Swimming Mammoths Beat Humans to California

A fossil tusk rescued from the sea proves mammoths swam to Southern California's Channel Islands much earlier than thought.

VANCOUVER - A fossil tusk rescued from the sea proves mammoths swam to Southern California's Channel Islands much earlier than thought.

The new fossil is one of two recently discovered tusks that challenge the idea that climate change killed off the Channel Islands' pygmy mammoths, said Daniel Muhs, a geologist with the U.S. Geological Survey in Denver, who described the find Sunday (Oct. 19) here at the Geological Society of America's annual meeting. The pint-size beasts disappeared from the islands about 12,000 years ago. Most researchers blame either the Earth's warming climate or the arrival of humans on the islands for the mammoth's demise, he said.

But pygmy mammoths likely survived a steamier, more severe climate swing about 125,000 years ago. "This new find suggests they had to have lived during a period even warmer than the present," Muhs told Live Science. [In Photos: Stunning Mammoth Unearthed in Siberia]

Muhs and his collaborators discovered an 80,000-year-old pygmy mammoth tusk half-buried in the edge of a sea stack on Santa Rosa Island's northwest coast. With a few more storms, the rare fossil - just 3 inches (8 centimeters) wide and 2 feet (62 cm) long - might have disappeared forever into the Pacific, washed out of the rock pedestal. "It was a miracle," Muhs said of the well-timed find. The tusk is now in the Santa Barbara Museum of Natural History, he said.

Fossil corals buried with the tusk allowed scientists to date the find. But 80,000 years ago, sea level was higher than today. So Muhs said he thinks that mammoths crossed during an earlier glacial period, some 150,000 years ago. "We're going on the assumption that they only swim when the distance [to the mainland] is at a minimum," Muhs said. "Sea level was really low only at 150,000 years ago."

Scientists think mammoths reached the four northern Channel Islands when sea level dropped during past ice ages. At their peak, the planet's giant ice sheets socked away ocean water like sponges, lowering sea level around the Channel Islands nearly 400 feet (120 meters). Twice in the past 150,000 years, when the ice sheets expanded, the islands joined together into one large island, called Santarosae. The distance to the mainland near the city of Oxnard, along the coast of Southern California, shrank to about 4.5 miles (7.2 kilometers), easily reachable by a swimming, 10-ton (9,000 kilograms) Columbian mammoth. The island where the tusks were found, Santa Rosa, now sits about 26 miles (42 km) offshore.

Modern elephants, which share a common ancestor with mammoths, can cover at least 30 miles (48 km) with their ungainly underwater crawl. There are anecdotal reports of elephants swimming to islands in search of food, guided by the scent of ripe fruit.

During the late Pleistocene epoch, winds blew from the northwest across the islands, carrying the scent of unmunched forests to the mainland.

"Mammoths could have swum over to the Channel Islands several times during different glacial periods, because mammoths have been in North America for 1 million years," Muhs said. However, despite more than a century of searching, no one had found older mammoth fossils on the islands until now.

Recently, Muhs and his collaborators uncovered a second pygmy mammoth tusk from a different rock layer, in sand and landslide deposits. Dating of snail shells with the tusk, and an older marine layer below the sand, reveal that this mammoth died sometime between 46,000 and 100,000 years ago. Even that broad age range is helpful to scientists piecing together the history of these pony-size mammoths.

Until now, researchers had thought the most recent ice age transformed the Channel Islands mammoths into pipsqueaks. That glacial period peaked about 20,000 years ago, and then Earth's climate started to gradually warm.

As the ice sheets melted, sea level rose and trapped the mammoths on separate islands. Once the animals were confined, the competition for a limited food supply favored smaller mammoths, and the animals shrunk until they were half the size of their ancestors. These pygmy mammoths are a unique species, called Mammuthus exilis, found so far only on San Miguel, Santa Rosa and Santa Cruz islands. [6 Extinct Animals That Could Be Brought Back to Life]

"There is every good reason to get small because of reduced forage, and no particularly good reason to stay large, because they've lost the predators," Muhs said. "Fortunately, the big predators do not swim."

Most fossils of pygmy and full-size mammoths discovered so far on the islands are between 20,000 and 12,000 years old, Muhs said. A handful hit 30,000 years old. And one spectacular, 5.5-foot-tall (1.7 m), nearly complete skeleton was uncovered in 1994, dating to about 13,000 years ago.

With the two older tusks, scientists may need to rethink how this textbook example of dwarfism evolved on the island. For example, did the mammoths settle Santarosae 150,000 years ago and then die out before the next ice age? Or did their descendants mix with a new wave of settlers? And what happened when people joined the mix? The earliest human remains overlap with the youngest pygmy mammoth fossils on the Channel Islands, suggesting the first humans arrived just before the mammals went extinct.

"This is one of the coolest fossil stories in the National Parks, which are full of amazing fossil stories," said Jason Kenworthy, a geologist with the National Park Service in Denver who was not involved in the study. "To push the time back and still be finding new information is really exciting. They've added a whole new chapter to the story."

More from LiveScience:

Dwarf Gallery: Fossils of a Little Mammoth Channel Islands: Photos of North America's Galapagos Wipe Out: History's Most Mysterious Extinctions Copyright 2014 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Article originally appeared on LiveScience.

An intact pygmy mammoth skeleton found on Santa Rosa Island in 1994. It was 5.5 feet tall and nearly 13,000 years old.

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.

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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.

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