Paleontologists from Museum Victoria, Australia, and the Smithsonian Institution have rediscovered what they claim are the oldest sirenian fossils ever found in the Indo-Pacific region.

The 12-million-year-old fossils – vertebrae and ribs – were discovered in the Selminum Tem cave in the Hindenburg Range, Western Province of Papua New Guinea, more than 30 years ago, but remained unstudied.

“Until now, Australasia didn’t have a particularly ancient fossil record of sea cows, the group of marine mammals that includes our living dugongs,” said Dr Erich Fitzgerald from Museum Victoria, who with colleagues described the fossils in the Journal of Vertebrate Paleontology.

“The records only went back some five million years. Elsewhere in Asia, sea cow fossils are found in much older rocks, so it was always a mystery as to why the fossils hadn’t been found in this part of the world. Now, with this one discovery, we’ve more than doubled the length of their evolutionary history in Australasian seas.”

“The fossils provide a vital perspective on the relationship modern sea cows have with Australia’s northern marine ecosystems,” Dr Fitzgerald said.

“Modern-day dugongs are major consumers of sea-grass, and, by doing so, have a tremendous impact on the structure of the ecosystem.

“They participate in a delicate balancing act: their feeding allows diversity in sea-grass and animal species that would otherwise be lacking.”

Previously, it was thought that sea cows were fairly new arrivals in Australasia, and that their relationship with sea-grass ecosystems here was a recent event.

This new evidence suggests sea cows have been an important component of Australasia’s marine ecosystems for at least 12 million years and that their role in the long-term health of these environments may be substantial.

The Miocene sea cow fossils are also the earliest mammal recorded from the island of New Guinea.

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Bibliographic information: Erich M. G. Fitzgerald et al. 2013. Miocene sea cow (Sirenia) from Papua New Guinea sheds light on sirenian evolution in the Indo-Pacific. Journal of Vertebrate Paleontology, vol. 33, no. 4; doi: 10.1080/02724634.2013.753081