What Does 'No Backbone Definition' Mean?

The term 'vertebrates' is often associated with animals that have a backbone or spine. However, this definition may not be entirely accurate, as it excludes certain groups of animals that lack vertebrae but are still considered chordates.

Chordates are a group of animals that include vertebrates and invertebrates. Invertebrates do not have a vertebral column, which is the defining characteristic of vertebrates. However, some chordates do have vertebrae, while others do not. For example, hagfish, which are often considered to be among the most ancient living vertebrates, lack proper vertebrae due to evolutionary losses.

Despite this, the vast majority of described animal species are invertebrates, with only a small percentage being vertebrates. Vertebrates can vary greatly in terms of body length, ranging from the tiny Paedophryne amauensis frog, which measures just 7.7 mm, to the massive blue whale, which can reach lengths of up to 33 meters.

In addition to fish and amphibians, vertebrates also include reptiles, birds, and mammals. These groups are further divided into infraphyla and classes, such as synapsids (mammals and their extinct relatives), sauropsids (reptiles and birds), and sarcopterygii (lobe-finned fish).

Some examples of vertebrates include the African bush elephant, a Tiger shark, and a River lamprey. These animals all share certain characteristics, including a bony or cartilaginous axial endoskeleton that includes the vertebral column, spine, or backbone.

In conclusion, while the term 'no backbone definition' may seem contradictory, it highlights the diversity of chordates and the complexity of their evolutionary history. By understanding the different groups of animals that make up this phylum, we can gain a deeper appreciation for the incredible variety of life on Earth.

No backbone definition