'Dwarf' mammoths outlived last ice age.

Woolly mammoths, those icons of the ice age that most paleontologists assume died out around 9,500 years ago, survived in miniature form - or what passed for miniature among mammoths - until about 4,000 years ago on an Arctic Ocean island, according to new findings.

Mammoth teeth found in 1991 on Wrangel Island, located 120 miles off the coast of northeast Siberia, range from approximately 7,000 to 4,000 years old, report Andrei V. Sher and Vadim E. Garutt, paleontologists at the Russian Academy of Sciences in Moscow. The relatively small teeth suggest that Wrangel "dwarf mammoths" reached at most 70 percent of the size of their Siberian kin, the researchers say.

"[This is] one of the most extraordinary fossil finds of recent times," writes Adrian M. Lister, a biologist at University College in London, England, in a comment accompanying the new report in the March 25 NATURE.

He estimates that the Wrangel animals stood 6 feet high and weighed 2 tons, compared with 10 1/2 feet and 6 tons for typical European mammoths.

The Wrangel finds may reignite debate over the reasons for the widespread mass extinctions of large mammals between 12,000 and 10,000 years ago, Lister notes. Some researchers contend that the waning ice age produced abrupt environmental changes that doomed many creatures. Others argue that human hunters, at least in North America, rapidly killed off many large-bodied species (SN: 10/31/87, p.284).

"This is a wonderful discovery, however we end up interpreting its significance regarding mass extinctions," remarks Paul S. Martin, an ecologist at the University of Arizona in Tucson, who favors the latter theory,

Sher and Garutt studied 29 adult mammoth cheek teeth found by Sergei L. Vartanyan, a paleontologist at Wrangel Island State Reserve. Five of them are comparable in size to mammoth teeth previously found in Siberia, the researchers contend. Radiocarbon dating places these five specimens at about 20,000 to 13,000 years old.

The remaining 24 teeth are considerably smaller and date from around 7,000 to 4,000 years ago. This confirms similar radiocarbon ages derived last year from more than two dozen mammoth tusk and bone fragments discovered on Wrangel Island, Sher and Garutt assert.

Radiocarbon dating of bone "can be tricky," Martin points out. But fewer soil contaminants seep into bone buried in cold regions, he says. And two independent laboratories produced nearly the same ages for tusk and bone samples, the Russian scientists note.

Siberian mammoths probably reached Wrangel Island during the ice age, when low sea levels created a land bridge to the mainland, Sher and Garutt theorize. By 12,000 years ago, that connection had been submerged.

Unlike nearby islands, Wrangel currently contains vegetation similar to that of ice age grasslands and may have provided a hospitable environment for mammoth survival, the scientists hold. Full-bodied mammoths then evolved into smaller forms on Wrangel, they suggest. Dwarf forms of other large animals existed on late-ice-age islands elsewhere, Sher and Garutt note.

Why the Wrangel mammoths shrank remains unclear, Sher says. Some Siberian mammoths showed body-size decreases by 12,000 years ago, a process that may have accelerated on Wrangel because of the genetic isolation of a small population under nutritional pressures, he suggests.

Scientific reconstruction of plant and animal histories on the island is now under way, Sher points out, as well as an anatomical analysis of large and small Wrangel mammoth teeth.