DENVER (KDVR) — Details about a juvenile Tyrannosaurus rex fossil discovered by three boys in North Dakota are beginning to take shape at the Denver Museum of Nature and Science, including its size, age and how its body worked. The T. rex fossil, affectionately named the "Teen Rex" because of its possible age, was discovered in the summer of 2023. Juvenile T. rex fossils are rare, according to the museum, which said there have been only a handful found in the world. Fossil preparator Alex Polich exposes the fossil specimen in the Teen Rex Prep Lab at the Denver Museum of Nature & Science. (DMNS photo / Rick Wicker)Teen Rex's foot bone in the jacket after it was air abraded. (DMNS photo/ Alex Polich)Dr. Tyler Lyson, lead scientist of the project, and the trio of young fossil finders, Liam Fisher, Jessin Fisher, and Kaiden Madsen who discovered the remains of a juvenile T. rex skeleton while out looking for fossils with their dad Sam Fisher. (DMNS - Dr. Kirk Johnson)In this photo provided by Giant Screen Films, chief preparator Natalie Toth, left, of the Denver Museum of Nature and Science, examines fossilized plants from the Cretaceous period in a moment captured by the crew of the documentary "T.REX," at a fossil dig site in North Dakota, named “The Brothers.” (Andy Wood/Giant Screen Films via AP)Denver Museum of Nature & Science volunteer Aidan Skelly poses by the partial juvenile T. rex skeleton. (DMNS - Dr. Tyler R. Lyson)The fossil finding family (clockwise from upper left: Sam Fisher, Emalynn Fisher, Danielle Fisher, Liam Fisher, Kaiden Madsen, and Jessin Fisher) pose with the field jacket after it was rolled into a helicopter net. (DMNS - Dr. Tyler R. Lyson)Three tooth emerging from the sandstone. (DMNS - Dr. Tyler R. Lyson)Denver Museum of Nature & Science volunteer Aidan Skelly poses by the partial juvenile T. rex skeleton. (DMNS - Dr. Tyler R. Lyson) In June, the science museum opened its temporary "Discovering Teen Rex" exhibit. Inside the exhibit, visitors can see the meticulous process of uncovering and studying fossils as well as ask scientists questions as more bones are uncovered from plaster field jackets. The T. rex bones found in 2023 - which included parts of the skull, tail, leg, and hip - were wrapped in plaster jackets and transported to Denver. Scientists estimated the juvenile dinosaur's dimensions at about 25 feet long and with plaster jackets, weighed about 6,000 pounds. Paleontologists said they believe the actual dinosaur weighed about 3,500 pounds and was alive millions of years ago. In early December 2024, the museum reported that it had uncovered the Teen Rex's lower jaw and had discovered a "beautiful, fossilized palm frond from the same late Cretaceous Period 67 million years ago." Additionally, the team of paleontologists has discovered "significant portions" of the young dinosaur's skull, including the upper jaw and many teeth. Visitors to the Discovery Teen Rex exhibit can see most of its face now, as scientists have also uncovered the dinosaur's nose and nostril area, as well as its eye socket and "an impressive array of maxillary teeth." Alex Polich, a full-time fossil preparer for the museum, noted in an Instagram video that while uncovering the fossils, they've discovered tiny maxillary teeth replacements, which Polich said points to how the T. rex likely was in a constant process of losing teeth and regrowing them throughout its life. Also over the summer, the museum team has begun uncovering the leg and foot bones, revealing how tall the teenage dinosaur was when alive. The bones, which are being carefully preserved and articulated, include the T. rex's tibia, or shin bone, which was the first one spotted by the children in North Dakota. Now, paleontologists have uncovered the tibia, fibula and femur to showcase the entire leg of Teen Rex. "The tibia is significant because it is the bone that first clued us into the fact that this T. rex was a juvenile," the museum said in a blog post. "We used the tibia length to estimate the age of this dinosaur to be between 13 and 15 years old when plotted on a Tyrannosaurus growth curve." An exact age will be determined through a closer examination of the tibia bone, the museum explained. "This will be accomplished by carefully removing a portion of the bone and looking at its cross-section," the museum said. "Similar to the growth rings in trees, some dinosaur bones also contain evidence of growth on the interior bone."