On an island just off the coast of Ventura County, scientists say they have discovered the remains of an “unusual” mammoth that lived alongside some of the earliest known human inhabitants of Southern California.

The fossil was found in a stream bank on Santa Rosa Island in Channel Islands National Park, which is also the site of the discovery of Arlington Man, the oldest set of human remains yet known in North America.

The find so far consists of a complete mammoth skull, with tusks intact, which the Park Service is describing as “exceptionally well preserved.”

“This mammoth find is extremely rare and of high scientific importance,” said paleontologist Justin Wilkins in a press statement.

“It appears to have been on the Channel Islands at the nearly same time as humans.

“I have seen a lot of mammoth skulls, and this is one of the best preserved I have ever seen.”

Part of what’s perplexing about this specimen, however, is that it’s not clear exactly what kind of mammoth it is.

Some of the most commonly found mammoth fossils are of Columbian mammoths, ginger-haired giants larger more than 4 meters (14 feet) tall that first appeared in North America about 1,000,000 years ago. [How do we know what color they were?: “First Columbian Mammoth With Hair Discovered on California Farm“]

But the Channel Islands have also produced many fossils of pygmy mammoths — animals that were substantially smaller, a mere 2 meters tall at the shoulder, after living for eons in evolutionary isolation.

The newly found mammoth appears to be too large to be a pygmy, but is not large enough to be an adult Columbian, the experts said.

And equally confusing is the growth of its tusks, they added.

The right tusk is 1.4 meters (about 4 feet 7 inches) long and is tightly curved, a sign of a fully grown mammoth.

But the left tusk is much shorter and features more of a “slope” than a coiled curve, which is indicative of a juvenile.

Whether the specimen is a young Columbian mammoth or some mid-sized species that’s new to science might become more clear when researchers are able to study its teeth.

The layers of enamel within the teeth allow scientists to track the mammoth’s growth to within two years, they said.

But for now, the most useful clue researchers have to work with is a deposit of charcoal that was found near the skull.

It has been radiocarbon dated to 13,000 years ago, about the same age as the average dates from the Arlington Man site. [Learn about some of the earliest sites found on the islands: “11,000-Year-Old Seafaring Indian Sites Discovered on California Island“]

This helps researchers understand the environment that the weird mammal lived in, but it doesn’t yet help them understand where the specimen fits within the surprisingly long and complex history of mammoths in the Channel Islands.

In 2013, geologist Dan Muhs with the U.S. Geological Survey discovered the tusk of a pygmy mammoth eroding out of a pillar of rock on Santa Rosa that was dated to 80,000 years ago.

Some species of mammals are known to become smaller over time when they’re isolated on islands, because smaller body size is easier to maintain in habitats that have fewer resources. [Learn more about dwarfism: “Prehistoric Global Warming Caused Dwarfism in American Mammals, Fossils Show“]

So Muhs believes that mammoths first arrived in the Channel Islands as much as 150,000 years ago, when sea levels were substantially lower and many of the islands were a single land mass whose shores were closer to the mainland.

But since the newly found mammoth is clearly not a pygmy, this suggests that there must have been a second, more recent wave of mammoth migration to the island, Muhs said.

“The discovery of this mammoth skull increases the probability that there were at least two migrations of Columbian mammoths to the island — during the most recent ice age 10,000 to 30,000 years ago, as well as the previous glacial period that occurred about 150,000 years ago,” Muhs said in the statement. [When did mammoths really go extinct? “Woolly Mammoths Survived on Alaska Island Until Just 5,600 Years Ago, New Study Shows“]

Once field researchers have finished excavating the skull, it will be taken by helicopter, and then boat, and finally by truck to the Santa Barbara Museum of Natural History, where it will be prepared and investigated.

“One of the purposes of the park is to provide scientific value,” Channel Islands National Park Superintendent Russell Galipeau pointed out in the press statement.

“This project is a great example of a multidisciplinary collaboration to learn about the prehistory of the park.”