Soft part preservation in hyolithids from the lower Cambrian (Stage 4) Guanshan Biota of South China and its implications

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

“…The gut of Doliutheca orientalis is generally preserved as a straight, linear structure and is reddish in color and probably represents the rectum of the U-shaped hyolithid gut ( Figure 5 A–D). However, one specimen preserves a linear, black-stained cavity ( Figure 5 E,F), which is similar to preserved guts in hyolithids from the Guanshan Biota, where it was likely formed by the demineralization of soft parts that were originally calcified by microbial activity [ 37 ]. Elemental mapping of μ-XRF analyses indicates that conchs have been replaced by silica and phosphatic material, and that organic soft tissues are preserved predominantly as films of iron oxide showing the enrichment of iron ( Figure 5 I–K), presumably as a weathering product of pyrite [ 37 ].…”

Hyolithid-like hyoliths without helens from the early Cambrian of South China, and their implications for the evolution of hyoliths

“…Most of the selected taxa are well-known typical hyolithids or orthothecids, preserving morphologies of both conch and opercula, which eases character coding. Eleven typical hyolithids consisting of Haplophrentis Babcock & Robison, 1988 [ 57 ] , Slapylites Marek, 1980 [ 58 ] , Nevadalites Marek, 1976 [ 59 ] , Microcornus Mambetov, 1972 [ 48 ] , Parkula Bengtson in Bengtson et al, 1990 [ 43 ] , ‘Linevitus’ (Guanshan hyoliths) [ 15 ] , Pauxillites Marek, 1966 [ 4 ] , Parakorilithes He & Pei in He et al, 1984 [ 60 ] , Carinolithes Sysoev, 1958 [ 40 ] , Oboedalites Marek, 1981 [ 61 ], Maxilites Marek, 1972 [ 62 ] as well as eleven typical orthothecids including Triplicatella Conway Morris in Bengtson et al, 1990 [ 43 ] , Paratriplicatella Pan, Skovsted, Sun & Li, 2019 [ 37 ] , Conotheca Missarzhevsky, 1969 [ 63 ] , Cupitheca Duan in Xing et al, 1984 [ 64 ] , Guduguwan Kruse, 1990 [ 47 ] , Gracilitheca Sysoev, 1968 [ 44 ] , Circotheca Sysoev, 1958 [ 40 ] , Bactrotheca Novák, 1891 [ 65 ] , Probactrotheca Valent in Valent et al, 2012 [ 66 ] , Longxiantheca Li in Li et al, 2020 [ 7 ] , Pedunculotheca Sun in Sun et al, [ 55 ] were selected . Two genera combining key morphological characters typical of the Hyolithida and Orthothecida; Protomicrocornus and Paramicrocornus were also added to the matrix in addition to the genus Aladraco which was recently described by Geyer [ 67 ] as another taxon combining hyolithid and orthothecid morphological characters.…”

“…Orthothecids appear first in the fossil record and are usually composed of two simple skeletal components, a conical conch with a variable cross section and a flat, retractable operculum [ 4 – 9 ]. In contrast, hyolithids typically consist of four skeletal components, a cone-shaped conch, an externally fitting and folded operculum with distinct cardinal and conical shields, and a pair of curved spine-shaped helens [ 10 – 15 ]. However, some hyoliths have been described with unique combinations of characters that cannot be easily assigned to either of these two groups [ 16 , 17 ].…”

“…In terms of general morphology, ‘Ambrolinevitus’ ventricosus resembles typical hyolithids (triangular conch cross section, an operculum divided into cardinal and conical shields and with separate clavicles and cardinal processes). However, no evidence exists that indicates the presence of helens, which sets this taxon apart from typical hyolithids preserved in similar Lagerstätten such as the Guanshan [ 15 ], Spence Shale or Burgess Shale biotas [ 26 ]. After comparing the Chengjiang specimens with new collections of Paramicrocornus from the Shuijingtuo Formation across various localities in Hubei province, South China, ‘Ambrolinevitus’ ventricosus we suggest, should be reassign to the genus Paramicrocornus .…”

New Middle Ordovician hyoliths from the Ossa Morena Zone, southwestern Spain

“…The hard- and soft-part of morphologies of hyolithids have been discussed in detail (Marek, 1963, 1967; Sysoev, 1976a; Meshkova and Sysoev, 1981; Martí Mus and Bergström, 2005, 2007; Martí Mus et al, 2014; Sun et al, 2015, 2016, 2018; Liu et al, 2020a, b) and need not be presented in the same detail here. We mention only those features that directly relate to our specimens in order for their morphology to be better understood.…”