San Sebastián Limestone

{{short description|Geologic formation in Puerto Rico}}

{{Infobox rockunit

| name = San Sebastián Formation

| image =

| caption =

| type = Formation

| age = Early to Late Oligocene, {{fossil range|29.8|26.5}}

| period = Oligocene

| prilithology = Limestone

| otherlithology =Sandstone, mudstone

| namedfor =San Sebastián, Puerto Rico

| namedby =

| region = {{flag|Puerto Rico}}

| country = {{flag|United States}}

| coordinates ={{coord|18.4|N|67.0|W|display=inline}}

| unitof =Rio Guatemala Group

| subunits =

| underlies =

| overlies =

| thickness =

| extent =

| area =

| map =

| map_caption =

|paleocoordinates={{coord|17.6|N|66.0|W|display=inline}}}}

The San Sebastián Formation is a geologic formation in Puerto Rico. It preserves fossils dating back to the Oligocene period.{{Cite web |title=PBDB Strata Results |url=https://paleobiodb.org/classic/displayStrata?geological_group=Rio%20Guatemala&formation=San%20Sebastian&group_formation_member=San%20Sebastian |access-date=2024-11-16 |website=Paleobiology Database}}

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.{{Cite journal |last1=Marivaux |first1=Laurent |last2=Vélez-Juarbe |first2=Jorge |last3=Merzeraud |first3=Gilles |last4=Pujos |first4=François |last5=Viñola López |first5=Lázaro W. |last6=Boivin |first6=Myriam |last7=Santos-Mercado |first7=Hernán |last8=Cruz |first8=Eduardo J. |last9=Grajales |first9=Alexandra |last10=Padilla |first10=James |last11=Vélez-Rosado |first11=Kevin I. |last12=Philippon |first12=Mélody |last13=Léticée |first13=Jean-Len |last14=Münch |first14=Philippe |last15=Antoine |first15=Pierre-Olivier |date=2020-02-12 |title=Early Oligocene chinchilloid caviomorphs from Puerto Rico and the initial rodent colonization of the West Indies |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=287 |issue=1920 |pages=20192806 |doi=10.1098/rspb.2019.2806 |issn=0962-8452 |pmc=7031660 |pmid=32075529}}{{Cite journal |last1=Blackburn |first1=David C. |last2=Keeffe |first2=Rachel M. |last3=Vallejo-Pareja |first3=María C. |last4=Vélez-Juarbe |first4=Jorge |date=2020 |title=The earliest record of Caribbean frogs: a fossil coquí from Puerto Rico |journal=Biology Letters |language=en |volume=16 |issue=4 |pages=20190947 |doi=10.1098/rsbl.2019.0947 |issn=1744-9561 |pmc=7211465 |pmid=32264782}} 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.{{Cite journal |last1=Marivaux |first1=Laurent |last2=Vélez-Juarbe |first2=Jorge |last3=Viñola López |first3=Lázaro W. |last4=Fabre |first4=Pierre-Henri |last5=Pujos |first5=François |last6=Santos-Mercado |first6=Hernán |last7=Cruz |first7=Eduardo J. |last8=Grajales Pérez |first8=Alexandra M. |last9=Padilla |first9=James |last10=Vélez-Rosado |first10=Kevin I. |last11=Cornée |first11=Jean-Jacques |last12=Philippon |first12=Mélody |last13=Münch |first13=Philippe |last14=Antoine |first14=Pierre-Olivier |date=2021 |editor-last=Lautenschlager |editor-first=Stephan |title=An unpredicted ancient colonization of the West Indies by North American rodents: dental evidence of a geomorph from the early Oligocene of Puerto Rico |url=https://onlinelibrary.wiley.com/doi/10.1002/spp2.1388 |journal=Papers in Palaeontology |language=en |volume=7 |issue=4 |pages=2021–2039 |doi=10.1002/spp2.1388 |hdl=2027.42/170885 |issn=2056-2799|hdl-access=free }}