The Evolution of Jawed Fishes
The Evolution of Jawed Fishes
Ancient vertebrates evolved about 520 million years ago. They were small and jawless and had to use their lips to grab prey. These jawless vertebrates dominated the seas, but now only a few species of them have survived, namely the lampreys and hagfishes. Originally, most ancient fishes consisted of bottom-feeding armored fishes that lacked jaws called the ostracoderms, who swam the Silurian and Devonian seas. They had protective armor that was made of plates of bones, and it is assumed that they used a muscular pharynx to suck food into their mouths. After about 100 million years of dominating, some members started to show some changes and evolved new accessories in their mouths. These were faster moving fish called gnathostomes which are now extinct, and were the closest relatives of the jawed fishes. About 408 million years ago, in the Middle Devonian the first jawed vertebrates called placoderms evolved. They had bumpy gums or blade like structures in their mouths to catch prey. It was widely believed that the reason teeth evolved in a number of Placoderms was to be able to better capture prey. Placoderms are the ancestor of other groups of jawed fish such as sharks, bony fishes and acanthodians which are now extinct. There is now evidence that teeth evolved either along with or after jaws evolved. The cross disciplinary research between Paleontologists and physicist on the fossil of a primitive jawed fish named the Compagopiscis revealed interesting information about the structures and development of bones and teeth. The results of their study present strong evidence that placoderms possessed teeth and presumably solves the debate surrounding the origin of teeth. It is contended that jaws evolved only one time in contrast to being evolved multiple times in different species (parallel evolution). The morphological changes that started to appear in fishes appeared at a time where the environment was changing, with increase
Ancient vertebrates evolved about 520 million years ago. They were small and jawless and had to use their lips to grab prey. These jawless vertebrates dominated the seas, but now only a few species of them have survived, namely the lampreys and hagfishes. Originally, most ancient fishes consisted of bottom-feeding armored fishes that lacked jaws called the ostracoderms, who swam the Silurian and Devonian seas. They had protective armor that was made of plates of bones, and it is assumed that they used a muscular pharynx to suck food into their mouths. After about 100 million years of dominating, some members started to show some changes and evolved new accessories in their mouths. These were faster moving fish called gnathostomes which are now extinct, and were the closest relatives of the jawed fishes. About 408 million years ago, in the Middle Devonian the first jawed vertebrates called placoderms evolved. They had bumpy gums or blade like structures in their mouths to catch prey. It was widely believed that the reason teeth evolved in a number of Placoderms was to be able to better capture prey. Placoderms are the ancestor of other groups of jawed fish such as sharks, bony fishes and acanthodians which are now extinct. There is now evidence that teeth evolved either along with or after jaws evolved. The cross disciplinary research between Paleontologists and physicist on the fossil of a primitive jawed fish named the Compagopiscis revealed interesting information about the structures and development of bones and teeth. The results of their study present strong evidence that placoderms possessed teeth and presumably solves the debate surrounding the origin of teeth. It is contended that jaws evolved only one time in contrast to being evolved multiple times in different species (parallel evolution). The morphological changes that started to appear in fishes appeared at a time where the environment was changing, with increase