OLIGOCENE VERTEBRATE FAUNAS FROM PUERTO RICO

The origins of the Greater Antillean terrestrial vertebrate fauna have been a topic of debate. Hypotheses regarding the when and how they reached these islands are conflicting. One proposing overwater dispersal from South America throughout the Cenozoic. The other, place their arrival during the late Eocene-early Oligocene through a short-lived landspan connecting South America with the Greater Antilles. Here I focus on the Oligocene terrestrial and marine vertebrate fauna of Puerto Rico and its role in the understanding of the origins of the Greater Antillean vertebrate faunas. In addition to previous reports, new material from the San Sebastian Formation (Fm.) and Lares Limestone (Ls.) in northwestern Puerto Rico, and Juana Diaz Formation in the southwestern part of the island, add to our knowledge of the fauna. Isotopic and paleontological dating, place the San Sebastian and Juana Diaz formations within the early Oligocene and the Lares Ls. as late Oligocene.

The early Oligocene faunas include elasmobranches, osteichthyans, anurans, podocnemidid turtles, gryposuchine gavialoid, megalonychid sloths, caviomorph rodents and dugongid sirenians. The elasmobrances, osteichthyans and sirenians include taxa that are known from Eocene (Jamaica and Cuba) and/or Miocene (Panama, Cuba, Venezuela) deposits throughout the Cenozoic of the Caribbean region. The Oligocene age of the fauna studied here serves as a link between these two periods showing that the marine vertebrate fauna of the Caribbean region can be considered as a single faunal region with little overall change through the Cenozoic.

Other members (i.e. megalonychid sloth and caviomorph rodents) of the early Oligocene fauna represent taxa with strictly South American affinities; which is consistent with the landspan hypothesis for the origins of the fauna. Others, such as the gryposuchine gavialoid and possibly the podocnemidid turtles, likely used this landspan to disperse southwards to the South American landmass. The new finds reported here as underline the importance of paleontological and geological research in Oligocene age deposits to further understand the origins of the Greater Antillean vertebrate fauna.