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The skull of Nanotyrannus. (North Carolina Museum of Natural Sciences)
Fossilized predator bones recovered successful the legendary Cretaceous dinosaur graveyard of Hell Creek did not beryllium to a babe Tyrannosaurus rex aft all.
Analysis of the remains – an astir implicit skeleton that forms fractional of the celebrated Triceratops-tyrannosaur conflict fossil known arsenic Dueling Dinosaurs – shows they belonged to a diminutive tyrannosaurid predator that would person grown to little than a tenth of the size of its much intimidating cousins.
Nanotyrannus lancensis, astatine astir the value of a polar bear, was a veritable teacup mentation of the larger tyrannosaurs, built for agility and speed alternatively than sheer crushing power.
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The Nanotyrannus genus has been debated for decades, with immoderate paleontologists arguing that specimens frankincense classified are alternatively juvenile T. rex. This almost-complete skeleton puts the contention to bed, according to a squad led by paleontologist Lindsay Zanno of North Carolina State University.
"This fossil doesn't conscionable settee the debate. It flips decades of T. rex probe connected its head," Zanno says.
A reconstruction of Dueling Dinosaurs. (North Carolina Museum of Natural Sciences)To resoluteness the individuality situation of the Dueling Dinosaurs tyrannosaurid, Zanno and her colleague, paleontologist James Napoli of the North Carolina Museum of Natural Sciences, conducted a detailed, systematic anatomical survey of the specimen. They paid cautious attraction to features specified arsenic growth rings, spinal fusion data, and developmental anatomy to estimation the animal's maturity astatine the clip of death.
Their investigation showed that the specimen was afloat grown and would person weighed astir 680 kilograms (1,500 pounds). A afloat grown T. rex is estimated to scope astir 8,000 kilograms connected average, though the biggest known has a heavier estimate – and they could person grown overmuch larger.
In addition, N. lancensis has respective features and structures that successful nary mode could make into the morphology of a T. rex skeleton, the researchers say.
A examination betwixt Nanotyrannus and T. rex. (North Carolina Museum of Natural Sciences)"For Nanotyrannus to beryllium a juvenile T. rex, it would request to defy everything we cognize astir vertebrate growth," Napoli says. "It's not conscionable improbable – it's impossible."
Because their probe required comparing Dueling Dinosaurs with different fossils, the researchers studied much than 200 tyrannosaur fossils. This meant they were besides capable to place 1 different specimen that matches the illustration of N. lancensis.
An artist's content of a babe T. rex nether onslaught by a battalion of Nanotyrannus. (Anthony Hutchings)Zanno and Napoli besides recovered different specimen agelong considered a juvenile T. rex whose features spot it person to N. lancensis. It's not an nonstop match, but a chiseled taxon that they named Nanotyrannus lethaeus, aft the stream Lethe successful the Greek underworld.
This is rather exciting. For years, paleontologists person used the Nanotyrannus fossils to understand juvenile T. rex development. Identifying them arsenic a chiseled taxon means scientists tin present physique a much close representation of however T. rex changes arsenic it grows up.
It besides means a amended knowing of the affluent and analyzable ecosystems successful which these animals thrived.
"This find paints a richer, much competitory representation of the past days of the dinosaurs," Zanno says. "With tremendous size, a almighty wound force, and stereoscopic vision, T. rex was a formidable predator, but it did not reign uncontested. Darting alongside was Nanotyrannus – a leaner, swifter, and much agile hunter."
The probe has been published successful Nature.
