Stratigraphie et sédimentologie des « Couches rouges » continentales du Jurassique-Crétacé du Haut Atlas central (Maroc) : implications paléogéographiques et géodynamiques

In several synclines of the central High Atlas, the “Redbeds” following the closure of the marine Tethyan Atlasic trough during the Middle Jurassic are constituted by three successive formations or units of continental deposits dated recently with biostratigraphical elements. Some micropaleontological markers, mainly charophytes and ostracods, allow to precise the stratigraphy in agreement with a Bathonian-?Callovian assignment for the lower unit (Guettioua Formation), and in dating the middle and upper units. The Upper Jurassic, mainly the Kimmeridgian, is developed in the lower part of the middle unit (Iouaridene Formation). The Barremian has been recognized in this middle unit and in the upper unit (Jbel Sidal Formation). The Jurassic/Cretaceous boundary is thus delimited for the first time with micropaleontological data. These new data are very significant for the Atlasic history during the Mesozoic. The basaltic flows inserted in the continental Jurassic-Cretaceous deposits of the central High Atlas result from two separate events in the Middle Jurassic and in the Barremian. The tectogenesis in the basins is characterized by a polyphase process including notably a synsedimentary tectonic activity conspicuous in the Barremian. The evidence of marine to brackish intercalations allows moreover to date the first Cretaceous transgressive event on the NW boundary of the High Atlas during the Lower Barremian and to consider an Atlantic paleogeographical interaction. SW margin of the Tethyan trough in the Lower and Middle Jurassic, the central High Atlas is merged with the margin of the central Atlantic Ocean during the Lower Cretaceous.     

Faunal turnover of marine tetrapods during the Jurassic–Cretaceous transition

Marine and terrestrial animals show a mosaic of lineage extinctions and diversifications during the Jurassic–Cretaceous transition. However, despite its potential importance in shaping animal evolution, few palaeontological studies have focussed on this interval and the possible climate and biotic drivers of its faunal turnover. In consequence evolutionary patterns in most groups are poorly understood. We use a new, large morphological dataset to examine patterns of lineage diversity and disparity (variety of form) in the marine tetrapod clade Plesiosauria, and compare these patterns with those of other organisms. Although seven plesiosaurian lineages have been hypothesised as crossing the Jurassic–Cretaceous boundary, our most parsimonious topology suggests the number was only three. The robust recovery of a novel group including most Cretaceous plesiosauroids (Xenopsaria, new clade) is instrumental in this result. Substantial plesiosaurian turnover occurred during the Jurassic–Cretaceous boundary interval, including the loss of substantial pliosaurid, and cryptoclidid diversity and disparity, followed by the radiation of Xenopsaria during the Early Cretaceous. Possible physical drivers of this turnover include climatic fluctuations that influenced oceanic productivity and diversity: Late Jurassic climates were characterised by widespread global monsoonal conditions and increased nutrient flux into the opening Atlantic‐Tethys, resulting in eutrophication and a highly productive, but taxonomically depauperate, plankton. Latest Jurassic and Early Cretaceous climates were more arid, resulting in oligotrophic ocean conditions and high taxonomic diversity of radiolarians, calcareous nannoplankton and possibly ammonoids. However, the observation of discordant extinction patterns in other marine tetrapod groups such as ichthyosaurs and marine crocodylomorphs suggests that clade‐specific factors may have been more important than overarching extrinsic drivers of faunal turnover during the Jurassic–Cretaceous boundary interval.     

A new, nearly complete stem turtle from the Jurassic of South America with implications for turtle evolution

Turtles have been known since the Upper Triassic (210Myr old); however, fossils recording the first steps of turtle evolution are scarce and often fragmentary. As a consequence, one of the main questions is whether living turtles (Testudines) originated during the Late Triassic (210Myr old) or during the Middle to Late Jurassic (ca 160Myr old). The discovery of the new fossil turtle, Condorchelys antiqua gen. et sp. nov. from the Middle to Upper Jurassic (ca 160-146Myr old) of South America (Patagonia, Argentina), presented here sheds new light on early turtle evolution. An updated cladistic analysis of turtles shows that C. antiqua and other fossil turtles are not crown turtles, but stem turtles. This cladistic analysis also shows that stem turtles were more diverse than previously thought, and that until the Middle to Upper Jurassic there were turtles without the modern jaw closure mechanism.     

Tithonian-Berriasian foraminiferal faunas from the Torinosu-type calcareous blocks of the southern Kanto Mountains, Japan: their implications for post-accretionary tectonics of Jurassic to Cretaceous terranes

The Torinosu-type limestones, having many lithologic characters showing their original deposition on shallow shelves, are widely distributed in the Jurassic to Cretaceous terranes of Japan. The foraminiferal faunas from the Jurassic to the lowermost Cretaceous of Japan were first revealed in the calcareous blocks of the southern Kanto Mountains. Distinguished microfaunas consist of 39 species including many marker species of the Upper Jurassic to Lower Cretaceous in Europe, West Asia, and North Africa such as Melathrokerion spirialis, Charentia evoluta, Freixialina planispiralis, Nautiloculina oolithica, Everticyclammina cf. virguliana, Haplophragmium lutzei and Pseudocyclammina lituus. These faunas suggest a Tithonian to Berriasian age of Torinosu-type limestones. They are contained in four tectonostratigraphic units (Kamiyozawa, Hikawa and Gozenyama Formations; Ogouchi Group) continuously accreted from Middle Jurassic to Late Cretaceous. The younger deposition age of Torinosu-type limestones than the accretion age (Bajocian to Bathonian) in the Kamiyozawa Formation and their older age than the accretion age of the Ogouchi Group (late Albian to middle Maastrichtian) are important to date the post-accretionary tectonics of Jurassic to Cretaceous terranes of Japan and to explain the emplacement process of Torinosu-type limestones.     

The palaeoxylological record of Metapodocarpoxylon libanoticum (Edwards) Dupéron-Laudoueneix et Pons and the Gondwana Late Jurassic–Early Cretaceous continental biogeography

Aim Vertebrates, palynomorphs and leaf floras each give a different picture of continental biogeography of Northern Gondwana during the Middle Jurassic–Early Cretaceous interval. A new biogeographical marker is required to get a clearer picture. Location Northern part of the Gondwana during the Middle Jurassic–Early Cretaceous interval. Methods Comparisons and correlations of wood data from the literature and new material. Results We have selected Metapodocarpoxylon Dupéron‐Laudoueneix et Pons because it has a restricted distribution, temporally and geographically; it is a well‐defined Mesozoic fossil wood monospecific genus, and there are wide‐ranging data on its distribution. Conclusions Metapodocarpoxylon distribution draws a clear latitudinal belt extending from Lebanon westward to Peru. Climate being the main factor of plant distribution at a global scale, the Metapodocarpoxylon area probably underlines a climatic belt. This has several implications, for example, choosing among different Global Circulation Models or discussing dinosaur distribution.     

New data on the colonial morphology of the Jurassic bryozoans of the class Stenolaemata

The radiation of the Jurassic bryozoans of the class Stenolaemata, which started in seas of the Bajocian and Bathonian of western Europe, is shown to be continued in basins of eastern Europe during the extensive Middle Callovian transgression. The taxonomic composition of stenolaemate bryozoans from the Jurassic of central European Russia and main features of their colonial morphology are discussed.     

Bivalves and evolutionary resilience: old skills and new strategies to recover from the P/T and T/J extinction events

Diversity dynamics among bivalves during the Triassic and Early Jurassic provides the opportunity to analyse the recovery patterns after two mass extinctions: Permian/Triassic and Triassic/Jurassic (T/J). The results presented here are based on a newly compiled worldwide genus-level database and are contrasted to the main morphological characters of the different taxonomical (orders and their constituent families and genera) and ecological groups. Many of such morphological characters are innovations appearing during the time span considered. Diversity and evolutionary rates were assessed and compared between these groups. During the Early Triassic there was a slow recovery, dominated by epifaunal taxa, the order Pectinida being the most diverse. The major post-Permian radiation took place during the Anisian, with several morphological and ecological innovations appearing and/or diversifying. The Late Triassic was a time of great diversification and ecological specialisation. Although the T/J was a true mass extinction for bivalves, it was not indiscriminate as its impact was stronger on specialised orders and not all ecological categories were equally affected. Recovery during earliest Jurassic was fast, confirming the high-evolutionary resilience of bivalve molluscs, except for groups with thick shells and tropical distribution, probably because of a biocalcification crisis.     

Re-description of a putative Early Cretaceous “teleosaurid” from France,with implications for the survival of metriorhynchids and teleosaurids across the Jurassic-Cretaceous Boundary

Thalattosuchia was a diverse clade of marine crocodylomorphs known from the Early Jurassic to the Early Cretaceous. Recent studies have hypothesized that their extinction was two-phased: (1) habitat loss near/at the Jurassic-Cretaceous boundary heavily reduced their morphofunctional diversity, particularly in Europe, while (2) climate change and a shift in marine fauna during the Early Cretaceous (either at the Valanginian-Hauterivian boundary or during the early Hauterivian) finished off the already stressed clade. Unfortunately, the Cretaceous fossil record of thalattosuchians is poor, with only one putative “teleosaurid” specimen and approximately ten metriorhynchid specimens. Here we re-describe the youngest known teleosaurid from the Cretaceous (Valanginian of south-eastern France). Originally considered to be a teleosaurid (possibly Steneosaurus), we demonstrate that it belongs to Metriorhynchidae, and a newly discovered subclade, Plesiosuchina. It differs from Plesiosuchus in the pattern of tooth enamel ornamentation and the variation in dentary alveoli size. Referring this specimen to Metriorhynchidae means there are no definitive Cretaceous teleosaurid specimens. Furthermore, it suggests that both durophagous and piscivorous teleosaurids became extinct at the end of the Jurassic. Interestingly, this is the fourth metriorhynchid lineage known to cross the Jurassic-Cretaceous boundary. As such, it would appear that the two thalattosuchian families responded very differently to the lowering sea levels at the end of the Jurassic: teleosaurids possibly became extinct, while metriorhynchids were seemingly unaffected.     

A revised ammonite zonation of the Boreal Oxfordian and its application in northeast Greenland

A revised ammonite zonation for use in the Middle–Upper Oxfordian of the Boreal province is put forward. The zonation is used to date late Jurassic sediments in the Wollaston Forland area of northeast Greenland. The sediments broadly comprise basinal mudstones and shallow marine and shoreline sandstones, which were deposited in westerly tilted fault blocks during three transgressive pulses. On the peneplaned surfaces of wide tilted fault blocks a thick sequence of tidally and fluvially influenced marine sandstones of Middle Jurassic age was deposited. In the Upper Jurassic deposition initially took place in the centre of the basin where 80 m of shoreface sandstones accumulated (Jakobsstigen Member). In the second pulse the upthrown margin of the next fault block to the west was transgressed and deposition of basinal mudstones (Bernbjerg Formation) commenced in the basin centre on the main part of the dip-slope of the eastern block. Finally the crestal areas of the block on Kuhn Ø were inundated in Kimmeridgian times, and then subsided rapidly.     

A new decapod crustacean faunule from the Middle Jurassic of north‐west France

Abstract: Decapod crustacean material collected recently from the lower Callovian (Middle Jurassic) in Maine‐et‐Loire (north‐west France) comprises two new species of prosopid and one new species of tanidromitid crabs, of the genera Nodoprosopon and Tanidromites, respectively. Also represented in this faunule is a probable paguroid anomuran, in the form of isolated chelae here assigned to the genus Orhomalus, as well as appendicular remains of unknown affinity; some of the latter might belong to prosopid crabs. These anomurans and brachyurans co‐occur with a diverse benthic fauna in limestones with abundant iron ooids; their main interest lies in the fact that they add valuable data to the rather poor record of Middle Jurassic decapod crustaceans.     

Microaerophilic Fe‐oxidizing micro‐organisms in Middle Jurassic ferruginous stromatolites and the paleoenvironmental context of their formation (Southern Carpathians,Romania)

Ferruginous stromatolites occur associated with Middle Jurassic condensed deposits in several Tethyan and peri‐Tethyan areas. The studied ferruginous stromatolites occurring in the Middle Jurassic condensed deposits of Southern Carpathians (Romania) preserve morphological, geochemical, and mineralogical data that suggest microbial iron oxidation. Based on their macrofabrics and accretion patterns, we classified stromatolites: (1) Ferruginous microstromatolites associated with hardground surfaces and forming the cortex of the macro‐oncoids and (2) Domical ferruginous stromatolites developed within the Ammonitico Rosso‐type succession disposed above the ferruginous microstromatolites (type 1). Petrographic and scanning electron microscope (SEM) examinations reveal that different types of filamentous micro‐organisms were the significant framework builders of the ferruginous stromatolitic laminae. The studied stromatolites yield a large range of δ⁵⁶Fe values, from ?0.75‰ to +0.66‰ with predominantly positive values indicating the prevalence of partial ferrous iron oxidation. The lowest negative δ⁵⁶Fe values (up to ?0.75‰) are present only in domical ferruginous stromatolites samples and point to initial iron mobilization where the Fe(II) was produced by dissimilatory Fe(III) reduction of ferric oxides by Fe(III)‐reducing bacteria. Rare‐earth elements and yttrium (REE + Y) are used to decipher the nature of the seawater during the formation of the ferruginous stromatolites. Cerium anomalies display moderate to small negative values for the ferruginous microstromatolites, indicating weakly oxygenated conditions compatible with slowly reducing environments, in contrast to the domical ferruginous stromatolites that show moderate positive Ce anomalies suggesting that they formed in deeper, anoxic–suboxic waters. The positive Eu anomalies from the studied samples suggest a diffuse hydrothermal input on the seawater during the Middle Jurassic on the sites of ferruginous stromatolite accretion. This study presents the first interpretation of REE + Y in the Middle Jurassic ferruginous stromatolites of Southern Carpathians, Romania.     

THE GENESIS OF CONDENSED SEQUENCES IN THE TETHYAN JURASSIC

Pelagic limestones of the west Sicilian Middle Jurassic are used as type examples in this examination of Tethyan condensed sequences. Two main processes were involved in the genesis of this type of deposit: stratigraphic condensation (minimal sediment input) and reworking. The lack of nannoplankton during most of the Jurassic caused stratigraphic condensation, and the particular environment in which these beds were deposited – that of topographic high – was considerably influenced by currents; thus reworking led to a further reduction in sediment thickness. The presence of algal stromatolites in certain condensed sequences and the traces of boring algae in associated ferromanganese nodules suggest deposition within the photic zone. A maximum depth of 200 metres is inferred. Many features of condensed sequences are comparable with those on Recent seamounts; these include presence of ferromanganese nodules and crusts, mixed faunas, calcarenite lenses, algal biscuits, and evidence of submarine solution and lithification. Jurassic Tethyan condensed sequences can thus be interpreted as ancient seamount deposits.     

A revision of the sauropod dinosaur genus ‘Bothriospondylus’ with a redescription of the type material of the Middle Jurassic form ‘B. madagascariensis’

Abstract: The sauropod dinosaur ‘Bothriospondylus’, originally named on the basis of Late Jurassic remains from England, is demonstrated to be invalid, and the characters used to diagnose it are shown to be obsolescent features which are widespread throughout Sauropoda. Material referred to this genus spans a temporal range from the Middle Jurassic until the early Late Cretaceous and has been described from five different countries, across three continents. These remains represent a wide array of sauropod groups, comprising non‐neosauropod eusauropods, a macronarian, titanosauriforms (including at least one definite brachiosaurid) and a rebbachisaurid. The type material of the Middle Jurassic ‘B. madagascariensis’ represents a derived non‐neosauropod eusauropod and possesses two potential autapomorphies. However, as a result of the fragmentary nature of the material and the uncertainty surrounding its association, a new taxon is not erected. Of the numerous specimens referred to ‘Bothriospondylus’, however, several remains are considered diagnostic: Ornithopsis hulkei (Early Cretaceous, UK), Lapparentosaurus madagascariensis (Middle Jurassic, Madagascar) and Nopcsaspondylus alarconensis (early Late Cretaceous, Argentina). At least three types of sauropod were present in the Bathonian (Middle Jurassic) of north‐west Madagascar, with a basal eusauropod (Archaeodontosaurus), a more derived eusauropod (‘B. madagascariensis’) and a titanosauriform (Lapparentosaurus) all approximately contemporaneous. Palaeocontinental reconstructions suggest that Middle Jurassic Madagascan sauropods would still have been capable of global biotic interchange, and this is perhaps reflected in their diverse assemblage. Re‐evaluation of these Malagasy forms has shed new light on this important time period in sauropod evolution.     

A diverse Upper Jurassic dinosaur ichnofauna from central‐west Portugal

Mateus, O. & Milàn, J. 2009: A diverse Upper Jurassic dinosaur ichnofauna from central‐west Portugal. Lethaia, Vol. 43, pp. 245–257. A newly discovered dinosaur track‐assemblage from the Upper Jurassic Lourinhã Formation (Lusitanian Basin, central‐west Portugal), comprises medium‐ to large‐sized sauropod tracks with well‐preserved impressions of soft tissue anatomy, stegosaur tracks and tracks from medium‐ to large‐sized theropods. The 400‐m‐thick Lourinhã Formation consists of mostly aluvial sediments, deposited during the early rifting of the Atlantic Ocean in the Kimmeridgian and Tithonian. The stratigraphic succession shows several shifts between flood‐plain mud and fluvial sands that favour preservation and fossilization of tracks. The studied track‐assemblage is found preserved as natural casts on the underside of a thin bivalve‐rich carbonate bed near the Tithonian–Kimmeridgian boundary. The diversity of the tracks from the new track assemblage is compared with similar faunas from the Upper Jurassic of Asturias, Spain and the Middle Jurassic Yorkshire Coast of England. The Portuguese record of Upper Jurassic dinosaur body fossils show close similarity to the track fauna from the Lourinhã Formation. □Dinosaur tracks, Lusitanian Basin, Portugal, skin impressions, Upper Jurassic.     

Archosauromorph extinction selectivity during the Triassic–Jurassic mass extinction

Many traits have been linked to extinction risk among modern vertebrates, including mode of life and body size. However, previous work has indicated there is little evidence that body size, or any other trait, was selective during past mass extinctions. Here, we investigate the impact of the Triassic–Jurassic mass extinction on early Archosauromorpha (basal dinosaurs, crocodylomorphs and their relatives) by focusing on body size and other life history traits. We built several new archosauromorph maximum‐likelihood supertrees, incorporating uncertainty in phylogenetic relationships. These supertrees were then employed as a framework to test whether extinction had a phylogenetic signal during the Triassic–Jurassic mass extinction, and whether species with certain traits were more or less likely to go extinct. We find evidence for phylogenetic signal in extinction, in that taxa were more likely to become extinct if a close relative also did. However, there is no correlation between extinction and body size, or any other tested trait. These conclusions add to previous findings that body size, and other traits, were not subject to selection during mass extinctions in closely‐related clades, although the phylogenetic signal in extinction indicates that selection may have acted on traits not investigated here.     

QUALITY OF THE TRIASSIC–JURASSIC BIVALVE FOSSIL RECORD IN NORTHWEST EUROPE

Abstract: The quality of the Triassic–Jurassic bivalve fossil record in northwest Europe has been measured using the Simple Completeness Metric (SCM). The SCM has been applied to the fossil record of total bivalve diversity and to the records of different ecological guilds. The Westbury and Lilstock Formations record high SCM values for most ecological groups. The ‘Pre‐Planorbis Beds’ of the lower Lias Group, however, witness a precipitous decline in the completeness of most guilds and emigration of taxa due to localized marine anoxia is a likely cause. Neither variation in lithofacies, shell mineralogy, sedimentary rock outcrop area, nor sequence architecture can convincingly explain the observed patterns of completeness. Our SCM data reveal that the Early Jurassic fossil record of infaunal suspension‐feeding bivalves is significantly poorer than that of epifaunal bivalves. Any differences in the apparent Rhaetian extinction rates between these two guilds should therefore be viewed with caution. Analyses of selectivity during the Late Triassic mass extinction based on studies of global databases appear robust in light of our SCM data. Nevertheless, future investigations of the Triassic–Jurassic benthic marine ecosystem undertaken at a finer‐resolution, may need to account for the poor quality of the Early Jurassic fossil records of certain ecological guilds, such as the infaunal suspension‐feeding taxa.     

The ‘Giant of Ksour’, a Middle Jurassic sauropod dinosaur from Algeria

Continental strata of Early and Middle Jurassic age are seldom-exposed, and little is known of the history of sauropod dinosaurs prior to the neosauropod radiation of the end of the Middle Jurassic. Here, we report, in the Middle Jurassic of the Occidental Saharan Atlas (Algerian High Atlas), the discovery of a skeleton, including cranial material, of a new cetiosaurid sauropod. Chebsaurus algeriensis n. g., n. sp. represents the most complete Algerian sauropod available to date, only few remains were found before. To cite this article: F. Mahammed et al., C. R. Palevol 4 (2005).     

Ophiuroid remains from the Toarcian of Sainte-Verge (Deux-Sèvres, France): paleobiological perspectives

The Toarcian sediments exposed at Sainte-Verge (Deux-Sèvres, France) are especially rich in echinoderm remains. The present paper describes and illustrates the ophiuroids. On the basis of lateral arm plates, 13 species are distinguished, including two new ones: Sinosura fasciata sp. nov. and Sinosura extensa sp. nov. Most of the recognized species have been recorded previously from the Late Toarcian and Aalenian in Germany and, to a lesser extent, from the late Early Jurassic of England and Switzerland. High similarities between the faunas of northwest Europe suggest a boreal provincialism of ophiuroids. The recognition of 13 species is comparable to the diversity known from other stratigraphic levels (Jurassic and Cretaceous) or in the richest stations of recent oceans. The species association of the Toarcian of Sainte-Verge, with two Ophiolepididae, one Ophiacanthidae, four Ophioleucidae, two Ophiodermatidae, two Ophiuridae, and one Hemieuryalidae may be compared with species associations of recent shelf, offshore environments. Such persistence of components of diversity and ecological affinities of species suggests strong evolutionary conservatism of the ophiuroids, after a rapid radiation during the earliest Jurassic. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.     

Changes in lifestyle and habitat of Zoophycos‐producing animals related to evolution of phytoplankton during the Late Mesozoic: geological evidence for the ‘benthic‐pelagic coupling model’

The trace fossil Zoophycos characterized by complex, three‐dimensional morphology with systematic internal structures occurs throughout the Phanerozoic marine sediments. The specimens of Zoophycos examined herein consist of a downward and helical spreite and are a product of the excretory behaviour of endobenthic detritus feeders. They are divided into two basic types: pre‐Jurassic and post‐Cretaceous types on the basis of whorls of spreiten in a single specimen. The pre‐Jurassic type has fewer than four whorls. In contrast, most of the post‐Cretaceous specimens exhibit spreite with multiple coils more than ten whorls. The abrupt increase in whorl number during the Cretaceous suggests that the sedentary lifestyle of the producer should change from a short‐term stay to long‐term or permanent occupation of the same burrow. Timing of the lifestyle change the Zoophycos producers seems to be closely related to the deep‐seaward migration of their habitats. The change in lifestyle and migration of Zoophycos‐producing animals during the Cretaceous might be attributable to the establishment of eutrophic bottom conditions in the deep sea. These changes seem to be associated with the flux of large amounts of phytodetrital food produced by phytoplankton, which experienced an explosive increase in species diversity during the Late Jurassic to the Late Cretaceous. The series of changes in lifestyle and habitat of the Zoophycos animals during the Late Mesozoic can serve as one piece of geological evidence for the ‘benthic‐pelagic coupling model’.     

Morphology and environment in the Jurassic Nucleatidae (Brachiopoda) from Western Tethys

Colás, J. & García Joral, F. 2011: Morphology and environment in the Jurassic Nucleatidae (Brachiopoda) from Western Tethys. Lethaia, Vol. 45, pp. 178–190. Nucleatidae (Brachiopoda, Terebratulida) are commonly considered as typical members of the Mediterranean assemblages during the Jurassic. However, nucleatids occasionally also occur in the margins of Western Tethys (Northwestern European shelf). Some of these occurrences in northeastern Spain are analysed, detecting a relation between nucleatid morphology and palaeoenvironment during the Jurassic. The validity of this relationship for the whole of the representatives of the group in the Western Tethys during the Jurassic is tested by means of morphofunctional analyses (principal components analysis and discriminant analysis), concluding that reduction of the lateral expansion of the shell is the key morphological feature whereby epioceanic and epicontinental taxa differ. This change can have functional significance because it can be interpreted as a mechanism to reduce the area exposed when the valves gape, increasing protection against harmful particles in environments characterized by higher terrigenous input. Some modifications on the systematics of the Nucleatidae at the genus level are proposed on the basis of the temporal and biogeographical distribution of these adaptations. □Brachiopods, Nucleatidae, functional morphology, adaptation, systematics, Jurassic, Spain.