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Associated Smithsonian Expert: Hans-Dieter Sues, Ph.D.

Dr. Hans Sues holding the skull of a lion hunted by Theodore Roosevelt

Photo by Smithsonian

Dr. Hans Sues is a senior research geologist at the Smithsonian National Museum of Natural History who specializes in the study of dinosaurs and other vertebrates from the Mesozoic Era. He first became attracted to dinosaurs when he was four years old. After earning his doctorate from Harvard University, he worked as a postdoctoral fellow at McGill University and the National Museum of Natural History. Later Sues was curator and senior manager at the Royal Ontario Museum in Toronto and Carnegie Museum of Natural History in Pittsburgh before returning to the Smithsonian. He has collected fossil vertebrates across the United States as well as in Canada, China, Germany, and Morocco. Among his many discoveries are several new species of dinosaurs.

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Fossil, late Cretaceous shark (Hemiscylliidae)
Photo by Chip Clark, Smithsonian, National Museum of Natural History

About Cartilaginous Fishes (Class Chondrichthyes): Paleobiology

Fish skeletons made of cartilage are rare in the fossil record because cartilage rarely fossilizes. However, the mineralized teeth and scales of these fishes can be abundant as fossils. Shark teeth are made of dentin laid down around the pulp cavity with a thin, durable outer layer of enameloid (enamel-like biomineral). Possible shark teeth have been found in fossil beds dating to the Ordovician (about 450 million years ago). Complete specimens of early sharks are first known from about 400 million-year-old rocks (the Devonian). Most of these ancient sharks died out at the end of the Permian (about 250 million years ago). New groups of sharks diversified during the Mesozoic, along with dinosaurs. These neoselachians (“new sharks”) included the ancestors of modern sharks. They ate cephalopods, fish, and perhaps even reptiles living in the sea. The body plan of modern sharks, including powerful jaws and a streamlined body propelled by a powerful tail fin, has allowed them to diversify and persist to the present day.