A new suction feeder and miniature teleosteomorph, Marcopoloichthys mirigioliensis, from the lower Besano Formation (late Anisian) of Monte San Giorgio

Abstract

A new species (Marcopoloichthys mirigioliensis) of the stem teleosteomorph genus Marcopoloichthys is described from the lower Besano Formation (late Anisian at Monte San Giorgio, southern Switzerland), making this new species distinct from Marcopoloichthys furreri from the Prosanto Formation (early Ladinian at Ducanfurgga, southeastern Switzerland). Marcopoloichthys mirigioliensis n. sp. is smaller (ca. 32 mm standard length) than M. furreri (ca. 40 mm standard length), and in addition, the two species have some important differences in the caudal endoskeleton and fin, e.g., number of epaxial and hypaxial basal fulcra, uroneural structure, size of hypurals, and presence versus absence of urodermals. Marcopoloichthys mirigioliensis n. sp. is the smallest member of Marcopoloichthyidae which is currently known from at least five species living in the Triassic of China (one species), Italy (two and others that remain undescribed), and Switzerland and according to current information, with its ca. 32 mm standard length is candidate to be considered a miniature fish. Additionally, this size makes it the smallest known stem teleost. As in other marcopoloichthyids, the buccal and suspensorium anatomy of M. mirigiolensis n. sp. corresponds to that of suction-feeder fishes.