Peromyscus nesodytes, a “giant” deer mouse, became extinct approximately 8,000 years Before Present and lived during the late Pleistocene on California’s Channel Islands.

Overview

In 1934 Robert W. Wilson designated P. nesodytes as a new species after discovering a mouse bone (a right ramus of the mandible). He writes, “The outstanding character of P. nesodytes is its large size, which is greater than any living species of Peromyscus native to the United States.” The only larger mice known are the extant mice of the genus Megadontomys

Megadontomys

Megadontomys is a genus of rodent in the family Cricetidae, found in Mexico.It contains the following species:* Oaxaca Giant Deer Mouse * Nelson's Giant Deer Mouse...

, which are found in Mexico and Central America.

The mouse “generally considered ancestral to P. nesodytes” is Peromyscus anyapahensis. P. anyapahensis is also extinct, and it is smaller in body size than P. nesodytes.

The engrossed size of P. nesodytes follows Foster's rule

Foster's rule

Foster's rule is a principle in evolutionary biology stating that members of a species get smaller or bigger depending on the resources available in the environment. This is the core of the study of island biogeography. For example, it is known that pygmy mammoths evolved from normal mammoths on...

 of insular gigantism and dwarfism in which some rodents become enlarged because of their inhabitation of islands lacking a multitude of predators. Foster’s rule also helps to explain the diminished sizes of the extinct pygmy mammoth

Pygmy Mammoth

The Pygmy Mammoth or Channel Islands Mammoth is an extinct species of dwarf elephant descended from the Columbian mammoth . A case of island or insular dwarfism, M. exilis was only to tall at the shoulder and weighed about , in contrast to its tall, ancestor.Remains of M...

 and the critically endangered island fox

Island Fox

The island fox is a small fox that is native to six of the eight Channel Islands of California. There are six subspecies of the fox, each unique to the island it lives on, reflecting its evolutionary history...

 of the Channel Islands.

Habitat

The habitat of P. nesodytes was exclusively located on the northern California Channel Islands. Remains of P. nesodytes have been found on San Miguel Island

San Miguel Island

San Miguel Island is the westernmost of California's Channel Islands, located across the Santa Barbara Channel in the Pacific Ocean, within Santa Barbara County, California. San Miguel is the sixth-largest of the eight Channel Islands at , including offshore islands and rocks. Prince Island, off...

 and Santa Rosa Island, California

Santa Rosa Island, California

Santa Rosa Island is the second largest of the Channel Islands of California at 53,195 acres . Defined by the United States Census Bureau as Block 3009, Block Group 3, Census Tract 29.10 of Santa Barbara County, California, the 2000 census showed an official population of 2 persons. It is part of...

. The northern Channel Islands were once connected as a “super-island” called Santa Rosae

Santa Rosae

Santa Rosae was an ancient landmass off the coast of present-day southern California, near Ventura County and Santa Barbara County, of which the northern Channel Islands of California are remnants....

, but increased sea levels have separated the islands for thousands of years.

Extinction

P. nesodytes probably became extinct because of the possibly accidental introduction of a smaller mouse, Peromyscus maniculatus, by the Chumash people who lived in the Santa Barbara area. The Chumash traded on the northern Channel Islands and could have been unknowing transporters of P. maniculatus to the islands. Phillip Walker notes, “Considering the nesting and feeding opportunities provided by the plant foods traded to the islands, it is possible that Peromyscus occasionally crossed the Santa Barbara Channel secreted in baskets of cargo.”

P. maniculatus probably fared better in avoiding the most frequent mouse predator on the islands, the barn owl, than P. nesodytes. A possible example of this is shown in an archaeological site on San Miguel Island, Daisy Cave. Daniel Guthrie writes, “The smaller numbers of P. maniculatus from the lower levels of Daisy Cave may be due to preference by owls for the larger mouse species [P. nesodytes] that was on the island at the time.”

Further information

For behavior and information on deer mice in general, see the Wikipedia entries for Peromyscus

Peromyscus

The genus Peromyscus contains the animal species commonly referred to as deer mice. This is a genus of New World mouse only distantly related to the common house mouse and laboratory mouse, Mus musculus...

and Peromyscus maniculatus

Peromyscus maniculatus

Peromyscus maniculatus is a rodent native to North America. It is most commonly called the Deer Mouse, although that name is common to most species of Peromyscus and is fairly widespread across the continent, with the major exception being the southeast United States and the far north.Like other...

.