Gennaeocrinus tariatensis, a new Emsian (Devonian) monobathrid crinoid from the Tarvagatay Terrane of Mongolia

Gennaeocrinus tariatensis new species is an Emsian (Devonian) monobathrid crinoid described from the Tarvagatay Terrane of Mongolia and part of the Central Asian Orogenic Belt. The Tarvagatay Terrane is an arc terrane that accreted to the southern margin of the Siberian Craton. Gennaeocrinus tariatensis was collected from the Emsian Tariat Formation, a terrigenous sequence of conglomerates, sandstones, and siltstones. Associated faunas include brachiopods, molluscs, and rare tabulate corals. Although Gennaeocrinus is well known from the Emsian–Givetian of North America, this is the first occurrence of the genus outside Laurussia. Mongolia is a large country with many terranes having varied paleogeographic, sedimentological, and tectonic histories; but reports of Paleozoic echinoderms are rare. The crinoid occurrence from the Tariat Formation is from the same age as previously described Emsian crinoids from the Chuluum Formation but differs significantly in sedimentology, paleogeography, and paleolatitude. UUID: http://zoobank.org/d87cb083-4360-41e5-ac90-1b8ef625a31d

2. Ancient reefs and islands

Reefs in deep geological time have been built by a succession of different kinds of life: plant, bacterial, and animal. Stromatolites and bryozoans were major reef-builders that persist today in minor or non-reef-building forms, sponges built entire reefs and are still important reef components, while several groups of major reef-builders flourished for a while and then became extinct: archaeocyathids which were similar to sponges, and coral-like forms including rugose and tabulate corals. Today’s reef-builders, cnidarian corals, appeared well after the great Permian-Triassic extinction event. All of these groups deposited vast quantities of limestone rock on which they live, often visible today as low mountain ranges. Reefs grow to the surface but not beyond, but upon them sand and sediments may build up, forming an island that attracts plants, then birds and other terrestrial forms of life. The sediments become cemented with the aid of rainwater too, and ‘low islands’ develop. Many islands also show their old, central volcanoes, resulting in the vast array of different combinations of coral island type. Today, however, there is a coral reef crisis due to overexploitation of a reef’s rich resources, from pollution of several kinds, and climate change.

Unusual shallow water Devonian coral community from Queensland and its recent analogues from the inshore Great Barrier Reef

Palaeozoic coral communities were dominated by two extinct coral groups: Tabulata and Rugosa. Whilst they are not closely related to modern Scleractinia, they are morphologically convergent, displaying many morphological characters that allow comparisons between recent and ancient coral reef communities. The extensive shallow-water reef communities of the Devonian were generally dominated by stromatoporoid sponges, with corals occupying deeper environments. Here, we describe an unusual, shallow water coral reef community from the Middle Devonian (Givetian, approx. 385 Ma) of the Fanning River area, Queensland, Australia. The coral community is dominated by tabulate corals, but also includes solitary and occasionally colonial rugose corals. Tabulate corals most commonly exhibit foliose and massive morphologies, but encrusting and branching growth forms also occur. The depositional environment was characterized by a shallow water depth, moderate hydrodynamic energy, high sedimentation rate, and high turbidity. Since these environmental factors influence the morphological composition of modern coral communities, we hypothesize that similar environments may result in morphologically equivalent coral assemblages throughout the Phanerozoic. To test this idea, we qualitatively compare the Fanning River reefs with modern scleractinian coral assemblages in a similar environmental setting at Magnetic Island. Both reefs are located in a shallow water less than 10 m deep, with high sediment flux, moderate wave energy, and generally high turbidity. Like Fanning River, Magnetic Island coral communities are dominated by foliose morphologies, with contributions from massive and branching forms. The Fanning River reef, together with previously identified Silurian and Devonian mesophotic coral ecosystems, suggest that Palaeozoic coral assemblages may share many functional characteristics with modern scleractinian reefs in similar environments. Therefore, the geological record of inshore, high turbidity-adapted coral communities can be traced back as far as 385 Ma.

First report of Devonian corals from the Bitlis-Pötürge Massif (SE Turkey): a rare occurrence of corals on the northern margin of Gondwana

The Bitlis-Pötürge Massif of SE Turkey is a metamorphic belt separating the Arabian Plate from the Taurides. It includes a non-metamorphic Palaeozoic sequence that contains locally fossiliferous strata. Here is reported for the first time an assemblage of Upper Devonian rugose and tabulate corals from the Meydan Formation, composed of the rugose Frechastraea schafferi (PENECKE), Peneckiella cf. teicherti HILL, Pseudopexiphyllum supradevonicum (PENECKE), and Macgeea desioi VON SCHOUPPÉ, and the tabulate Thamnopora reticulata (DE BLAINVILLE), Alveolites ex. gr. suborbicularis and Scoliopora sp. The rugose corals suggest a Late Frasnian age. The palaeobiogeographic affinities of corals are discussed. The species F. schafferi and the genus Pseudopexiphyllum –so far only reported from Turkey, Iran and Afghanistan– are probably limited to the northern margin of Gondwana and therefore diagnostic for this palaeogeographic area. Until now, the northern margin of Gondwana yielded very few Upper Devonian corals so this occurrence in SE Turkey is particularly important to estimate the relationship between these corals and the ones from the northern margin of the Palaeotethys Ocean.

The “earliest tabulate corals” are not tabulates

Putative tabulate-like corals dating to the Cambrian Explosion are not true tabulates. Early Ordovician fossils identified as Lichenaria and previously accepted as the earliest tabulate corals actually belong to Amsassia, which may be a calcareous alga. The earliest definite tabulates appeared in the latest Middle Ordovician as part of the Great Ordovician Biodiversification Event, prior to the earliest confirmed occurrence of tabulate species that do belong to Lichenaria in the Late Ordovician. With Cambrian (Epoch 2) tabulate-like fossils being separated from the appearance of true tabulates by a time span of ~50 m.y., a direct phylogenetic connection is unlikely. Thus, the prevailing understanding of the origin and evolutionary history of tabulate corals needs to be reconsidered. The appearance of both major groups of Paleozoic corals, tabulates and rugosans, at the same time on separate paleocontinents must be taken into account in determining biological and geological factors involved in the Great Ordovician Biodiversification Event.

Supplemental Material: The “earliest tabulate corals” are not tabulates

Table S1 (locations, stratigraphic positions, and ages of specimens, and references and annotations).<br>

Supplemental Material: The “earliest tabulate corals” are not tabulates

Table S1 (locations, stratigraphic positions, and ages of specimens, and references and annotations).<br>

Halysis Høeg, 1932 — an ancestral tabulate coral from the Ordos Basin, North China

The problematic calcareous microfossil Halysis is abundant in the Middle Ordovician Darriwilian Stage of the western edge of the Ordos Basin, North China. The rich and well-preserved specimens of Halysis in this area facilitate detailed studies for its skeletal construction and tube microstructure. Halysis differs from calcified cyanobacteria and calcareous red and green algae in morphology, skeletal construction and microstructure, as well as reproduction mode. Halysis typically consists of multiple juxtaposed parallel tubes arranged in sheets (‘multiple-tube’ type) or is just composed of one tube (‘single-tube’ type). In ‘multiple-tube’ Halysis, tube fission by bifurcation results from the insertion of a microcrystalline wall at the center of a mother tube. This study demonstrates for the first time that the tube walls of Halysis have a laminofibrous (fibronormal) microstructure, composed of fibrous calcite perpendicular to wall surface, and recognizes the ‘single-tube’ type Halysis composed of one tube; in addition, for the first time, this study finds out that ‘multiple-tube’ Halysis develops buddings from the conjunction of two tubes and ‘single-tube’ Halysis shows wide-angle Y-shaped branchings. Based on these findings, this study further compares Halysis with tabulate corals. Halysis appears stratigraphically earlier than Catenipora and Aulopora, and has a smaller tube size. ‘Multiple-tube’ Halysis resembles Catenipora and ‘single-tube’ Halysis resembles Aulopora in skeletal construction and microstructure, and in their tube walls of laminofibrous microstructure composed of fibrous calcite perpendicular to the tube wall surface. Catenipora and Halysis are both characterized by the absence of septal spines. The similarities suggest that Halysis may be the ancestor of Catenipora-like and Aulopora-like tabulate corals.