Scientists looked at the stunningly well-preserved fur of a 125-million-year-old rat-sized mammal, and found the ancient animal suffered from fungal infections still seen today and had hedgehog-like spines.
The animal, dubbed Spinolestes xenarthrosus, represents the earliest-known examples of microscopic structures of hair and spines in mammalian evolutionary history, the University of Chicago Medical Center reported.
"Spinolestes is a spectacular find. It is stunning to see almost perfectly preserved skin and hair structures fossilized in microscopic detail in such an old fossil," said study co-author Zhe-Xi Luo, professor of organismal biology and anatomy at the University of Chicago. "This Cretaceous furball displays the entire structural diversity of modern mammalian skin and hairs."
The specimen was discovered at the Las Hoyas Quarry in east-central Spain, which was a lush wetland during the early Cretaceous period. The Spinoleste had compound follicles in which multiple hairs emerge from the same pore and spines on its back similar to what is seen in modern hedgehogs and African spiny mice. The researchers also observed abnormally truncated hairs that indicated a fungal skin infection called dermatophytosis, which is seen in animals today.
"Hairs and hair-related integumentary structures are fundamental to the livelihood of mammals, and this fossil shows that an ancestral, long-extinct lineage had grown these structures in exactly the same way that modern mammals do," Luo said. "Spinolestes gives us a spectacular revelation about this central aspect of mammalian biology."
The specimen also provides the earliest-known record of mammalian organ systems. It's anatomy included microscopic bronchiole structures in the lungs, a large external ear, and a extra articulations between vertebrae that strengthened the spinal column. These articulations are seen in modern armored shrews and armadillos, and use this added spinal strength to destroy logs and feast on the insects within.
"With the complex structural features and variation identified in this fossil, we now have conclusive evidence that many fundamental mammalian characteristics were already well-established some 125 million years, in the age of dinosaurs," Luo concluded.