Question

Describe the major events of vertebrate evolution, when they occurred, and what groups of vertebrates resulted

Answer 1

First vertebrates

Vertebrates originated around 550 million years ago (Cambrian explosion). An increase in organism diversity was seen in this era. Sone early vertebrates are Myllokunmingia and  Haikouichthys ercaicunensis. They had notochord, rudimentary vertebrae, defined head, and tail but lacked jaws. They did filter-feeding adjacent to the sea bed. A group of vertebrates called conodonts had paired tooth segments and lived in the late Cambrian to Triassic period.

From fish to amphibians

The jawless vertebrates were followed by the evolution of jawed vertebrates in the late Ordovician period. They became more prevalent in the Devonian period or More commonly known as the Age of Fishes. It was around 400-450 million years ago. This period saw the evolution of bony fishes, the 2 groups being, the Actinopterygii and sarcopterygians. There was an end of jawless fishes except for lampreys and hagfish and Placodermi. The transition from fishes to amphibians was also seen in this period in the form of labyrinthodonts.

Mesozoic vertebrates

Labyrinthodonts underwent evolution to give rise to Amniotes in Carboniferous period around 365 million years ago. During the late Paleozoic era, parareptilia and synapsid amniotes were prevalent with the Mesozoic era seeing the development of diapsid amniotes. Bony fishes started to dominate the seas. The Jurassic period saw evolution of birds. These birds were a derived form of dinosaurs. The end of non-avian dinosaurs was followed by the expansion of mammals.

After the Mesozoic

There was an increase in the diversification of bony fishes, amphibians, reptiles, birds, and mammals in the Cenozoic era (66 million years ago till present age). Fishes constitute almost half of the vertebrate species. The rest of the vertebrates are formed by tetrapods that include amphibians, mammals, reptiles, and birds.