The Tres Marias raccoon (Procyon lotor insularis) is a subspecies of the common raccoon endemic on the two main islands of the Islas Marías, an archipelago off the western coast of the Mexican state of Nayarit.
In its initial description in 1898, the Tres Marias raccoon was classified as a subspecies of the common raccoon (Procyon lotor) by Clinton Hart Merriam. In 1950, Edward Alphonso Goldman identified it as a distinct species; a view that has been upheld by most scientists until recently. In a study of a couple of mounted speciemen in 2005, Kristofer M. Helgen and Don E. Wilson came to the conclusion that there are morphological differences between the Tres Marias raccoon and the subspecies Procyon lotor hernandezii of the common raccoon found on the Mexican mainland, but that they are not large enough to justify the classification as distinct species. It is therefore assumed that the Tres Marias raccoon was introduced to the Islas Marías not long ago. Subsequently, the Tres Marias raccoon was listed as a subspecies of the common raccoon in the third edition of Mammal Species of the World by Wilson and DeeAnn M. Reeder published in 2005.
The average body length of five adult males, including the tail, was stated with 84.1 cm (33.1 in) by Edward William Nelson in 1898. Three mounted speciemen, which were between 84.0 and 90.4 cm (33.1–35.6 in) long, were meassured in 2005. Of the same tenor, Samuel I. Zeveloff calls the Tres Marias raccoon large compared to an average sized common raccoon, making it not an example of insular dwarfism. The coat of the Tres Marias raccoon is pale and short and on its underparts only few guard hairs cover the light brown ground hairs. The most distinctive feature compared to other subspecies is its angular skull.
In 1996, the Tres Marias raccoon was classified as endangered by the IUCN since less than 250 mature individuals were living in the wild. The subspecies Procyon insularis vicinus endemic on María Magdalena is assumed to be extinct. Since only two mounted speciemen exist in museums, it will probably never be known if it is taxonomically distinct from the subspecies endemic on María Madre. The Tres Marias raccoon is hunted by the islanders and no conservation efforts have been made to protect the species from extinction. Considering its small range, the Tres Marias raccoon was most likely never numerous, just as well as the four other island raccoons (Cozumel raccoon, Bahaman raccoon, Guadeloupe raccoon and the extinct Barbados raccoon).