Rare fossils, discovered in play

Rare fossils of a juvenile Tyrannosaurus rex have been excavated in the swamplands of North Dakota - a discovery worthy of attention for the scientific knowledge it could provide about the life and history of this famous dinosaur species and for children's stories who discovered them. The discovery of the fossils, nicknamed "Teen Rex", was announced by the Denver Museum of Nature and Science, where they will be studied and exhibited. In July 2022, siblings Liam and Jessin Fisher, then aged seven and 10 respectively, and their cousin Kaiden Madsen, aged nine, were hiking and searching for fossils with Sam Fisher, Liam's father and Jessin, in an area managed by the United States Bureau of Land Management, about 10 miles away from the city of Marmath, in southwestern North Dakota. Liam and his father noticed a large femur bone sticking out of the ground.

Sam Fisher sent a photo to paleontologist Tyler Lyson, a Marmath native and former high school classmate now curator of the Vertebrate Paleontology Department at the Denver Museum of Nature and Science. Tyler Lyson obtained the excavation permits, and in July 2023 the entire group returned to that site. Initially, it appeared that the femur belonged to a duck-billed herbivorous dinosaur. "However, on the first day of the dig, Jessin and I discovered the mandible with several T-rex teeth protruding from it. That image still gives me chills," said Tyler Lyson. Tyrannosaurus rex, which dominated the food chain in western North America, was one of the largest carnivorous dinosaurs in the world. That T-rex specimen was apparently 13-15 years old, two-thirds the size of an adult, 7.6 meters long and 1,600 kilograms in weight. T-rex specimens reached their mature size around the age of 18-21 years. The fossils of the largest known specimen of Tyrannosaurus rex, a specimen named Sue and exhibited at the Field Museum in Chicago, are 12.3 meters long. The specimen from North Dakota lived about 67 million years ago, towards the end of the Cretaceous period. The T-rex and the other dinosaurs, except for the birds that are their descendants, disappeared 66 million years ago after an asteroid hit the Earth.

Having fossils of juvenile specimens helps to track the T-rex's growth rate and body changes during maturation, he added. Only a few fossils of this type are available for study. The North Dakota fossils appear to be slightly larger than those of another juvenile T-rex, named "Jane" and on display at the Burpee Museum of Natural History in Rockford, Illinois. A minority of paleontologists believe that Tyrannosaurus rex lived alongside a smaller cousin called Nanotyrannus, based on fossils that most paleontologists believe represent juvenile Tyrannosaurus rex. Tyler Lyson said the new fossil could shed light on the issue.