no, we still don't know why t. rex had little arms
Popular science outlets continue to do a terrible job of explaining studies on primeval evolution and pretending we have answers we don't.
According to Pop Sci, the magazine once known as Popular Science, scientists have finally figured out why the iconic Tyrannosaurus rex ended up with such teeny arms. Except for the part where they didn't and the headline is actually confusing unless you think that evolution works like a corporate CEO with a Six Sigma black belt and runs genetic drift with the ruthless efficiency of a factory floor. The article says that it was a case of use it or lose it, which, okay, sure fine, but not really a good answer.
Your own body is proof that the body doesn't lay off organs and parts just because they're not entirely necessary anymore. You still have an appendix even through our diet does not require us to ferment leaves and grasses to help break them down for digestion. You still have toes even though you don't need to swing from branch to branch. And you still have a coccyx despite not having or needing a tail. Why? The genes in your DNA still have instructions for creating them.
Similarly, just because a T. rex now has enormous jaws and a huge skull doesn't mean its body will now shrink its arms as a side-effect. It might, if the genes are somehow related, but that's not what the study in question shows. What it does say is that there's correlation between increased skull and jaw size and smaller forelimbs in non-avian predatory dinosaurs called theropods, and that the trend was widespread, and asks if there was some sort of reason for this given the data, but doesn't provide a definitive answer without more fossils and genetic analysis.
So, it may be that the mutation that favored large skulls and jaws, which meant more success hunting larger prey, also impacted forelimb genes. It could be that one set of mutations increased skull and jaw size, then other mutations that made the forelimbs smaller also improved balance while chasing down meals. Or the two changes could be unrelated and having small forelimbs didn't hurt or help, so these small arms just propagated by pure chance.
Why does this matter though? What's the difference between this and Pop Sci's "use it or lose it" explanation? The former ideas highlight the role of chance and selection in evolution, the latter reeks of Lamarckism and is perfect as fodder for your run of the mill creationist propaganda. If you want to give your audience a scientifically accurate representation of how evolution works, you need to be comfortable with giving them the messy, more technical answer. If you don't, all you're doing is adding to the tsunami of bad information polluting the web and harming scientific education today.
See: Scherer, C., et al. (2026) Drivers and mechanisms of convergent forelimb reduction in non-avian theropod dinosaurs. Proc Biol Sci 293 (2071), DOI: 10.1098/rspb.2026.0528
