One of the most compelling pieces of evidence that dinosaurs were cold-blooded was the presence of what’s called “lags.” Lags are marks that form in bone during periods of suspended growth, most notably during cool weather. As warmer weather returns, the animal resumes growing. Over time, these marks can provide a record of physical development. The only modern creatures that have lag marks are reptiles and amphibians, thus inferring that dinosaurs themselves were cold-blooded. It seemed like a safe bet…at least until now.
A team of scientists led by paleontologist Meike Koehler of the Catalan Institute of Paleontology in Barcelona recently completed a survey of mammal thigh bones from around the world. Astonishingly enough, the team found lag marks in all of them. While it’s not slam-dunk evidence that dinosaurs were warm-blooded, it is compelling evidence that we may need to rethink what we knew about the dinosaurs.
It’s amazing to think about warm-blooded dinosaurs, and that’s the great thing about science: Ideally, it’s free of dogma, and we’re always free to revise our picture of the world based on new evidence.