They identify a strange group of sharks and rays that inhabited Madagascar 55 million years ago – 02/28/2019

The Mahajanga Basin in northwestern Madagascar produces abundant remnants of terrestrial and marine ecosystems, but little is known about sharks and fossil rays during the Eocene Era, between 55 and 34 million years, in this region. This contrasts with the many known sharks and rays from other Eocene sites around the world and with shark and ray ecosystems found in the ancient and younger sediments of the Mahajanga Basin.

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In this study, Karen Samonds of the University of Northern Illinois and colleagues collected isolated teeth, dental plaques, and stingray spines on ancient coastal sediments from the Ampazony and Katsepy areas of the basin, dating from Middle and upper Eocene. They identified at least ten species of sharks and rays, including a new species, 'Carcharhinus underwoodi'. It is the oldest identified species of 'Carcharhinus', a genus that is distributed worldwide for 35 million years, but is rarely known from the past. Eocene.

In addition to the new species, the Eocene fauna of Madagascar shares many species with the Eocene ecosystems of North Africa, suggesting that these animals were widespread in the southern seas at that time. On the other hand, the fauna of Madagascar has a unique lack of sand sharks and is dominated by eagle rays, indicating a rather unusual ecosystem, somewhat surprising given the long history of isolation of Madagascar.

The researchers cautioned that this study provides an incomplete picture since they only collected fossils larger than 2 millimeters. In addition, they recommend that future studies focus on smaller materials for a more complete view of the old ecosystem.