With the recent excavation and transport of the remains of a new species of prehistoric sea cow from Santa Rosa Island, scientists are just now delving into the fossils originally discovered on the windswept isle 2014 and 2017.

Santa Rosa Island is once again proving to be an archeological hot spot. Scientists from the United States Geological Survey discovered the fossils while studying earthquake faults in a steep, eroding ravine in the middle of the windswept isle. The first sea cow specimen found in 2014 had mostly eroded away when geologists came to investigate in July 2017. That’s when the second, more complete fossils were discovered.

Found by chance, the site represents the first sirenian, or sea cow (think manatees and dugongs), known on the Channel Islands National Park. The fossils are from marine rocks near the center of the island. The rocks are orders of magnitude older than the north shore sediments that have produced multiple pygmy mammoth remains. The rock that the sea cows were discovered in is tens of millions of years old instead of tens or hundreds of thousands of years old rock mammoths were discovered in.

“It is on a part of the island that hasn’t been heavily surveyed for fossils,” said Dr. Jonathon M. Hoffman, Dibblee Collection Manager of Earth Science at the Santa Barbara Museum of Natural History (SBMNH). “It demonstrates our need to keep looking for fossils from these rocks.”

Scientists know this sirenian’s estimated age of 20 million to 25 million years old is a time frame in their evolutionary history that is not well represented in Southern California. This discovery helps fill in a gap giving insight into what drove this distribution of sirenians that includes the modern dugong.

Roughly 20 million years ago the four northern Channel Islands (Anacapa, Santa Cruz, Santa Rosa and San Miguel Islands) were one “mega island” scientists dubbed Santarosae. That hunk of land broke off what is now the San Diego/Baja region. These sirenian fossils came over when that large block of continental crust broke off the North American tectonic plate and was pulled northwest by the Pacific Plate.

Hoffman said the “mega island” was geologically ephemeral, existing at sea levels when they were at their lowest during the last 200,000 years, when peaks in continental glaciation trapped water on land during ice ages.

“Another way to think of it is that mammoths lived on Santarosae over the last 200,000 years while the sea cow fossils were in the rocks that formed the super island,” continued Hoffman.

Excavation of the sirenian was completed in August 2018 and brought to the SBMNH this past October. Scientists are just now studying the fossils, especially the skull. The skull contains the most diagnostic features for potentially describing new species. Hoffman said Dr. Jorge Velez- Juarbe, an expert in sirenian paleontology, is confident this specimen is likely a new species based on what’s been exposed thus far. Scientists are also identifying the invertebrate fossils surrounding the sirenian fossils, such as marine snails, clams, etc. These give insight to the age of the rock layer.

Other physical characteristics scientists have gleaned from this species of sirenian are that it’s slightly smaller than modern dugongs, which average three meters in length. This animal would have a forked tail instead of a paddle tail like a manatee. Its ribs are dense and robust like modern day dugongs and manatees, allowing them to weigh themselves down underwater while feeding. Its teeth are different though. Modern dugong molars are peg-like, while this specimen’s molars are more complex and have two cusps with ridges running across the width of the tooth.

“We will learn more about the similarities and differences as the fossils are prepared and studied,” said Hoffman. “The specimen’s traits particularly on the skull, will be used to determine how this animal is related to other extinct sirenians and where it belongs within the evolutionary tree of sirenians.”