Dinosaurs may have ruled the Mesozoic Era, but they were far from the only creatures that roamed the Earth. Hiding beneath the prehistoric plants were tiny squirrel-sized mammals with a porcupine armor that carried a nasty fungus. According to a report from Reuters, researchers digging near the Spanish town of Cuenca announced that they had discovered a perfectly preserved fossil of the prehistoric mammal Spinolestes xenarthrosus.

Paleontologists unearthed a complete skeleton with well-preserved fur, spines, and keratin-based armor plates called dermal scutes, as well as components of the rodent’s face, skin, and internal organs.

According to paleontologist Thomas Martin from the University of Born, the discovery offers incredible insight into the biology of organisms that existed millions of years ago. Researchers have never been able to take this close of a look at prehistoric biology, and it provides a solid landmark for the ongoing quest to clarify the history of life’s evolution on Earth.

The rodent was roughly nine and a half inches, and weight about 2.5 ounces. It is believed to have lived on the ground, occasionally burrowing holes for shelter. It likely consisted on a diet of insects and worms, and shared a vegetative wetland habitat with prehistoric dinosaurs, birds, and flying reptiles.

The mammal looked like a tiny rat, with a slightly more pointed snout. It had a coat like a mixture between an armadillo and a porcupine, with tough plates of armor made of keratin, and hair bulbs in the skin and filaments comprising the spines.

Researchers believe the fossil is roughly 65 million years older than the next oldest mammal specimen with preserved internal and external features. Spinolestes derives its name from an African spiny mouse, and means “spiny robber.” Despite the name, it is not closely related to the African spiny mouse or any living mammal.

The fossil belonged to the mammal group eutriconodonts, which appeared on Earth roughly 170 years ago. They met their fate roughly 66 years ago along with the dinosaurs after a massive asteroid changed the fate of life on Earth forever.

The study was published in the journal Nature.