Fuyuanichthys wangigen. et sp. nov. from the Middle Triassic (Ladinian) of China highlights the early diversification of ginglymodian fishes

Abstract

A series of well-preserved fossil assemblages from the Middle Triassic marine rock succession in Southwest China provide unique evidences for studying the early evolution of holostean fishes, including Halecomorphi (e.g., bownfin) and Ginglymodi (e.g., gars). Ginglymodi have the earliest record in the early Middle Triassic (Anisian, ∼244 Ma) of China, represented by Kyphosichthys and Sangiorgioichthys sui from Yunnan and S. yangjuanensis from Guizhou. Here, we report the discovery of a new ginglymodian, Fuyuanichthys wangi gen. et sp. nov., based on 22 well-preserved specimens from the lower part of the Zhuganpo member of the Falang Formation in eastern Yunnan and western Guizhou, which documents the first discovery of convincing ginglymodians from the late Middle Triassic (Ladinian, ∼240 Ma) Xingyi biota in China. Fuyuanichthys possesses a unique combination of features that easily distinguishes it from other ginglymodians, such as presence of a median gular and short and edentulous maxillae, and absence of a supramaxilla and supraorbitals. As one of the smallest known ginglymodians with a maximum standard length of ∼75 mm, the new finding further supports that the Middle Triassic Ginglymodi have a relatively small range of body sizes compared with the Halecomorphi from the same ecosystems in China. Results of a phylogenetic analysis recover Fuyuanichthys as a sister taxon to Kyphosichthys at the ginglymodian stem, and provide new insights into the early evolution of this clade.

Osteology and phylogeny ofRobustichthys luopingensis, the largest holostean fish in the Middle Triassic

“…Patterson (1973) first proposed the double jaw joint (involving both symplectic and quadrate) as a halecomorph synapomorphy, and his hypothesis is widely accepted by many authors (Gardiner, Maisey & Littlewood, 1996; Grande & Bemis, 1998; Alvarado-Ortega & Espinosa-Arrubarrena, 2008; Lane & Ebert, 2012; Brito & Alvarado-Ortega, 2013; Xu, Zhao & Coates, 2014; Xu, Ma & Ren, 2018a; López-Arbarello, Stockar & Bürgin, 2014; Xu & Shen, 2015; Taverne, 2015; Ma & Xu, 2017). Olsen (1984) noticed Nielsen’s (1942, 1949) descriptions of the symplectic articulating with the lower jaw in non-neopterygian Birgeria , Boreosomus and Pteronisculus , and challenged Patterson’s (1973) hypothesis in suggesting that the double jaw joint is plesiomorphic for halecomorphs.…”

“…The phylogenetic framework for the discussions provided in the present paper is based on the results of a cladistic analysis of neopteryigan phylogeny including 224 morphological characters and 60 extant and fossil terminal taxa. The characters were mainly adopted or modified from previous analyses of neopterygian phylogeny (Gardiner & Schaeffer, 1989; Olsen & McCune, 1991; Gardiner, Maisey & Littlewood, 1996; Grande & Bemis, 1998; Coates, 1999; Arratia, 1999, 2013; Cavin & Suteethorn, 2006; Alvarado-Ortega & Espinosa-Arrubarrena, 2008; Cavin, 2010; Grande, 2010; Xu & Gao, 2011; Xu et al, 2012, 2019; Xu, Zhao & Coates, 2014; Xu, Gao & Coates, 2015; Xu, Ma & Ren, 2018a; Xu, Ma & Zhao, 2018b; Xu & Ma, 2016; Xu & Zhao, 2016; López-Arbarello, 2012; Brito & Alvarado-Ortega, 2013; Cavin, Deesri & Suteethorn, 2013; Deesri et al, 2014; Deesri, Jintasakul & Cavin, 2016; Giles et al, 2017; Ebert, 2018; López-Arbarello & Sferco, 2018). All characters were unordered and equally weighted.…”

“…This hypothesis, more clearly expressed by Patterson (1973), was later widely accepted by many authors (Rosen et al, 1981; Grande & Bemis, 1998; Liem et al, 2001). It was not until the last decade that morphological and molecular data reached a consensus on the sister group relationship between Halecomorphi and Ginglymodi and, consequently, the Holostei concept was resurrected (Hurley et al, 2007; Grande, 2010; Nakatani et al, 2011; Xu & Wu, 2012; Near et al, 2012; Broughton et al, 2013; Cavin, Deesri & Suteethorn, 2013; Giles et al, 2017; Sun et al, 2017; López-Arbarello & Sferco, 2018; López-Arbarello et al, 2016, 2019; Xu, Ma & Ren, 2018a; Xu, Ma & Zhao, 2018b; Xu et al, 2019).…”

“…Up to date, 14 holostean species (in 13 genera) have been reported from a series of well-preserved fossil assemblages from the Middle Triassic marine rock succession in Southwest China, including seven in the Anisian Luoping biota (Tintori et al, 2010; López-Arbarello et al, 2011; Xu & Wu, 2012; Wen et al, 2012; Xu, Zhao & Coates, 2014; Xu et al, 2019; Ma & Xu, 2017), two in the Anisian Panxian biota (Chen et al, 2014; Xu & Shen, 2015), and five in the Ladinian Xingyi biota (Su, 1959; Liu, Yin & Wang, 2002; Liu et al, 2003; Xu & Ma, 2018; Xu, Ma & Ren, 2018a). Among them, most holosteans from the Xingyi biota were known as early as 60 years ago but many were incompletely described.…”

“…Three other holosteans from this biota, Sinoeugnathus (Su, 1959), Guizhouamia (Liu, Yin & Wang, 2002) and Xingyia (Liu et al, 2003), although placed in the Amiiformes, lack formal phylogenetic analyses and need further studies. The recently reported kyphosichthyiform Fuyuanichthys documents the first ginglymodian known in the Xingyi biota (Xu, Ma & Ren, 2018a). All seven holosteans from the Luoping biota were named in the last decade but received more attention than those from the Xingyi biota because of their superb preservation and older age, including three kyphosichthyiform ginglymodians ( Lashanichthys sui , López-Arbarello et al, 2011; Kyphosichthys , Xu & Wu, 2012; Yudaiichthys , Xu et al, 2019), two ionoscopiform halecomorphs ( Robustichthys , Xu et al, 2014; Subortichthys , Ma & Xu, 2017) and two specialized, taxonomically controversial holosteans (the naked Gymnoichthys , Tintori et al, 2010; and the deep-bodied Luoxiongichthys , Wen et al, 2012).…”