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Gorgosaurus libratus feeding on Citipes elegans. Illustration by Julius Csotonyi (C) Royal Tyrrell Museum of Palaeontology.

Chicken Legs? The Preservation of a Juvenile Tyrannosaurid's Last Meal

Illustration by Julius Csotonyi - Royal Tyrrell Museum

Paleontology News

Video from the Royal Tyrrell Museum discussing the discovery

Chicken Legs? The Preservation of a Juvenile Tyrannosaurid's Last Meal

The remarkable preservation of two sets of Citipes thropod legs in a juvenile Gorgosaurus.

Summary Points

Figure 2A from Francois Therrien et al., 2023- Science Advances - showing the outlines of the two Citipes specimens and the Gorgosaurus specimen highlighting the articulated bones found.

Unprecedented find: Stomach contents from a juvenile Tyrannosaurid reveal its last meals, offering glimpses into its diet.

Citipes legs: The remains two sets of legs from turkey-sized feathered theropods called Citipes were found in the stomach.

Shifting menu: The juvenile Gorgosaurus meals suggest dietary changes as they aged.

Coexistence achieved: Juveniles and adult Tyrannosaurids likely cohabited without conflict thanks to their different food preferences.

Evolutionary triumph: Dietary flexibility may have played a key role in their success as apex predators.

Chicken Legs? The Preservation of a Juvenile Tyrannosaurid's Last Meal

This news article is based on a release by the Royal Tyrrell Museum of Paleontology - December 8, 2023, and the Open Access (CC BY 4.0) Journal Article (Francois Therrien et al., 2023) from Science Advances.

Figure 1B from Francois Therrien et al., 2023- Science Advances - showing the showing an anteriolateral view of the fossils with the preserved stomach contents highlighted in the red box.

In a groundbreaking discovery, the first preserved stomach contents have been found in a Tyrannosaurid. This apex predator, a Gorgosaurus libratus, lived in Western North America during the Cretaceous period. Notably, Gorgosaurus predates the iconic Tyrannosaurus Rex by roughly 10 million years and was slightly smaller in stature. Leading the research on this remarkable fossil were Francois Therrien and Darla Zelenitsky, whose findings offer invaluable insights into the dietary habits of these ancient predators.

Discovered in Dinosaur Provincial Park, Alberta, the remarkable fossil was unearthed by the Royal Tyrrell Museum in 2009. However, it wasn't until during preparation that technician Darren Tanke made a startling discovery: tiny toe bones nestled within the Gorgosaurus' ribcage. Following careful preparation, it was revealed the Gorgosaurus had its last meals preserved within its gut, containing two sets of legs from turkey-sized feathered theropods known as Citipes elegans. Darla Zelenitsky, says "This is a once-in-a-career fossil."

This incredible find marks the first time stomach contents have been found in any tyrannosaurid, offering a unique glimpse into the diet of these apex predators. The two Citipes individuals were approximately a year old and were consumed within a week of the Gorgosaurus dying. Zelenitsky also noted that varying degrees of bone digestion between individuals show they were consumed at separate times, within hours or days of each other. Did this Gorgosaurus have a preference for Citipes legs?

By analyzing the femur length of the Gorgosaurus, researchers determined it was a juvenile weighing around 700 pounds and aged between 5 and 7 years old. This represents only 13% of the mass of a fully grown Gorgosaurus, which, like an adult T-Rex, was robust and possessed a bone-crushing bite. These formidable predators are believed to have hunted large animals such as duck-billed dinosaurs and ceratopsians.

However, before reaching their colossal size, juveniles were built much lighter and lacked the powerful bite of their adult counterparts. This led paleontologists to believe that juveniles underwent a dietary shift, favoring smaller prey during their youth before transitioning to larger prey as adults. Until this discovery, such a dietary shift remained purely theoretical. Now, paleontologists have tangible evidence that the diets of Tyrannosaurids like Gorgosaurus changed significantly as they aged, offering valuable insights into their developmental and ecological roles within the Cretaceous ecosystem.

Such dietary shifts offer a crucial competitive advantage by minimizing intraspecific competition for limited resources. This dynamic likely played a key role in enabling juvenile and adult Tyrannosaurids to coexist within the same environment without conflict, ultimately contributing to their remarkable evolutionary success as some of the largest carnivorous theropods the Earth has ever known.

Figure 3 from Francois Therrien et al., 2023- Science Advances - showing the details of the stomach contents. White are bones from the Gorgosaurus, Green shades are one Citipes specimen, while Blue shades are the other.

Journal Article:
Francois Therrien et al. Exceptionally preserved stomach contents of a young tyrannosaurid reveal an ontogenetic dietary shift in an iconic extinct predator. Sci. Adv.9,eadi0505(2023). DOI:10.1126/sciadv.adi0505

Recommended Dinosaur Books and Educational Items:

The Rise and Fall of the Dinosaurs: A New History of a Lost World
Steve Brusatte, 2019

This dinosaur book is light-hearted and easy to read. The author, a renowned Paleontologist, does a great job at engaging the reader. It is packed with details without being overwhelming. Check out the reviews; it's a great new dinosaur book! Available in Kindle, Paper, and Audio.

Dinosaurs Rediscovered: The Scientific Revolution in Paleontology
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This is a great general book on dinosaurs. It's up-to-date and goes over the new discoveries over the last 20 years that has completely changed our views on dinosaurs. The book is broken up into easy chapters that goes over their colors, speeds, bite force, child caring, and more... stuff we didn't know just years ago! Check out the reviews and the sample pages. Available in Kindle, Paper, and Audio.

Nifeliz Dinosaur Fossils Building Kit

From 8 dinosaurs to choose from, The Nifeliz Dinosaur sets are nearly 500 pieces. They are a great gift for those 12+ who enjoy solo or group building with LEGOs. Constructing these models enhances hand-eye coordination and creativity. Perfect for family or friends, It's also compatible with existing LEGO pieces, facilitating the creation of a personalized toy museum! Check out the reviews!

High quality Dinosaur teeth by Fossilera

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