A new genus of sinogaleaspids (Galeaspida, stem-Gnathostomata) from the Silurian Period in Jiangxi, China

Abstract

Galeaspids are an endemic clade of jawless stem-gnathostomes known as ostracoderms. Their existence illuminates how specific characteristics developed in jawed vertebrates. Sinogaleaspids are of particular interest among the galeaspids but their monophyly is controversial because little is known about Sinogaleaspis xikengensis. Newly discovered sinogaleaspids from the Lower Silurian of Jiangxi, China provide a wealth of data and diagnostic features used to establish the new genus, Rumporostralis gen. nov., for Sinogaleaspis xikengensis. A morphological study showed that the sensory canal system of sinogaleaspids had mosaic features similar to those of three known galeaspids. There are 3–8 pairs of transverse canals in the Sinogaleaspidae, which suggests that the sensory canal system of galeaspid probably had a grid distribution with transverse canals arranged throughout the cephalic division. Phylogenetic analysis of Galeaspida supports the monophyly of the Sinogaleaspidae, consisting of Sinogaleaspis, Rumporostralis, and Anjiaspis. However, Shuyu and Meishanaspis form another monophyletic group, Shuyuidae fam. nov., which is outside all other eugaleaspidiforms. We propose a cladistically-based classification of Galeaspida based on our analysis.

A New Family of Galeaspids (Jawless Stem‐Gnathostomata) from the Early Silurian of Chongqing, Southwestern China

“…A previous analysis (Shan et al, 2020) indicated that the Eugaleaspidiformes is a monophyletic group composed of the Shuyuidae (Shan et al, 2020), Sinogaleaspidae (Pan and Wang, 1980), Tridensaspidae (Liu, 1986), Eugaleaspidae (Liu, 1980), and an Incertae Familiae comprising Yunnanogaleaspis and Nochelaspis.…”

“…In order to explore the position of Yongdongaspis, a new phylogenetic analysis was conducted based on previous datasets Zhu and Gai, 2006;Gai et al, 2018;Gai et al, 2020;Shan et al, 2020;Jiang et al, 2021). One new character was added: [64] central canal (cc): (0) absent; (1) present.…”

“…Yongdongaspis bears a close resemblance to Yunnanogaleaspis (Pan and Wang, 1980) and Nochelaspis Zhu and Gai, 2006;Gai et al, 2018;Gai et al, 2020;Shan et al, 2020;Jiang et al, 2021). Artwork credit, Dinghua Yang.…”

“…There is a short median transverse canal branching from the middle dorsal canal in Yongdongaspis. Over one median transverse canal is regarded as a primitive feature found in plesiomorphic galeaspid taxa such as Dayongaspidae, Hanyangaspidae, Xiushuiaspidae and Sinogaleaspidae Wang, 1980, 1983;Wang, 1991b;Gai et al, , 2020Shan et al, 2020), whereas in the 'eugaleaspid cluster', only one median transverse canal remained. This remanent feature further implies that Yongdongaspis is a plesiomorphic taxon relative to the 'eugaleaspid cluster' (Fig.…”

“…Strict consensus tree of five most parsimonious trees with a cladistically based classification of the Galeaspida. Tree length = 194, consistency index (CI) = 0.418, retention index (RI) = 0.767, Numbers on branches denote bootstrap frequencies (above node) and Bremer support values (below node), bootstrap frequencies below 50 are not shown (analysis based on the dataset revised from GaiZhu and Gai, 2006;Gai et al, 2018;Gai et al, 2020;Shan et al, 2020;Jiang et al, 2021). Artwork credit, Dinghua Yang.…”