 |
| Gorgosaurus libratus feeding on Citipes elegans. in Therrien, Zelenitsky, Tanaka, Voris, ... et Kobayashi, 2023. Illustration by Julius Csotonyi |
Abstract
Tyrannosaurids were large carnivorous dinosaurs that underwent major changes in skull robusticity and body proportions as they grew, suggesting that they occupied different ecological niches during their life span. Although adults commonly fed on dinosaurian megaherbivores, the diet of juvenile tyrannosaurids is largely unknown. Here, we describe a remarkable specimen of a juvenile Gorgosaurus libratus that preserves the articulated hindlimbs of two yearling caenagnathid dinosaurs inside its abdominal cavity. The prey were selectively dismembered and consumed in two separate feeding events. This predator-prey association provides direct evidence of an ontogenetic dietary shift in tyrannosaurids. Juvenile individuals may have hunted small and young dinosaurs until they reached a size when, to satisfy energy requirements, they transitioned to feeding on dinosaurian megaherbivores. Tyrannosaurids occupied both mesopredator and apex predator roles during their life span, a factor that may have been key to their evolutionary success.
 |
| Juvenile Gorgosaurus TMP 2009.12.14 preserving stomach contents. Photographs of specimen in (A) right lateral view and (B) left anterolateral view. (C) Interpretive illustration of specimen in right lateral view. Skeleton consists of a nearly complete skull, the left side of the body and limbs, and a nearly complete pelvis. Red rectangle delineates location of stomach contents. (D) Histological photomicrograph of tibia showing the presence of five lines of arrested growths and two annuli (marked by asterisks), indicating that the individual was between 5 and 7 years old. Scale bars, 50 cm (A) to (C) and 1 mm (D). |
 |
| Juvenile Citipes remains preserved as stomach contents. (A) Diagram illustrating relative body sizes of predator and prey and skeletal elements preserved in TMP 2009.12.14. Scale bar, 50 cm. Histological photomicrographs of (B) posterior Citipes individual (metatarsal II) and (C) anterior Citipes individual (tibia), showing highly vascularized woven bone with reticular and longitudinally oriented vascular canals and lacking growth lines, indicative of young individuals that are less than 1 year old. Scale bars, 500 μm. |
 |
| Gorgosaurus libratus feeding on Citipes elegans. Illustration by Julius Csotonyi |
Francois Therrien, Darla K. Zelenitsky, Kohei Tanaka, Jared T. Voris, Gregory M. Erickson, Philip J. Currie, Christopher L. Debuhr, and Yoshitsugu Kobayashi. 2023. Exceptionally preserved Stomach Contents of A Young tyrannosaurid reveal An Ontogenetic Dietary Shift in an iconic Extinct Predator. SCIENCE ADVANCES. 9, 49. DOI: 10.1126/sciadv.adi0505
