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Giant trilobite burrows and their paleobiological significance (Lower-to-Middle Ordovician from Penha Garcia, Portugal)
No full textThe largest ever described Cruziana, more than 200 mm wide, are not uncommon in the Lower-to-Middle Ordovician Armorican Quartzite Formation, at the Ichnological Park of Penha Garcia, central Portugal. They are the most visible trace fossils of ichnocoenoses dominated by classic arthropod intrastratal burrows, tunnels, and trackways, and Skolithos piperocks in a shallow marine, transgressive siliciclastic succession. The typical “Armorican Quartzite” of the Skolithos Ichnofacies is overlaid by a sequence of alternating storm-related quartzites and pelites of the Cruziana Ichnofacies, where the Cruziana rugosa Group is far abundant and shows a unique diversity of behaviors. A quantitative comparison of the Cruziana ichnospecies from Penha Garcia with the trilobite communities from the Middle Ordovician of Canelas, where large body clusters of asaphids are common, was preliminarily performed with the aim of establishing a genetic relationship and eventual trophic migratory paths across trilobite ontogenesis. The gregarious behavior commonly found in discrete beds totally covered by Cruziana is explained under the trilobite clustering paleobiology, as detritus feeding congregations where the opportunity for scavenging cannot be ruled out. The large body size inferred for some of the Cruziana rugosa trilobite producers may be correlated with the high latitude position of Penha Garcia in the shores of Gondwana during the Ordovician times, the diversification of food resources and abundance, and the capacity to explore them and thrive in oxygen-depleted substrates, that may have resulted in “polar gigantism” among them
Ichnology of Alluvial-Fan related sequences: The example of Sarzedas Basin (Upper Miocene, UNESCO Naturtejo Geopark)
No full textTrace fossils from alluvial fan deposits were only rarely described worldwide. Here we document an association of meniscate backfilled burrows in the alluvial cone of Sarzedas. The upper Tortonian-Messinian Torre Formation is composed of syntectonic debris flows and sheet-flood facies that pass distally into fine-grained micaceous sandstones and mudstone facies. The section at Lomba de Sarzedas butte has fine-grained sandstones and very fine-grained greenish siltstone showing evidence for incipient edaphic processes and is characterized by a dense full-relief Beaconites coronus-Taenidium barretti-Scoyenia gracilis bioturbation. This bioturbate texture is inferred to record multiple phases of deposit feeding by arthropods (millipedes or insect larvae) following short-lived ephemeral flooding under semi-arid conditions and in response to a highly fluctuating water table. We compare the meniscate backfilled burrows ichnoguild of substrate-controlled, and moisture-related, mobile detritivores documented in this paper with similar ichnological assemblages from alluvial fan successions from few other regions recorded worldwide, dating back to the Middle Devonian
Evolution of Crustaceans at the edge of the end-Permian crisis: Ichnonetwork analysis of the fluvial succession of Nurra (Permian-Triassic, Sardinia, Italy)
No full textDecapod crustaceans are among the most efficient ecosystemengineers of the Phanerozoic, but the path that led to their engineering success is poorly known. The Permian-Triassic continental succession of Nurra (early Cisuralian-early Middle Triassic; Sardinia, Italy) sheds light on this obscure subject, because it preserves the oldest (Roadian) fluvial Ophiomorpha and Camborygma, ascribed to ghost shrimps (Decapoda: Axiidea, Gebiidea) and crayfishes (Decapoda: Astacidea, Parastacidea), respectively. These crustacean trace fossils are part of awellpreserved ichnofauna including Arenicolites, Diplocraterion, Helminthoidichnites, Palaeophycus, Planolites, rhizoliths, Skolithos, Spongeliomorpha, Taenidium, Treptichnus, alongside an undetermined tetrapod footprint, helical burrows and Sinusichnus-like traces. In light of the abundance of crustacean trace fossils, the Cala Viola section (Roadian-Anisian) was selected for ichnonetwork analysis. This novel approach, focusing on the topology of the association relationships of ichnotaxa, revealed six ichnoassociations, i.e., Rhizohaloes, Taenidium/Ophiomorpha, Helminthoidichnites, Palaeophycus, Skolithos and Arenicolites ichnoassociations. In addition, ichnonetwork analysis shown that Camborygma and Ophiomorpha colonised adjacent, partially overlapping fluvial subenvironments, ranging from active fluvial channels to periaquatic overbanks. As the Nurra occurrences are penecontemporaneous of the astacid/thalassinid diversification (Carboniferous-Early Permian) and coeval with the appearance of crayfishes (Middle Permian), fluvial environments played an important role in the evolution of both crayfishes and ghost shrimps. The most parsimonious explanation of the observed scenario is that astacid-thalassinid diversification happened in fluvial environments between the Carboniferous and Early Permian, while ghost shrimps invaded marine environments at the Permian-Triassic boundary. In addition, ichnonetwork analysis revealed that the ichnological system simplified across the Permian-Triassic boundary, accounting for a structured Permian ecosystem and fragmented, stressed habitats during the Early Triassic. This scenario is explained by a progressive drying trend that dramatically changed the hydrological features across the Permian-Triassic boundary. This supports the crucial role of global warming in driving the end-Permian crisis and its prolonged recovery
The ichnological importance and interest of the Geological Museum of Lisbon collections: Cladichnus lusitanicum in continental facies from the Lower Cretaceous of the Lusitanian Basin (Portugal)
No full textThe revision of the classic collections of trace fossils housed in the Geological Museum of the former Geological Survey of Portugal is bringing new information to well established ichnogenera. Through the revision of the type material of Taenidium lusitanicum Heer, 1881 and other specimens housed in the Geological Museum of Lisbon and the National Museum of Natural History and Science we reinstate the ichnospecies Cladichnus lusitanicum (Heer). This is the only ichnospecies of Cladichnus occurring in environment typical from the Scoyenia ichnofacies in otherwise typical turbidite forms
Daedalus mega-ichnosite from the Muradal Mountain (Naturtejo Global Geopark, Central Portugal): Between the Agronomic Revolution and the Ordovician Radiation
No full textThick quartzite beds with large bedding planes exposures thoroughly bioturbated with Deadalus desglandi, that can be followed for several kilometers, were discovered in the Lower Ordovician (Floian) of the Armorican Quartzite Formation at Muradal Mountain, UNESCO Naturtejo Geopark (Central Portugal). The complex architecture of this form of Daedalus is discussed and the model of “subtidal pumping”, based on the presence of a draft-fill channel in each one of the burrows, is introduced to explain the feeding pattern in “clean” quartzites. Extremely crowded monoichnospecific levels show that they were strongly controlled by shifting substrate conditions but mostly limited in time, pointing to the colonization of event beds by soft-bodied populations in very shallow marine and very dynamic settings. The magnitude of the Daedalus ichnofabric fluctuations shows that sandflat substrate colonization by the Daedalus producer after each event was intense, mostly sequential, with an exclusive and almost total occupation of the emptied ecospace. The presence of only one preserved behavioral strategy, the substrate depth affected by these structures, the high density of burrows and passive patchiness rates are characteristics of rselected populations. Such large-scale and frequent disturbance events as storms, extreme on a gradient of disturbance intensities, were responsible for some of the earliest opportunistic behaviours in the fossil record. Daedalus was among the most resilient of them in the Early Paleozoic of this part of the world
Evolution of Crustaceans at the edge of the end-Permian crisis: ichnonetwork analysis of the fluvial succession of Nurra (Permian-Triassic, Sardinia, Italy).
No full textDecapod crustaceans are among the most efficient ecosystemengineers of the Phanerozoic, but the path that led
to their engineering success is poorly known. The Permian–Triassic continental succession of Nurra (early
Cisuralian–early Middle Triassic; Sardinia, Italy) sheds light on this obscure subject, because it preserves the
oldest (Roadian) fluvial Ophiomorpha and Camborygma, ascribed to ghost shrimps (Decapoda: Axiidea, Gebiidea)
and crayfishes (Decapoda: Astacidea, Parastacidea), respectively. These crustacean trace fossils are part of awellpreserved
ichnofauna including Arenicolites, Diplocraterion, Helminthoidichnites, Palaeophycus, Planolites,
rhizoliths, Skolithos, Spongeliomorpha, Taenidium, Treptichnus, alongside an undetermined tetrapod footprint, helical
burrows and Sinusichnus-like traces.
In light of the abundance of crustacean trace fossils, the Cala Viola section (Roadian–Anisian) was selected for
ichnonetwork analysis. This novel approach, focusing on the topology of the association relationships of
ichnotaxa, revealed six ichnoassociations, i.e., Rhizohaloes, Taenidium/Ophiomorpha, Helminthoidichnites,
Palaeophycus, Skolithos and Arenicolites ichnoassociations. In addition, ichnonetwork analysis shown that
Camborygma and Ophiomorpha colonised adjacent, partially overlapping fluvial subenvironments, ranging from
active fluvial channels to periaquatic overbanks. As the Nurra occurrences are penecontemporaneous of the
astacid/thalassinid diversification (Carboniferous–Early Permian) and coeval with the appearance of crayfishes
(Middle Permian), fluvial environments played an important role in the evolution of both crayfishes and ghost
shrimps. The most parsimonious explanation of the observed scenario is that astacid–thalassinid diversification
happened in fluvial environments between the Carboniferous and Early Permian, while ghost shrimps invaded
marine environments at the Permian–Triassic boundary. In addition, ichnonetwork analysis revealed that the
ichnological system simplified across the Permian–Triassic boundary, accounting for a structured Permian ecosystem
and fragmented, stressed habitats during the Early Triassic. This scenario is explained by a progressive
drying trend that dramatically changed the hydrological features across the Permian–Triassic boundary. This supports
the crucial role of global warming in driving the end-Permian crisis and its prolonged recovery
Life in a Gilbert-type delta system: Ichnoassociations of the Ventimiglia palaeovalley and their sequence stratigraphic significance (Pliocene, NW Italy).
No full textMicrobial-related biogenic structures from the Middle Ordovician slates of Canelas (Northern Portugal)
No full textA review with the description of the low diverse ichnoassembla - ges from the slates of Valongo Formation is made for the first time. Among the organic-rich mining, simple trace fossils dominated by Planolites-like worm burrows and very rare Chondrites developed in short-termed dysoxic intervals, we describe Phycodes canelensis nov. isp. as an adaptation to store faecal pellets poorer in nutrients away from the feeding area or for cultivating bacteria. The most remarkable are very large-size, concentrically ringed, pyritized structures, developed in relation with the decomposition of orthoconic cephalopods and dissolution of their shells, which are reinterpreted now as microbialites. This study documents a dysoxic-dominated ecosystem in dependence of bacterial metabolism, still with a relative abundance of Ediacaran holdovers that was developed in the wider period of tiering complexification and diversification of ecospaces, feeding habits and optimization, with the generalized appearance of deeper deposit-feeding patterns in the offshore during the Ordovician radiation
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