March 12, 2012

Fossils Show Multiple Seacow Species Coexisted

These days, only four species of Sirenian, more commonly known as the seacow, manatee or dugong exist in a given world region. Smithsonian scientists, however, have been studying fossil records of the ancient mammals and have discovered evidence that this hasn´t always been the case. According to these fossil records, which date back 50 million years ago, multiple species of seacow once existed together. The research also suggests the environment these seacows resided within, as well as their food source was much different than it is today. The smithsonian scientists posted their findings in the journal PLoS ONE.

Of the four species of seacow that exist today, 3 of them are manatees. These manatees live in different regions of the Atlantic ocean. The other species, the dugong, can be found in the waters of the Indo-Pacific ocean.

In studying these fossil records, the scientists found many examples of seacows in the same fossil bed at the same depth. This is prime evidence that more than one species of seacow lived in the same area at the same time.

In a piece published by LiveScience, researcher Nicholas Pyenson said “We were culling through the fossil record of sea cows and finding those few cases we could be certain that these things lived together. In some cases we found the fossils literally on top of each other.”

The scientists studied fossil records from three different time periods and three different regions: The Oligocene period (23 million to 28 million in Florida, the Miocene period(16 million to 23 million) in India and the Pilocene period (3 million to 5 million) in Mexico. In each location, scientists found fossils of multiple species of seacow living together.

As herbivores, these creatures eat mainly sea grasses. The fact that multiple species were found together in the same fossil bed raised questions about the availability of food sources for the ancient seacows.

“The discovery that these multi-species seacow communities once existed revealed answers, but it also created new questions,” said Nicholas Pyenson, curator of fossil marine mammals at the Smithsonian´s National Museum of Natural History and co-author of the research. “Were these species competing against each other for seagrass resources, or were they avoiding competition by each species feeding in separate areas or on different grasses? Also, were seagrass beds structured differently in the past, or were they dominated by one seagrass species like we see today?”

To answer this question, the research team studied the body size of the creatures as well as the size and shape of the skulls. Using this information, they were able to deduce that each different species of seacow had the characteristics to feed on different types of seagrasses. Therefore, any need for competition for food between the species was removed, allowing them to live together in harmony. This find also suggests that as multiple species of sea cow existed in early days, so too did multiple species of seagrass.


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