Mackerel Shark

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.

Meet our associated expert

This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws.

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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.

Fossil, predatory fish from the Cretaceous (Xiphactinus sp.)
Photo by Chip Clark, Smithsonian, National Museum of Natural History

About Bony Fishes (Superclass Osteichthyes): Paleobiology

The earliest evidence of bony fishes is from fossils found in China dated to the early Cambrian (about 530 million years ago). The fossils are fragments of the head and gill covering of jawless fish (Agnatha), of which a few species persist today. The jawless bony fishes are not only the earliest bony fishes, but also among the earliest known animals with backbones (vertebrates) on Earth. Lacking jaws for chewing, they were filter feeders, straining small organisms from the water. By the early Devonian (about 400 million years ago), various groups of bony fishes with jaws had arisen. The earliest group of jawed fishes was the small, freshwater Ancanthodii, but they went extinct less than 150 million years later. Today's wildly successful group, the ray-finned bony fishes (Actinopterygii) began to diversify during the Devonian. Their earliest representatives had heavy scales, large eyes, and wide mouths.