Eddie Gonzales Jr. – AncientPages.com –\u00a0<\/strong>What if everything we know about T. rex growth is wrong? A complete tyrannosaur skeleton has just ended one of paleontology\u2019s longest-running debates \u2013 whether Nanotyrannus is a distinct species, or just a teenage version of Tyrannosaurus rex.<\/p>\n A pack of Nanotyrannus attacks a juvenile T. rex. Image credit: Anthony Hutchings<\/em><\/p>\n The fossil, part of the legendary \u201cDueling Dinosaurs\u201d specimen unearthed in Montana, contains two dinosaurs locked in prehistoric combat: a Triceratops and a small-bodied tyrannosaur. That tyrannosaur is now confirmed to be a fully grown Nanotyrannus lancensis \u2013 not a teenage T. rex, as many scientists once believed.<\/p>\n \u201cThis fossil doesn\u2019t just settle the debate. It flips decades of T. rex research on its head,\u201d says Lindsay Zanno, associate research professor at North Carolina State University, head of paleontology at the North Carolina Museum of Natural Sciences and co-author of the study published in\u00a0Nature<\/em>.<\/p>\n Lindsay Zanno, associate research professor at North Carolina State University and head of paleontology at the North Carolina Museum of Natural Sciences, with the Dueling Dinosaurs fossil. Image credit: <\/em>N.C. State University<\/em><\/p>\n Using growth rings, spinal fusion data and developmental anatomy, the researchers demonstrated that the specimen was around 20 years old and physically mature when it died. Its skeletal features \u2013 including larger forelimbs, more teeth, fewer tail vertebrae, and distinct skull nerve patterns \u2013 are features fixed early in development and biologically incompatible with T. rex.<\/p>\n Nanotyrannus and Tyrannosaurus Rex arm comparison. Image credit: NC Museum of Natural Sciences<\/em><\/p>\n<\/div>\n \u201cFor Nanotyrannus to be a juvenile T. rex, it would need to defy everything we know about vertebrate growth,\u201d says James Napoli, anatomist at Stony Brook University and co-author of the study. \u201cIt\u2019s not just unlikely \u2013 it\u2019s impossible.\u201d<\/p>\n The implications are profound. For years, paleontologists used Nanotyrannus fossils to model T. rex growth and behavior. This new evidence reveals that those studies were based on two entirely different animals \u2013 and that multiple tyrannosaur species inhabited the same ecosystems in the final million years before the asteroid impact.<\/p>\n Snout of Nanotyrannus. Image credit: N.C. Museum of Natural Sciences<\/em><\/p>\n As part of their research, Zanno and Napoli examined over 200 tyrannosaur fossils. They discovered that one skeleton, formerly thought to represent a teenage T. rex, was slightly different than the Dueling Dinosaurs\u2019 Nanotyrannus lancensis. They named this fossil a new species of Nanotyrannus, dubbed N. lethaeus. The name references the River Lethe from Greek mythology \u2013 a nod to how this species remained hidden in plain sight and \u201cforgotten\u201d for decades.<\/p>\n James Napoli is a research adjunct at the North Carolina Museum of Natural Sciences and an anatomy instructor at the Renaissance School of Medicine at Stony Brook University in New York. Image credit: James Napoli<\/em><\/p>\n<\/div>\n Confirmation of the validity of Nanotyrannus means that predator diversity in the last million years of the Cretaceous was much higher than previously thought, and hints that other small-bodied dinosaur species might also be victims of mistaken identity.<\/p>\n \u201cThis discovery paints a richer, more competitive picture of the last days of the dinosaurs,\u201d Zanno says. \u201cWith enormous size, a powerful bite force and stereoscopic vision, T. rex was a formidable predator, but it did not reign uncontested. Darting alongside was Nanotyrannus \u2013 a leaner, swifter and more agile hunter.\u201d<\/p>\n![\"Nanotyrannus](\"https:\/\/www.ancientpages.com\/wp-content\/uploads\/2025\/11\/tr111exnov3.jpg\")
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