New York ? Dwarf dinosaurs? It sounds like the old George Carlin joke about jumbo shrimp: two words that just don’t go together.

But fossils from northern Germany have revealed a dinosaur that evolved into a dwarf, ending up only about one-third the size of its closest known relatives, scientists report.

The four-legged plant-eater was no lap dog: It measured about 20 feet from its snout to the tip of its long tail and it weighed about a ton.

But next to its close evolutionary cousin Camarasaurus, a well-known beast that stretched some 59 feet long, this guy was a runt.

What happened? The researchers say it’s a case of island dwarfism, the tendency of big species to shrink over time when they find themselves on an island. It’s well-known among mammals, as with fossil elephants only about 3 feet tall found in Sicily and elsewhere.

Scientists think that in an environment of limited resources, smaller body size becomes an advantage, and so captive populations shrink in body size over long periods of time.

The new creature is the best documented case of island dwarfism among dinosaurs, said P. Martin Sander, a paleontologist at the University of Bonn in Germany and lead author of a report in today’s issue of the journal Nature.

Newly unveiled models of a group of new dinosaur species, Europasaurus, are on display at the Dinopark Munchehagen near Hanover, Germany. Scientists say they've discovered a dinosaur species that had evolved into a dwarf, ending up only about one-third the size of its closest known relatives.

The creature, dubbed Europasaurus holgeri, lived 154 million years ago near what is now the German town of Goslar. At that time, the region was covered by shallow seas and the creature evidently lived on an island, Sander said. It’s not clear whether a bigger ancestor reached the island from elsewhere and founded a colony, or an existing population found itself isolated by rising sea levels, he said.

The bone analysis also showed that Europasaurus grew more slowly than bigger dinosaurs. Its small size was a normal growth pattern for the species and not the result of disease, Sander said.

That has been a point of contention in trying to explain the so-called hobbits of Indonesia, fossil remains that have been interpreted as revealing that a dwarf species of humans lived on a remote island thousands of years ago.

Mark Norell, a dinosaur expert at the American Museum of Natural History, said island dwarfism had been talked about for the hobbits and many animals, and “to find it in dinosaurs is pretty neat.” The new Nature paper presents the best case for the phenomenon in a dinosaur, he said.