For more than two decades, a small dinosaur from China has left scientists scratching their heads.
Known as Liaoningosaurus paradoxus, this strange fossil looked like an armored dinosaur—but every specimen ever found was tiny, no longer than 40 centimeters.
That’s confusing, because adult armored dinosaurs, called ankylosaurs, usually grow to three meters or more.
Now, new research has finally solved the puzzle.
These dinosaurs were not miniature adults or odd semi-aquatic species, as some scientists once suggested.
They were babies. In fact, one fossil represents the youngest ankylosaur ever discovered—a hatchling that had only just emerged from its egg.
Liaoningosaurus was first described in 2001 and quickly became controversial. While its body shape and early armor suggested it belonged to the ankylosaur group, no adult fossils were ever found.
Every new discovery seemed to confirm the same odd pattern: all individuals were small and similar in size.
Without larger specimens, researchers could not tell whether the dinosaur was truly tiny or simply young.
A new study published in the Journal of Vertebrate Paleontology took a closer look at the dinosaur’s bones.
Instead of focusing on size, the research team examined bone microstructure. Like tree trunks, dinosaur bones record growth over time. Each year of life usually leaves behind a visible growth line inside the bone.
When scientists examined bone samples from both the largest and smallest Liaoningosaurus fossils, they found something striking—no growth lines at all. This means both individuals were less than one year old.
Even more remarkably, the smallest fossil showed a “hatching line,” a tiny ring in the bone that forms when a dinosaur breaks out of its egg. This confirms that the animal had only just hatched when it died.
All known Liaoningosaurus fossils come from Liaoning Province in northeastern China, a region famous for exceptionally preserved dinosaur remains from the Cretaceous Period.
Many animals there were buried in fine lake sediments, often sealed under volcanic ash. This unusual environment has given scientists rare, detailed fossils, including feathered dinosaurs like Microraptor.
Although no adult Liaoningosaurus has been found, the baby fossils still offer valuable clues. Young ankylosaurs are extremely rare, and most known juveniles lack the heavy armor seen in adults. Liaoningosaurus shows that at least some armored dinosaurs developed protective plates very early in life.
By revealing that these fossils belong to hatchlings rather than tiny adults, the study gives scientists their clearest look yet at how armored dinosaurs began life. Finding an adult one day would be even better—but for now, these tiny fossils have already made a big impact on our understanding of dinosaur growth.
