Story highlights
- Rare pregnant Tyrannosaurus rex has been found out West
- Very difficult to determine gender of fossils
(CNN)Through the years of searching for fossils of the ever-popular Tyrannosaurus rex, locating a pregnant one has been understandably difficult.
But scientists now believe they've located one, determining this particular T. rex that roamed Montana was female.
Traditionally, it's been extraordinarily difficult to figure out a dinosaur fossil's gender.
Specifically, the researchers from North Carolina State University and the North Carolina Museum of Natural Sciences found a medullary bone in a T. rex femur.
Photos: China's dinosaur discoveries
Photos: China's dinosaur discoveries
The fossil of 195-million-year-old dinosaur Lufengosaurus preserved as found in the ground in Yunnan Province, China. Researchers discovered ancient collagen and protein in one of its ribs.
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Photos: China's dinosaur discoveries
An artist impression of the Limusaurus. The Ostrich-sized dinosaur was found in Xinjiang in China's far west. Researchers say it lost its teeth as it matured.
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Photos: China's dinosaur discoveries
An artist's impression of the feathered Tongtianlong limosus or 'mud dragon' dinosaur. A paper on its discovery was published in Nature Scientific Reports on November 10, 2016.
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Photos: China's dinosaur discoveries
Hualianceratops – The discovery of the hualianceratops, from the same family of dinosaurs as the triceratops, was announced December 9 2015. Its fossils were discovered in the Gobi Desert, western China.
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Photos: China's dinosaur discoveries
Gigantoraptor – In 2005, paleotologist Xu Xing and a group Chinese paleontologists excavated the bones of this giant bird-like dinosaur. It's believed to be 8 meters long and weigh 1.4 tons. Its arms were long and legs were bird-like.
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Photos: China's dinosaur discoveries
Sinosauropteryx – Revealed in 1996, this was the very first feathered fossil to be unearthed and offered the first evidence that birds are descended from dinosaurs.
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Photos: China's dinosaur discoveries
Yutyrannus huali – At nine meters long and weighing more than 1.4 tonnes, it's the largest feathered animal known to have lived. Named by Xu Xing in 2012, it's been described as a feathered Tyrannosaur.
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Photos: China's dinosaur discoveries
Microraptor – Xu announced the discovery of the four-winged microraptor in 2003 although scientists believe it glided rather than flew -- shedding light on how birds' ancestors learned to fly.
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Photos: China's dinosaur discoveries
Zhenyuanlong suni – This mule-sized, four-winged dinosaur was discovered in Liaoning Province. At two-meters high, it's the largest winged dinosaur found but although its short arms have substantial quill like feathers, researchers think it couldn't fly. It was memorably described by one paleontologist as a "fluffy feathered poodle from hell."
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Photos: China's dinosaur discoveries
Yi qi – This unusual dinosaur with bat-like wings existed for a very short time 160 million years ago during the Jurassic Period.
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Photos: China's dinosaur discoveries
Linhenykus – This parrot-sized species of dinosaur had only finger. It was discovered in Inner Mongolia and named after the city of Linhe.
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Photos: China's dinosaur discoveries
Qijianglong – Paleontologists discovered a 50-ft "dragon" dinosaur species in 2006 in southwestern China's Chongqing. The species is thought to have roamed the earth 160 million years ago in the Late Jurassic period.
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Photos: China's dinosaur discoveries
Guanlong – Named by Xu in 2006, this dinosaur, half the size of a man, may have had a coat of primitive feathers.
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These bones are found only in female birds in the period before or during egg-laying.
Now, the scientists believe they will be able to find differences between male and female dinosaurs of this kind (theropod dinosaurs), and learn more about the evolution of egg-laying in birds.
"It's a dirty secret, but we know next to nothing about sex-linked traits in extinct dinosaurs. Dinosaurs weren't shy about sexual signaling, all those bells and whistles, horns, crests, and frills, and yet we just haven't had a reliable way to tell males from females," said Lindsay Zanno, a Museum of Natural Sciences paleontologist, in a press release.
"Just being able to identify a dinosaur definitively as a female opens up a whole new world of possibilities. Now that we can show pregnant dinosaurs have a chemical fingerprint, we need a concerted effort to find more."
