Biggest-Ever Bunny Didn't Hop, Had No Enemies

A newly found species of rabbit, Nuralagus rex, weighed in at over 26.4

pounds and lived three to five million years ago on the small island of Minorca.

Meike Köhler

No floppy-eared Easter-type bunny, this rabbit had small ears, smallish eyes and enormous heft.

By Jennifer Viegas
Mon Mar 21, 2011 03:00 PM ET

THE GIST

• The world's largest known rabbit lived three to five million years ago on the island of Minorca.
• It weighed over 26.4 pounds, had no enemies, and did not hop.
• The rabbit exemplifies what's known as the "island rule."

An enormous bunny that lived three to five million years ago was so hefty -- six times the size of most rabbits today -- that it didn't hop and had no enemies.

The new species, dubbed the Minorcan King of the Rabbits (Nuralagus rex), weighed in at over 26.4 pounds and lived on the small island of Minorca.

"N. rex was a very robust and peculiar rabbit," project leader Josep Quintana told Discovery News. "Surely he was a very calm and peaceful animal that moved with slow, but powerful, movements."

Quintana, a scientist at the Catalan Institute of Paleontology, and colleagues Meike Kohler and Salvador Moya-Sola describe the giant fossil rabbit in a Journal of Vertebrate Paleontology paper. They believe the rabbit lost the ability to hop, because the long, springy spine typical of modern bunnies was replaced by a short, stiff backbone.

The researchers think N. rex spent most of its days peacefully digging, searching for roots and tubers to eat.

"The ancestors of N. rex arrived at Minorca during the Messinian crisis 5.3 million years ago," Quintana said. "During this geological time, the Mediterranean Sea dried up and the Balearic islands connected with the surrounding mainland (of Europe and Africa), so the proto-Nuralagus rex arrived walking to Minorca."

When the seawater returned and Minorca returned to its island status, the rabbit found itself with no predators. Over time, it grew to become 10 times the size of its now-extinct mainland cousin. Other inhabitants of the island at the time included a bat, a large dormouse and a giant tortoise.

With no need for defense, the rabbit lost visual and hearing acuity. Its eye socket reduced in size over time, as did its ears.

The changes, especially the increase in body size, add to the growing evidence for what's known as "the island rule." Simply put, this states that when on islands, big animals often tend to become smaller and small animals frequently tend to grow larger.

On the small side of that equation, other islands have been home to tiny elephants and even, in the case of Homo floresiensis, tiny humans.

"It is as if nature experimented with form and function, not without a wicked sense of humor," Lucja Fostowicz-Frelik, an American Museum of Natural History paleontologist, told Discovery News.

Fostowicz-Frelik continued that the newly found rabbit "is just another manifestation of the island rule ... We know that their closest relations, rodents, did produce some gigantic forms, not necessarily on islands, which averaged several hundred kilos. Now we see that the lagomorphs (the animal order that includes rabbits, hares and pikas) did not escape the trend."

Brian Kraatz, an assistant professor in the Department of Anatomy at the College of Osteopathic Medicine of the Pacific, agrees.

"There is an underlying assumption that rabbits appeared some 40 million years ago and have been perfectly happy to stay just about the same," Kraatz told Discovery News. "This new species is interesting in that it's quite different from what we know of living or fossil rabbits. Aside from its incredibly large size, its hind legs are rather short, not so good for hopping."

He added, "It's unclear whether their feet would have been decent good luck charms."

Bad luck affected the rabbit when a climate cooling likely ruined comfortable living conditions for the species on its island. The researchers suspect this climate change led to the rabbit's extinction.

Through the recent science, however, it lives on, with more studies of its fossils in the works. Quintana also hopes this rabbit "king" will become a popular mascot for the island.

He explained, "I would like to use N. rex to lure students and visitors to Minorca!"