EVOLUTION
Sharks have swum in the oceans for almost 450 million years. That extra few million years of evolution have enabled many shark species to develop some extraordinary abilities as perfect predators.
Paleontologists piece together the history of ancient living things, largely through the discovery and analysis of fossils. Problem is, sharks generally don’t fossilize as well as other animals because their skeletons are made of cartilage, a softer and more flexible tissue. Cartilage isn’t as easily fossilized as is bone.
Fortunately, shark teeth do fossilize well, and sharks produce thousands of teeth in a lifetime. Fossilized shark skin scales and, over time, other body parts have also been found.
Paleontologists piece together the history of ancient living things, largely through the discovery and analysis of fossils. Problem is, sharks generally don’t fossilize as well as other animals because their skeletons are made of cartilage, a softer and more flexible tissue. Cartilage isn’t as easily fossilized as is bone.
Fortunately, shark teeth do fossilize well, and sharks produce thousands of teeth in a lifetime. Fossilized shark skin scales and, over time, other body parts have also been found.
- The oldest fossilized evidence of prehistoric sharks comes from shark-like scales that date to 455 million years ago during the Ordovician Period, in Colorado.
- The oldest shark teeth are from the Devonian Period, about 400 million years old, found in Europe. Nothing beyond these scales or the teeth is known about these early sharks.
- More complete fossil shark remains date to 380 million years old, including a fossilized shark braincase, possibly a xenacanth, found in Australia. Other remains of this or similar species have been found in Antartica and Saudi Arabia.
Five major mass extinction events have occurred during the past 439 million years. Sharks have survived all five of these mass extinctions, a testament to their versatile design. They have also benefited from a few adaptive radiations, giving rise to many interesting sharks.
- The first major shark radiation occurred 360 to 286 million years ago.
- Sharks enjoyed another period of adaptive radiation throughout the Jurassic and Cretaceous periods, beginning about 200 million years ago. Among the groups of sharks that thrived during this time are the Hybodonts, one of which was an 8 foot shark named Hybodus, that lived in shallow seas 180 million years ago.
- Another early shark is Mcmurdodus, which had an even earlier start of 390 million years ago.
Many sharks had evolved into fast-swimming, off-shore predators. It is during this period that modern shark families originated. At the end of the Cretaceous, about 65 million years ago, another global catastrophe destroyed a mass number of species, including the dinosaurs. The sharks who survived that extinction include the modern sharks of today.