Vent and mound rugose coral associations from the Middle Devonian of Hamar Laghdad (Anti-Atlas, Morocco)

Peculiar associations of small, solitary, deep-water rugose corals are described from the Middle Devonian buildups situated in the easternmost part of Hamar Laghdad area of southern Morocco. The most of them are monospecific and consist of simplified taxon “Amplexus” florescens but one is polyspecific and composed of specimens belonging to four different species representing three families. These rugosan associations form isolated nest-like aggregations where numerous densely packed specimens are arranged mostly in life position. The polyspecific and two monospecific associations are interpreted as growing in close proximity to venting fields. They reveal a unique “calice-in-calice” recolonization pattern expressed by successive settlement of juvenile specimens in the calice of dead individuals. This pattern was presumably a consequence of selective survival of coral larvae settling in extreme vent habitats. Although, the “calice-in-calice” pattern is common in both, mono- and polyspecific associations, there are differences expressed in the character of larval attachments and various types of the calice fillings. The trophic interaction between corals and ostracods is discussed. Additionally, associations of “Amplexus” florescens, not displaying “calice-in-calice” pattern of growth have been found within the mound where polyspecific association occurs. These are interpreted as growing away from venting fields. Comparisons of Amplexus-type coral faunas with the other North African and European corals allow the classification of these ampleximorph rugosan taxa as characteristic biotic components of the Middle Devonian mound environments influenced by venting activity. Two new genera and species, Weyeraia prima and Vesiculolasma erfoudi, are introduced.     

Epizoans immured in the heterocoral Oligophylloides maroccanus Weyer, 2017: a unique record from the Famennian (Upper Devonian) of Morocco

Exceptionally well-preserved proximal parts of colonies of the late Famennian heterocoral Oligophylloides maroccanus Weyer, 2017 with immured epizoans are described here from the Jebel Bou Ifarherioun ridge of the eastern Anti-Atlas, Morocco. This is the first evidence of unique syn vivo interactions between a heterocoral and numerous epizoans, that is the colonial tabulate corals Zemmourella? sp. and Aulopora? sp.; solitary rugose corals Czarnockia? sp. and Gorizdronia? sp.; and other juvenile, undeterminable solitary rugosans, crinoids, as well as microbial structures. Detailed analysis of sectioned specimens allowed mutual interactions to be traced during growth of the host and infesting encrusting taxa. The studied associations show that the epizoans must have settled on the proximal parts of Oligophylloides in places devoid of soft tissue. The encrusted proximal portions of the colonies show that soft tissue of the heterocoral could have retracted and expanded again, fouling and immuring dead epizoans. The process of bioimmuration is perfectly marked by thin layers of microbial encrustations developing on the epibiont skeletons prior to their overgrowth by the skeleton of the heterocoral. The studied encrustations seem to be widespread, but the association provided the epizoans with additional substrate for encrustation, as well as an elevated position above the seafloor, beneficial for access to nutrients. We suggest that the host bioimmured the encrusters after their death, because of noticeable microbial encrustations and veneers of sediment, a lack of malformations, relatively rapid growth and aggressive activity of epizoans.     

Hydrothermal vent myodocopid ostracods from the Eifelian (Middle Devonian) of southern Morocco

A monospecific assemblage of myodocopid ostracods has been found in the Middle Devonian of a unique hydrothermal vent system of Hamar Laghdad (eastern Anti-Atlas, southern Morocco), which developed over a submarine eruption of basaltic rocks. This fauna has been recovered from a neptunian dyke representing the sediment infill of an Eifelian venting fissure discovered in the central part of Hamar Laghdad. The assemblage consists of thousands of relatively large shells forming a coquina layer in which the valves are disarticulated, perfectly washed, well sorted and stacked into each other. Their orientation points to transport due to fluids migrating in the vent system. The ostracod specimens, on the base of the general outline, the presence of rostrum and rostral incisure is assigned to the order Myodocopida. The new genus and species Hamaroconcha kornickeri is proposed, most likely representing a new family. Its carapace morphology gives no clear clue to its mode of life; however, a relatively long rostral incisure may suggest that frontal appendages of this species were sufficient for active swimming. Therefore, a nectobenthic lifestyle is postulated for H. kornickeri nov. gen., nov. sp. Isotope data from the sediment infill provide evidence for the activity of hydrothermal fluids.     

Body size of orthoconic cephalopods from the late Silurian and Devonian of the Anti‐Atlas (Morocco)

Fluctuations in body size of orthoconic cephalopods are reported from late Silurian to Late Devonian sediments at several locations in the Tafilalt and in the Dra‐Valley (Anti‐Atlas, Morocco). The combination of measurements of diameters and apical angles allows the reconstruction of their total conch size (length and volume), which revealed a strongly right‐skewed size distribution with an average length of 278 mm, while the largest Devonian actinocerids exceeded 2 m. Within the examined groups (Actinocerida, Orthocerida, Pseudorthocerida), there is no uniform trend, but rather frequent fluctuations with maximum sizes in the late Lochkovian and early Emsian. Body size decreased in times of extinction events, while stable periods are mostly associated with a size increase. Additionally, conch size correlates well with gamma diversity and global δ¹³C values. Furthermore, the apical angle and septal diameter of orthocones appear to correlate, but only when their mean values are compared across beds.     

A cyanolichen from the Lower Devonian Rhynie chert

The 400 million-year-old Rhynie chert has provided a wealth of information about various types of fungal interactions that existed in this Early Devonian paleoecosystem. In this paper we report the first unequivocal evidence of a lichen symbiosis from the Rhynie chert. Specimens of a new genus, Winfrenatia, consist of a thallus of superimposed layers of aseptate hyphae and, on the upper surface, numerous uniform depressions. Extending into the base of each depression are hyphae that form a three-dimensional netlike structure. Enclosed within each of the net spaces is a coccoid cyanobacterium, each cell of which is surrounded by a thick sheath. These photobiont cells divide in three planes, resulting in cell clusters of up to perhaps 64 individuals. The photobiont is parasitized by the fungus in the base of each net as new cyanobacterial cells are formed distally. Reproduction is by endospores and soredia. Affinities of the mycobiont appear closest to members of the Zygomycetes, while the photobiont is most similar to coccoid cyanobacteria of the Gloeocapsa and Chroococcidiopsis types. We speculate that this cyanobacterial symbiosis was well adapted to exploit and colonize new ecological niches, especially in the periodically desiccated environment postulated for the Rhynie chert paleoecosystem.     

Lower Middle Devonian,Eifelian, crinoids from central Guangxi,South China

The extensive Devonian marine deposits of South China have yielded few articulated crinoid cups or theca. Two Eifelian specimens, from the Gupa Member, are the first ones reported from the Yingtang Formation, Eifelian, from the Ma’anshan section, Guangxi, South China. The new taxon Guangxicrinus xiangzhouensis n. gen. n. sp. is the first report of a marsupiocrinid in China, extending the paleogeographic range of the family into the Paleotethys and the stratigraphic range of the family upward from the upper Silurian into the lower Middle Devonian, Eifelian. The occurrence of Halocrinites sp. is the third occurrence of a cupressocrinitid in China and extends the paleogeographic range from Yunnan to Guangxi.     

First selenosteid placoderms from the eastern Anti‐Atlas of Morocco; osteology,phylogeny and palaeogeographical implications

Abstract: A new placoderm assemblage is reported from the Kellwasser facies of the eastern Anti‐Atlas, Morocco. This is the first record of an abundant Frasnian placoderm assemblage from Africa. The following new selenosteid taxa are described: Draconichthys elegans gen. et sp. nov., Enseosteus marocanensis sp. nov. and Walterosteus lelievrei sp. nov. In addition, material of Rhinosteus cf. parvulus is figured and described for the first time from Gondwana. The genera Enseosteus, Rhinosteus and Walterosteus are reviewed. ‘Wildungenichthys’ is regarded as a junior subjective synonym of Walterosteus. The new material and a revision of the taxa from Bad Wildungen, Germany, are the basis for a new phylogenetic analysis of the selenosteid arthrodires. The monophyly of the selenosteids is confirmed. The North American selenosteids are a sister group of Moroccan and European selenosteids, excluding Pachyosteus. The Moroccan vertebrate assemblage resembles that of Bad Wildungen. This supports the close palaeogeographical positions of Gondwana and Laurussia during the Late Devonian and indicates that biogeographical barriers for placoderms that could have separated the two assemblages were absent.     

The northern most Emsian crinoids known, a Devonian fauna from the Chuluun Formation, Shine Jinst area, Southern Mongolia

The most northerly known Emsian crinoids were located at approximately 45° to 50° N latitude. They are the first Devonian crinoid cups discovered in Mongolia. Specimens are reported from excellent exposures of the informally designated crinoidal beds in the upper part of the stratotype section of the Chuluun Formation, between N44° 22.119', E99° 27.130' and N44° 22.201', E99° 26.906', near the Tsakhir Well, in the foothills south of Tsagaan Khaalga Mountain, Shine Jinst area, southern Mongolia. All specimens are crushed, altered by low-grade metamorphism, and ossicles flake as they weather. Five genera are present including a new genus of the Periechocrinidae, two indeterminant camerates, an undesignated new species of Cyathocrinites, and one indeterminant crinoid. These genera agree with a middle Emsian age previously assigned to the upper part of the Chuluun Formation on the basis of brachiopods and conodonts. They show affinity to European and North American Emsian faunas.     

Tube foot preservation in the Devonian crinoid Codiacrinus from the Lower Devonian Hunsrück Slate,Germany

Fossilized tube feet are described on Codiacrinus schultzei Follmann from the Lower Devonian Hunsrück Slate of Germany. This is the first definitive proof of tube feet on any fossil crinoid. Three lightly pyritized, flattened tube feet are preserved in a single interray of this cladid crinoid. The tube feet were at least 7 mm long. Their preservation is very similar to the tube feet reported previously from a Hunsrück ophiuroid, except that the Codiacrinus tube feet have small papillae, similar to living crinoids.     

Infestation of Middle Devonian (Givetian) camerate crinoids by platyceratid gastropods and its implications for the nature of their biotic interaction

One of the classic examples of biotic interactions preserved in the fossil record is that between crinoids and infesting platyceratid gastropods. This relationship, spanning an interval from the Middle Ordovician to the end of the Permian, is recognized by the firm attachment and positioning of platyceratids over the anal vent of their hosts. Several hypotheses have been proposed to explain this interaction; the most widely accepted is that the gastropods were coprophagous commensals, feeding on crinoid excrement without any significant detriment to their hosts. The purpose of this investigation was to test this hypothesis. Two species of Middle Devonian camerate (Monobathrida, Compsocrinina) crinoids, Gennaeocrinus variabilis Kesling & Smith 1962 and Corocrinus calypso (Hall 1862), were used in this investigation. The data consisted of 426 individuals of G. variabilis collected near Rockport, Michigan, 30 of which were infested, and 188 individuals of C. calypso collected near Arkona, Ontario, Canada, of which 25 were infested. Length and volume were measured for each crinoid to determine whether a significant difference existed in the size of infested versus uninfested individuals. The results indicated that for both species of crinoids individuals infested by snails were significantly smaller than uninfested individuals (p < 0.05). We explored a variety of scenarios to explain this pattern and conclude that they falsify the null hypothesis that the crinoid-gastropod relationship was strictly commensal. The smaller size of the infested crinoids is interpreted as a consequence of nutrient-stealing by the parasitic gastropods, a strategy that finds analogs in modern seas. Moreover, the absence of platyceratids on the largest crinoids suggests that large size may have inferred immunity from lasting infestation.     

Signatures of hydrocarbon venting in a Middle Devonian Carbonate Mound (Hollard Mound) at the Hamar Laghdad (Antiatlas, Morocco)

Summary The Middle Devonian Hollard Mud Mound is situated in the eastern Hamar Laghdad, which is a small mountain range in the Tafilalt in SE Morocco. In contrast to the well known Lower Devonian Kess-Kess mounds, the Hollard Mound is of Middle Devonian age. The facies in the core of this mud mound differs from that of the other parts of the mound, and exhibits signatures of ancient hydrocarbon venting. The carbonate phases of the core facies are derived from the oxidation of vent fluids and consist of clotted micrite, a cryptocrystalline carbonate associated with spheres of uncertain origin, and a calcitic rim cement (rim cement B). These vent carbonates show δ¹³C values in the range of −11 to −20% PDB indicating that some of their carbon is derived from isotopically light hydrocarbons. Fossiliferous micrite has been affected by hydrocarbon venting in the proximity of the vent site, which is indicated by intermediate δ¹³C values between vent carbonates and not affected sediments. Bivalves occur in dense populations within the core facies. They form autochthonous shell accumulations and are almost exclusively articulated. it is likely that these bivalves were dependent on chemosynthesis similar to their counterparts at modern vents. The vent deposits also exhibit an unusual prasinophyte assemblage, which might have been linked to the specific nutrient availability at the vent site. The ancient vent site is characterized by an enhanced carbonate precipitation and rapid lithification. The latter is corroborated by the three-dimensional preservation of phytoplankton (prasinophytes and acritarchs) and the occurrence of stromatactoid pores. An early phase of carbonate corrosion predating the formation of vent carbonates affected the fossiliferous micrite of the core facies and is thought to be related to a phase of H₂S-rich venting.     

The oldest Gondwanan cephalopod mandibles (Hangenberg Black Shale,Late Devonian) and the mid‐Palaeozoic rise of jaws

It is widely accepted that the effects of global sea‐level changes at the transition from the Devonian to the Carboniferous are recorded in deposits on the shelf of northern Gondwana. These latest Devonian strata had been thought to be poor in fossils due to the Hangenberg mass extinction. In the Ma'der (eastern Anti‐Atlas), however, the Hangenberg Black Shale claystones (latest Famennian) are rich in exceptionally preserved fossils displaying the remains of non‐mineralized structures. The diversity in animal species of these strata is, however, low. Remarkably, the organic‐rich claystones have yielded abundant remains of Ammonoidea preserved with their jaws, both in situ and isolated. This is important because previously, the jaws of only one of the main Devonian ammonoid clades had been found (Frasnian Gephuroceratina). Here, we describe four types of jaws of which two could be assigned confidently to the Order Clymeniida and to the Suborder Tornoceratina. These findings imply that chitinous normal‐type jaws were likely to have already been present at the origin of the whole clade Ammonoidea, i.e. in the early Emsian (or earlier). Vertebrate jaws evolved prior to the Early Devonian origin of ammonoids. The temporal succession of evolutionary events suggests that it could have been the indirect positive selection pressure towards strong (and thus preservable) jaws since defensive structures of potential prey animals would otherwise have made them inaccessible to jawless predators in the course of the mid‐Palaeozoic marine revolution. In this respect, our findings reflect the macroecological changes that occurred in the Devonian. [Correction added on 28 July 2016 after first online publication: In the Abstract, the sentence “Vertebrate jaws probably … in the Early Devonian” was amended]     

Pseudoplanktonic lifestyle of the Triassic crinoid Traumatocrinus from Southwest China

Colonies of Traumatocrinus (Echinodermata, Crinoidea) attached to driftwood from the lower Upper Triassic (Carnian) Xiaowa Formation of the Guanling area (Guizhou, Southwest China) document a pseudoplanktonic lifestyle for this specialized offshoot of the otherwise benthic Middle Triassic Encrinidae. After the end-Carnian decline of Traumatocrinus, its ecological niche was subsumed in Norian by genera derived from another benthic family (Holocrinidae) with convergent morphological modifications. After the Toarcian (Lower Jurassic), this niche disappeared, possibly due to the emergence of wood-boring bivalves.     

A new Middle Devonian gasterocomid crinoid from central Turkey and revision of the Gasterocomidae

A juvenile cup, disarticulated arm plates, and columnals of the crinoid Arachnocrinus sarizensis n. sp. are described from the Eastern Taurus Mountains of central Turkey. This is the first Paleozoic crinoid based on a cup and arm plates reported from Turkey. Suggested revision of the Gasterocomidae includes transfer of Arachnocrinus and Ancyrocrinus to the family and rejection of Kopficrinus from the family. The stratigraphic range of Arachnocrinus is extended upward into the Middle Devonian from the Early Devonian. The Devonian of Turkey is of special interest because it includes Laurasian and Gondwanan components on different tectonic blocks. The paleogeographic range of Arachnocrinus is extended from the North American plate onto the Anatolian block, which would have been located on the southern edge of the Paleotethys Sea in the Middle Devonian in a shelf basin off the northern coast of Gondwana at approximately 42° south latitude.     

Survival of crinoid stems following decapitation: evidence from the Ordovician and palaeobiological implications

It was recently discovered that the stems of extant crinoids may survive after detachment of the crown, presumably feeding by the absorption of nutrients through the ectoderm. Previously, only one analogous, albeit morphologically dissimilar, pattern of crownless survival has been recognized from the fossil record. Certain Upper Ordovician (Cincinnatian) crinoid pluricolumnals from Kentucky, Ohio and Indiana, derived from the disparids Cincinnaticrinus spp., have rounded terminations reminiscent of some modern bourgueticrinid overgrowths. Such specimens have hitherto been interpreted as distal terminations of mature individuals that have become detached from their attachment structures and taken to an eleutherozoic existence. However, it is considered more probable that they represent overgrowths of the column following predatory decapitation. If this new interpretation is correct, then post-decapitation survival of crinoid stems is now recognized for most of the history of the crinoids, 'lethal' predation on crinoid crowns occurred at least as early as the Late Ordovician and ancient crinoid populations can no longer be determined merely by counting crowns.     

Lower Devonian Polyplacophora from New South Wales, Australia

Silicified polyplacophorans are common in the Lower Devonian Garra Formation in New South Wales. Four taxa occur within the lower 237 m of the formation at 14 horizons associated with an abundant and diverse fauna. Chelodes calceoloides Etheridge ranges through the section. New taxa are Chelodes cordatus sp. nov., Acutichiton depressolatus sp. nov., and Jugochiton patulus gen. and sp. nov. A single plate of an indeterminate genus occurs in the lower portion of the Camelford Limestone.     

Restudy of the Early Devonian rugose coral Xystriphylloides from South China

Early Devonian rugose coral Xystriphylloides in South China is restudied from the perspective of its taxonomic definition, biostratigraphy, paleoecology, and implication for the Yujiang Event. The diagnostic characters of the genus are clarified and its taxonomic position is also revised. In particular the septa of Xystriphylloides are shown to be fibrous rather than trabeculate. Xystriphylloides distinctus Yu n. sp. is described. Species of Xystriphylloides are widely distributed in South China and North Vietnam, so they are useful for regional biostratigraphic correlation and regional geological mapping. As an important biostrome builder, Xystriphylloides became extinct below the base of the nothoperbonus Conodont Zone, so it can be considered as one of the important pieces of evidence for recognizing the first episode of the Early Devonian Emsian Yujiang Event, which is also significant for studying paleoecology and event stratigraphy.     

The youngest African clymeniids (Ammonoidea, Late Devonian) – failed survivors of the Hangenberg Event

A co-occurrence of the clymeniid Postclymenia evoluta Schmidt, 1924 and the goniatite Acutimitoceras hilarum Korn, 2002 is reported from the Anti-Atlas of Morocco. Both species occur in the same limestone horizon within the Acutimitoceras prorsum Zone, that has yielded an exclusive conodont fauna of the Upper praesulcata Zone (latest Devonian, above the Hangenberg Black Shale). This record is firm evidence that some clymeniids survived the global Hangenberg Event, but soon later became extinct without descendants.     

Orthid brachiopods from the Lower and Middle Devonian of northeastern Russia

Brachiopods of the order Orthida from the Lower and Middle Devonian of northeastern Russia: Skenidium diversus Baranov (family Skenidiidae); Datnia gen. nov., with the type species D. asiatica sp. nov. (subfamily Prokopiinae); Janzhinshinia gen. nov., with the type species J. datnensis sp. nov. (subfamily Isorthinae); Cortezorthis chobotchalensis (Alekseeva) (subfamily Cortezorthinae); Elenia gen. nov., with the type species E. gerensis sp. nov. (family Dicoelosiidae); Seimtchania communis (family Seimtchaniidae); Simakovia gen. nov., with the type species S. rara sp. nov. (family Draboviidae); Schizophoria distenta sp. nov., S. grande Baranov, S. striatula (Schlotheim) (family Schizophoriinae); and Hypsomionia sinsera Baranov (family Hypsomioniidae) are described.     

<Emphasis Type="Italic">Oredezhosteus</Emphasis>, a new psammosteid genus (Heterostraci,Psammosteiformes) from the Lower Frasnian (Upper Devonian) of the Main Devonian Field

A new psammosteid, Oredezhosteus kuleshovi gen. et sp. nov., from the Amata Regional Stage (Lower Frasnian) of the Leningrad Region is described. In addition, Psammosteus livonicus Obruchev from beds of the same age from Latvia is included in the new genus. The major diagnostic characters distinguishing Oredezhosteus gen. nov. from Psammosteus Agassiz are the large rounded striated tubercles, which cover more than half width of the branchials, and the long base of the branchial plates.