10


Journal of Paleontology 92(1):3–13


Table 1. Morphological comparisons among olivooids, hexangulaconulariids, carinachitids, and conulariids. Characteristics\taxa


tube shape longitudinal folds longitudinal striations


apical/abapical differentiation periodical growth radial symmetry oral lobes


adradial lobes


thorn-like spines face/corner septa/carina facial midline mineralization


apex ornaments


thickening of tube wall displacement


yes/no no no no no no no


yes yes yes yes 4, 5 yes yes


stellae


Olivooids cone


Hexangulaconulariids cone


yes yes


yes ?


3, 4, 5 no no no


yes no no


yes no


yes smooth


tube aperture in both Carinachites spinatus and Olivooides has four or five prominent plicate apertural lobes (usually termed ‘lobate folds’ in Yue and Bengtson, 1999; Han et al., 2016a, b; termed ‘oral lobes’ in Steiner et al., 2014, in Olivooides multisulcatus Qian, 1977) (Fig. 5). (3) Lateral ornaments on the tube wall, including plicate thorns (Fig. 5.1) (termed ‘plicate cornice’ in O. multisulcatus [see Han et al., 2016a, fig.2] and ‘triangular thickening’ by Steiner et al., 2014, fig.10), are derived fromthe tube aperture (Yasui et al., 2013). (4)Asmentioned in the preceding, the soft tissues are always connected to the tube aperture. (5) There are similar patterns of tube formation except for lateral thickening, in both cases with tube formation mediated by soft tissue at the oral end (Yasui et al., 2013; Liu et al., 2014b; Han et al., 2016a, b). (6) Rare preservation of the apertural end in olivooids and carinachitids as well as Paleozoic conulariids probably indicates that the newly secreted tube aperture was predominantly organic or weakly sclerotized and thus less resistant to decay than the lateral ribs. Differences between carinachitids and olivooids also are


evident. Although carinachitid tubes bear regular ribs, they were never compressed during diagenesis along the longitudinal axis as in olivooid tubes. This difference may be partially attributed to the presence in carinachitids of deeply concave corner sulci, outwardly bulging faces, and later ontogenetic thickening, thus providing stronger support for the soft body. The face-corner configuration in carinachitids also reflects an incipient differ- entiation of the meridian planes. The apertural lobes among different taxa of olivooids vary greatly in morphology. Thus, unlike Olivooides multisulcatus (Fig. 5.1–5.3), Quadrapygites and O. mirabilis Yue, 1984 in Xing et al., 1984 lack clear differentiation in size between the principle apertural lobes and the adradial apertural lobes. By contrast, carinachitids exhibit only the principle apertural lobes. The corner sulci in carinachitids may correspond to the adradial apertural lobes in olivooids. In addition, carinachitids exhibit greater morpholo- gical variation on the faces than do olivooids, including variation in rib shape and height, displacement of ribs along the midline, and convergence of the striations. The facial ribs of carinachitids may represent a derived feature in comparison with the continuous transverse crests in olivooids. Finally, it has generally been accepted that the periderm of olivooids was organic and uniform in thickness. By contrast, the tubes of carinachitids, hexangulaconulariids, and conulariids, although


yes yes ?


yes 2


yes no


yes yes no


no/yes weak yes yes ?


Carinachitids cone


Conulariids cone


yes yes


yes no


2, 3, 4 yes no no


yes/no yes yes yes yes yes


smooth


showing some degree of flexibility, are relatively thick and slightly mineralized (e.g., Brood, 1995; Qian et al., 1997; Leme et al., 2008; Ford et al., 2016). Similarities between carinachitids and hexangulaconular-


iids include: (1) sclerotization of the tube wall, (2) development of faces and corner sulci, (3) transverse ornament showing displacement/offset along the midline of the faces and corner sulci, and (4) sessile benthic mode of life on firm substrates or hard parts (e.g., Van Iten et al., 2016a). The displacement mechanism of carinachitids may have also been present


in hexangulaconulariids (Conway Morris and Chen, 1992, fig. 11.12; Van Iten et al., 2010, fig. 2e) and latest Ediacaran Paraconularia (e.g., Van Iten et al., 2014, fig. 3c–d; Van Iten et al., 2016b). In this connection, it should be noted that relics of small soft parts extending along the tube axis of conulariids, originally interpreted as remains of an alimentary tract (Babcock, 1989), most likely represent polyps as previously suggested by Van Iten (1991) and supported by currently available material of carinachitids and the internal anatomy of Olivooides (e.g., Han et al., 2016a). Differences between carinachitids and hexangulaconular-


iids also are evident. In particular, the pseudohexaradial symmetry of hexangulaconulariid tubes, which exhibit a fundamental bimerous tetraradial symmetry, reflects further morphological differentiation of the meridian planes within a framework of tetraradial symmetry. Such meridian plane differentiation, oriented perpendicular to the longitudinal axis, probably indicates unknown differentiation of soft part struc- tures such as gonads, septa, and the vascular system. Finally, the apertural lobes of hexangulaconulariids are not triangular as in carinachitids and olivooids. Carinachitids share detailed similarities with Paleozoic


conulariids (except for Cambrian Baccaconularia in Hughes et al., 2000) in face/corner sulcus differentiation and formation of apertural lobes (equivalent to the apertural lappets of Sendino et al., 2011), and both taxa exhibit tri-, tetra- or pentaradial symmetry. However, biradial symmetry, common in conular- iids, has not been observed in carinachitids. In addition, the corners of some conulariids, for example Eoconularia loculata (Wiman, 1895 in Jerre, 1994), are much thicker than the faces (Jerre, 1994), contrasting with the relatively thickened faces of carinachitid Emeiconularia trigemme (Fig. 2.1b). Moreover, in addition to plicate apertural lobes (Ford et al., 2016), conulariids


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