A team of international scientists has unearthed fossils of a prehistoric rat-like creature whose skin, fur, and other organs are still intact. The small, furry creature was named Spinolestes xenarthrosus because of its hedgehog-like spines. The fossils were spotted in July 2011 at the Las Hoyas Quarry in east-central Spain. Researchers estimate that Spinolestes’ fossils are about 125 million years old.

Spinolestes: 125-Million Years Old Mammal Fossils Found In Spain

Fossils contain the oldest known remnants of hair

Findings of the study were published in the journal Nature. Though researchers have recovered fossils of frogs, birds, and reptiles from the same quarry in the past, it’s the first time a true mammal has been discovered at the site. The Spinolestes fossils contained the oldest known remnants of hair, suggesting that small, furry creatures coexisted with giant dinosaurs.

Thomas Martin of the University of Bonn, Germany, said it had the oldest mammal lungs and liver ever found. You could see the creature’s fur and liver with the naked eye, but it required a microscope to study the structures of the lung. The rat-like creature grew hair like modern mammals and belonged to an extinct species of triconodonts. The species went extinct a long time ago, which indicates that mammals evolved spines separately several times in history.

Spinolestes had an extraordinarily strong back

The fossils also showed long external ears, indicating that the animal relied more on hearing that on eyesight. It showed the structural diversity of modern mammals such as hedgehog-like spines on its back, and multiple hairs coming from the same pore, said Zhe-Xi Luo of the University of Chicago. Scientists now have “conclusive evidence” that many of the mammalian features were well-established in the age of dinosaurs about 125 million years ago.

Spinolestes xenarthrosus measured 24cm in length and weighed just 70g. The fossils were so perfectly preserved because there were very special conditions at Las Hoyas at the time. The quarry was a lush wetland back then, so fossils were frozen within hours of its death. Researchers said features in its spine gave Spinolestes an extraordinarily strong back. The tiny creature fed on insects.