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Earliest Mammal Flesh and Fur Dates to Dino Era

Tiny organs, fur, spines and a fungal hair infection are still intact in a Cretaceous Era fossil.

The recently discovered remains of a 125-million-year-old mouse-resembling animal are so well preserved that they contain fur, hair follicles, hedgehog-like spines, organs, and even a fungal hair infection, according to a new study.

The find pushes back the earliest record of preserved inner organs and mammal hair structures by more than 60 million years. The fossils, described in the journal Nature and belonging to the Dinosaur Era critter Spinolestes xenarthrosus, also reveal the early evolution of hair and spines in animals.

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"Spinolestes shows remarkable soft-part preservation," lead author Thomas Martin, a paleontologist at the University of Bonn, told Discovery News.

"In the chest, lung tissue has been fossilized that shows the branched pattern of the airways and the fine terminal bulbs typical for lung tissue," he continued. "There is also a brownish-red spot in the abdominal cavity just behind the lung tissue, which derives from the liver (liver tissue is very rich in iron and its fossilized remainders therefore have a reddish-brown color). The lung and liver are in the exact anatomical position, clearly separated from each other, which indicates the presence of a diaphragm in between, like in modern mammals. The breathing pattern of Spinolestes therefore was like in modern mammals."

He added that there is also one external ear (called a "pinna") preserved. It is the first known fossil outer ear of any mammal. It provides evidence that this body part was well-developed and was similar to that of living rodents.

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"Modern small mammals are mostly nocturnal," he explained, "and hearing is very important for detecting predators on the one hand and detecting prey on the other hand."

Affectionately called a "Cretaceous furball" by the researchers, Spinolestes lived in a once swampy environment in what is now Spain. It spent most of its time searching for insects and other small animals, digging and scratching them up with its strong back legs.

During the mammal's lifetime, the region was also home to carnivorous dinosaurs such as 20-foot-long Concavenator, the much smaller bird-like Pelicanimimus, and multiple plant-eating dinos. Martin suspects that Pelicanimimus might have preyed upon the small furry animal. It was too tiny, however, to have been of much interest to Concavenator, he said.

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"Spinolestes looked like a modern spiny mouse (Acomys), although it is not closely related to spiny mice or any other living mammal," Martin shared. "It had spiny fur on its lower back and was a ground-dwelling animal. These spines most probably functioned as protective device."

As for existent spiny mice, the spines easily shed when they were pulled. It is frequently an effective security system, because the predator could take a big bite, and wind up with a nasty mouthful of spines. While the hunter deals with this problem, its intended victim makes a speedy getaway.

This evolved system, along with its other features, reveal that many characteristics of today's mammals were already fully established millions of years before the dinosaurs (aside from birds) went extinct.

Cretaceous mammal Spinolestes (life reconstruction) in its natural environment.

Aug. 30, 2011 --

Evolution and natural selection have played a role in the ever-changing landscape of plants, animals, bacteria and fungi. Although species evolve as they find their niche and adapt to new opportunities, some animals have remained relatively unchanged over the course of history. These animals are known as living fossils. Compared to the animals on this list, humans are relative newcomers to this planet. Homo sapiens emerged out of Africa a mere 200,000 years ago. Many living fossils are considerably older than humans and other mammals; some have even outlasted the dinosaurs. In this slideshow, take an up-close look at animals that have persevered virtually unchanged through the ages and continue to thrive today. We begin with the platypus, an unusual egg-laying animal with fur, a bill and a venomous bite. Charles Darwin himself coined the term "living fossil" while observing the platypus. Native to eastern Australia, the animal is the only surviving example of its family, Ornithorhynchidae. This group of animals is believed to have split from mammals some 166 million years ago.

The horseshoe crab could hold the distinction of being the oldest animal species still in existence. Dating back to the Paleozoic era, the horseshoe crab existed on Earth before the dinosaurs and soldiered on through several mass extinction events. In 2008, a horseshoe crab fossil, the oldest in existence found so far, dated back to around 445 million years ago, according to a report by LiveScience.

The tadpole shrimp, Triops cancriformis, is another contender for the title of oldest living animal species. This shrimp is related to the horseshoe crab so its longevity should come as no surprise. According to a report by The Telegraph, the tadpole shrimp as it appears today is virtually identical to a fossil of a specimen that lived some 200 million years ago just as dinosaurs rose to prominence. Despite the animal's remarkable endurance, the tadpole shrimp is currently listed as an endangered species.

Once thought to be extinct in the same event that killed off the dinosaurs some 65 million years ago, the coelacanth is a lobe-finned fish that sparked a debate over whether this species represented a missing link between aquatic animals and four-legged terrestrial creatures, according to National Geographic. The animal was rediscovered in 1938 and only two species of coelacanth still exist today. In 2007, a fossilized coelacanth fin was found dating back roughly 400 million years.

Snapping turtles as we know them first walked the earth some 40 million years ago, but they have been virtually unchanged over the past 215 million years of their evolution, according to Tortoise Trust. Although not among the most endangered tortoises and turtles according to the Turtle Conservation Coalition, the snapping turtle is listed as threatened.

The more than 20 species of alligators and crocodiles living today have evolved beyond their more primitive ancestors. But the basic physical design of these reptiles has remained essentially the same for the past 320 million years or so. Alligators and crocodiles share a common ancestry, though the two groups separated from each other some 60 million years ago.

The nautilus is the most primitive cephalopod in existence, a group that includes the most complex squid and octopus. Dating back to more than half a billion years ago, the nautilus reached the high point in its evolution during the Paleozoic era about 505 million to 408 million years ago. Several species of nautilus still survive today -- relatively unchanged from their ancestral counterparts.

Goblin sharks are rare, deep-sea dwellers with a unique elongated nose that distinguishes them from other sharks. They're also ancient, and are between 112 million to 124 million years old as a species. Around 2,000 different species of fossil sharks have been discovered, according to the ReefQuest Centre for Shark Research. The earliest sharks predate the dinosaurs by more than 200 million years.

The cockroach is famous for being a survivor. These insects can survive for weeks without their heads and even withstand the fallout following a nuclear blast. Cockroaches are also an especially long-surviving animal. Roaches have thrived on Earth for some 320 million years, with an estimated 5 million to 10 million individual species ranging in shape, size and habitat. This photo shows Blaberus giganteus, one of the largest species of cockroach on Earth.

Hagfish may have had to endure a less-than-flattering name since scientists first described them in the 18th century. However, these famously ugly marine animals have existed for about half a billion years. The hagfish also represents an important evolutionary step in the development of vision. These ancient fish may have been among the earliest animals to evolve more complex, camera-like eyes as opposed to the strictly photosensitive vision possessed by more primitive species. As such, the hagfish represents a kind of missing link in the evolution of the eye.

Compared to other animals on this list, the mouse deer, better known as a chevrotain, is a relative newcomer. For a large mammal, however, it's relatively old. This animal is among the only survivors of a group of hoofed mammals that lived some 35 million years ago.