Rico, a border collie with what appears to be an uncanny talent for human language, may be a genius among dogs or just your average pooch. Either way, he has scientists wondering if man's best friend is smarter than they thought.

A series of careful studies concluded that the energetic German house dog has a stunningly large vocabulary of about 200 words and can even do something scientists thought only humans could do: figure out by the process of elimination that a sound he has never heard before must be the name of a toy he has never seen before.

That feat, described in today's issue of the journal Science, suggests that dog owners who claim their pets understand what they are saying and are trying to respond may have been right all along.

"Maybe this is the Albert Einstein of dogs. Or maybe this is something that other dogs can do, too," said Julia Fischer, a biologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who helped test Rico. "We just don't know. We need to find out."

While many species can be trained to recognize the names of objects, what makes Rico unusual is that he knows so many words, can puzzle out the names of new objects on the first try and weeks later is surprisingly good at remembering what he learned, the researchers said.

"This is an extremely provocative paper," said Robert Seyfarth, a University of Pennsylvania psychologist who studies monkey behavior and communication. "Dog owners will say a lot of things about their dogs. The question is always, 'Are dogs really as smart as they think they are?' This says they might be."

The findings are the latest evidence that animals are capable of more complex communication than had been thought, and that dogs, in particular, are especially astute at comprehending their human companions.

Rico's talents are prompting some scientists to go so far as to speculate that dogs might even have the capacity to speak -- like Mister Ed, the talking horse in the 1960s television show -- if only they had the necessary anatomy.

"If Rico had a human vocal tract, one would presume that he should be able to say the names of the items as well, or at least try to do so," said Sue Savage-Rumbaugh, who studies animal communication and intelligence at Georgia State University. "It also raises the issue of whether Rico and/or other dogs or other mammals might already be trying to say words, but have great difficulty being understood."

While praising the new work, some scientists remained cautious, saying the research needed to be repeated to confirm the findings and that it was far from clear what Rico understands about the sounds to which he responds.

"I think it's a gorgeous study. It's clever and impressive," said Paul Bloom, a Yale University psychologist who wrote an article accompanying the new study. "But I'm skeptical about exactly what he has learned. I'm not sure I would call it a 'word.' "

Scientists have long debated the ability of animals to think and communicate. At the turn of the 20th century, a horse named Clever Hans that supposedly could add and subtract became infamous when researchers showed the stallion was just responding to subtle cues from his owner.

But scientists have since determined that many species have complex vocalizations that enable them to communicate sophisticated information among themselves. And researchers have been able to teach many creatures to recognize human symbols and language. A bonobo ape named Kanzi, for example, can understand dozens of symbols. Alex, an African gray parrot, can identify a wide array of objects, shapes, colors and materials. And recent studies have shown that dogs are remarkably adept at reading human gestures.

Researchers had thought, however, that the only creatures capable of instantly assigning meaning to a novel word -- called "fast mapping" -- were human toddlers, who use the strategy to learn language.

"Fast mapping was thought to be something exclusively human. It is how children learn the meanings of new words," Fischer said. "Nobody thought this could be done by an animal."

She and her colleagues conducted a series of experiments on the 9-year-old border collie after his owners claimed he knew the names of about 200 objects -- his collection of toys, balls and stuffed animals.

In the first experiment, the researchers put 10 of Rico's toys in one room and Rico and his owner in another. The investigators then instructed the owner to order Rico to fetch two randomly selected items. As Rico ran into the other room and began searching for the items, he could not have picked up any hints from his owner because the owner was out of sight.

In 40 tests, Rico got it right 37 times, demonstrating he had a vocabulary comparable to dolphins, apes, sea lions and parrots that have undergone extensive training.

The researchers then repeated the test, except this time they put seven of his toys in the other room along with one he had never seen before. His owner then called out the unfamiliar name of the new toy. Rico correctly retrieved the new item in seven out of 10 tries.

"This tells us he can do simple logic," Fischer said in a telephone interview. "It's like he's saying to himself, 'I know the others have names, so this new word cannot refer to my familiar toys. It must refer to this new thing.' Or it goes the other way around, and he's thinking, 'I've never seen this one before, so this must be it.' He's actually thinking."

About a month later, the researchers tested Rico again, prompting him to retrieve objects from groups of four familiar and four new toys. He got it right three out of six times, a rate comparable to what a typical 3-year-old human toddler could do.

"Of course, for a child, a word very rapidly means much more than it does for a dog. They will quickly know it's a color word or an activity word. Their representation will be much richer than it is for a dog," Fischer said. "But in terms of this task, he is as smart as kids are."

Other scientists said important questions remain about whether animals are capable of complex syntax, which makes human communication unique. But many said Rico's apparent capabilities nevertheless appeared remarkable.

"A lot of people have argued that the perceptual and cognitive mechanism that underlie what we call language and speech acquisition are unique to humans," said Mark Bekoff, who studies dogs at the University of Colorado. "What this study shows clearly is that is not the case. What this shows is that other animals possess those cognitive and perceptual abilities."

Savage-Rumbaugh, who works with the bonobo Kanzi, said she has demonstrated, although not yet published, similar findings from tests on at least two other dogs.

"No doubt others will quickly replicate this study," Savage-Rumbaugh wrote in an e-mail, "and Rico will be shown to be an ordinary dog with a large vocabulary."