Vertebrate
Vertebrates (/ˈvɜːrtəbrɪts, -ˌbreɪts/)[3] are deuterostomal animals with bony or cartilaginous axial endoskeleton — known as the vertebral column, spine or backbone — around and along the spinal cord, including all fish, amphibians, reptiles, birds and mammals. The vertebrates consist of all the taxa within the subphylum Vertebrata (/ˌvɜːrtəˈbreɪtə/)[4] and represent the overwhelming majority of the phylum Chordata, with currently about 69,963 species described.[5]
For an explanation of similar terms, see Craniate.
Vertebrates comprise groups such as the following infraphyla and classes:
Extant vertebrates vary in body lengths ranging from the frog species Paedophryne amauensis, at as little as 7.7 mm (0.30 in), to the blue whale, at up to 33 m (108 ft). Vertebrates make up less than five percent of all described animal species; the rest are described as invertebrates, an informal polyphyletic group comprising all that lack vertebral columns, which include non-vertebrate chordates such as lancelets.
The vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution,[7] though their closest living relatives, the lampreys, do.[8] Hagfish do, however, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as Craniata or "craniates" when discussing morphology. Molecular analysis since 1992 has suggested that hagfish are most closely related to lampreys,[9] and so also are vertebrates in a monophyletic sense. Others consider them a sister group of vertebrates in the common taxon of Craniata.[10]
Etymology[edit]
The word vertebrate derives from the Latin word vertebratus (Pliny), meaning joint of the spine.[11] A similarly derived word is vertebra, which refers to any of the irregular bones or segments of the spinal column.[12]
Molecular signatures[edit]
In addition to the morphological characteristics used to define vertebrates (i.e. the presence of a notochord, the development of a vertebral column from the notochord, a dorsal nerve cord, pharyngeal gills, a post-anal tail, etc.), molecular markers known as conserved signature indels (CSIs) in protein sequences have been identified and provide distinguishing criteria for the subphylum Vertebrata.[27] Specifically, 5 CSIs in the following proteins: protein synthesis elongation factor-2 (EF-2), eukaryotic translation initiation factor 3 (eIF3), adenosine kinase (AdK) and a protein related to ubiquitin carboxyl-terminal hydrolase are exclusively shared by all vertebrates and reliably distinguish them from all other metazoan.[27] The CSIs in these protein sequences are predicted to have important functionality in vertebrates.
A specific relationship between Vertebrates and Tunicates is also strongly supported by two CSIs found in the proteins Rrp44 (associated with exosome complex) and serine palmitoyltransferase, that are exclusively shared by species from these two subphyla but not Cephalochordates, indicating Vertebrates are more closely related to Tunicates than Cephalochordates.[27]
Population trends[edit]
The Living Planet Index, following 16,704 populations of 4,005 species of vertebrates, shows a decline of 60% between 1970 and 2014.[85] Since 1970, freshwater species declined 83%, and tropical populations in South and Central America declined 89%.[86] The authors note that, "An average trend in population change is not an average of total numbers of animals lost."[86] According to WWF, this could lead to a sixth major extinction event.[87] The five main causes of biodiversity loss are land-use change, overexploitation of natural resources, climate change, pollution and invasive species.[88]