Gavin Sutter and his fossil find.
Gavin Sutter, aged eight, from Auburn, found the prehistoric bones of a horse dating back 15 million years.
Crucially, the remains he found were of a three-toed horse.
Horses are known to have evolved from small five-toed animals into the horses we know today, which have only one toe, and the tiny boney remnants of two others.
Gavin's find fills a crucial gap in the evolutionary path of the horse, as it evolved from a five-toed to effectively a single-toed animal.
The bones have been prepared for display to take pride of place at the Sierra College Natural History Museum, where they will remain a permanent fixture.
Gavin, a keen rock collector, has declared his find "very cool".
Dick Hilton, who is with the museum, was on the expedition which led to the discovery, in July 2006. The expedition had aimed to find middle Miocene 15-million-year-old plant and animal fossils in northern Nevada.
Hilton was joined by scientists George Bromm and Brian Hausback, film-maker Paul Goldsmith, and Gavin's father, Keith Sutter, who is a photographer.
Sutter's wife and their two boys also joined the trip.
The scientists were working under a United States government Bureau of Land Management permit to survey the area for vertebrate fossils.
The expedition took them to remote and wild places near the Black Rock Desert, where they saw lots of wildlife, including coyotes, mustangs, prong-horned antelope, deer, rabbits and big-horned sheep.
Gavin, then seven, found the bones and teeth of the small three-toed horse.
His mother, Cara, found an antler of an early deer-like animal.
The bones that Gavin found.
Other bones found belonged to early rhinos, turtles, beavers, canaids (the dog family) and badgers. They also found fossil oak leaves and the winged seed of a maple tree.
"Fifteen million years ago, when these animals roamed Nevada, the Sierra Nevada and many of the mountains along the west coast of North America had not risen to their current elevation," Hilton explains.
"Rains that are now blocked by these mountains found their way to Nevada. Nevada was as lush as California is today but it had wildlife that looked more like the plains of Africa.
"Along with all of the animals already mentioned, there were lions, sabertooth cats, dog-bear, camels and primitive elephants (gomphotheres). There were even redwood forests."
Horses are known to have evolved from rabbit-sized creatures that originally had five toes on each foot. As time went on horses evolved into bigger animals that had to run faster to avoid larger, faster predators. To run faster they evolved fewer toes so that by 15 million years ago they had just three toes on each foot - one large center toe and two smaller ones along the sides.
The modern horse has just one toe on each foot, although remnants of their former toes still exist as vestigial bones that are no longer used. This is similar to the hip bones that whales have, even though they no longer have rear limbs.
A large slab of rock containing the horse bones found by Gavin was excavated and brought back to the laboratory at the Sierra College Natural History Museum.
There, George Bromm carefully prepared the specimen so that the bones and teeth still protruded from the rock, making it an excellent display specimen.
As for Gavin, he can look forward to another day in the sun - showing off possibly one of the best show-and-tell exhibits any kid has ever taken to school. The museum says Gavin will be allowed to take the fossils to school to show fellow students.