EXCAVATIONS AND FOSSIL COLLECTIONS FROM TLAPACOYA AND LOLTUN CAVES, MEXICO

Much of the vertebrate fossils recovered from Mexican caves remain unstudied or unpublished, lacking absolute dating and accessible excavation and stratigraphic information. In this study, we present a revision of published and unpublished information of the excavations and stratigraphy of the caves of Tlapacoya and Loltun, as well of the fossil small mammals collected during those excavations, housed at the Paleontological Collection of the INAH.

Tlapacoya is an eroded andesite volcano located at the temperate region of central Mexico. Two rock shelters were systematically excavated there in 1967 and 1970, involving the screening of sediments. A 7-meter trench was excavated in Tlapacoya II cave, where around 7,000 mammal specimens were recovered, mostly of rodents, but lagomorphs and shrews were also represented. Also, an extinct species of vampire bat indicated a Late Pleistocene age. In this cave, the stratigraphy is not clear as the sediments appeared disturbed. At Tlapacoya V cave, approximately 17,000 small mammal specimens were recovered from an eight-layer sequence on the 64 m²excavated area; a Holocene age is suggested by cultural materials.

Loltun comprises a series of karstic chambers connected by tunnels located at tropical southeastern Mexico. Within one cavity, two units were excavated in a methodically way between 1977 and 1980, screening of the sediments included. The 4 x 4 m pit from El Tunel Unit comprised seven cultural levels. A total of 16 strata were excavated from a larger area in El Toro Unit, with the lower half of the sequence of Pleistocene age. In addition of extinct megafauna, thousands of specimens of rodents, bats, lagomorphs, opossums, and shrews were collected, including an extinct mouse-opposum and the giant vampire bat. Some incongruences within published data were found, and a possible mixture of materials is indicated by archaeological studies.

Although the mentioned issues, the sample size and fossil diversity are adequate for their paleontological study. The absolute dating of bones will be carried out to refine the chronology of the deposits. Tlapacoya and Loltun caves would allow to determinate the changes of small mammal faunas and their environment driven by the climatic fluctuations of the Late Quaternary on distinct temperate and tropical regions of Mexico.