Sirenians in Madagascar

By Rebekah Ernat |

I started planning for my project within the past year, but its true origins go back much further than that.  In 1927, a team of French paleontologists led by M. Collignon and J. Cottreau conducted a dig on the island of Nosy Makamby, off the northwest coast of Madagascar.  They were primarily interested in invertebrates, but they also found several fossils that they identified as sea cow bones.  (Sea cows, or more accurately, “sirenians,” are an order of large aquatic mammals that include modern-day manatees and dugongs, and many extinct species.)

Modern-day sirenians

These bones included part of a braincase, other skull fragments, several ribs, and two vertebrae.  In the paper published following the expedition, Collignon and Cottreau attributed the sirenian remains to the genus Halitherium; however, this designation was weak due to Halitherium’s status as something of a “garbage can taxon.”

Following this initial discovery and report, there was little interest in the specimen, which resided in the National Museum of Natural History in Paris, until Dr. Karen Samonds and her team returned to the same site on Nosy Makamby.   Between 2005 and 2015, they found a sirenian jaw, more ribs and vertebrae, and other bones that appear to be part of the pelvic girdle.

The island of Nosy Makamby

Ernat 3

Believed to belong to the same species as those discovered by the French, these fossils exhibit several unique characteristics that differentiate them from other ancient sirenian species.  For example, the ribs are long and slender, distinctly different from those dense, banana-shaped ribs of another Malagasy sea cow (Eotheroides lambondrano).  Skull morphology, including the concave sloping frontal roof, indicates that these remains may belong to a new member of the genus Rytiodus, but more analysis is needed before we can be certain about their taxonomic status.  This is where my research comes in!

Sea cow fossils: braincase, ribs, and lower jaw

My work this summer included going to the National Museum of National History in France to take pictures and measurements of Collignon and Cottreau’s original sea cow fossils.  Throughout the rest of the summer and into the school year, I will be using that data to compare the material in France and in Dr. Samonds’ lab at NIU with previously published papers about other sirenian species.  The end goal of my project will be to describe and name this new species of extinct sea cow.  Not only will this contribute to sirenian evolutionary and biogeographic history, but it will also help to fill in the 65-million year gap in Madagasar’s fossil record, as the only Malagasy mammalian fossils described from the Miocene epoch (23-5 million years ago).


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