A drawing of the early Cretaceous mammal Spinolestes from Spain. (Oscar Sanisidro)

Finding a new species is always exciting. But when it comes to the 125 million-year-old Spinolestes xenarthrosus, there's more than one reason to celebrate. The fossil, described in a paper published Wednesday in Nature, features remarkably well-preserved hair and soft tissues -- making it the oldest specimen with fossilized internal organs by some 60 million years.

[Were dinosaurs warm or cold blooded? Ancient eggshells could reveal the truth.]

"Normally, in paleontology, you only see mineralized hard parts, like the bones," corresponding author Thomas Martin of the University of Bonn told The Post. "We know, from other mammals, that there was hair on mammals at this time -- but you usually only see impressions of the fur in the fossil. Here the hair is preserved down to the cellular level."

Skeleton of the Cretaceous mammal Spinolestes with preserved fur shadows. (Georg Oleschinski)

That allowed Martin and his colleagues to determine that Spinolestes xenarthrosus, which lived in what's now Spain, ate bugs, and was probably the size of a juvenile rat, had hair that grew just like the fur we see on mammals today. It had compound follicles, where multiple hairs grew from the same pore, and small spines -- like those found on hedgehogs and African spiny mice -- on its back.

Martin and his colleagues can't be sure exactly how the fossil was so perfectly preserved, but they'll be doing chemical analysis to find out more. For now, he said, their best guess is that large colonies of bacteria swiftly covered the creature's remains when it died in its swampy home, spurring a process known as phosphatic fossilization.

In addition to the remarkable hair findings, the researchers were able to identify soft tissues from the liver, lungs, and diaphragm. They also found remains of a large external ear -- the earliest known example of such a structure in the mammalian fossil record. It also had skin plates similar to those seen on armadillos. Put together, Martin said, these qualities could potentially tell us a lot about the ancient furball's life.

Spinolestes xenarthrosus probably relied on hearing over sight -- most likely because it was nocturnal, hunting insects at night. Its spine is similar to that of an armadillo's, suggesting that (like those modern creatures) it might have been adapted for pushing over logs to get to bugs inside. Its back spine would have protected it from predators, hedgehog-style. And the presence of a diaphragm indicates an advanced, robust metabolism.

All in all, it's a lot of information to get from one fossil. Martin and his colleagues are hoping that the dig site -- which has already yielded many other well-preserved, non-mammalian species -- will have more furry secrets to reveal.

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