| San Sebastián Formation | |
| Type: | Formation |
| Age: | Early to Late Oligocene, |
| Period: | Oligocene |
| Prilithology: | Limestone |
| Otherlithology: | Sandstone, mudstone |
| Namedfor: | San Sebastián, Puerto Rico |
| Region: |  Puerto Rico |
| Country: |  United States |
| Coordinates: | 18.4°N -67°W |
| Unitof: | Rio Guatemala Group |
| Paleocoordinates: | 17.6°N -66°W |
The San Sebastián Formation is a geologic formation in Puerto Rico. It preserves fossils dating back to the Oligocene period.[1]
It was primarily deposited as limestone in a marine environment, but some localities with a significant amount of terrestrial fauna appear to have been deposited in a deltaic environment. It contains some of the earliest fossils of terrestrial Caribbean vertebrates, including chinchilloid rodents and Eleutherodactylus frogs.[2] [3] In addition, taxa that are no longer known from the Caribbean, such as gavialid crocodilians and geomyoid rodents, have also been recovered from the formation.[4]
Based on the Paleobiology Database:
| Genus | Species | Material | Notes | Images | |
|---|---|---|---|---|---|
| Aktiogavialis | A. puertoricensis | Incomplete braincase, cranial elements | A gavialid crocodilian. Type locality of genus and species. | ||
| Pelomedusidae indet. | A pelomedusid side-necked turtle. |
| Genus | Species | Material | Notes | Images | |
|---|---|---|---|---|---|
| Borikenomys | B. praecursor | Teeth | A chinchilloid rodent. Type locality of genus and species. | ||
| Caribeomys | C. merzeraudi | Teeth | A geomyoid rodent. Type locality of genus and species, first evidence of geomyoids from the Caribbean. | ||
| Caribosiren | C. turneri | A dugongid sirenian. | |||
| Priscosiren | P. atlantica | A dugongid sirenian. |