo in the original JVP paper that people keep repeating without doing the basic scientific procedures of actually looking at the quarry map and doing a skeletal). The people who devised higher estimates -- and you know who you are -- did not bother to follow basic mass estimating practices of simply doing old fashioned skeletals of the taxa concerned and measure their volumes. Instead we got elaborate paleobiological calculations of how the Triassic oceans were somehow so super productive that they sustained such amazing -- i. e. probably impossible -- size expansions so quickly (as implied for whales by the outlandish Perucetus mass values that also never should have seen the light of day) that makes good papers for Science and lots of press coverage. No one has contradicted my restorations because it is not possible to do so (those researchers have dropped their size claims in more recent works without acknowledging my refutations as my technical manuscript gets rejected I suspect by some of those people in some cases). The authors of these papers should retract them unless they can show their mass estimates are correct with skeletals (I change my mass estimates when new data or analysis shows up all the time, the Dinoguide3 is the first to have fully solid supertitanosaur masses after years of trying to sort through the data). I am not holding my breath on that. 

GSPaul

https://groups.google.com/d/msgid/DinosaurMailingGroup/c6b3750f-9b55-46ba-bb5e-ae641105223fn%40googlegroups.com

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[Russell Engelman]

Greg, it does consider those. It specifically mentions your observation that there was a lapsus in the quarry map of "Shastasaurus" sikannensis and cites you as the source of that observation. Did you read the supplementary information? Check pages 58 and 59. We cited you because you were the one who pointed it out, and giving you credit for that observation was the proper thing to do.

The problem is your observations are not formally published, so we could not easily evaluate evidence for your claim as to why the size of these animals are overestimated and thus it was difficult to discuss in more detail. An off-the-cuff post on the DMG is not the same as a formal paper where someone can go through your logic and data step by step. We would very much like to see your arguments for smaller size estimates for "Shastasaurus" sikannensis and Ichthyotitan published, so they can be properly evaluated, especially given the broader pattern we observed. We actually got criticized by some ichthyosaur workers for even considering size estimates for "S." sikannensis and I. severnensis controversial at all and were told you were not an acceptable reference and should not be cited. So we're getting it from both ends here. If this is a major concern for you, I encourage you to get those ichthyosaur manuscripts resubmitted and formally published.

Russell

[Gregory Paul]

Ha ha ha. The review system is pernicious. Always has been and always will be. There are people whose noted careers are dependent on not being shown up and they will suppress the opposition. As noted in earlier messages here I have been verbally threatened by some of these people over the decades a few times, that has its amusement factor and is not an actual problem. But having papers suppressed is another. As pointed out in another post, Asier Larremendi and I were charged with sexism in a manuscript on Perucetus by a nut job for merely mentioning that female blue whales are larger than the males and person refused to read entire paper they being so offended, and the other more sane reviewer was obviously not familiar with whole animal biology and skeletals -- also accused us of not using the common drone top view shots of whales to restore them when we directly cited a paper that provides such views which we used. My ichthyosaur paper was suppressed with the charge that it uses old fashioned methods, not the sophisticated means of miscalculating 40-80 tonnes. I will resubmit it, but that does not mean it will ever be published. The fix may be in. Don't blame me. 

And do consider I am getting no grant money or salary to cover times and expenses (cannot publish in journals that require large fees) or staff to help out. My ability to reformat and resubmit is limited. 

There is a gross inconsistency going on here. People cite conference abstracts all the time, even though they are brief with no figures and sometimes the contents are not further published. But an academic press book containing skeletals that can be measured and volume examined etc is off limits? Makes no sense. It should be the people that make extreme claims of size without skeletals to back them up that should be required to withdraw the masses unless they can produce the needed restorations. That would be actual science, not the cynical manipulation of refusing to consider books. It is a further form of suppression -- I suspect there may not have been objections had my book supported the super sea reptiles. I had a paper rejected because a reviewer got after me for not citing a dinosaur skeletal by Hartman that was years out of date (a new paper had redecribed the taxon) and it was never published in print much less peer review. They just say what they need to when it serves their purposes. One thing that is useful is when an academic multi-author chapters book is being published and the editor may toss aside bogus peer reviews for their colleagues. 

GSPaul