Coralomorphs

The mass radiation of Metazoans included mineralized skeletons of solitary calcium carbonate cups and, later, slender irregular cerioid polygonal tubes, near the beginning of the Cambrian. These were originally grouped as coralomorphs because of their probable cnidarian affinities (Jell 1984). New descriptions of Early Cambrian coralomorphs, including studies of the biocrystals characteristic of their microstructure, their systematic position, and their stratigraphic distribution, have recently been made (Zhuravlev et al. 1993; Sorauf and Savarese 1995).

The oldest coralomorph, Cysticyathus (figure 14.6B), occurs in middle Tommotian calcimicrobial-archaeocyath bioherms of Siberia. It was previously included in archaeocyaths, despite its aporous skeleton. Tannuolaiids (=khasaktiids) (figure 14.6A) appeared in the Atdabanian of Siberia, diversifying as they migrated throughout the Ural-Mongolian Belt, and are always associated with reefs.

Hydroconozoa began with the Atdabanian but are not known later than the Botoman, when modular ramose forms developed. The skeletal microstructure of Hydro-conus is most likely similar to that of genuine corals (Lafuste et al. 1990).

The Botoman was the acme for all Cambrian coralomorphs. In addition to tannuolaiids and hydroconozoans, which are characteristic of Siberia, one of the most convincing cnidarians, Tabulaconus (low modular) (Debrenne etal. 1987) (figure 14.6C), also appeared in Laurentia, along with the solitary Aploconus (Debrenne et al. 1990a) and the high modular Rosellatana (Kobluk 1984). In Australia, Flindersipora occurs. It was thought to comprise the oldest tabulate corals (Lafuste et al. 1991) (figure 14.6D) but is considered by Scrutton (1992) to be an unassigned early skeletonized anthozoan lacking linear descent to any major coral group. The newly discovered Moorowipora and Arrowipora, with their cerioid coral forms and typical coralline wall structure, short septal spines, and tabulae, suggest an assignment with Tabulata (Fuller and Jenkins 1994, 1995; Sorauf and Savarese 1995). The latter authors also propose inclusion of Tabulaconus in the Tabulata, thereby greatly extending the strati-graphic range of the group. Scrutton (1997), however, prefers to classify Cambrian

Figure 14.6 Coralomorphs in thin section. A, Encrusting Khasaktia vesicularis Sayutina, PIN, Lower Cambrian, Atdabanian Pestrotsvet Formation (middle Lena River, Siberian Platform, Russia). B, Branching Cysticyathus tunicatus Zhuravleva, MNHN M81016, Lower Cambrian, Tommotian Pestrotsvet Formation (middle Lena River, Siberian Platform, Russia).

Figure 14.6 Coralomorphs in thin section. A, Encrusting Khasaktia vesicularis Sayutina, PIN, Lower Cambrian, Atdabanian Pestrotsvet Formation (middle Lena River, Siberian Platform, Russia). B, Branching Cysticyathus tunicatus Zhuravleva, MNHN M81016, Lower Cambrian, Tommotian Pestrotsvet Formation (middle Lena River, Siberian Platform, Russia).

C, Branching Tabulaconus kordae Handfield, UA 2526, Lower Cambrian, Botoman Adams Argillite (Tatonduk area, Alaska, USA). D, Association of archaeocyaths (Ajacicyathus aequi-triens [Bedford and Bedford]) and tabulate Flin-dersipora bowmanni Lafuste, MNHN M42048, Lower Cambrian, Botoman Moorowie Limestone (Arrowie Basin, Australia).

zoantharian corals as a separate order Tabulaconida without an assignment to other Paleozoic coral clades.

All Atdabanian and Botoman coralomorphs are associated with calcimicrobial-archaeocyath reef environments, with Flindersipora and Yaworipora even participating in bioconstruction (Zhuravlev 1999). Khasaktia and Rosellatana can be cryptobionts in calcimicrobial-archaeocyathan reef cavities.

The modular Laurentian Labyrinthus is known from the late Botoman Forteau Formation of Labrador. Colonies are often attached to archaeocyath skeletons, indicating a preference for hard substrates. They are found in the "upper biostrome complex," which underlies and interfingers with ooid beds containing oncoids and diverse skeletal fragments. This implies shallow, agitated water conditions in the vicinity of a bioconstruction (Kobluk 1979).

Lipopora and Cothonion, from New South Wales, Australia, are the latest Early Cambrian (Ordian) coralomorphs (Jell and Jell 1976). Solitary or modular, they occur in carbonate beds, associated with Girvanella oncoids and a rich fauna of trilobites, brachiopods, mollusks, and sponges. The high faunal diversity, the predominance of cyanobacteria, and the carbonate petrology suggest a warm shallow-water carbonate bank environment.

Other proposed Early Cambrian cnidarians have doubtful records (inorganic concretions, algae, bryozoans, or synonyms of already described tannuolaiids or hydro-conozoans) and consequently are not considered here.

A Middle Cambrian (Floran-Undillan) coralomorph Tretocylichne is found in reworked clasts within inner submarine fan deposits of northeastern New South Wales (Engelbretsen 1993). The single example of a possible Late Cambrian coral is found in Montana (Fritz and Howell 1955).

Coralomorphs were suspension feeders living in warm waters and generally associated with calcimicrobial-archaeocyath bioherms as coconstructors or cryptobionts. Some lived in agitated waters near biostromes or carbonate banks.

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