Marine fossils unearth stories of Panama’s deep past

Between 6.4 and 5.8 million years ago, most of the land bridges connecting North and South America had appeared and the channels connecting the Pacific and Atlantic oceans were shallow. Recent fossil discoveries in the northern Panama Canal region indicate that an exchange of marine species persisted in these shallow waters during the late stages of isthmus formation.

In 2017 and 2019, Aldo Benites-Palomino was studying fossils collected in Panama in the Caribbean, when he came across some unexpected specimens. He was a biology student in Peru, where his training was classical. As an intern and then fellow at the Smithsonian Tropical Research Institute (STRI), his mindset changed. Her mentor, STRI staff scientist and paleobiologist Carlos Jaramillo, encouraged his students to change their focus when looking at fossils: instead of thinking about specimens or methods, to thinking about questions that fossils could answer.

“I wanted to go to STRI because it is the most important center for tropical biology in the world,” said Benites-Palomino. “There I could learn a lot about how biology and ecology work in the modern world.”

The fossilized remains belong to undersized cetaceans, a group of aquatic mammals that includes whales and dolphins, and the specimens are new to the region. Most were collected by Carlos de Gracia of STRI and Jorge Velez Juarbe of the Los Angeles Museum of Natural History, both co-authors in a new paper published in Biology Letter. In the article, Benites-Palomino and his colleagues not only describe the specimens, but also explore the stories they tell about the isthmus’ past.

The fossils date from the Late Miocene, around 6.4 to 5.8 million years ago, when the final stages of isthmus formation had already begun. These events affect oceanic waters and ocean currents around the world and trigger speciation events, in which species separated by land bridges develop their own unique characteristics in one of the oceans.

However, this cetacean found in the Panamanian Caribbean shares similarities with other Late Miocene species from the North and South Pacific Oceans, particularly the Pisco Formation in Peru, suggesting that some organisms could still disperse through shallow seas at times of deep water exchange. between the two oceans is no longer the case.

The paucity of fossil marine mammals from the western Caribbean has so far hampered understanding of the region’s deep past, so these new findings help strengthen current knowledge regarding the connectivity between Pacific and Caribbean marine fauna during the late phases of the isthmus formation.

“Panama’s fossil record of marine vertebrates has barely been explored,” said Carlos Jaramillo, STRI staff scientist and one of the study’s authors. “There are still many specimens to study and many more in the rock waiting to be discovered.”