A new species ofPlatysiagumfrom the Luoping Biota (Anisian, Middle Triassic, Yunnan, South China) reveals the relationship between Platysiagidae and Neopterygii

Abstract

Four complete platysiagid fish specimens are described from the Luoping Biota, Anisian (Middle Triassic), Yunnan Province, southwest China. They are small fishes with bones and scales covered with ganoine. All characters observed, such as nasals meeting in the midline, a keystone-like dermosphenotic, absence of post-rostral bone, two infraorbitals between dermosphenotic and jugal, large antorbital, and two postcleithra, suggest that the new materials belong to a single, new Platysiagum species, P. sinensis sp. nov. Three genera are ascribed to Platysiagidae: Platysiagum, Helmolepis and Caelatichthys. However, most specimens of the first two genera are imprints or fragmentary. The new, well-preserved specimens from the Luoping Biota provide more detailed anatomical information than before, and thus help amend the concept of the Platysiagidae. The Family Platysiagidae was previously classed in the Perleidiformes. Phylogenetic analysis indicates that the Platysiagidae is a member of basal Neopterygii, and its origin seems to predate that of Perleidiformes. Moreover, platysiagid fishes are known from the Middle Triassic of the western Tethys region. The newly found specimens of platysiagids from Luoping provide additional evidence that both eastern and western sides of the Tethys Ocean were biogeographically more connected than previously thought.

Feroxichthys yunnanensis gen. et sp. nov. (Colobodontidae, Neopterygii), a large durophagous predator from the Middle Triassic (Anisian) Luoping Biota, eastern Yunnan, China

“…Consistent with previous hypotheses ( Xu, Gao & Coates, 2015 ; Xu, Ma & Zhao, 2018 ; Wen et al, 2019 ; Xu, 2020a ), the results suggest that the ‘Perleidiformes’ or even the ‘Perleididae’ are paraphyletic groups composed of a series of independent stem neopterygian lineages. Notably, the fuyuanperleidid ‘perleidiform’ Fuyuanperleidus is recovered sister to the luganoiid Luganoia (represented by Luganoia lepidosteoides and L. fortuna ), supported by the presence a fused parieto-dermopterotic (independently evolved in Feroxichthys gen. nov. and thoracopterids), a fused lacrimo-maxilla (independently evolved in Feroxichthys gen. nov.), absence of fringing fulcra (independently evolved in thoracopterids, habroichthyids and most crown neopterygians), and greatly deepened anterior flank scales corresponding to two or three horizontal rows of relatively shorter scales posteriorly.…”

“…Additionally, given its large size, Feroxichthys may have also preyed upon many other heavily armoured but small-sized neopterygian fishes (e.g, peltopleurids, habroichthyids, venusichthyids and platysiagids). These invertebrates and small-sized fishes are mainly primary consumers in the food web of the Luoping Biota ( Hu et al, 2011 ; Benton et al, 2013 ; Xu & Ma, 2016 ; Xu & Zhao, 2016 ; Wen et al, 2019 ).…”

“…In the early Middle Triassic (Anisian), members of the Neopterygii are mainly represented by stem neopterygians and holosteans ( Hurley et al, 2007 ; Cavin, 2010 ; Grande, 2010 ; Romano et al, 2016 ; Xu et al, 2019 ). The Triassic stem neopterygians, traditionally grouped in the paraphyletic ‘Subholostei’, have long attracted the attention of palaeoichthyologists interested in the early diversification of this clade ( Bürgin, 1992 ; Lombardo, 2001 ; Mutter, 2002 , 2004 ; Sun et al, 2009 ; Xu, Gao & Coates, 2015 ; Xu, Zhao & Shen, 2015 ; Xu, Ma & Zhao, 2018 ; Wen et al, 2019 ; Xu, 2020a ).…”

“…In the past decade, 11 stem neopterygian species (in 11 genera) were recovered from the early Middle Triassic Luoping Biota or Lagerstätte in eastern Yunnan, China ( Lombardo et al, 2011 ; Geng et al, 2012 ; Sun et al, 2009 , 2012 , 2015 ; Lin et al, 2011 ; Xu & Ma, 2016 ; Xu & Zhao, 2016 ; Wen et al, 2019 ; Xu, 2020a ). Among them, the peltopleurids, habroichthyids, venusichthyids, platysiagids and basal louwoichthyids are small-sized fishes with a standard length (SL) of 30–50 mm, and the rest ( Luopingichthys , Fuyuanperleidus and several ‘perleidids’) medium-sized with a SL of 85–190 mm.…”

“…The early Middle Triassic Luoping Biota is a Lagerstätte renowned by its exceptional preservation and taxonomic richness (including abundant invertebrates, fishes, marine reptiles and plants; Zhang et al, 2009 ; López-Arbarello et al, 2011 ; Wu et al, 2011 ; Xu & Wu, 2012 ; Feldmann et al, 2012 ; Huang et al, 2013 ; Xu, Zhao & Coates, 2014 ; Xu & Ma, 2016 ; Xu & Zhao, 2016 ; Wen et al, 2019 ; Xu et al, 2019 ; Xu, 2020a ; see review of Benton et al, 2013 ). The age of this Lagerstätte (Pelsonian, Anisian, ~244 Ma) is well constrained by conodont studies ( Zhang et al, 2009 ), and consequently it provides a unique window into the recovery and radiation of Triassic ecosystems ~8 Myr after the end-Permian mass extinction.…”