Early Cambrian eodiscoid trilobite Hupeidiscus orientalis from South China: ontogeny and implications for affinities of Mongolitubulus-like sclerites

Abstract

Delicately phosphatized specimens of the eodiscoid Hupeidiscus orientalis were documented from the lower Cambrian Shuijingtuo Formation through acetic acid maceration of limestone samples. The material enables us to better understand the meraspid to holaspid ontogenetic development of H. orientalis, and to evaluate its relations with other eodiscoid taxa occurring in South China. The development of its pygidium and thoracic segments is very similar to that of "Shizhudiscus" longquanensis, suggesting that Shizhudiscus is a junior synonym of Hupeidiscus. However, the synonymization of Hupeidiscus with Tsunyidiscus remains open as little is known about the ontogeny of the latter genus. The spines of H. orientalis are of particular importance. Like the enigmatic sclerite taxon Mongolitubulus, its spines are ornamented with a distinctive scaly sculpture, shedding new light on the origin and affinities of Mongolitubulus-like sclerites. The squamose ornament was gradually transformed from granules on the exoskeletal surface at the base of the spines. Other strands of evidence, e.g., the outline, exuviating growth, and the spatio-temporal distribution, also suggest that some isolated sclerites previously assigned to Mongolitubulus are possibly related to the spines of eodiscoid trilobites. This finding implies that such morphologically similar spines may be essentially of multiple pan-arthropod origins (bradoriids, eodiscoids, etc.), and they may be of morphologic analogues rather than homologues, suggesting that Mongolitubulus shall be cautiously used as a generic name unless the circumstance of its type specimens from Mongolia gets clarified. •

Early Cambrian palaeobiogeography of the Zhenba–Fangxian Block (South China): Independent terrane or part of the Yangtze Platform?

“…To date there is only sparse information on the distribution of Cambrian fossils of the South Qinling Terrane and Zhenba-Fangxian Block Duan, 1983;Li and Holmer, 2004;Li et al, 2004a;Li et al, 2012), while most reports and discussions are on later Paleozoic radiolarians (Feng et al, 1996;Wang et al, 1999). Here we attempt to test the application of Cambrian Stage 3 SSFs for reconstructing the palaeobiogeographic pattern and develop a hypothesis for the palaeogeographic relationship of the Zhenba-Fangxian Block.…”

“…Previous studies mostly focused on the description of specific faunal components of the SSF assemblages of Zhenba County, such as the conodont-like fossils (Xie, 1988), bradoriids (Zhang, 2007), brachiopods (Li and Holmer, 2004), phosphatic tubular fossils (Li et al, 2004b), eodiscid trilobites and disarticulated trilobite spines (Li et al, 2012). Li et al (1991) reported echinoderm skeletal plates with a brief introduction of the fossils from Zengjiapo.…”

“…Eodiscoid trilobites are represented by Tsunyidiscus niutitangensis Chang et al, 1964 in the Zhenba regions. Formerly, this individuals were assigned to Hupeidiscus orientalis (Li et al, 2004a;Li et al, 2012), however, are different from the type-material of Hupeidiscus (Zhang, 1953). The former has typical axial rings and no pleural ribs on the pygidium.…”

Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians

“…The best studied of these is Mongolitubulus, a demonstrably polyphyletic form-taxon that includes components of bradoriid and trilobite carapaces [14,15] and has speculatively been linked to lobopodians [16]. Most specimens assigned to Mongolitubulus are readily distinghuished from hallucigeniid spines, including the type material of the type species, Mongolitubulus squamifer; this has rhomboidal rather than triangular scales that form an uninterrupted spiral from the spine base to tip.…”

A bradoriid and brachiopod dominated shelly fauna from the Furongian (Cambrian) of Västergötland, Sweden

“…Ranges of morphological variability in both form species are, however, broad and overlap, so that it is not possible to associate them with a single or several natural species (Barragán et al 2014a, b). Topper et al 2007), lobopodians (Dzik 2003;Caron et al 2013), or trilobites (Li et al 2012 Mongolitubulus spinosus (Hinz, 1987) Description.-Gently curved hollow calcium phosphatic spines nearly circular in cross-section. The wall consists of two layers.…”