Amami spiny rat / Tokudaia osimensis / Amami toge-nezumi / アマミトゲネズミ
This small, forest-dwelling rodent is unusual for several reasons. It gets its name from the needle-shaped hairs on its back, which grow 2 millimeters wide and 20 millimeters long. Its strong hind legs allow it to jump like a kangaroo for distances up to 50 centimeters, which is how it escapes the venomous habu viper. But what makes the spiny creature particularly interesting is that it is born without a Y chromosome, one of the two chromosomes that determine the sex of most mammals. While its standing as an endangered species makes the Amami spiny rat a difficult subject for research, scientists have determined that it is an endemic species that separated from a similar spiny rat on the neighboring island of Tokunoshima between 6 million and 2 million years ago.