Sphenothallus sica: A branching Conularid from the Early Devonian of Brazil.

The Conularids are an enigmatic group of organisms with possible affinities to the Cnidarians, which first appeared very close to the beginning of the Cambrian (or possibly at the End of the Ediacaran), and disappeared in the Early Triassic. They form cones comprised of concentric disks stacked within one another; these disks have four-fold radial symmetry, as is seen in modern Jellyfish, and it has therefore been suggested that the Conularids may represent something similar to the Attached Medusa stage of the living Stalked Jellyfish, Stauromedusae, from which new free-swimming Jellyfish arise by budding off.

In a paper published in the journal Acta Palaeontologica Polonica on 3 April 2019, Heyo Van Iten of the Department of Geology at Hanover College, and the Department of Invertebrate Paleontology at the Cincinnati Museum Center, Juliana de Moraes Leme of the Department of Sedimentary and Environmental Geology at the University of São Paulo, Marcello Simões of the Department of Zoology at São Paulo State University, and Mario Cournoyer of the Musée de Paléontologie et de l’Évolution, describe a new species of Conularid from the Early Devonian Ponta Grossa Formation of Paraná State in Brazil.

The description of the new species is based upon specimens first described by the palaeontologist John Mason Clarke in 1903, and which he identified as a problematic fossil, and possibly a Hydroid, which he named Serpulites sica, and later redescibed by Friedrich Sommer in 1954 as an algae, which he named Euzebiola clarkei. Van Iten et al. accept Clarke's specific name, sica, but refer the specimen to the Conularid genus Sphenothallus, on the basis of that it apparently has a soft body covered by a tubular or steeply pyramidal organic or organo-phosphatic periderm with fine laminations, that this periderm ends in a sub-conical expansion, and exhibits a transverse internal wall.

Medusozoan Cnidarian Sphenothallus sica from the Early Devonian Ponta Grossa Formation, Paraná State, southern Brazil. The numbers 1–16 indicate the evident, marginal daughter tubes, while the letter P indicates the parent tube. (A) Reproduction of Clarke’s (1913) drawing. (B) Light photographs. (B₁), general view; 17?, the possible basal portion of a seventeenth daughter tube; (B₂), detail, the arrow indicates a short longitudinal cross section through one of the marginal thickenings. Also present, near this site, is apparent spalling of fine lamellae. Scale bars: (A), (B₁) 16 mm; (B₂) 4 mm. Van Iten et al. (2019).

The specimen comprises a partial branching periderm about 40 mm long and bearing at least 16 variably curved daughter tubes. Two of the daughter tubes originate at the widest point of the parent, while the remaining daughter tubes are arrayed in single file along each side. Both the daughter and parent tubes are narrowest at the base and widen towards the tips. This pattern of branching is similar to that seen in modern Cnidarians such as the Hydrozoan Eudendrium ramosum, or Scyphozoans such as Stephanoscyphus racemosus, which Van Iten et al. regard as evidence supporting the proposed relationship between the Conularids and the Cnidarians.

The extant Scyphazoan Nausitho punctata. Chapman & Werner (1972).

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Exceptional preservation in Early Ordovician fossils from Hubei Province, China.

Fossil Lagerstätten are deposits which produce exceptional fossils, providing us with valuable insights into vanished ecosystems. There are a number of Ordovician Fossil Lagerstätten known which produce invertebrate fossils with soft tissues, providing information on organisms otherwise not seen in the fossil record. These are the Early Ordovician Fezouata Formation of Morocco, the Middle Ordovician Winneshiek Lagerstätte in northeast Iowa and the Late Ordovician Beecher’s Trilobite Bed of New York, Llanfawr Mudstone of Wales, Soom Shale of South Africa and Late Ordovician deposits from Manitoba.

In a paper published in the Chinese Science Bulletin on 17 March 2015, Andrzej Baliński of the Instytut Paleobiologii and Yuanlin Sun of the Key Laboratory of Orogenic Belts and Crustal Evolution at Peking University discuss a new Early Ordovician Fossil Lagerstätten from Hubei Province in China. These fossils come from the Fenxiang Formation, a deepwater shale, and show fossils phosphatised in a similar manner to the Burgess Shale and Chengjiang Cambrian Fossils, a form of preservation extremely rare in post-Cambrian deposits (so rare that until quite recently such preservation was not thought to be seen in post-Cambrian deposits at all). The fossils were deposited in a deepwater environment, but many are of shallow-water organisms, thought to have been moved there by a submarine landslip, in a similar way to the shallow water fossils seen in the Burgess Shale. They were deposited about 470 million years ago, slightly before the Great Ordovician Biodiversification Event, in which the Cambrian Evolutionary Fauna (dominated organisms such as Trilobites, Polychaete Worms, Monoplacophorans and Inarticulate Brachiopods) was largely replaced by the Palaeozoic Evolutionary Fuana (dominated by organisms such as Articulate Brachiopods, Crinoids, Cephalopod Molluscs and Anthozoan Corals), and contains organisms from both faunas.

The first fossils described are Linguloid Brachiopods assigned to the genus Leontiella with soft tissues preserved. Linguloids are considered to have been the first Brachiopods to have appeared, and are documented with soft tissue preservation from the Burgess Shale, but reliably interpreted soft-body preservation in post-Cambrian Linguloid Brachiopods is extremely rare, with the earliest unquestionable examples coming from the Early Lower Devonian Hunsrück Slate of Germany, and possible examples from the Devonian of England, Middle Ordovician of New York State and Late Ordovician of South Africa. The Fenxiang Brachiopods show three-dimensional preservation of the pedicle, showing details of the external morphology. Leontiella has a streamlined shell with radial ornamentation, characteristics associated with true burrowing behaviour in Brachiopods (unlike the simpler shells of the Cambrian Linguloids); the Fenxiang specimens have long, vermiform pedicles, which appears to support this, suggesting that Linguloid Brachiopods had indeed evolved true burrowing behaviour by this point.

Linguloid brachiopod Leontiella sp. with preserved pyritized vermiform pedicle. Balinski & Sun (2015).

The Fenxiang Biota also contains a variety of trace fossils, which also show evidence of burrowing behaviour not seen in Cambrian deposits. These include numerous sinusoidal horizontally-orientated cylindrical burrows 20–60 μm in diameter, tightly packed with framboid structures, thought to be replacement minerals occupying spaces which formerly contained pyrite crystals, which themselves would have been formed by bacterial decomposition of an organic infilling of the burrows, such as fecal pellets. Balinski and Sun interpret these as the burrows of free-living Nematodes, which form very similar burrows in modern environments. These traces considerably predate the first Nematode body-fossils, which are found in the Early Devonian Rhynie Chert of Scotland, and the earliest trace fossils previously ascribed to Nematodes, from the Middle Triassic of Germany. Nematodes are thought to have diversified from a common ancestor before the appearance of the earliest Arthropods and Velvet Worms, both groups which appear in the Early Cambrian, so the presence of such organisms in the Early Ordovician is not surprising, however Nematodes are not thought to have been able to adopt a burrowing lifestyle until larger burrowing and bioturbating organisms had broken up a layer of microbial matting which covered most of the seafloor in the Cambrian and prevented much oxygen from penetrating to the sediments bellow.

Sinusoidal trace fossil from the Fenxiang Formation interpreted as a Nematode burrow. Balinski & Sun (2015).

The Fenxiang Biota has also produced an upright colonial Hydroid, possibly belonging to the Haleciidae, preserved as part and counterpart on a split rock. Hydras and Medusas (Jellyfish) are thought to have been the earliest Cnidarians to appear, due to their simple body-plans and placement on genetically-based phylogenetic trees, and are expected in the fossil record very early. However numerous fossils assigned to these groups from Ediacaran, Cambrian, Ordovician and Silurian deposits have subsequently been re-assigned to different groups, leaving the earliest confidently assigned Medusas coming from the Late Carboniferous Mazon Creek Formation and the earliest known Hydras those from the Late Ordvician of Kentucky and (possibly) Wales. The Fenxiang specimen represents an advanced colonial Hydroid, the earliest known example of such an organism.

Pyritized colony of Hydroid. Balinski & Sun (2015).

The Fenxiang Biota also includes a variety of other Cnidarians, including Conulariids, an extinct group of Palaeozoic Scyphozoans, and numerous Black Corals (Antipatharia), an important group of modern Corals, particularly in deeper waters, but until know not known from the fossil record at all (though they have been predicted to have been an ancient group from genetic studies of their phylogenetic position). These Fenxiang fossils have been processed in acetic acid revealing extremely well preserved details of their anatomy, which leave little doubt on their assignment to the group.

Phosphatic coralla of Antipatharian Coral  showing basal part of a colony with crowded spines (l), spinose branch (m), and partly preserved spinose basal part of colony and erect stem (n). Balinski & Sun (2015).

The deposits also contain numerous fossils which have yet to be identified or studied in detail, including branching feather-like fossils, which may prove to be another form of colonial Hydroid, numerous Arthropod fragments, and a possible Scalidophoran Worm embryo similar to those known from Cambrian deposits in China, Russia and Australia and earliest Ordovician of the United States.

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Soft tissue preservation in Linguloid Brachiopods from the Early Ordovician Fenxiang Formation of Hubei Province, China.

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