Lower Ordovician Fezouata Research Articles

Post-Cambrian survival of the tubicolous scalidophoran Selkirkia.

Scalidophoran worms represent common infaunal components of early and middle Cambrian Burgess Shale-type fossil biotas. Early scalidophorans resemble extant priapulids based on overall morphology, but the genus Selkirkia represents the earliest record of tube dwelling for the group. Despite its ubiquitous presence in exceptional marine deposits, whether the exclusively Cambrian occurrence of Selkirkia reflects its entire evolutionary history or is affected by taphonomic biases remains unresolved. Here, we demonstrate the post-Cambrian survival of Selkirkia based on new material from the Lower Ordovician Fezouata Shale biota of Morocco. The discovery of Selkirkia in the Fezouata Shale extends the biostratigraphic range of the genus by 25 million years and its palaeobiogeographic occurrence to the high latitudes of Gondwana, strengthens the evolutionary links between Cambrian and Ordovician Burgess Shale-type biotas and increases scalidophoran diversity for the Fezouata Shale biota otherwise consisting exclusively of the palaeoscolecid Palaeoscolex? tenensis. The tube of Selkirkia underwent negligible external change for over 40 million years, indicating a high degree of morphological stasis during the Early Palaeozoic. A tubicolous mode of life is rare among extant priapulids and expressed only in Maccabeus, which forms a delicate tube from agglutinated plant debris, unlike the macroscopic secreted cuticular tube of Selkirkia.

Early developmental stages of a Lower Ordovician marrellid from Morocco suggest simple ontogenetic niche differentiation in early euarthropods

Early developmental stages of euarthropods are exceptionally rare in the fossil record. This hampers our understanding of the biology, phylogeny, and development of this extremely diverse metazoan group. Herein, we use classical paleontological methods in combination with synchrotron X-ray microtomography to explore the morphology in ca. 480 million-year-old early developmental stages of the Lower Ordovician Fezouata Shale marrellid euarthropod. These stages range between 3.8 and 5.3 mm in length and are characterized by three distinct pairs of gently curved spines that projects from the head shield. The first pair of cephalic appendages are represented by uniramous antenullae of a sensory function. The second pair of cephalic appendages is robust, and had an anchoring or stabilizing function. The third cephalic appendage pair is composed of long cylindrical podomeres and was used for walking. The trunk appendages are biramous and consist of an endopod and a lamellate exopod. Two anterior trunk endopods are composed of long slender podomeres and were used for walking, while the more posterior trunk endopods bear robust endites and associated setae and were used for food gathering. The trunk of the earliest developmental stages is composed of thirteen segments, in contrast to more than 22 segments in the adult trunk. The similar appendage morphology and differentiation along the body is evident in adult individuals of the Fezouata marrellid, suggesting these different developmental stages shared similar methods of locomotion and food processing. Given that adults and juveniles are often preserved in the same or nearby sites, the niche differentiation between these life stages would be the result of the absolute smaller appendage size in immature stages compared to larger adults, effectively differentiating the size of food resources consumed by each. In addition, the delicate setae present in the posterior trunk appendages of early developmental stages might have been used to capture smaller food particles. This simple mode of ontogenetic niche differentiation might have been common in the early diverging euarthropod groups.

Novel marrellomorph moulting behaviour preserved in the Lower Ordovician Fezouata Shale, Morocco

Exoskeleton moulting is the process of shedding the old exoskeleton to enable growth, development and repair, representing a crucial recurrent event in the life histories of all euarthropods. The fossil record of moulting allows us to interpret the evolution of this important behaviour and its impact on the evolutionary trajectories of extinct and extant euarthropods. Current knowledge of Palaeozoic euarthropod moulting relates largely to trilobites, with fewer examples known for non-mineralised extinct taxa from early in euarthropod evolutionary history. We describe exuviae from a marrellid marrellomorph found abundantly in the Early Ordovician Fezouata Shale Lagerstätte of Morocco, which allow a novel reconstruction, the second ever, of marrellid moulting behaviours. We identify the moulting suture location, describe preserved moulting assemblages, and suggest how its moulting behaviours are adaptive to its morphology. Several specimens represent complete and nearly complete assemblages and additional disarticulated specimens confirm the suture line location. The suture line is located between the mediolateral and posterolateral spine pairs, dividing the cephalic shield into anterior and posterior parts. The Fezouata marrellid likely exited the exoskeleton during exuviation using posterior and upwards movements, analogous in terms of movement to lobster-like extant arthropods. The suture line is comparable in the closely related marrellid Mimetaster, and distinctive from that of another marrellid, Marrella splendens, which has an exuvial opening at the anterior of the cephalic shield and exited the exoskeleton anteriorly. This difference in moulting behaviour as compared to Marrella is likely adaptive to the greater complexity of the Fezouata marrellid, with upwards rather than forwards movement presumably providing a more favourable angle for the extraction of complex spines. This description of the moulting behaviours and related morphological features of marrellomorphs expands our understanding of this crucial characteristic in extinct euarthropods.

A new nektaspid euarthropod from the Lower Ordovician strata of Morocco

AbstractNektaspids are Palaeozoic non-biomineralized euarthropods that were at the peak of their diversity during the Cambrian Period. Post-Cambrian nektaspids are a low-diversity group with only a few species described so far. Here we describeTariccoia tazagurtensis, a new species of small-bodied nektaspid from the Lower Ordovician Fezouata Shale of Morocco. The new species differs from the type (and only other known) species from the Ordovician strata of Sardinia (Italy),Tariccoia arrusensis, in possessing more pointed genal angles, a cephalon with marginal rim, a pygidium with anterior margin curved forwards, a rounded posterior margin, and longer and more curved thoracic tergites. The two specimens ofT. tazagurtensissp. nov. show remains of digestive glands that are comparable to those seen in the Cambrian nektaspidNaraoia. The rare occurrence ofT. tazagurtensissp. nov. in the Fezouata Shale and the distribution of other liwiids suggest that these liwiids were originally minor members of open-marine communities during the Cambrian Period, and migrated into colder brackish or restricted seas during the Ordovician Period.

Upper Ordovician planktic and benthic graptolites and a possible hydroid from the Tafilalt Biota, southeastern Morocco

Abstract Upper Ordovician planktic and benthic graptolites are generally rare in North Africa. Four localities in southern Morocco have yielded graptolitic material from the top of the First Bani Group and the Lower Ktaoua, Upper Tiouririne and Upper Ktaoua formations, the lithostratigraphic units that contain the Tafilalt Biota. Three species of planktic graptolite (in the genera Climacograptus , Diplograptus ? and Neodiplograptus ), six species of benthic graptolite (in the genera Dendrograptus , Callograptus , Ptilograptus and ‘ Dictyonema ’) and one probable hydroid ( Webbyites ? sp.) are described from these sites. Two species are new: ‘ Dictyonema ’ khadijae sp. nov. and ‘ Dictyonema ’ villasi sp. nov. Another probable hydroid, a Plumalina -like form from the Lower Ordovician Fezouata Formation, is also illustrated. Some of the Tafilalt graptolites are similar to Bohemian species, indicating faunal links between the regions during the Late Ordovician. The graptolite dating of some isolated localities helps to evaluate the chronostratigraphic and lithostratigraphic assignment of those outcrops, implying an earlier appearance of the ‘ Dendrocystites fauna’ (echinoderm-dominated: c. Sandbian 2–Katian 1) and a late placement for the ‘ Declivolithus fauna’ (trilobite-dominated: c. Katian 2).

Large trilobites in a stress-free Early Ordovician environment

AbstractUnderstanding variations in body size is essential for deciphering the response of an organism to its surrounding environmental conditions and its ecological adaptations. In modern environments, large marine animals are mostly found in cold waters. However, numerous parameters can influence body-size variations other than temperatures, such as oxygenation, nutrient availability, predation or physical disturbances by storms. Here, we investigate trilobite size variations in the Lower Ordovician Fezouata Shale deposited in a cold-water environment. Trilobite assemblages dominated by small- to normal-sized specimens that are a few centimetres in length are found in proximal and intermediate settings, while those comprising larger taxa more than 20 cm in length are found in the most distal environment of the Fezouata Shale. Drill core material from distal settings shows that sedimentary rocks hosting large trilobites preservedin situare extensively bioturbated with a high diversity of trace fossils, indicating that oxygen and nutrients were available in this environment. In intermediate and shallow settings, bioturbation is less extensive and shallower in depth. The rarity of storm events (minimal physical disturbance) and the lack of predators in deep environments in comparison to shallower settings would also have helped trilobites attain larger body sizes. This highly resolved spatial study investigating the effects of numerous biotic and abiotic parameters on body size has wider implications for the understanding of size fluctuations over geological time.

Taxonomy and evolution of the protomonaxonid sponge family Piraniidae

The protomonaxonid sponge Pirania is an iconic member of the Burgess Shale community, but recent discoveries show that piraniids are morphologically diverse and also occur in Ordovician strata. Here we establish three new piraniid genera on the basis of Ordovician material from China, Wales, Scotland and Morocco: Auraeopirania gen. nov., Cannapirania gen. nov. and Pellipirania gen. nov. We also establish eight new species: Pirania? peregrinata sp. nov. (Lower Ordovician Ningkuo Formation, China); P.? ericia sp. nov. (Lower Ordovician Afon Gam Biota, Wales); Auraeopirania pinwyddeni gen. et sp. nov. (Middle Ordovician Llanfallteg Biota, Wales); A. pykitia gen. et sp. nov. (Upper Ordovician, Scotland); A. sciurucauda gen. et sp. nov. (Early Ordovician, China); Cannapirania canna gen. et sp. nov. (Middle Ordovician Llanfawr Mudstones, Wales); C. vermiformis gen. et sp. nov. (Upper Ordovician Anji Biota, China); and Pellipirania gloria gen. et sp. nov. (Lower Ordovician Fezouata Biota, Morocco). Piraniids have now been widely reported (South China, Avalonia, Laurentia and Gondwana) from Ordovician strata, but in Cambrian strata have been documented only from the Burgess Shale. The Burgess Shale species Pirania muricata appears to be among the most derived members of the Piraniidae, implying a substantial hidden Cambrian diversity of piraniids. Over the family's history there is a tendency for species to become smaller and inhabit deeper-water environments.

Digestive and appendicular soft-parts, with behavioural implications, in a large Ordovician trilobite from the Fezouata Lagerst\xe4tte, Morocco

Trilobites were one of the most successful groups of marine arthropods during the Palaeozoic era, yet their soft-part anatomy is only known from a few exceptionally-preserved specimens found in a handful of localities from the Cambrian to the Devonian. This is because, even if the sclerotized appendages were not destroyed during early taphonomic stages, they are often overprinted by the three-dimensional, mineralised exoskeleton. Inferences about the ventral anatomy and behavioural activities of trilobites can also be derived from the ichnological record, which suggests that most Cruziana and Rusophycus trace fossils were possibly produced by the actions of trilobites. Three specimens of the asaphid trilobite Megistaspis (Ekeraspis) hammondi, have been discovered in the Lower Ordovician Fezouata Konservat-Lagerstätte of southern Morocco, preserving appendages and digestive tract. The digestive structures include a crop with digestive caeca, while the appendages display exopodal setae and slight heteropody (cephalic endopods larger and more spinose than thoracic and pygidial ones). The combination of these digestive structures and the heteropody has never been described together among trilobites, and the latter could assist in the understanding of the production of certain comb-like traces of the Cruziana rugosa group, which are extraordinarily abundant on the shallow marine shelves around Gondwana.

Biostratigraphic and palaeoenvironmental controls on the trilobite associations from the Lower Ordovician Fezouata Shale of the central Anti-Atlas, Morocco

Trilobites are a major component of both biomineralized and soft-bodied assemblages of the Fezouata Biota, central Anti-Atlas, Morocco. Trilobite taxa of the Fezouata Shale (Tremadocian–Floian) in the Zagora area are typical of Lower Ordovician communities from shallow shelf environments, and show strong affinities with Early Ordovician assemblages from the Montagne Noire (southern France). Dramatic variations in both taxonomic composition and taphonomic attributes, together with the sedimentological facies changes, allow us to discriminate the palaeoenvironmental versus stratigraphic control on trilobite assemblages. Three communities are described along an onshore–offshore profile, namely the pilekiid-bavarillid, Agerina and raphiophorid biofacies. Additionally, three stratigraphic assemblages are identified: assemblage 1 is confined to the late Tremadocian, assemblage 2 ranges from late Tremadocian to middle Floian and assemblage 3 is restricted to the Floian. The higher diversity of some levels is explained by storm-induced inputs of debris from taxa living in adjacent environments. Additionally, control of relative seal level variation on some peculiarities of the trilobite fauna (specific endemicity, lack of some expected taxa) is evidenced in the Fezouata Shale. Finally, temporary dysoxic events are highlighted by preliminary geochemical analyses, probably allowing episodic exceptional preservation.

Palaeoscolecid worms from the Lower Ordovician Fezouata Lagerstätte, Morocco: Palaeoecological and palaeogeographical implications

The Lower Ordovician Fezouata Lagerstätte from Morocco (central Anti-Atlas, Zagora area) has yielded abundant and diverse soft-bodied fossils. Most described taxa were epibenthic or pelagic, so that little is known about the endobenthic components of the fauna. Here we report the discovery of a locally abundant element of the biota, a palaeoscolecid worm, which may have played an important ecological role in the community. Palaeoscolecids had a long, annulated body with an eversible tooth-bearing pharynx. They probably represent stem priapulids, but unlike them, they were protected by biomineralized (phosphatic) microscopic plates covering most of the body. These sclerites are commonly found isolated within SSF assemblages, thus considerably extending the fossil record of the group that ranges from the Cambrian Series 2 (Stage 3) to the upper Silurian. Like priapulids, palaeoscolecids might have been important bioturbators, contributing to the substrate colonization in the lower Palaeozoic. The discovery of abundant material (38 specimens) in the Fezouata Shale (Lower Ordovician, Morocco) allows us to reconsider their possible lifestyle, habitat and feeding habits. All the specimens belong to Palaeoscolex? tenensis, a species previously only known from a fragment of cuticle from the Floian of Bohemia (Czech Republic). Some exhibit remains of the gut and aboral spines, features that are highly informative with regard to the ecology of these extinct organisms, but rarely preserved. The phosphatic nature of the plates is demonstrated by compositional analyses and interpreted with regard to the diagenetic context of the Fezouata Shale as primary. We also hypothesize that (at least) some palaeoscolecids were makers of Tomaculum-type ichnofossils, which are elongate clusters of faecal pellets, and show that they ingested a notable amount of sediment during the normal course of feeding. The presence of Palaeoscolex? tenensis in the Lower Ordovician of Morocco further documents the great faunal similarities between Perunica and northern Gondwana at that time.

A new aglaspidid euarthropod with a six-segmented trunk from the Lower Ordovician Fezouata Konservat-Lagerstätte, Morocco

AbstractA new euarthropod with an uncommon morphology,Brachyaglaspis singularisgen. et sp. nov., is described from the Early Ordovician (middle Floian) Fezouata biota of Morocco. The presence of a pair of postventral plates, widely attached to each other and located under the posterior-most trunk tergite and the base of the tailspine, indicates a phylogenetic relationship with the enigmatic group Aglaspidida. The overall morphology ofBrachyaglaspismost closely resembles that of the ‘Ordovician-type’ aglaspidids, more specifically the late Cambrian – Early Ordovician genusTremaglaspis. However, the presence of a prominent cephalon and only six trunk tergites in the new genus deviates from the organization of all other known aglaspidid species, notably extending the known range of morphological disparity of the group. A taxonomic revision of this euarthropod group indicates that the most accurate name and authorship combination correspond to Aglaspidida Walcott, 1912.

The Lower Ordovician Fezouata Konservat-Lagerstätte from Morocco: Age, environment and evolutionary perspectives

The Lower Ordovician Fezouata Konservat-Lagerstätte from southern Morocco has been one of the major palaeontological discoveries of the last decade. It provides a unique insight into one of the most critical periods in the evolution of marine life: the Cambrian–Ordovician transition. However, its potential for deciphering key trends in animal diversification was hitherto largely limited by major uncertainties concerning its stratigraphic position, age and environmental setting. Based on extensive fieldwork, fossil evidence, and facies recognition, our study provides clarification on these three crucial issues. Exceptional preservation is limited to two intervals within the Fezouata Shale. Graptolites indicate a late Tremadocian age for the Fezouata Konservat-Lagerstätte as a whole, which is supported by biostratigraphical evidence provided by acritarchs. Sedimentological features and reconstructed patterns of relative sea-level changes indicate relatively shallow-water environmental conditions, under distal storm influence, in an offshore to lower shoreface siliciclastic ramp setting. The Fezouata Biota represents a unique and exceptional window into the palaeobiodiversity in open-marine conditions, thus contrasting with the other Ordovician Konservat-Lagerstätten presently known. In our analyses of this new set of data, we pave the way for accurate temporal, faunal and environmental comparisons with other Lower Palaeozoic Konservat-Lagerstätten, and unlock the full potential of the Fezouata Biota to better understand the processes and scenarios of early animal radiations.