biostudies-literatureLee SNational Research Foundation of Korea (NRF)1185https://www.ebi.ac.uk/biostudies/studies/S-EPMC9715538biostudies-literatureUnknown5(1)Streamlining a body is a major adaptation for aquatic animals to move efficiently in the water. Whereas diving birds are well known to have streamlined bodies, such body shapes have not been documented in non-avian dinosaurs. It is primarily because most known non-avian theropods are terrestrial, barring a few exceptions. However, clear evidence of streamlined bodies is absent even in the purported semiaquatic groups. Here we report a new theropod, Natovenator polydontus gen. et sp. nov., from the Upper Cretaceous of Mongolia. The new specimen includes a well-preserved skeleton with several articulated dorsal ribs that are posterolaterally oriented to streamline the body as in diving birds. Additionally, the widely arched proximal rib shafts reflect a dorsoventrally compressed ribcage like aquatic reptiles. Its body shape suggests that Natovenator was a potentially capable swimming predator, and the streamlined body evolved independently in separate lineages of theropod dinosaurs.Communications biologyA non-avian dinosaur with a streamlined body exhibits potential adaptations for swimming.PMC97155382022R1I1A20609192022R1A6A3A01085883Lee STsogtbaatar KKim SHSissons RPark JYLee YNCurrie PJBarsbold RfalseA non-avian dinosaur with a streamlined body exhibits potential adaptations for swimming.Streamlining a body is a major adaptation for aquatic animals to move efficiently in the water. Whereas diving birds are well known to have streamlined bodies, such body shapes have not been documented in non-avian dinosaurs. It is primarily because most known non-avian theropods are terrestrial, barring a few exceptions. However, clear evidence of streamlined bodies is absent even in the purported semiaquatic groups. Here we report a new theropod, Natovenator polydontus gen. et sp. nov., from the Upper Cretaceous of Mongolia. The new specimen includes a well-preserved skeleton with several articulated dorsal ribs that are posterolaterally oriented to streamline the body as in diving birds. Additionally, the widely arched proximal rib shafts reflect a dorsoventrally compressed ribcage like aquatic reptiles. Its body shape suggests that Natovenator was a potentially capable swimming predator, and the streamlined body evolved independently in separate lineages of theropod dinosaurs.2022-01-01T00:00:00Z2022 Dec2025-04-26T12:43:12.48Z2025-04-06T14:00:29.661ZS-EPMC97155383645682310.1038/s42003-022-04119-9