Theropod forelimbs got smaller when heads got larger...

[Richard W. Travsky]

Last month I read a newspaper (old school) article on theropods which outlined how (some) theropod arms got smaller and the heads got bigger. Was that mentioned here? If so I missed it or it didn't register. I've since recycled the paper and now I'm wanting to know a bit more about it. Would someone have a reference? TIA

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

The article was posted here back in May:

Free pdf:

Charlie Roger Schere, Elizabeth Steell & Paul Upchurch (2026)
Drivers and mechanisms of convergent forelimb reduction in non-avian theropod dinosaurs
Proceedings of the Royal Society B: Biological Sciences 293(2071): 20260528.
doi: https://doi.org/10.1098/rspb.2026.0528
https://royalsocietypublishing.org/rspb/article/293/2071/20260528/481779/Drivers-and-mechanisms-of-convergent-forelimb


Forelimb reduction has been observed in numerous and disparate non-avian theropod dinosaurs, resulting in the hypothesis that reduced forelimbs evolved convergently. Clades with reduced forelimbs also possess high degrees of cranial robusticity and gigantic body sizes. Here, we provide a novel quantification of forelimb reduction across Theropoda, and create and implement a cranial robusticity scoring system, and analyse this dataset using bivariate and comparative phylogenetic analyses. Results indicate that forelimb reduction is strongly correlated with cranial robusticity and gigantism. Reduced/vestigial forelimbs evolved in at least five theropod lineages in concert with increased cranial robusticity and gigantism. Abelisaurids, carcharodontosaurids and tyrannosaurids show the greatest forelimb reduction relative to the skull. Repeated forelimb reduction across theropods was facilitated by increased cranial robusticity and greater body size that was potentially influenced by an upward trend in prey body size. These events resulted in a shift from subduing prey using grasping forelimbs to using powerful bites and robust skulls.

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News:

https://phys.org/news/2026-05-meat-dinosaurs-rex-evolved-tiny.html

https://nautil.us/we-finally-have-the-answer-for-t-rexs-tiny-arms-1280997

On Wed, Jul 15, 2026 at 9:21 AM 'Richard W. Travsky' via Dinosaur Mailing Group <DinosaurMa...@googlegroups.com> wrote:

Last month I read a newspaper (old school) article on theropods which outlined how (some) theropod arms got smaller and the heads got bigger. Was that mentioned here? If so I missed it or it didn't register. I've since recycled the paper and now I'm wanting to know a bit more about it. Would someone have a reference? TIA

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[Jerry Harris]

This subject has been discussed (more specifically in tyrannosaurids) in older publications, too, notably:

Lockley, M.G., Kukihara, R., and Mitchell, L. 2008. Why Tyrannosaurus rex had puny arms: an integral morphodynamic solution to a simple puzzle in theropod paleobiology, pp. 131–164 in Larsen, P. and Carpenter, K. (eds.), 100 years of Tyrannosaurus rex. Baltimore, Johns Hopkins University Press.

Padian, K. 2022. Why tyrannosaurid forelimbs were so short: an integrative hypothesis. Acta Palaeontologica Polonica 67(1): 63–76.

I mention these just for the sake of completeness on the topic.