Dirección Nacional del Antártico - Instituto Antártico Argentino

Finding of the oldest whale fossil in the world: "Antarctic archaeocete"

Scientists of the Instituto Antártico Argentino (depending from the Dirección Nacional del Antártico) found remains of an "archaeocete" (very ancient whale) that dates back around 49 million years, at isle Marambio, close to the Weddell sea, at the Northeast of the Antarctic Peninsula.

This find that took place in the last summer campaign (2011) is highly relevant as it represents the most primitive record of the group that gave origin to modern whales and dolphins. This find was carried out by Argentine paleontologists Claudia P. Tambussi (CONICET-Museum of La Plata) and Marcelo A. Reguero (CONICET, Instituto Antártico Argentino and Museum of La Plata); and the Swedish Thomas Mörs and Jonas Hagström, both from the Swedish Museum of Natural History, Stockholm, Swede.

The tasks were performed from a camp and different sectors of La Meseta formation were explored, particularly in two pieces that date back 49 and 34 million years, respectively.

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Paleontological Camp of the Instituto Antártico Argentino in the study area

In the most ancient piece (49 million years) among others, numerous remains of sharks’ teeth belonging to 11 different species, (Hexanchus, Squalus, Centrophorus, Pristiophorus, Squatina, Striatolamia, Odontaspis, Isurus, Carcharias, Cetorhinus y Galeorhinus), osteichthyes, penguins and other marine vertebrates as turtles, devilfish, chimaera, and cetaceans were collected.

But the most relevant find in these fossiliferous horizons was a buried archaeocete’s jawbone with multidenticulated teeth. This piece is approximately 60 cm long and has a tooth in its position, together with fragments of other teeth. It has a widened mandibular canal which reason could be that this group already had the ability to hear by vibrations, and it can be inferred that they were already adapted to marine life. The teeth found exhibit some wear what suggests that it was a predator. The approximate size of this specimen would be around 4 to 6 meters long and it could be a big young animal or a small adult one.

At present this jawbone is under preparation and final restoration at the CENPAT Laboratories, Puerto Madryn, where paleontologists Mónica Buono (CONICET-CENPAT) and Marta Fernández (CONICET- Museum of La Plata) are carrying out systematic and comparative studies of this new specimen.

Based on this find, today we dare say that the evolution (from terrestrial to aquatic animals) and distribution that the “semi-aquatic whales” have undergone in the southern seas have been much more quickly than previously thought. This statement takes into account that the Protocetidae reported in the Indian-Pakistan region (of terrestrial origin and with 4 developed feet) where assigned an age of 53 million years, while the "Antarctic archaeocete" (already fully acquatic), has been assigned an age of 49 million years.

Concisely, this find is relevant as it confirms the presence of " archaeocetes" in the Antarctica. But what is most relevant of the Antarctic " archaeocete" is that it is the most ancient record of an “aquatic whale” in the world (dated 49 million years back). It belongs to the Basilosauridae, group from which all present cetaceans were originated. Another important fact that emerges from this find, is that the archaeocetes’ diversification time, that is currently estimated in 15 million year, is brought to fewer million years (4 million years).

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Representation of a Basilosauridae

These studies were developed within the PICT 2007-00365 "Continental Vertebrates from the late Cretaceous - Paleogene period of the Antarctic Peninsula” Project co-financed by the Agencia Nacional de Ciencia y Técnica (National Office of Science and Technology) and the Instituto Antártico Argentino, through the Dirección Nacional del Antártico.

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