A fresh look at the Hyolithid Doliutheca from the Early Cambrian (Stage 4) Shipai Formation of the Three Gorges Area, Hubei, South China

Abstract

New hyolith specimens from the early Cambrian (Stage 4) of the Three Gorges area, western Hubei Province are described and assigned to the species Doliutheca orientalis. Doliutheca are preserved in two taphonomic modes: casts in silty mudstone revealing gross morphology and some soft parts, and internal molds in calcareous pelites, which exhibit new morphological details of the conch and operculum. SEM and Micro-CT analyses show that Doliutheca preserve well-developed platy clavicles and cardinal processes on the interior of the operculum composed of rod-shaped tubular elements. This observation and the distinct cardinal and conical shields of the operculum indicate that Doliutheca could be placed within the Family Paramicrocornidae, most recently established as a group of hyoliths closely related to hyolithids.

Morphological disparity and evolutionary patterns of Cambrian hyoliths

“…6P, U), but for crack‐out hyolith material the apical part consists of flattened triangular areas on the sides of a linear tube (Liu et al . 2020, 2022b). The opercula of Cambrian Series 2 hyoliths are increasingly complex compared with their earlier counterparts in the Terreneuvian.…”

“…The recently erected family Paramicrocornidae first appeared in Series 2, and has been suggested as being representative of an intermediate evolutionary stage between the Orthothecida and the Hyolithida (Liu et al . 2022a, 2022b). It contains the species Paramicrocornus ventricosus (Fig.…”

“…5K-W) and Paramicrocornus zhenbaensis (Fig. 6I-K, M-P), taxa that both possess many hyolithid features, such as a complex platyclaviculate operculum with a prominent cardinal process, but lack helens, a characteristic feature of hyolithids (Zhang et al 2018;Pan et al 2019;Skovsted et al 2020;Liu et al 2022aLiu et al , 2022b. Moreover, typical hyolithid possessing the helens in Series 2 are well preserved and frequently described with detailed systematic palaeontology, such as Microcornus parvulus, the 'Linevitus' malongensis from the Guanshan Biota (Liu et al 2021a), and Haplophrentis reesei from South China (Sun et al 2017).…”

“…This includes a more distinct cardinal and conical shield, and the development of clavicles and cardinal processes (Figs 5O, P, 6I-K). The recently erected family Paramicrocornidae first appeared in Series 2, and has been suggested as being representative of an intermediate evolutionary stage between the Orthothecida and the Hyolithida (Liu et al 2022a(Liu et al , 2022b. It contains the species Paramicrocornus ventricosus (Fig.…”

“…The high abundance of hyoliths during the Cambrian makes them one of the more important components of the Cambrian evolutionary fauna (Sepkoski 1981), with hyoliths frequently recovered from early and middle Cambrian deposits. The majority of recent hyolith studies have focused on their occurrence (Pan et al 2019;Peel et al 2020;Liu et al 2021aLiu et al , 2021bLiu et al , 2022b, biological affinities (Moysiuk et al 2017;Sun et al 2018a;Li et al 2019;Liu et al 2020) and palaeoecology (Kimmig & Pratt 2018;Sun et al 2018bSun et al , 2019Liu et al 2021a), which have all served to expand understanding of both hyolith biodiversity and distribution. Despite their known importance, studies of hyolith evolution are scarce, with little comparative work or broad-scale analysis of the evolutionary trajectory of hyoliths during the Cambrian.…”