PROECHIMYS YONENAGAE, A NEW SPECIES OF SPINY RAT (RODENTIA, ECHIMYIDAE) FROM FOSSIL SAND DUNES IN THE BRAZILIAN CAATINGA

A new species of the genus Proechimys, subgenus Trinomys (Rodentia: Ec himyidae) was found along with many new species and genera of Squamata in the main sand dune field on the left bank of the middle Sao Franci sco river, in the Brazilian Caatinga Morphoclimatic Domain. This new s pecies (whose karyotype was already described by Leal-Mesquita er al. (1992) as Proechimys sp. n.) is highly autapomorphic and may be easily distinguished from other spiny rats. Among other distinctive traits, it is smaller, has larger tail/body and hind foot/body ratios, and has more inflated tympanic bullae than other species; the tip of the tail has a well developed, bicolored brush of hairs; and there is only one counterfold in each cheek teeth. Some of these features are convergen t with those of ricocheteal small mammals from many deserts of the wor ld, and are related to the change of habits and habitat of the species compared to other congeners which are restricted to forested areas.