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.
Highlights
The Silurian–Devonian armored galeaspids were a prevalent and diverse clade of jawless stem-gnathostomes (Fig. 1A) that exhibited traits thought to belong to jawed gnathostomes (Gai et al, 2011; Gai & Zhu, 2012; Gai, Zhu & Donoghue, 2019)
Our phylogenetic analysis of Galeaspida shows that Shuyu and Meishanaspis are not included in Sinogaleaspidae and form another monophyletic group
The Sinogaleaspidae family was established by Pan & Wang (1980), and five species Sinogaleaspis shankouensis, Rumporostralis xikengensis, Shuyu zhejiangensis, Meishanaspis lehmani, and Anjiaspis reticularis are morphologically assigned to this family (Pan & Wang, 1980; Pan, 1986a; Pan, 1986b; Wang, 1991; Zhu, 1992; Gai & Zhu, 2005; Liu et al, 2015)
Summary
The Silurian–Devonian armored galeaspids were a prevalent and diverse clade of jawless stem-gnathostomes (Fig. 1A) that exhibited traits thought to belong to jawed gnathostomes (Gai et al, 2011; Gai & Zhu, 2012; Gai, Zhu & Donoghue, 2019). They contribute to our understanding of the conformation of the gnathostome body, which is significant to vertebrate evolution (Sansom, Rodygin & Donoghue, 2008). The family Sinogaleaspidae of the Eugaleaspidiformes within the Galeaspida, from the Lower Silurian of Xiushui, Jiangxi province and Changxing, Zhejiang province, is an important early clade
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