biostudies-literatureTagliavento MDeutsche Forschungsgemeinschafte2213987120https://www.ebi.ac.uk/biostudies/studies/S-EPMC10104568biostudies-literatureUnknown120(15)The dinosaur-bird transition involved several anatomical, biomechanical, and physiological modifications of the theropod bauplan. Non-avian maniraptoran theropods, such as <i>Troodon</i>, are key to better understand changes in thermophysiology and reproduction occurring during this transition. Here, we applied dual clumped isotope (Δ₄₇ and Δ₄₈) thermometry, a technique that resolves mineralization temperature and other nonthermal information recorded in carbonates, to eggshells from <i>Troodon</i>, modern reptiles, and modern birds. <i>Troodon</i> eggshells show variable temperatures, namely 42 and 29 ± 2 °C, supporting the hypothesis of an endothermic thermophysiology with a heterothermic strategy for this extinct taxon. Dual clumped isotope data also reveal physiolProceedings of the National Academy of Sciences of the United States of AmericaEvidence for heterothermic endothermy and reptile-like eggshell mineralization in <i>Troodon</i>, a non-avian maniraptoran theropod.PMC10104568FI-948-11/1FI-948-13/1Davies AJTherrien FGuo WSchulp ASBernecker MStaudigel PTMuller WDietzel MZelenitsky DKTagliavento MFiebig JDawson RRGotschl KGerdes AfalseEvidence for heterothermic endothermy and reptile-like eggshell mineralization in <i>Troodon</i>, a non-avian maniraptoran theropod.The dinosaur-bird transition involved several anatomical, biomechanical, and physiological modifications of the theropod bauplan. Non-avian maniraptoran theropods, such as <i>Troodon</i>, are key to better understand changes in thermophysiology and reproduction occurring during this transition. Here, we applied dual clumped isotope (Δ₄₇ and Δ₄₈) thermometry, a technique that resolves mineralization temperature and other nonthermal information recorded in carbonates, to eggshells from <i>Troodon</i>, modern reptiles, and modern birds. <i>Troodon</i> eggshells show variable temperatures, namely 42 and 29 ± 2 °C, supporting the hypothesis of an endothermic thermophysiology with a heterothermic strategy for this extinct taxon. Dual clumped isotope data also reveal physiol2023-01-01T00:00:00Z2023 Apr2025-04-05T15:22:55.587Z2025-04-05T15:22:55.587ZS-EPMC101045683701119610.1073/pnas.2213987120