Vertebrate

Vertebrates, also called craniates, are animals with a vertebral column and a cranium. The vertebral column protects the spinal cord, and the cranium protects the brain. They are part of the subphylum Vertebrata, the largest group in the phylum Chordata.

The vertebrates include mammals, birds, amphibians, and many kinds of fish and reptiles. Fish include the jawless Agnatha, and the jawed Gnathostomata. Jawed fish include cartilaginous fish and bony fish. Bony fish include lobe-finned fish, which led to the tetrapods, animals with four limbs.

The first vertebrates appeared in the Cambrian explosion about 518 million years ago. Jawed vertebrates evolved in the Ordovician or Silurian. Bony fishes appeared in the Silurian and became many different types in the Devonian. The first tetrapods appeared near the end of the Devonian, and the first amphibians lived on land in the Carboniferous. During the Triassic, mammals and dinosaurs appeared, and dinosaurs later led to birds in the Jurassic. Today, living species are about equally split between all kinds of fish and tetrapods. Many species have been decreasing since 1970 because of land-use change, overexploitation of natural resources, climate change, pollution, and the impact of invasive species.

Characteristics

Vertebrates are animals that have a backbone and a skull to protect their brain. They belong to a group called Chordata, which share some special features like a notochord and a hollow nerve cord.

What makes vertebrates unique is their backbone, which is made of bone or cartilage, and a large brain.

These animals come in many sizes, from tiny frogs to huge whales. They can live in water or on land. Most have a special way to get oxygen through gills, but land animals like amphibians and mammals use lungs instead. Their bodies are supported by a strong skeleton, and they have sense organs like eyes and ears to help them explore the world.

Evolutionary history

Vertebrates first appeared during the Cambrian explosion, when many animal groups began to appear. The earliest vertebrates lived about 518 million years ago and had a simple body with a notochord and a head and tail, but no jaws.

Later, in the Devonian period, called the "Age of Fishes," jawed vertebrates appeared. Some bony fishes developed limbs that let them move on land, leading to the first four-legged animals, or tetrapods. During the Mesozoic era, dinosaurs and many marine reptiles lived. At the end of this time, a big event changed life on Earth. The current era, the Cenozoic, is known as the "Age of Mammals" because mammals became the main land animals.

Approaches to classification

Scientists have studied how to group vertebrates for a long time. In 1801, Jean-Baptiste Lamarck described vertebrates as animals with backbones, separate from invertebrates. Later scientists added more details and changed how these animals are grouped.

Traditionally, vertebrates were divided into seven main classes: jawless fishes, cartilaginous fishes, bony fishes, amphibians, reptiles, birds, and mammals. Today, scientists know that birds evolved from reptiles. Because of this, scientists use evolutionary history to better understand how these animals are related.

Diversity

Vertebrates are animals that have a backbone and a skull to protect their brain. They are a large group with many different species, more than any other group of animals.

Recent studies show that many vertebrate populations have been getting smaller. Scientists say this loss could mean that many species might disappear. The main reasons for these losses include changes in land use, taking too many natural resources, climate change, pollution, and invasive species.