Fossilized Abdomen Contents Reveal What Younger Tyrannosaurs Ate | Sci.Information

Paleontologists in Canada have discovered a 75-million-year-old skeleton of a juvenile of the tyrannosaurid dinosaur Gorgosaurus libratus with the stays of two younger people of the small dinosaur Citipes elegans in its stomach cavity.

Tyrannosaurids are a bunch of carnivorous dinosaurs that dominated the ecosystems of Asia and North America close to the top of the Cretaceous interval, between 80 and 66 million years in the past.

Among the many largest land predators to have ever existed, they grew from meter-long hatchlings to multiton sizes (9- to 12-m lengthy, 2,000 to six,000 kg) over the course of their life span.

Juveniles have been gracile with slender skulls, blade-like tooth, and lengthy slender hind limbs, whereas adults have been sturdy with large skulls and enormous incrassate tooth and have been able to producing bone-crushing bites.

These modifications recommend that tyrannosaurids underwent a serious dietary shift, through which juvenile and grownup people occupied totally different ecological niches.

Fossil proof reveals that dinosaurian megaherbivores (i.e., species with an grownup mass of over 1,000 kg, together with ceratopsids, large ornithomimosaurs, hadrosaurids, and sauropods) have been widespread prey gadgets of enormous tyrannosaurids, a food regimen for which the mandatory variations and chunk forces solely developed when people reached late juvenile or early subadult development phases.

“Sadly, fossil proof for food regimen in younger tyrannosaurids is basically unknown, thus limiting our understanding of ontogenetic dietary shifts in these iconic predators,” mentioned lead creator Dr. François Therrien, a paleontologist on the Royal Tyrrell Museum, and colleagues.

Juvenile Gorgosaurus libratus preserving abdomen contents: images of specimen in (A) proper lateral view and (B) left anterolateral view; (C) interpretive illustration of specimen in proper lateral view; skeleton consists of an almost full cranium, the left aspect of the physique and limbs, and an almost full pelvis; crimson rectangle delineates location of abdomen contents; (D) histological photomicrograph of tibia displaying the presence of 5 strains of arrested growths and two annuli (marked by asterisks), indicating that the person was between 5 and seven years previous. Scale bars – 50 cm in (A-C) and 1 mm in (D). Picture credit score: Therrien et al., doi: 10.1126/sciadv.adi0505.

Of their analysis, the authors examined a well-preserved specimen of Gorgosaurus libratus present in Dinosaur Provincial Park in Alberta, Canada.

“Gorgosaurus libratus was a tyrannosaur that lived 75 million years in the past — a number of million years earlier than Tyrannosaurus rex — in what’s now southern Alberta,” they mentioned.

“The age of this particular person when it died has been estimated at between 5 and 7 years previous.”

“With an estimated physique mass of 335 kg based mostly on its thigh bone (femur) size, the juvenile would have been lower than 13% of the physique mass of an grownup.”

The researchers discovered the partial stays of two small dinosaurs contained in the abdomen cavity of the Gorgosaurus libratus specimen.

“Earlier than it died, the carnivore dismembered two younger, bird-like herbivorous dinosaurs of the species Citipes elegans,” they mentioned.

“Quite than swallowing its prey entire, the younger tyrannosaur solely ate the hind limbs (the meatiest components of the physique).”

“The prey have been caenagnathid dinosaurs, much like Oviraptor from Asia.”

The additional examine of the fossilized bones indicated that each Citipes elegans people have been inside their first yr of life once they died.

“The rock throughout the ribcage was eliminated to reveal what was hidden inside. The entire hind legs of two child dinosaurs, each underneath a yr previous, have been current in its abdomen,” Dr. Therrien mentioned.

As a result of the weather of the 2 people are at totally different phases of digestion, the scientists have been capable of conclude that Gorgosaurus libratus’ abdomen contents symbolize two totally different meals, ingested hours or days aside.

The presence of two dinosaurs of the identical species and age within the abdomen contents, ingested at totally different occasions, means that younger caenagnathids could have been among the many most popular prey of juvenile gorgosaurs.

This specimen is the primary to offer direct proof that younger gorgosaurs had totally different diets than their grownup counterparts.

Primarily based on tooth marks left on bones, grownup gorgosaurs are recognized to have hunted megaherbivore dinosaurs, corresponding to ceratopsians and hadrosaurs.

Grownup gorgosaurs used their large skulls and enormous tooth to seize massive prey, chunk via bone, and scrape and tear flesh from carcasses.

Nonetheless, juvenile gorgosaurs weren’t constructed to hunt such massive prey. Juveniles have been lean, with slender skulls, blade-like tooth, and lengthy, slender hind limbs. They have been ideally fitted to capturing and dismembering small and younger prey.

The proof means that tyrannosaurs occupied totally different ecological niches over their lifetime.

As younger tyrannosaurs grew and matured, they might have transitioned from looking small and younger dinosaurs to preying on massive herbivores.

This dietary shift probably started across the age of 11, when the tyrannosaurs’ skulls and tooth began turning into extra sturdy.

“It’s well-known that tyrannosaurs modified loads throughout development, from slender varieties to those sturdy, bone-crushing dinosaurs, and we all know that this modification was associated to feeding habits,” mentioned College of Calgary’s Dr. Darla Zelenitsky, co-author of the examine.

“They seem to have gone from looking prey like Citipes elegans (small fraction of their measurement) as youngsters to looking megaherbivore dinosaurs (as massive, or bigger, than their measurement) as adults.”

The crew’s paper was printed within the journal Science Advances.

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François Therrien et al. 2023. Exceptionally preserved abdomen contents of a younger tyrannosaurid reveal an ontogenetic dietary shift in an iconic extinct predator. Science Advances 9 (49); doi: 10.1126/sciadv.adi0505