Fossil Vertebrates of Greece Vol. 1 Basal Vertebrates, Amphibians, Reptiles, Afrotherians, Glires, and Primates / Ископаемые позвоночные Греции Том. 1 Базальные позвоночные, амфибии, рептилии, афротерии, глайры и приматы

Vertebrates (Chordata: Vertebrata) are animals closely related to other animals with a notochord, namely, the lancelets (Cephalochordata) and ascidians (Urochordata). Although traditionally considered as subphyla of the phylum Chordata, a recent review by Irie et al. (2018) proposes the recognition of Vertebrata as a separate phylum, because of new evidence from comparative genomic, geneexpression, and morphological studies. Chordates form a natural or monophyletic group defined by several shared derived characters (or synapomorphies) which separate them from other deuterostomians: the presence of an endostyle, the presence of a dorsal and hollow nerve cord, the presence of a notochord and myomeres, and the presence of a postanal tail (de Iullis and Pulerá 2019). Vertebrates are, of course, animals that have a backbone; however, this simplistic definition does not hold against modern definitions of this clade. During the last two decades, extensive discussions on the definition of vertebrates took place, especially considering
the relationships between vertebrates without jaws (e.g., lampreys and hagfishes) and vertebrates with jaws (i.e., gnathostomatans). Lampreys possess only rudimentary vertebrae, termed arcualia, considered as precursors of true vertebrae (de Iullis and Pulerá 2019). Solving the relationships between these three groups was crucial to define Vertebrata: the currently accepted scheme groups lampreys and hagfishes (= cyclostomatans) which form the sister group of jawed vertebrates (= gnathostomatans) (de Iullis and Pulerá 2019 and references therein). <...>