Journal of Paleontology, 91(5), 2017, p. 871–882 Copyright © 2017, The Paleontological Society 0022-3360/17/0088-0906 doi: 10.1017/jpa.2017.49
A problematic cnidarian (Cambroctoconus; Octocorallia?) from the Cambrian (Series 2–3) of Laurentia
John S. Peel Department of Earth Sciences (Palaeobiology), Uppsala University, Villavägen 16, Uppsala, SE-75236, Sweden ⟨
john.peel@
pal.uu.se⟩
Abstract.—The problematic calcified cnidarian Cambroctoconus is described from the Henson Gletscher Formation (Cambrian Series 2, Stage 4–Series 3, Stage 5) of North Greenland, representing the first record from Laurentia of a genus otherwise recently described from China, Kyrgyzstan, and Korea. Internal molds produced by penetrative phosphatization mirror the pervasive pore system of the calice walls and septa. The pore system is compared to the network of gastrodermal solenia that distributes nutrients between polyps and surrounding stolon tissues in present day octocorals. In conjunction with the octagonal form of the individual coralla and eight-fold symmetry of septa, the pore system promotes assignment of Cambroctoconus to the Octocorallia, a basal clade in cnidarian phylogeny. Octocorals (‘soft corals’) are diverse in present day seas, but have a poor fossil record despite the general develop- ment of distinctive calcareous spicules. New taxa: Order Cambroctoconida new; Cambroctoconus koori new species.
Introduction
Cnidarians have a geological record extending back to the Ediacaran (Van Iten et al., 2014, 2016a; Liu et al., 2014; Grazhdankin, 2016; Han et al., 2016; Dzik et al., 2017), but the heavily calcified groups of tabulate and rugosan corals that dominate the Paleozoic fossil record first appear in the Ordovician (Scrutton, 1997, 1999). There are, however, many mineralized Cambrian fossils, particularly in the early Cambrian, that have been considered as possible anthozoans, but their relationships to the major zoantharian and octocorallian groups are uncertain (Zhuravlev et al., 1993; Scrutton, 1997, 1999; Debrenne and Reitner, 2001; Han et al., 2016). Many of these mineralized taxa were informally grouped together as Coralomorpha by Jell (1984; corallomorphs of Zhuravlev et al., 1993). In reviewing the Cambrian record, Scrutton (1997, 1999) concluded that most coralomorphs represented independent, short-lived calcification events in various lineages of anemones and were unrelated to the later tabulate and rugose corals. Scrutton (1997, p. 199) proposed the Order Tabulaconida (inadvertently given as Tabuliconida by Peel, 2011) for mainly
early Cambrian undisputed corals, such as Tabulaconus Hand- field, 1969; Flindersipora Lafuste in Lafuste et al., 1991; Moorowipora Fuller and Jenkins, 1994; Arrowipora Fuller and Jenkins, 1995; Yaworipora Zhuravlev, 1999; and Blinmanipora Fuller and Jenkins, 2007. Hicks (2006) listed 16 taxa of coralomorphs while describing Harklessia Hicks, 2006 from Nevada.
Most early Cambrian coralomorphs are colonial, but Jell
and Jell (1976) described abundant specimens of a cup-shaped coral from the Coonigan Formation, First Discovery Limestone Member (Cambrian Series 3, Stage 5), of New South Wales, Australia, as Cothonion sympomatum Jell and Jell, 1976. This operculate, septate, coral reproduced by budding of daughter
corallites from the parent corallum and was placed in a new zoantharian Order Cothoniida by Oliver and Coates (1987; see also Scrutton, 1997). Peel (2011) described Cothonion sympomatum from the Paralleldal Formation (Cambrian Series 2, Stage 4) of southern Peary Land, North Greenland. Coralla of Tretocylichne perplexa Engelbretsen, 1993 from the Murra- wong Creek Formation (Cambrian Series 3, Drumian) of New South Wales often display an octagonal form and weak septation, while the holdfast is often perforated into the calice (Engelbretsen, 1993). Cambroctoconus orientalis Park et al., 2011 from the
Changhia Formation (Cambrian Series 3, Drumian) of Shandong Province, China developed a cup-shaped corallum reminiscent of later zoantharian corals. Its octagonal calice and the eight-fold symmetry of septa promoted comparison with octocorallians and staurozoans, but Cambroctoconus was interpreted by Park et al. (2011, 2016) as a stem-group cnidarian (Fig. 1.1, 1.5). Geyer et al. (2014) described a second species, Cambroctoconus kyrgyzstanicus Peel in Geyer et al., 2014, from Kyrgyzstan (Cambrian Series 3, Stage 5; Fig. 1.2, 1.4, 1.6), and drew comparisons with Tretocylichne perplexa from Australia. Park et al. (2016) described a third species, Cambroctoconus coreanensis Park et al., 2016, from the Daegi Formation (Cambrian Series 3, Drumian) of Korea and discussed the rela- tionship of this proposed group of stem-group cnidarians with crown-groups. Cambroctonus koori new species, described herein from
the Henson Gletscher Formation (Cambrian Series 2–3) of North Greenland (Fig. 2), represents the first record of Cambroctoconus from the Laurentian paleocontinent. In con- trast to previously described species of Cambroctonus, the new material from Greenland is mainly preserved as phosphatized internal molds etched free from limestone samples by the use of weak acids, whereas specimens of other species are preserved in
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