Peromyscus nesodytes facts for kids

The giant island deer mouse (Peromyscus nesodytes) was a very large mouse that lived a long time ago. It became extinct about 8,000 years ago. This mouse lived during the late Pleistocene and early Holocene periods on California’s Channel Islands.

What Was the Giant Island Deer Mouse?

In 1934, a scientist named Robert W. Wilson found a mouse bone. It was part of a jawbone. He realized it belonged to a new species, which he named P. nesodytes.

Wilson noted how big this mouse was. He wrote that its size was "greater than any living species of Peromyscus native to the United States." The only mice known to be larger are those from the genus Megadontomys, which live in Mexico and Central America today.

Scientists believe that Peromyscus anyapahensis was an ancestor of the giant island deer mouse. P. anyapahensis is also extinct, and it was smaller than P. nesodytes.

The huge size of P. nesodytes is an example of something called Foster's rule. This rule explains why some animals on islands become much larger or much smaller than their relatives on the mainland. For rodents like this mouse, they often grow bigger on islands because there are fewer predators around.

Where Did the Giant Island Deer Mouse Live?

The giant island deer mouse lived only on the northern Channel Islands in California. Scientists have found its remains on San Miguel Island and Santa Rosa Island.

Thousands of years ago, these northern Channel Islands were actually connected. They formed one big "super-island" that scientists call Santa Rosae. Over time, sea levels rose, and the single large island separated into the smaller islands we see today.

Why Did the Giant Island Deer Mouse Disappear?

The giant island deer mouse likely became extinct after a smaller mouse, Peromyscus maniculatus, arrived on the islands. It's thought that the smaller mouse was brought there by accident.

The Chumash people lived in the Santa Barbara area and traded on the northern Channel Islands. They might have unknowingly carried P. maniculatus to the islands. Sometimes, these smaller mice might have hidden in baskets of food. They could have been carried by boat to the islands during trading trips.

The smaller P. maniculatus was probably better at hiding from the main mouse predator on the islands, the barn owl. The giant island deer mouse, being larger, might have been an easier target.

Evidence from Daisy Cave, an old archaeological site on San Miguel Island, supports this idea. In the deeper, older layers of the cave floor, there are fewer remains of P. maniculatus. In the newer, upper layers, there are more. This suggests that barn owls might have preferred to hunt the larger P. nesodytes over the smaller P. maniculatus.