section_path: Classification/Phylogenetic relationships
section_name: Phylogenetic relationships
paragraph_text: Phylogenetic relationships
  
  In phylogenetic taxonomy, the relationships between animals are not typically divided into ranks but illustrated as a nested "family tree" known as a phylogenetic tree. The cladogram below is based on studies compiled by Philippe Janvier and others for the Tree of Life Web Project and Delsuc et al., and complemented (based on, and). A dagger (†) denotes an extinct clade, whereas all other clades have living descendants.
  
  Note that, as shown in the cladogram above, the †" Ostracodermi " (armoured jawless fishes) and †" Placodermi " (armoured jawed fishes) are shown to be paraphylectic groups, separated from Gnathostomes and Eugnathostomes respectively.
  
  Also note that Teleostei (Neopterygii) and Tetrapoda (amphibians, mammals, reptiles, birds) each make up about 50% of today's vertebrate diversity, while all other groups are either extinct or rare. The next cladogram shows the extant clades of tetrapods (the four-limbed vertebrates), and a selection of extinct (†) groups:
  
  Note that reptile-like amphibians, mammal-like reptiles, and non-avian dinosaurs are all paraphyletic.
  
  The placement of hagfish on the vertebrate tree of life has been controversial. Their lack of proper vertebrae (among with other characteristics found in lampreys and jawed vertebrates) led phylogenetic analyses based on morphology to place them outside Vertebrata. Molecular data, however, indicates they are vertebrates closely related to lampreys. A study by Miyashita et al. (2019), 'reconciliated' the two types of analysis as it supports the Cyclostomata hypothesis using only morphological data.