A rat-like critter that scampered between the feet of dinosaurs grew hair like modern mammals and probably had the same itchy ringworm afflicting pets and people today, according to a study published Wednesday.

Reporting on a remarkably intact 125-million year fossil in the journal Nature, scientists said it had the oldest mammal liver and lungs ever found, as well as the most detailed examples yet of hair and fur in its class.

"This furball... displays the entire structural diversity of modern mammalian skin and hairs," said study co-author Zhe-Xi Luo, a researcher at the University of Chicago.

Previous research has turned up evidence of hairs that date back 165 million years, but they were only fossilised impressions and lacked the detail of this new discovery.

The creature's fur and liver are visible with the naked eye, but a microscope was needed to see the intricate structures of the lung.  

Spinolestes xenarthrosus -- from the Latin for spiny -- had remarkably modern features: multiple hairs coming from the same pore, and spines on its back similar to those on a hedgehog.

"We now have conclusive evidence that many fundamental mammalian characteristics were already well-established some 125 million yeas ago, in the age of dinosaurs," said Luo.

The 24-centimetre (nine-inch) long and roughly 70-gram (2.5 ounce) critter also had some curious stumpy hairs on its back that researchers interpreted as evidence of dermatophytosis, a contagious, itchy skin infection commonly known as ringworm.

S. xenarthrosus was so perfectly frozen in time because it was likely fossilised within hours of its death in what was then a lush wetland in east-central Spain, said study co-author Thomas Martin, a scientist at the University of Bonn in Germany.

That area is now Las Hoyas quarry, which has produced hundreds of fossils, including scientifically important ones of birds and dinosaurs.

Luo told AFP that a research team member working there in July 2011 spotted the fossilised remains.

Researchers also found the earliest known example of a mammal ear in the S. xenarthrosus fossil, along with plate-like structures called scutes that can be seen on modern-day armadillos.

Based on the fossil, the team concluded S. xenarthrosus had features in its spine -- again similar to those in armadillos -- that gave it an extraordinarily strong back.

Researchers believed it was a ground dweller that lived on insects, and speculated its powerful spine might have helped it push apart logs or branches while in search of a meal.
Source: AFP