NEW RECORDS OF SMALL TERRESTRIAL VERTEBRATES IN THE NEOGENE OF CENTRAL MEXICO AND ITS BIOGEOGRAPHIC IMPORTANCE

Central Mexico, located in latitudes 23° and 19° north, is highly diverse in mammals, amphibians, and reptiles in North America. Its geography and complex topography straddle Nearctic and Neotropical ecosystems during the Great American Biotic Interchange (GABI) in the late Neogene (Hemphillian-Blancan). This area is recognized as one of the centers of diversification of megafauna, but small vertebrate communities and their biogeography remain unknown. We explore microvertebrates in the late Neogene of Juchipila, Zacatecas (Hh1-Hh2); Tecolotlán, Jalisco (Hh3); San Miguel de Allende, Guanajuato (Hh3-Hh4 to early Blancan); and La Goleta, Michoacán (early Blancan). Specimens were recovered through screen-washing in fluvial sedimentary sequences with precise chronology based on mammalian assemblages and radiometric dating. Fossils were prepared and classified at the Museo de Paleontología del Centro de Geociencias, Universidad Nacional Autónoma de México, except for those from La Goleta, Michoacán, which are housed in the Department of Vertebrate Paleontology at the Natural History Museum of Los Angeles. This study presents the first record of Lagomorpha during the late Miocene (Hh1-Hh2) in Zacatecas and explores Hypolagus and Notolagus during the latest Hemphillian (Hh4) and early Blancan in Guanajuato. We discuss cricetid rodent diversification during the late Hemphillian, including Prosigmodon, Bensonomys, Neotoma, and Reithrodontomyni indet. Early Blancan of Guanajuato shows a distinct assemblage with Neotoma sawrockensis, Sigmodon minor, and an Oryzomyini indet, which is key to understanding faunal integration from the Great Plains of North America and Central America in Mexico. Based on early Blancan records from Michoacán, we propose P. chihuahuensis as the last representative of this genus. Records of Sciuridae from late Hemphillian to early Blancan include Paenemarmota and Sciurus. Notably, the first occurrence of Soricidae (Eulipotyphla) in Hh3 of Jalisco, dating back to 4.89 million years ago, is the southernmost Pliocene record in North America. Additionally, we present Colubridae (Serpentes), Ranidae (Anura), and Ambystoma (Urodela) as the oldest record of this amphibian in Mexico. These records contribute significantly to our understanding of faunal evolution in central Mexico and faunistic interactions in the Americas.