Ammonites Dined on Plankton
Thursday, January 06 2:16 pm
Reconstructed radula of the straight shelled ammonite Baculites (70-80 Myr-old) with each color representing a different type of tooth; generated from Synchrotron Radiation microtomographic slices. Image credit: Tafforeau/Kruta.
Powerful synchrotron scans of Baculites fossils found on American Museum of Natural History expeditions to the Great Plains suggests that the extinct group of marine invertebrates to which they belong, the ammonites, had jaws and teeth adapted for eating small prey floating in the water. One ammonite also provided direct evidence of a planktonic diet because it died with its last meal in its mouth — tiny larval snails and crustacean bits. The detailed description of internal structure of ammonites, published by a Franco-American research team this week in Science, also provides new insights into why ammonites became extinct 65.5 million years ago when an asteroid impact led to the demise of the world’s nonavian dinosaurs and much of the plankton.
“I was astonished when I saw the teeth for the first time, and when I found the tiny plankton in the mouth,” says first author Isabelle Kruta of the Département Histoire de la Terre, Muséum National d’Histoire Naturelle in Paris, France. Kruta began the project as an Annette Kade fellow at the American Museum of Natural History. “For the first time we could observe these delicate, exceptionally well-preserved structures and obtain information on the ecology of these enigmatic animals.”
“When you take into consideration the large lower jaws of ammonites in combination with this new information about their teeth, you realize that these animals must have been feeding in a different way from modern carrion-eating Nautilus,” says Neil Landman, curator in the Division of Paleontology at the American Museum of Natural History. “Ammonites have a surprisingly large lower jaw with slender teeth, but the effect is opposite to that of the wolf threatening to eat Little Red Riding Hood. Here, the bigger mouth facilitates feeding on smaller prey.” Read more »
