Phylogenetic classification and evolution of Early Triassic conodonts

Abstract Conodonts are some of the most important biostratigraphic index fossils in the Paleozoic and Triassic because of their rapid evolution and extensive distribution. Here we present a cladistic analysis of Early Triassic conodonts to reexamine the systematic classification and evolutionary relationships of the three related families Anchignathodontidae, Ellisonidae, and Gondolellidae. The tree consists of 38 Early Triassic conodont species with multielement apparatus documented, based on parsimony analysis of 73 discrete morphological characters including 40 P1 element characters, 4 P2 element characters, 27 S element characters and 2 M element characters. Based on the phylogenetic time tree, a series of evolutionary lineages are supported: Parafurnishius xuanhanensis–Furnishius triserratus–Platyvillosus regularis; Scythogondolella mosheri–Scythogondolella milleri; Discretella–Conservatella–Paullella meeki; Triassospathodus homeri–Chiosella; and Triassospathodus symmetricus–Triassospathodus chioensis. Reassignment of Ellisonia agordina to be Hadrodontina agordina is supported while Neospathodus planus should be resigned to the genus Triassospathodus. Meanwhile, Parafurnishius and Furnishius may belong to Gondolellidae rather than Ellisonidae or Ellisonidae may be a polyphyletic group rather than a monophyletic group. The cladogram suggests that Hindeodus, Hadrodontina and Pachycladina are monophyletic, whilst Novispathodus and Triassospathodus are paraphyletic and polyphyletic, respectively. In addition, a P1 element with a round basal cavity is an important trait to distinguish Novispathodus from Triassospathodus. The cladogram and revised classification provide a robust phylogenetic foundation for further investigations on systematic classification and evolutionary rates of conodonts during the Early Triassic.