Accepted Manuscript
Title: New material of the biomineralizing tubular fossil
Sinotubulites from the late Ediacaran Dengying Formation,
South China
Author: Yaoping Cai Shuhai Xiao Hong Hua Xunlai Yuan
PII:
DOI:
Reference:

S0301-9268(15)00043-1
http://dx.doi.org/doi:10.1016/j.precamres.2015.02.002
PRECAM 4191

To appear in:

Precambrian Research

Received date:
Revised date:
Accepted date:

1-11-2014
3-1-2015
4-2-2015

Please cite this article as: Cai, Y., Xiao, S., Hua, H., Yuan, X.,New
material of the biomineralizing tubular fossil Sinotubulites from the late
Ediacaran Dengying Formation, South China, Precambrian Research (2015),
http://dx.doi.org/10.1016/j.precamres.2015.02.002
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Highlights

Description of three new species of the biomineralizing animal Sinotubulites
Detailed illustration of tube morphology and microstrutures of Sinotubulites

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Systematic re-evaluation of all published Sinotubulites fossils

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New material of the biomineralizing tubular fossil Sinotubulites from
the late Ediacaran Dengying Formation, South China

State Key Laboratory of Continental Dynamics, Department of Geology, Northwest

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Yaoping Caia,b,*, Shuhai Xiaoc,*, Hong Huaa, Xunlai Yuanb

University, Xian 710069, China

State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of

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Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
Department of Geosciences, Virginia Tech, Blacksburg, Virginia 24060, USA

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*Corresponding author:;  yaopingcai@nwu.edu.cn (Y. Cai); xiao@vt.edu (S. Xiao).

Abstract

Sinotubulites is a late Ediacaran biomineralizing tubular fossil with a

probable animal affinity. It is characterized by millimeter- to centimeter-sized
and multi-layered tubes open at both ends. The tube consists of two
morphologically different walls: a multi-layered inner wall with weak
ornamentations and a multi-layered outer wall with transverse or oblique
corrugations and sometimes longitudinal ridges. The majority of previously
published Sinotubulites species are considered as synonymous with the type

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species: S. baimatuoensis. Three new species—S. triangularis n. sp., S.
pentacarinalis n. sp., and S. hexagonus n. sp.—are reported from the late

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Ediacaran Beiwan Member of the Dengying Formation in southern Shaanxi
Province, South China. The three new species are similar to the type species in

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having nested, multilayered inner and outer tube walls. However, they are

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different in their polygonal cross sections and longitudinal ridges. S.

baimatuoensis is more or less circular in cross section and lack longitudinal

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ridges on the outer tube wall, whereas S. triangularis, S. pentacarinalis, and S.
hexagonus are respectively triangular, pentagonal, and hexagonal in cross section

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with three, five, and six longitudinal ridges on the exterior surface of the outer
wall. The new material adds to the diversity of late Ediacaran biomineralizing

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animals. The triradial, pentaradial, and hexaradial tubes of S. triangularis, S.
pentacarinalis, and S. hexagonus share some intriguing similarities in body

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symmetry with some early Cambrian tubular fossils, although these Cambrian
tubes are not open at both ends. Still, it would be interesting to explore the
tantalizing possibility of evolutionary continuity of triradial, pentaradial, and
hexaradial tubular animals across the Precambrian–Cambrian boundary.

Keywords: Ediacaran, Dengying Formation, Sinotubulites, biomineralization,
South China.

1. Introduction

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Animal biomineralization represents one of the most important evolutionary
innovations that fundamentally transformed the ecology of the biosphere and

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elemental cycles of the Earth systems. Paleontological investigation of this
evolutionary event has been focused on early Cambrian small shelly fossils (Bengtson

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et al., 1990), although animal biomineralization probably had its evolutionary root in

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the Ediacaran Period (Wood, 2011; Penny et al., 2014). Several biomineralizing
fossils of probable animal affinities have been reported from late Ediacaran carbonate

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rocks, including Cloudina (Germs, 1972), Namacalathus (Grotzinger et al., 2000),
Namapoikia (Wood et al., 2002), and Sinotubulites (Chen et al., 1981). Among these

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Ediacaran skeletal fossils, Cloudina has the widest geographic range and its
morphologies have been well characterized primarily based on three-dimensionally

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phosphatized material from China (Hua et al., 2005b; Cai et al., 2014; Cortijo et al.,
2014) and silicified material from Spain (Cortijo et al., 2010). Other taxa, however,

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have not been very well studied, partly due to poor fossil preservation and limited
occurrences.

In this paper, we provide a thorough morphological description and systematic

treatment of the genus Sinotubulites, based on material from the late Ediacaran
Beiwan Member of the Dengying Formation in southern Shaanxi Province, South
China. The Beiwan fossils are phosphatized (Zhang et al., 1992; Chen and Sun, 2001;
Chen et al., 2008; Sun et al., 2012), and together with silicified material from the
upper Dengying Formation in the Yangtze Gorges area (Chen and Wang, 1977; Chen
et al., 1981) they offer an excellent opportunity to characterize the three-dimensional

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morphology of this genus. Our investigation adds more morphological details to the
type species Sinotubulites baimatuoensis and also recovers three new species—S.

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triangularis, S. pentacarinalis, and S. hexagonus.
In addition to its occurrence in South China (Chen et al., 1981; Chen and Sun,

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2001; Chen et al., 2008), Sinotubulites has also been reported from Ediacaran

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successions in Mexico (McMenamin, 1985), California and Nevada (Signor et al.,
1983; Signor et al., 1987), and possibly Spain (Zhuravlev et al., 2012); a systematic

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study of these previously published species of Sinotubulites is long overdue. Armed
with a better understanding of the morphological variation of Sinotubulites based on

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three-dimensionally phosphatized material from China, we can now more thoroughly

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Mexico, Nevada, and Spain.

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evaluate the occurrence of Sinotubulites species from Ediacaran successions in

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2. Stratigraphic setting

The fossil locality (Lijiagou section; see Cai et al. 2014 for location) is located in

the northwestern margin of Yangtze Platform, ca. 20 km north to the city of Ningqiang.
The Ediacaran System in the Ningqiang area consists of the Doushantuo Formation
and the overlying Dengying Formation, which is overlain by the lower Cambrian
Kuanchuanpu Formation (Fig. 1). The Doushantuo Formation can be completely
observed only at a few sections in the Ningqiang area and typically consists of, in
ascending order, slate, sandstone–conglomerate, and carbonate sequences. The
overlying Dengying Formation in the Ningqiang area is dominated by medium- to

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thick-bedded dolostone and varies remarkably in thickness, ranging from only 24 m to
as much as 975 m (Bureau of Geology and Mineral Resources of Shaanxi Province,

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1989). It can be sub-divided into three members (Zhang, 1986)—the lower Algal
Dolomite and the upper Beiwan members are both characterized by medium- to

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thick-bedded peritidal dolostone, whereas the middle Gaojiashan Member is typically

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composed of interbedded fine-grained siliciclastic and carbonate rocks containing a
diverse fossil assemblage of the Gaojiashan Lagerstätte (Cai et al., 2010; Schiffbauer

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et al., 2014). The Beiwan Member of the Dengying Formation is unconformably
overlain by the basal Cambrian Kuanchuanpu Formation (limestone, chert, and

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phosphorite rich in small shelly fossils) where the earliest known priapulid-like
animal Eopriapulites sphinx has been reported (Liu et al., 2014). The Dengying

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Formation in the Ningqiang area is estimated to be 551–541 Ma by correlation with

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the Yangtze Gorges area where it has been dated (Condon et al., 2005).

3. Material and methods

All fossils reported here were recovered from dolostone of the Beiwan Member

of the Dengying Formation at the Lijiagou section (Fig. 1), except for the neotype
specimen which is from the Baimatuo Member of the Dengying Formation at the
Baishatuo section (Yangtze Gorges area, western Hubei Province). The topmost ca. 10
m of the Beiwan Member has yielded three-dimensionally phosphatized microfossils
including Sinotubulites, Cloudina, protolagenids, and other problematic forms

(Bengtson and Yue, 1992; Zhang et al., 1992; Chen and Sun, 2001; Hua et al., 2005a;

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Chen et al., 2008). In this study, over 100 Sinotubulites specimens have been extracted,
using standard acetic acid maceration technique (5–8 % acetic acid), from samples

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collected at 0.2–7 m below the Beiwan–Kuanchuanpu boundary. Extracted specimens
were examined on a FEI Quanta 600 field-emission scanning electron microscope.

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Descriptive terms employed here are modified from Sun et al. (2012) and illustrated

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in Fig. 2. All fossils illustrated in this paper are reposited in the Department of

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Geology, Northwest University (GEONWU), Xi’an, China.

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4. Systematic paleontology

Phylum, Class, Order, Family uncertain

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Genus Sinotubulites Chen, Chen and Qian, 1981, emended

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Type species: Sinotubulites baimatuoensis Chen, Chen and Qian, 1981.

Synonyms:

Cloudina? sp. Chen and Wang, 1977, p. 220.
Qinella Zhang, Li, and Dong in Ding et al., 1992, p. 94–98.
Qinella Hua et al., 2000b, p. 383 (junior homonym of Qinella Zhang, Li, and Dong in
Ding et al., 1992).

Emended diagnosis: Straight or slightly curved tubes with both ends open. Tube
can be cylindrical (circular in cross section) or prismatic (triangular, pentagonal, and

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hexagonal in cross section), consisting of a transversely corrugated outer wall and a
more or less smooth inner wall, both multiple-layered. Longitudinal ridges may be

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present on the outer wall.
Discussion: Tubular fossils from the Dengying Formation were initially reported

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in Chen and Wang (1977) as Cloudina? sp. These fossils were subsequently described

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as Sinotubulites Chen, Chen, and Qian, 1981, with its only constituent species, S.
baimatuoensis Chen, Chen, and Qian, 1981. Thus, although no type species was

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explicitly designated in the original publication (Chen et al., 1981), S. baimatuoensis
becomes the type species by monotypy.

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Sinotubulites was originally diagnosed as a straight or curved, thick hollow tube,
with the exterior surface smooth or ornamented with transverse annulations or ridges.

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In cross sectional views, outer rim (outer wall) circular or irregularly polygonal,
whereas inner rim (inner wall) circular. Inner rim (inner wall) centrally or

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eccentrically located (Chen et al., 1981). This diagnosis was subsequently emended
(McMenamin, 1985) to accommodate new observations that the tube sometimes
tapers, irregular ornaments such as ribs, striae, bands, and annular depressions may be
obliquely or transversely oriented, and annular ornamentation may be connected with
or cross-cut by longitudinal ridges. Chen and Sun (2001) further emended the
diagnosis to emphasize that the hollow tube is multilayered and open at both ends
with a “tube-in-tube” construction. The diagnosis is here again emended to
accommodate the three new species, S. triangularis, S. pentacarinalis, S. hexagonus,

which is characterized by prismatic tubes with three, five, or six longitudinal ridges,

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thus resulting in a triangular, pentagonal, or hexagonal cross-section.
Sinotubulites is differentiated from other Ediacaran and Cambrian tubular fossils

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by its “tube-in-tube” construction, transversely corrugated outer tube walls, and the
presence of longitudinal ridges in some species. The late Ediacaran fossil Cloudina is

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also characterized by multiple-layered tube walls, but it is conotubular in shape with a

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closed apex and its tube consists of nested funnels rather than nested tubes (Hua et al.,
2005b). Cloudina carinata Cortijo, Martí Mus, Jensen, and Palacios, 2010 is

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characterized by longitudinal ridges and thus similar to S. triangularis, S.
pentacarinalis, and S. hexagonus described here. Indeed, the similarity between

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Cloudina carinata and Sinotubulites has been noted previously (Cortijo et al., 2010).
However, well-preserved Cloudina carinata specimens have the characteristic

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funnel-in-funnel construction and they tend to have seven or more longitudinal ridges
(Cortijo et al., 2010), although some specimens have only six longitudinal ridges

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(Iván Cortijo, personal communication). In addition, some specimens illustrated as
Cloudina waldei (e.g., pl. 1, figs. 1–2 of Hahn and Pflug, 1985) have wrinkled tube

walls and are somewhat similar to Sinotubulites baimatuoensis, although a detailed

restudy of the C. waldei material is needed before any definitive conclusion is made.
Qinella Zhang, Li, and Dong in Ding et al., 1992 was originally diagnosed as a

multilayered tubular fossil with tube-in-tube construction, a feature used to distinguish
it from Sinotubulites (Ding et al., 1992). However, it was later shown that
well-preserved Sinotubulites tubes from the type locality in the Yangtze Gorges area
have multilayered walls, and the two genera are considered synonymous (Chen and

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Sun, 2001). Hua et al. (2000b) also synonymized Qinella (and its type species, Q.
shaanxiensis Zhang, Li, and Dong in Ding et al., 1992) with Sinotubulites, but they

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chose to retain the genus Qinella and designated Q. levis Zhang, Li, and Dong in Ding
et al., 1992 as its type species. Essentially, Hua et al. (2000b) created a junior

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homonym. As discussed under the species Sinotubulites baimatuoensis, both Q.

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shaanxiensis and Q. levis are considered junior synonyms of S. baimatuoensis. As

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such, both hononyms of Qinella are synonymous with Sinotubulites.

Sinotubulites baimatuoensis Chen, Chen and Qian, 1981, emended

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(Figures 3–4)

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Synonyms:

Cloudina? sp. Chen and Wang, 1977, p. 220, fig. 1a, b.

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Sinotubulites baimatuoensis Chen et al., 1981, p. 119–120, pl. I, fig. 1, 2; pl. II, fig.
1–6.

Skolithos miaoheensis Chen et al., 1981, p. 117–118, pl. I, fig. 4–5.

Multiple-walled tubular fossil, Signor et al., 1983, fig. 3e.
Smooth, single-walled shell, Signor et al., 1983, fig. 3f.
Irregularly annulated tube, Signor et al., 1983, fig. 3g.
Regularly annulated tube, Signor et al., 1983, fig. 3h.
Sinotubulites cienegensis McMenamin, 1985, p. 1416–1421, figs. 3.2–3.6, 4.1, 4.2,
4.4–4.7, 5.2, 5.5, 5.6.

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Sinotubulites baimatuoensis McMenamin, 1985, p. 1416–1421, fig. 6.
Sinotubulites cienegensis Signor et al., 1987, p. 431–432, fig. 5.1.

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Qinella shaanxiensis Zhang, Li, and Dong in Ding et al., 1992, p. 94–96, pl. VII, fig.
1–5, 8–10; pl. IX, fig. 5, 7, 10.

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Qinella levis Zhang, Li, and Dong in Ding et al., 1992, p. 96, pl. VII, fig. 6.

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Qinella lijiagouensis Zhang, Li, and Dong in Ding et al., 1992, p. 96–97, pl. VII, fig.
7.

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Qinella cf. lijiagouensis Zhang, Li, and Dong in Ding et al., 1992, p. 97–98, pl. XIV,
fig. 6a–c.

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?Qinella sp. Zhang, Li, and Dong in Ding et al., 1992, p. 98, pl. XIV, fig. 4.
Sinotubulites baimatuoensis Li et al. in Ding et al., 1992, p. 98–99, pl. XVI, fig. 1.

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Sinotubulites miaoheensis Ding et al., 1993, p. 120–121, pl. II, fig. 1–6.
Sinotubulites cienegensis Hua et al., 2000a, pl. I, fig. 1b (partim; not pl. II, fig. 6).

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Qinella levis Hua et al., 2000b , p. 383, pl. I, fig. 3, 4, 9–12 (partim; not pl. I, fig. 1).
Sinotubulites cienegensis Hua et al., 2000b, p. 381–383, pl. I, fig. 5–8; pl. II, fig. 1–5,
6a, b, 14.

Sinotubulites shaanxiensis Chen and Sun, 2001, p. 188-189, pl. III, fig. 7 (but not fig.
6); pl. IV, fig. 1, 2 (but not fig. 3).

Sinotubulites cienegensis Hua et al., 2003, fig. 2A–C.
Sinotubulites Hua et al., 2007, pl. V, fig. 7, 8.
Sinotubulites baimatuoensis Chen et al., 2008, fig. 2E.
Sinotubulites Chen et al., 2008, figs. 2A, 3A–E, 3G, 4A–C (but not figs. 2B–C, 3F).

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Sinotubulites baimatuoensis Cai et al., 2010, fig. 4N.
Sinotubulites sp. Zhuravlev et al., 2012, fig. 5.

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Sinotubulites Sun et al., 2012, figs. 3C–D, 3G–I, 4 (but not fig. 3A–B, 3E–F).

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Neotype: A silicified specimen from the Dengying Formation in the Yangtze

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Gorges area, where the original material of Sinotubulites baimatuoensis was collected
(Chen and Wang, 1977; Chen et al., 1981), is here designated as a neotype. The

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specimen is illustrated in Fig. 3 and reposited at Northwest University (Museum
catalog number: GEONWU-BST-006).

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Emended diagnosis: A species of Sinotubulites with a cylindrical tube consisting

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corrugated outer wall.

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of a weakly ornamented inner wall (circular in cross section) and a strongly

Description: The great majority of Lijiagou specimens are phosphatized, although

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some are silicified (Chen et al., 2008). Specimens are incompletely preserved (Figs. 3
and 4), ranging from 3 to 28 mm in length and 1.5–6 mm in diameter. Both the inner
and outer walls are multilayered: layers in inner wall 0.025–0.055 mm in thickness
and 0.010–0.050 mm in spacing, whereas layers in outer wall 0.040–0.095 mm in
thickness and 0.020–0.250 mm in spacing. The outer wall is ornamented with
transverse corrugations (Figs. 2A, 3A–C, 4A, B and D), although some corrugations
can be oblique (Fig. 4D). Corrugations can be densely or sparsely arranged (Fig. 4A),
and they can be strongly folded (Fig. 4B). The outer wall can be circular (Fig. 4C) or
slightly polygonal in cross-sectional view (Fig. 3D), partly due to diagenetic

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deformation. The transition from corrugated outer wall to smooth inner wall can be
gradational (Chen et al., 2008) or abrupt (Fig. 4E). The inner wall is often circular in

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cross section (Fig. 4C), and it is nearly smooth with only faint transverse annulations
(Fig. 4E). The total number of shell layers in both the outer and inner walls can be

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more than 10 (Fig. 4E) and up to 16.

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Occurrence: Deep Spring Formation, Mount Dunfee, Nevada, USA; Dengying
Formation, Hubei Province, South China; Dengying Formation, Shaanxi Province,

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South China; La Ciénega Formation, Sonora, Mexico; Ibor Group, Spain.
Discussion: Chen et al. (1981) illustrated a number of specimens of S.

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baimatuoensis, but they did not designate a holotype. Unfortunately we cannot
relocate the original material to select a lectotype. Thus, the specimen illustrated in

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Fig. 3 is here designated as a neotype.

Although the original composition of Sinotubulites tubes is inferred to have been

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calcareous (Chen et al., 1981; McMenamin, 1985) or aragonitic (Chen et al., 2008),
Sinotubulites can be preserved through different secondary mineralization processes,

including calcification (McMenamin, 1985; Signor et al., 1987), silicification (Chen et
al., 1981; Chen et al., 2008), phosphatization (Chen et al., 2008), and dolomitization
(Chen et al., 1981). These variable taphonomic pathways partly account for the
different morphologies among different Sinotubulites populations.
Previous morphological description and systematic treatment of Sinotubulites has

been primarily focused on the morphology of the outer wall (Chen and Wang, 1977;
Chen et al., 1981; McMenamin, 1985; Signor et al., 1987; Li et al., 1992; Zhang et al.,

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1992; Hua et al., 2000b; Chen and Sun, 2001; Chen et al., 2008). However, our
material shows that the external appearance of Sinotubulites is quite variable (Fig. 4A,

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B and D), depending on how strong the corrugations are. Recognizing this variability
as intraspecific variation, we regard Qinella shaanxiensis Zhang et al. in Ding et al.,

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1992, Q. levis Zhang et al. in Ding et al., 1992, Q. lijiagouensis Zhang et al. in Ding et

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al., 1992, and Sinotubulites cienegensis McMenamin, 1985, as junior synonyms of
Sinotubulites baimatuoensis.

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The genus Qinella was established by Zhang, Li, and Dong in Ding et al. (1992),
with Q. shaanxiensis as the type species and Q. lijiagouensis and Q. levis as two

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additional species. It shares strong morphological similarities with Sinotubulites (Hua
et al., 2000b; Chen and Sun, 2001), including the signature “tube-in-tube”

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construction and the development of transverse corrugations. Thus, Hua et al. (2000b)
synonymized Qinella shaanxiensis and Q. lijiagouensis with Sinotubulites cienegensis

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because all three species are characterized with transverse corrugations that are
developed to different degrees. Because Qinella shaanxiensis is the type species of
Qinella, Hua et al.’s (2000b) synonymization implies that Qinella is a junior synonym

of Sinotubulites, as they indicated in the synonym list under Sinotubulites. However,

Hua et al. (2000b) chose to retain the genus Qinella and designated Q. levis as its type
species, arguing that Q. levis is different from Sinotubulites in having a “tube-in-tube”
construction but with smooth or weakly ornamented tube walls. Essentially, Hua et al.
(2000b) created a junior homonym Qinella Hua, Zhang, Zhang, and Wang, 2000,
which is defined by a different type species than Qinella Zhang, Li, and Dong in Ding

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et al. (1992). Subsequently, Chen and Sun (2001) recognized the tube-in-tube
construction as a basic feature of Sinotubulites and transferred both Qinella

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shaanxiensis and Q. levis to Sinotubulites to become S. shaanxiensis and S. levis.
Chen and Sun (2001) also considered Q. lijiagouensis as stronlgy weathered variant of

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S. shaanxiensis, with its subdued corrugations resulting from the secondary loss of the

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outermost layers of the outer tube wall. This secondary loss argument can also be
applied to explain the weakly ornamented or smooth tube wall of S. levis. In other

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words, the weakly ornamented or smooth tube wall of S. levis may represent only the
inner wall, with the outer wall lost due to taphonomy or weathering. Thus, both Q.

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lijiagouensis and S. levis are regarded as taphonomic variants of S. shaanxiensis.
We further propose that S. shaanxiensis (along with Q. lijiagouensis and S. levis)

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is a junior synonym of S. baimatuoensis. Sinotubulites baimatuoensis was established
based on silificied material from the Dengying Formation in the Yangtze Gorgse area

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(Chen et al., 1981). The silicified material is poorly preserved and does not reveal as
much detail about the multi-layered tube walls as the phosphatized material from
southern Shaanxi. In a recent study, Chen et al. (2008) compared the phosphatized and
silicified material of Sinotubulites and concluded that S. baimatuoensis is a poorly
preserved form of S. shaanxiensis, and these two species are synonymous with S.
baimatuoensis taking priority. Chen et al.’s (2008) systematic evaluation is followed
in this paper.
We also propose that S. cienegensis is a junior synonym of S. baimatuoensis.
Sinotubulites cienegensis was established by McMenamin (1985) based on Mexican

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material. It differs from S. baimatuoensis in that the latter has more strongly obique
and bifurcating annulae. However, new material of S. baimatuoensis from southern

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Shaanxi shows that this species has a wide range of morphological variation that can
accomodate S. cienegensis. For example, Sun et al. (2012) have shown that the

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transverse corrugations (=annulations of McMenamin, 1985) occur on the tube at

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different densities (Fig. 4A). Where the corrugations are sparsely distributed, they
tend to be more regularly arranged (i.e., without bifurcation) and have lower reliefs,

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thus similar to S. cienegensis. The corrugations can be transversely or slightly
obliquely oriented relative to tube length (Fig. 4D). Thus, the morphological range of

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S. baimatuoensis from southern Shaanxi can accommodate that of S. cienegensis.
Isolated specimens from Ediacaran successions in Brazil described as Cloudina

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waldei Hahn and Pflug, 1985 (e.g., paratypes illustrated in pl. 1, figs. 1–2 of Hahn and
Pflug, 1985) are similar to Sinotubulites baimatuoensis in having transverse

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corrugations and a more or less circular cross section. According to Gaucher et al.
(2003), C. waldei is a junior synonym of Cloudina lucianoi (Beurlen and Sommer,

1957) Zaine and Fairchild, 1985. However, most Cloudina specimens from Brazil,

Paraguay, and Uruguay were observed in thin sections (Gaucher et al., 2003; Warren
et al., 2011; Warren et al., 2013; Warren et al., 2014), and it is difficult to ascertain
whether their tests are transversely corrugated and consist of nested tubes or funnels.
More study of extracted specimens is needed to determine the relationship between C.
waldei, C. lucianoi, and S. baimatuoensis.

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Sinotubulites triangularis n. sp.

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Figures 5, 6

Etymology: Species epithet derived from Latin triangularis, with reference to the

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triangular prismatic morphology of the new species.

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Holotype: Specimen illustrated in Fig. 5A, reposited at Northwest University
(Museum catalog number: GEONWU-LJGTL-1-2013-002).

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Additional material: There are sixteen specimens in our collection, seven of
which are illustrated in Figs. 5–6.

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Type locality and occurrence: Upper Ediacaran System, the uppermost Beiwan

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Province, South China.

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Member of the Dengying Formation at the Lijiagou section of Ningqiang, Shaanxi

Diagnosis: A species of Sinotubulites with triangular prismatic tubular

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morphology.

Description: The tube of S. triangularis n. sp. is a straight (Fig. 5B) or gently

curved (Fig. 5A), prismatic with an equilateral triangular cross section (Figs. 5C and
6B), and consists of outer and inner walls, both multi-layered (Figs. 5D, 6B–F).
Layers in the outer tube wall are 0.020–0.045 mm in thickness and 0.020–0.065 mm
in spacing. Transverse corrugations in outer wall are regularly arranged, with their
sharp crest spaced at 0.19–0.82 mm intervals. Straight or slightly helical longitudinal
ridges in outer wall are zig-zag-shaped, reflecting the alternate offset of the
corrugations on either side of the ridge (Fig. 5B). Layers in the inner wall are

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Page 17 of 46

relatively smooth (Fig. 6A, D–F), 0.020–0.035 mm in thickness, and 0.010–0.025 mm
in spacing. The longest tube in our collection is ca. 6.5 mm in length, with 18

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regularly spaced corrugations.
Discussion: The new species differs from the type species in its triradially

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prismatic tube and its regularly arranged transverse corrugations that are offset at the

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longitudinal ridges. Because there are multiple specimens of S. triangularis in our
collection, it is unlikely that the triradial symmetry is a taphonomic artifact due to

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compaction of round cylindrical tubes.

Triradial symmetry is common among a number of Ediacaran and Cambrian

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fossils (e.g., Fig. 7). Many Ediacaran discoidal fossils are triradially symmetrical,
including Tribrachidium Glaessner in Glaessner and Daily, 1959 (a discoidal

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organism with three spiral, fringed arms), Albumares Fedonkin in Keller and
Fedonkin, 1976 (a discoidal fossil with three lobes, each of which bearing radially

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directed, branching ridges), Anfesta Fedonkin, 1984 (similar to Albumares but more

discoidal and less lobate in shape), Triforillonia Gehling, Narbonne, and Anderson,
2000 (a discoidal fossil with three lobes), Triactindiscus Zhao et al., 2010 (a discoidal
fossil with three radiating carbonaceous traces), and Quasitriagondiscus Zhao et al.,

2010 (a discoidal fossil with three carbonaceous traces forming triangle). However,
these discoidal fossils do not have a tubular construction that is characteristic of
Sinotubulites triangularis. More relevant to the tubular morphology of S. triangularis
are several early Cambrian conotubular fossils with triradial symmetry. These include
Anabarites trisulcatus Missarzhevsky in Voronova and Missarzhevsky, 1969 (Fig.

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Page 18 of 46

7A–B), Anabarites trymatus Conway Morris and Bengtson in Bengtson et al., 1990,
Emeiconularia trigemme Qian et al., 1997, and Emeiconularia amplicanalis Liu et al.,

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2005 (Fig. 7C–D). These conotubular fossils have transverse ridges or wrinkles, and
are characterized by three sides or lobes separated by three longitudinal sulci or

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internal keels (Qian and Bengtson, 1989; Qian et al., 1997; Liu et al., 2005). These

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fossils invite the intriguing possibility that they may be phylogenetically related to S.
triangularis, although we note the important difference that, at least for Anabarites,

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the tubes are closed at the apical end. Nonetheless, it would be fruitful to explore
whether these triradial tubular fossils are phylogenetically related, and if so they can

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mutually illuminate each other to resolve their phylogenetic affinities and to

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understand the evolutionary continuity across the Ediacaran–Cambrian boundary.

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Sinotubulites pentacarinalis n. sp.
Figure 8

Synonyms:

Qinella levis Hua et al., 2000a, pl. II, fig. 1.
Qinella levis Hua et al., 2000b, p. 383, pl. I, fig. 1.
Sinotubulites cienegensis Hua et al., 2000a, pl. II, fig. 6 (partim; not pl. I, fig. 1b).
Sinotubulites shaanxiensis Chen and Sun, 2001, p. 188-189, pl. III, fig. 6 (but not fig.

7); pl. IV, fig. 3 (but not fig. 1, 2).
Sinotubulites levis Chen and Sun, 2001, p. 189–190, pl. III, fig. 8.

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Page 19 of 46

Sinotubulites Chen et al., 2008, fig. 2B–C, 3F.

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Sinotubulites Sun et al., 2012, fig. 3A, 3E.

Etymology: Species epithet derived from Greek penta- and Latin carinalis, with

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reference to the pentagonal cross section and the five ridges of the new species.

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Holotype: Specimen illustrated in Fig. 8, reposited at Northwest University
(Museum catalog number: GEONWU-LJG-2014-006).

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Additional material: Seven additional specimens.

Type locality and occurrence: Upper Ediacaran System, the uppermost Beiwan

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Member of the Dengying Formation at the Lijiagou section of Ningqiang, Shaanxi
Province, South China.

morphology.

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Diagnosis: A species of Sinotubulites with pentagonal prismatic tubular

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Description: The tube of S. pentacarinalis n. sp. is straight or gently curved (Fig.

8A–B), and prismatic with a pentagonal cross section (Fig. 8C). Both inner and outer
walls are multi-layered (Fig. 8C). Outer layers are 0.035–0.075 mm in thickness and
0.030–0.075 mm in spacing. Transverse corrugations in outer wall are regularly
arranged, with their crest spaced at 0.12–1.8 mm intervals. Longitudinal ridges are
helical and zig-zag-shaped due to the alternate offset of the corrugations on either side
of the ridge (Fig. 8A–B). Inner layers are relatively smooth (Fig. 8A), 0.015–0.045
mm in thickness, and 0.015–0.035 mm in spacing. The longest tube in our collection
is ca. 23 mm in length.

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Page 20 of 46

Discussion: The new species differs from the type species in its pentagonal
prismatic tube and five longitudinal ridges that divide the tube wall into five sides.

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The helical longitudinal ridges and prismatic tube are not considered as taphonomic
modification of a round cylindrical tube, because these features can be produced

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taphonomically only in the unlikely scenario of simultaneous twist and compaction.

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A pentaradial symmetry is characteristic of several Ediacaran and early

Cambrian taxa, including Olivooides Qian, 1977 (a tubular organism with a multiple

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of five oral lobes, a test with five-fold symmetry, and a pentaradial apex), Arkarua
Gehling, 1987 (a discoidal fossil with five radial ridges), and Pentaconularia

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ningqiangensis Liu et al., 2011 (a tubular fossil consisting of five faces separated by
five sulci). Of these taxa, Pentaconularia ningqiangensis (Liu et al., 2011) and

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Olivooides (Steiner et al., 2014) are tubular organisms and thus more similar to S.

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pentacarinalis than is Arkarua, although Olivooides has a closed apical end.

Sinotubulites hexagonus n. sp.
Figure 9

Synonyms:

Sinotubulites Sun et al., 2012, fig. 3B, 3F.

Etymology: Species epithet derived from Latin hexagonus, with reference to the
hexagonal prismatic morphology of the new species.

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Page 21 of 46

Holotype: Specimen illustrated in Fig. 9, reposited at Northwest University
(Museum catalog number: GEONWU-LJG-2014-016).

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Additional material: Twelve additional specimens.
Type locality and occurrence: Upper Ediacaran System, the uppermost Beiwan

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Member of the Dengying Formation at the Lijiagou section of Ningqiang, Shaanxi

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Province, South China.

Diagnosis: A species of Sinotubulites with hexagonal prismatic tubular

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morphology.

Description: The tube of S. hexagonus n. sp. is nearly straight (Fig. 9A–C), and

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prismatic with an equilateral hexagonal cross section (Fig. 9D–E). Both the outer and
inner walls are multi-layered (Fig. 9D–E). Outer layers are 0.045–0.095 mm in

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thickness and 0.025–0.065 mm in spacing. The crests of transverse corrugations in
outer wall are spaced at 0.16–3.1 mm intervals. Longitudinal ridges in outer wall are

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slightly helical and are zig-zag shaped due to the alternate offset of the corrugations
on either side of the ridge (Fig. 9A–C). Layers in the inner wall are relatively smooth
(Fig. 9D–E), 0.025–0.065 mm in thickness, and 0.020–0.040 mm in spacing. The
longest tube in our collection is ca. 19 mm in length.
Discussion: The new species differs from other Sinotubulites species in its

hexagonal prismatic tube. Like in S. pentacarinalis, the helical longitudinal ridges and
prismatic tube are probably biological rather than taphonomic features.
Hexaradially symmetrical organisms are rare in the Ediacaran Period (Xiao and
Laflamme, 2009), with the exception of Protechiurus edmondsi Glaessner, 1979 and

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Page 22 of 46

Vendoconularia triradiata Ivantsov and Fedonkin, 2002. P. edmondsi is a
spindle-shaped fossil with six longitudinal ridges, indicative of hexaradial symmetry

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(Dzik, 2003). V. triradiata is a conical test with six faces, each consisting of two series
of transverse structures, and it may be related to Paleozoic conulariids, thus

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suggestive of phylogenetic and evolutionary connections across the

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Ediacaran–Cambrian boundary (Ivantsov and Fedonkin, 2002). Additionally, some
specimens of Cloudina carinata have six longitudinal ridges (Iván Cortijo, personal

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communication) and thus may be hexaradially symmetrical, but their tubular
structures consist of nested funnels with outward projecting collars. In the Cambrian

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Period, the conotubular fossil Anabarites sexalox Conway Morris and Bengtson in
Bengtson et al., 1990 is well known for its hexaradial symmetry. In addition, the

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Cambrian fossil Hexaconularia sichuanensis He and Yang, 1986 has a six-sided test,
but its test is flattened and the six sides are unequal in size, resulting in a biradial

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p

symmetry (Van Iten et al., 2010; Steiner et al., 2014). Moreover, V. triradiata, A.
sexalox, and H. sichuanensis all have a closed apex, thus different from Sinotubulites

hexagonus that is presumably open at both ends.

5. Conclusions

New Sinotubulites material from the uppermost Beiwan Member of the
Dengying Formation at the Lijiagou section in southern Shaanxi Province provides
new morphological insights about this genus, confirming its tube-in-tube construction
with multi-layered inner and outer tube walls. Three forms of the Lijiagou

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Page 23 of 46

Sinotubulites fossils are characterized by prismatic tubes, two of which have helical
longitudinal ridges. The prismatic tubes and helical longitudinal ridges are interpreted

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as biological rather than taphonomic features. These forms are described as three new
species, Sinotubulites triangularis, S. pentacarinalis, and S. hexagonus. The three new

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species are characterized by triradial, pentaradial, and hexaradial symmetries, adding

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to the morphological diversity of biomineralizing tubular fossils in the Ediacaran
Period. In light of the widespread occurrences of triradial, pentaradial, and hexaradial

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tubular fossils in the Ediacaran and Cambrian periods, it would be interesting to
explore whether these body symmetries have any phylogenetic significance or they

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Acknowledgments

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arose repeatedly through convergence.

This work was supported by the National Natural Science Foundation of China

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(41202006; 41030209; 41272011), National Science Foundation (EAR-1124062),
State Key Laboratory of Continental Dynamics Research Project (BJ14263), Key
Area Science and Technology Innovation Team Project of Shaanxi Province
(2012KCT-08), Talented Young Scientists Fund of Northwest University (PR14164),
and China Postdoctoral Science Foundation (2013M531410). We thank Drs. Yunhuan
Liu and Xin Wang for providing microphotographs of early Cambrian small shelly
fossils. Reviews by Iván Cortijo and an anonymous reviewer greatly improved the
manuscript.

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Page 24 of 46

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Figure captions
Fig. 1. Stratigraphic column of the Ediacaran Dengying Formation at the Lijiagou

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section. See fig. 1 of Cai et al. (2014) for location.

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Fig. 2. Schematic diagram showing morphological reconstructions and descriptive

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terms of Sinotubulites baimatuoensis (A), S. triangularis (B), S. pentacarinalis

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(C), and S. hexagonus (D).

Fig. 3. Reflected light photographs of the neotype of Sinotubulites baimatuoensis

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from the Dengying Formation in the Yangtze Gorges area. (A–C) Three views
of the same specimen showing outer tube wall with transverse corrugations

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(white arrows). (D) Cross section view of the tube (see labeled arrow in A).
Note the slightly polygonal shape of the outer wall and the multilayered tube

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wall. Museum catalog number: GEONWU-BST-006.

Fig. 4. Secondary electron microphotographs of Sinotubulites baimatuoensis from the
Dengying Formation at the Lijiagou section. (A) Outer tube wall with
segments of denser corrugations (black arrows) interspersed with sparser
corrugations (white arrows). (B) Outer tube wall with strongly irregular
corrugations. (C) Circular cross-sectional profile. (D) Tube with transverse
(black arrows) and slightly oblique (white arrows) corrugations. (E) A

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fractured tube showing multiple-layered and corrugated outer wall (black
double-headed arrow) and smooth inner wall (white double-headed arrow).

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Note the corrugated outer wall can be pinched inward (white arrow) or
outward (black arrow). Also note faint ornaments (arrowheads) on the inner

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wall. Museum catalog numbers: A (GEONWU-LJG01-010), B

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(GEONWU-LJGST-2013-1004), C (GEONWU-LJGST-2013-007), D

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(GEONWU-LJGST-2013-009), E (GEONWU-LJG01-080).

Fig. 5. Secondary electron microphotographs of Sinotubulites triangularis n. sp. from

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the Dengying Formation at the Lijiagou section. (A–B) Slightly curved (A)
and straight (B) tubes showing triangular prismatic morphology and regularly

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corrugated outer wall. Note that corrugations are alternately offset across
longitudinal ridge in (B). (C) Cross sectional view (see labeled arrow in A). (D)

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Fractured tube showing multi-layered and corrugated outer wall (arrows).
Museum catalog numbers: A (Holotype; GEONWU-LJGTL-2013-0002), B
(GEONWU-LJGTL-1-2013-0014), D (GEONWU-LJGTL-1-2013-0015).

Fig. 6. Secondary electron microphotographs of Sinotubulites triangularis n. sp. from
the Dengying Formation at the Lijiagou section. (A) A fractured specimen
showing smooth inner wall (white double-headed arrow) and corrugated outer
wall (black double-headed arrow). (B) Cross sectional view of a tube with

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outer wall stripped away taphonomically. (C) Close-up view of a multilayered
inner wall (white double-headed arrow), surrounded by a thick multilayered

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outer wall. (D–F) Three different views of a fragmented specimen, showing
the interior surface of the corrugated outer wall. Museum catalog numbers: A

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(GEONWU -LJGTL-1-2013-004), B (GEONWU-LJGTL-2013-0016), C

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(GEONWU-LJGTL-2013-002), D–F (GEONWU-LJGTL-1-2013-013).

Fig. 7. Secondary electron microphotographs of triradial anabaritids (A–B) and

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conularids (C–D) from the early Cambrian Kuanchuanpu Formation at the
Shizhonggou section in Ningqiang County of southern Shaanxi Province,

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South China. (A–B) Anabarites trisulcatus, probably an internal mold with
helical sulci (black arrows) corresponding to internal keels. Images courtesy of

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Xin Wang. (C–D) Emeiconularia amplicanalis, with three faces separated by
wide longitudinal sulci. Images courtesy of Yunhuan Liu. Note transverse
wrinkles (D).

Fig. 8. Reflected light photographs (A–C) and secondary electron microphotograph
(D) of Sinotubulites pentacarinalis n. sp. from the Dengying Formation at the
Lijiagou section. (A–B) Two views of the same specimen showing five sides
(numbered) of the tube separated by five longitudinal ridges (black dots). Note
transverse corrugations (white arrows) and longitudinal ridges (black dots) on

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the outer wall. Also note smooth inner wall (black arrow in (A). (C)
Pentagonal cross-section view (see labeled arrow in A) showing five faces

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(numbered). Note the more or less circular inner wall and the pentagonal outer
wall. Golden color due to Au coating in preparation for SEM observation. (D)

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Close-up view (see labeled rectangle in B) showing that transverse

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corrugations (white arrows) are slightly offset across the longitudinal ridge

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(black arrows). Museum catalog number: GEONWU-2014-LJG-020.

Fig. 9. Reflected light photographs of Sinotubulites hexagonus n. sp. from the

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Dengying Formation at the Lijiagou section. (A–C) Three views of the same
specimen showing six sides (numbered) of the tube separated by six

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longitudinal ridges (black dots). Note transverse corrugations (white arrows)
and longitudinal ridges (black dots) on the outer wall. (D–E) Hexagonal

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cross-section views (see labeled arrows in A). Note the multilayered tube wall,
more or less circular inner wall in (E), and hexagonal outer wall in (D).
Museum catalog number: GEONWU-2014-LJG-033.

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Figure 8

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Figure 9

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