A Homerian Silurian Arthropod had a Unique Brood Caring Mode

Tiny individuals attached to a new Silurian arthropod suggest a unique mode of brood care

Authors:

Briggs et al

Abstract:

The ∼430-My-old Herefordshire, United Kingdom, Lagerstätte has yielded a diversity of remarkably preserved invertebrates, many of which provide fundamental insights into the evolutionary history and ecology of particular taxa. Here we report a new arthropod with 10 tiny arthropods tethered to its tergites by long individual threads. The head of the host, which is covered by a shield that projects anteriorly, bears a long stout uniramous antenna and a chelate limb followed by two biramous appendages. The trunk comprises 11 segments, all bearing limbs and covered by tergites with long slender lateral spines. A short telson bears long parallel cerci. Our phylogenetic analysis resolves the new arthropod as a stem-group mandibulate. The evidence suggests that the tethered individuals are juveniles and the association represents a complex brooding behavior. Alternative possibilities—that the tethered individuals represent a different epizoic or parasitic arthropod—appear less likely.

This is how a Cambrian Trilobite Hunted

The Cambrian Period, which occurred between 541 million and 485 million years ago, is an important point in evolutionary history where most of the major groups of animals first appear in the fossil record. Often called the "Cambrian explosion," fossils from this time provide glimpses into evolutionary history as the world's ecosystems were rapidly diversifying. Most fossils preserve the physical remains of organisms and their structure; however, geologists and paleobiologists at the University of Missouri recently collaborated to study fossils that reveal the behaviors of predators preserved as traces in ancient sediments. Thus, fossils from southeast Missouri are helping scientists unlock clues about the behaviors of these predators and their interactions with their prey. Evidence shows that these ancient organisms were behaviorally sophisticated, tailoring their attacks for effectiveness.

Trilobites are a fossil group of extinct marine invertebrate animals with external skeletons (see photo). As predators and scavengers, they flourished in the Cambrian period and were very prominent in the oceans that once were located in Missouri.

"The Saint Francois Mountains in southeastern Missouri have been the focus of geological research for decades and were once islands in the Cambrian ocean," said Kevin Shelton, professor of geological sciences in the MU College of Arts and Science. "I've worked as a geologist studying ore deposits in the area for more than 30 years. In that time, I've run across thousands of fossilized trilobite burrows. It is rare that we get to study the activities of 500 million-year-old organisms, yet the fossils in this locality are helping us determine how these organisms behaved."

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Cambrian Arthropod Waptia From Burgess Shale Brooded its Eggs

Long before kangaroos carried their joeys in their pouches and honey bees nurtured their young in hives, there was the 508-million-year-old Waptia. Little is known about the shrimp-like creature first discovered in the renowned Canadian Burgess Shale fossil deposit a century ago, but recent analysis by scientists from the University of Toronto, Royal Ontario Museum, and Centre national de la recherche scientifique has uncovered eggs with embryos preserved within the body of the animal. It is the oldest example of brood care in the fossil record.

"As the oldest direct evidence of a creature caring for its offspring, the discovery adds another piece to our understanding of brood care practices during the Cambrian Explosion, a period of rapid evolutionary development when most major animal groups appear in the fossil record," said Jean-Bernard Caron, curator of invertebrate palaeontology at the Royal Ontario Museum and associate professor in the Departments of Earth Sciences and Ecology & Evolutionary Biology at the University of Toronto.

Caron, along with Jean Vannier at the Centre national de la recherche scientifique in Lyon, France, describe the findings in a study published December 17 in Current Biology.

Waptia fieldensis is an early arthropod, belonging to a group of animals that includes lobsters and crayfish. It had a two-part structure covering the front segment of its body near the head, known as a bivalved carapace. Caron and Vannier believe the carapace played a fundamental role in how the creature practised brood care.

"Clusters of egg-shaped objects are evident in five of the many specimens we observed, all located on the underside of the carapace and alongside the anterior third of the body," said Caron.

The clusters are grouped in a single layer on each side of the body with no or limited overlapping among the eggs. In some specimens, eggs are equidistant from each other, while in others, some are are closer together, probably reflecting variations in the angle of burial and movement during burial. The maximum number of eggs preserved per per individuals probably reached 24.

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The BRAAAAAAAAAAAINNNNNSSSSS of Cambrian Euarhropod Fuxianhuia protensa

Preservational Pathways of Corresponding Brains of a Cambrian Euarthropod

Authors:

Ma et al

Abstract:

The record of arthropod body fossils is traceable back to the “Cambrian explosion,” marked by the appearance of most major animal phyla. Exceptional preservation provides crucial evidence for panarthropod early radiation. However, due to limited representation in the fossil record of internal anatomy, particularly the CNS, studies usually rely on exoskeletal and appendicular morphology. Recent studies [ 1–3 ] show that despite extreme morphological disparities, euarthropod CNS evolution appears to have been remarkably conservative. This conclusion is supported by descriptions from Cambrian panarthropods of neural structures that contribute to understanding early evolution of nervous systems and resolving controversies about segmental homologies [ 4–12 ]. However, the rarity of fossilized CNSs, even when exoskeletons and appendages show high levels of integrity, brought into question data reproducibility because all but one of the aforementioned studies were based on single specimens [ 13 ]. Foremost among objections is the lack of taphonomic explanation for exceptional preservation of a tissue that some see as too prone to decay to be fossilized. Here we describe newly discovered specimens of the Chengjiang euarthropod Fuxianhuia protensa with fossilized brains revealing matching profiles, allowing rigorous testing of the reproducibility of cerebral structures. Their geochemical analyses provide crucial insights of taphonomic pathways for brain preservation, ranging from uniform carbon compressions to complete pyritization, revealing that neural tissue was initially preserved as carbonaceous film and subsequently pyritized. This mode of preservation is consistent with the taphonomic pathways of gross anatomy, indicating that no special mode is required for fossilization of labile neural tissue.

Yawunik kootenayi: a new Leanchoiliid Arthropod From Cambrian British Columbia

A large new leanchoiliid from the Burgess Shale and the influence of inapplicable states on stem arthropod phylogeny

Authors:

Aria et al

Abstract:

Characterized by atypical frontalmost appendages, leanchoiliids are early arthropods whose phylogenetic placement has been much debated. Morphological interpretations have differed, some of which concern critical characters such as the number of eyes and head appendages, but methodological approaches also have diverged. Here, we describe a new leanchoiliid, Yawunik kootenayi gen. et sp. nov., based on 42 specimens from the newly discovered Marble Canyon locality of the Burgess Shale (Kootenay National Park, British Columbia; middle Cambrian). This new morphotype demonstrates the presence of a four-segmented head in leanchoiliids, along with two small antero-median eyes in addition to lateral eyes. Yawunik is characterized by a 12-segmented trunk and a carinate, lanceolate telson adorned with minute spines. The ‘great appendages’ of the animal bear teeth on their two distal rami, which would have enhanced their ability to grasp prey. Attitudes of specimens, resulting from burial at multiple aspects of bedding, suggest the ‘great appendages’ were flexible and capable of antero-posterior rotation. We also discuss the nature of intersegmental tissues and filaments present within the ‘great appendages’. Our phylogenetic analyses extend the monophyly of leanchoiliids to include Haikoucaris and Yohoia in a new clade, the Cheiromorpha nom. nov. (within Heptopodomera nom. nov.). Other nodes are poorly resolved unless implied weights are used, and in this case, the topology is critically sensitive to the coding prerogative of inapplicable states (NAs). Both the traditional ‘Arachnomorpha’ hypothesis (NAs as additional states) and the more recently favoured ‘Artiopoda + Crustacea’ (NAs as uncertainties) were obtained using the same data set and outgroup. This result stresses, first, the historical importance of polarization over data content in scenarios of early arthropod evolution, and second, a pressing need to investigate the impacts of coding inapplicables, especially given the inflating effect of implied weights.

Evidence of Arthropod Herbivory and Detrivory From Bolsovian/Asturian Pennsylvanian Carboniferous Britain

HERBIVOROUS AND DETRITIVOROUS ARTHROPOD TRACE FOSSILS ASSOCIATED WITH SUBHUMID VEGETATION IN THE MIDDLE PENNSYLVANIAN OF SOUTHERN BRITAIN

Authors:

Falcon-Lang et al

Abstract:

We describe plant–arthropod associations from the Middle Pennsylvanian (late Bolsovian–early Asturian) Pennant Sandstone Formation of southern Britain. Our material comprises calcified cordaitaleans and tree-fern axes, preserved in braided channel deposits, and interpreted as remains of subhumid riparian vegetation distinct from that of coeval coal swamps. The first plant–arthropod association, attributed to herbivorous insects, comprises cambial damage to cordaitalean leafy branches, resulting in traumatic wound response. The second and most widespread association, attributable to detritivorous oribatid mites, includes tunnels and galleries containing widely scattered, clustered, or densely packed microcoprolites within the inner root mantle of marattialean tree ferns and cordaitalean trunks and branches. Diameter data for tunnels and microcoprolites are multimodal, recording four or five instars of oribatid mites that parallel instar-based fecal pellet and body lengths in modern taxa. The third association attributed, possibly, to an arthropleurid, comprises a single, very large (19 × 14 mm) coprolite. Included plant fragments support a previous conjecture that arborescent lycopsids formed part of this iconic arthropod's diet. Mucus-lined burrows within the macrocoprolite imply that fecal material was processed by annelids. The high diversity and frequency of plant–arthropod associations are unusual for Mid-Pennsylvanian time, and may reflect previously undetected interactions in those ecosystems that lay outside “coal forest swamps.”

Aegirocassis benmoulae: a 2+ Meter (!!!) Long, Filter Feeding Anomalocaridid From Tremadocian Ordovician Morocco

Anomalocaridid trunk limb homology revealed by a giant filter-feeder with paired flaps

Authors:

Van Roy et al

Abstract:

Exceptionally preserved fossils from the Palaeozoic era provide crucial insights into arthropod evolution, with recent discoveries bringing phylogeny and character homology into sharp focus. Integral to such studies are anomalocaridids, a clade of stem arthropods whose remarkable morphology illuminates early arthropod relationships and Cambrian ecology. Although recent work has focused on the anomalocaridid head, the nature of their trunk has been debated widely. Here we describe new anomalocaridid specimens from the Early Ordovician Fezouata Biota of Morocco, which not only show well-preserved head appendages providing key ecological data, but also elucidate the nature of anomalocaridid trunk flaps, resolving their homology with arthropod trunk limbs. The new material shows that each trunk segment bears a separate dorsal and ventral pair of flaps, with a series of setal blades attached at the base of the dorsal flaps. Comparisons with other stem lineage arthropods indicate that anomalocaridid ventral flaps are homologous with lobopodous walking limbs and the endopod of the euarthropod biramous limb, whereas the dorsal flaps and associated setal blades are homologous with the flaps of gilled lobopodians (for example, Kerygmachela kierkegaardi, Pambdelurion whittingtoni) and exites of the ‘Cambrian biramous limb’ . This evidence shows that anomalocaridids represent a stage before the fusion of exite and endopod into the ‘Cambrian biramous limb’, confirming their basal placement in the euarthropod stem, rather than in the arthropod crown or with cycloneuralian worms. Unlike other anomalocaridids, the Fezouata taxon combines head appendages convergently adapted for filter-feeding with an unprecedented body length exceeding 2 m, indicating a new direction in the feeding ecology of the clade. The evolution of giant filter-feeding anomalocaridids may reflect the establishment of highly developed planktic ecosystems during the Great Ordovician Biodiversification Event.

Ordovician Eoharpes benignensis Trilobites Showed Gregarious Behaviour Hiding

SHELTERED GREGARIOUS BEHAVIOR OF MIDDLE ORDOVICIAN HARPETID TRILOBITES

Authors:

Fatka et al

Abstract:

The presence of six articulated exoskeletons of late holaspid specimens of the rare harpetid Eoharpes benignensis entombed under a pygidial shield of the large asaphid trilobite Nobiliasaphus repulsus from the Middle Ordovician Dobrotivá Formation of the Prague Basin, Czech Republic is interpreted as a unimodal monotaxic trilobite cluster. The sheltered preservation of the trilobites may be explained as; (1) hiding behavior associated with predation pressure; (2) storm disturbance; or (3) molting associated with feeding. It is herein suggested that these Middle Ordovician holaspid trilobites deliberately entered the restricted space under a large isolated asaphid trilobite pygidial shield to find a refuge and shared the space within restricted shelters with conspecifics. The completeness of all specimens of the rare taxon Eoharpes, combined with the presence of more than one individual in this restricted space, excludes the possibility of transportation by bottom currents. This exceptional find represents an example of “frozen behavior” and provides a new insight in the life strategy of Middle Ordovician benthic trilobites. Attack abatement, e.g., avoidance and dilution effects, is for the first time proposed as a possible explanation for this example of sheltered gregarious behavior in trilobites.

A Eurypterid Lagerstätte From Pridoli Silurian Pennsylvania

A NEW EURYPTERID LAGERSTÄTTE FROM THE UPPER SILURIAN OF PENNSYLVANIA

Authors:

Vrazo et al

Abstract:

Eurypterids are generally rare in the fossil record, but occasionally occur in abundance. The genus Eurypterus, in particular, is well known from certain upper Silurian Lagerstätten of the northern Appalachian basin (New York and Ontario), but occurs far less frequently in the central and southern Appalachian basin (Pennsylvania, Maryland, and West Virginia, respectively). The recent discovery of an exceptionally preserved mass assemblage of Eurypterus in the upper Tonoloway Formation (upper Ludlow–Přídolí) of Pennsylvania provides new information on the behavior and life habitat of the genus in this region. Eurypterids at this locality are found in thinly laminated, calcareous shale deposited within the lower intertidal to shallow subtidal zone of a coastal mudflat or sabkha. Rare associated fauna of limited diversity, and evaporitic and desiccation features in associated beds, suggest a stressed environment with variable salinity and possible hypoxic conditions. Most eurypterids are disarticulated and fragmentary, but several fully articulated, exceptionally preserved specimens are present. Exoskeletal features and taphonomic indices values indicate a molt rather than death assemblage, and the presence of arthropod trackways suggests that Eurypterus sp. may have molted en masse in the vicinity of the burial site. Sequence stratigraphic interpretation of the site suggests that preservation of eurypterid remains is the result of occupation of ephemeral environmental (salinity/oxygen) conditions during a transgression. The occurrence of this new Lagerstätte within the upper Silurian succession of the central Appalachians, an interval which had heretofore yielded only rare, fragmentary remains, indicates that eurypterids were more prevalent in this region than previously thought.

Falcatamacaris: a Non-trilobite Artiopodan Arthropod From Cambrian Utah

A rare non-trilobite artiopodan from the Guzhangian (Cambrian Series 3) Weeks Formation Konservat-Lagerstätte in Utah, USA

Authors:

Ortega-Hernández et al

Abstract:

We describe a weakly biomineralized non-trilobite artiopodan arthropod from the Guzhangian Weeks Formation of Utah. Falcatamacaris bellua gen. et sp. nov. is typified by a thin calcitic cuticle, broad cephalon without eyes or dorsal ecdysial sutures, an elongate trunk with distinctively sickle-shaped pleural spines and a long tailspine with a bifurcate termination. The precise affinities of Falcatamacaris gen. nov. are problematic due to the presence of unique features within Artiopoda, such as the peculiar morphology of the pleural and posterior regions of the trunk. Possible affinities with aglaspidid-like arthropods and concilitergans are discussed based on the possession of 11 trunk tergites, edge-to-edge articulations and overall body spinosity. The new taxon highlights the importance of the Weeks Formation Konservat-Lagerstätte for further understanding the diversity of extinct arthropod groups in the upper Cambrian.

Evolution of the Eyes of Two Very Different Trilobites

Eyes and vision in the coeval Furongian trilobites Sphaerophthalmus alatus (Boeck, 1938) and Ctenopyge (Mesoctenopyge) tumida Westergård, 1922, from Bornholm, Denmark

Authors:

Schoenemann et al

Abstract:

The two olenid species Sphaerophthalmus alatus (Boeck, 1838) and Ctenopyge (Mesoctenopyge) tumida Westergård, 1922, occur together in the Ctenopyge tumida Zone (Zone 19) of the Furongian of Scandinavia. Material from Bornholm, Denmark, forms the basis of this study of the morphology and partial ontogeny of the eyes. The eyes of both species are directed laterally and have virtually panoramic vision, looking out sideways like those of a rabbit. The eye of S. alatus is comparatively smaller, with fewer lenses and a larger eye parameter; calculations show that this trilobite was adapted for dim light intensity, possibly suggesting a vagrant benthic habit. Ctenopyge (Mesoctenopyge) tumida, with a smaller eye parameter, was adapted for a higher light intensity, and this trilobite was most likely a pelagic swimmer. The two species, although preserved together, inhabited different levels in the water column.

Cambrian Trilobites From Argentina

Early middle Cambrian trilobites from La Laja Formation, Cerro El Molle, Precordillera of western Argentina

Authors:

Pratt et al

Abstract:

A tectonically undeformed portion of the lower part of La Laja Formation is exposed at Cerro El Molle near San Juan, Precordillera of western Argentina. It consists of shallow-water, variably argillaceous lime mudstone and sporadically interbedded bioclastic grainstone deposited in an inner shelf setting. The El Estero Member and the basal 0.2 m of the Soldano Member contain a trilobite fauna of olenelloids and ‘simple' ptychoparioids indicative of the early Cambrian (series 2, stage 4; Dyeran stage of Laurentia). The succeeding 50 m of the lower Soldano Member yield trilobites characteristic of the early middle Cambrian (series 3, stage 5; Delamaran stage of Laurentia). In ascending order of occurrence, Amecephalus arrojosensis, Kochiella maxeyi and Eokochaspis nodosa, along with several other taxa, including Ptychobaba n. gen. (type species Ptychoparella buttsi), belong to the traditional lower Plagiura–Poliella Biozone. However, while this fauna is similar to that of the Great Basin, the nominative species of the Eokochaspsis nodosa and overlying Amecephalus arrojosensis biozones recognized in southern Nevada occur in reverse order in the Soldano Member. This suggests that the ranges of these species overlap, thereby reducing the temporal resolution in the Precordillera into a combined Amecephalus arrojosensis–Eokochaspis nodosa Biozone. Argillaceous lime mudstones at the top yield Mexicella mexicana, indicative of the Mexicella mexicana Biozone recognized in the Great Basin, which is equivalent to the traditional Albertella Biozone of Laurentia. Because corynexochids are almost absent, the low-diversity ‘kochaspid'-dominated biofacies appears to typify the platform interior. The fauna is entirely Laurentian in composition, reinforcing notions of a close proximity of Cuyania to Laurentia during the Cambrian that enabled faunal migration and interchange. The absence of a late early Cambrian to early middle Cambrian hiatus correlative with the Hawke Bay Event, however, suggests no close affinity to the Iapetus-facing margin of eastern Laurentia.

Ordovician Trilobites From Argentina

Early Ordovician trilobites from the Nazareno Area, northwestern Argentina

Authors:

Tortello et al

Abstract:

The upper part of the Santa Rosita Formation (Ordovician, Tremadocian) in the Nazareno area, Cordillera Oriental, northwestern Argentina, records the vertical passage of high-energy, shallow water platform environments to offshore settings. Eighteen trilobite species are described from this locality for the first time. Although the taxa from the lower part of the succession (Leptoplastides sp., Asaphellus sp.) are scarce and non-age diagnostic, those from the upper part include diverse assemblages partially assigned to the late Tremadocian Notopeltis orthometopa Zone. Systematic descriptions of several species (Geragnostus nesossii Harrington and Leanza, G. callaveiformis Harrington and Leanza, Asaphellus jujuanus Harrington, Notopeltis orthometopa [Harrington], Mekynophrys nanna Harrington, Ceratopyge forficuloides Harrington and Leanza, Apatokephalus tibicen Přibyl and Vanĕk) are improved, the genus Nileus Dalman (including N. australis n. sp.) is first reported from the Tremadocian of western Gondwana, and new species of Asaphellus Callaway (A. nazarenensis n. sp.), Conophrys Callaway, and Apatokephalus Brøgger are described. The trilobites have their closest affinities with faunas from Norway and Sweden. Notopeltis orthometopa and Mekynophrys nanna are restricted to the uppermost part of the succession, well above the first records of most other trilobites recognized.

Ordovician Trilobites From Greenland

Early Ordovician (Skullrockian) trilobites of the Antiklinalbugt Formation, northeast Greenland, and their biostratigraphic significance

Authors:

McCobb et al

Abstract:

The Antiklinalbugt Formation of northeast Greenland comprises peritidal to subtidal carbonate sediments, deposited in shallow shelf settings during an early Tremadocian transgressive-regressive megacycle. The succession of shales and microbial, muddy and grainy limestone, with minor dolostone at the base and top, terminates at the cryptic Fimbulfjeld disconformity. The formation has yielded trilobites collected on Ella Ø, Albert Heim Bjerge, and Kap Weber by C. Poulsen (1920s and 1930s), J. W. Cowie and P. J. Adams (1950s), and during recent field studies in 2000 and 2001. The fauna includes dimeropygids Tulepyge cowiei and T. tesella n. spp., hystricurids Millardicurus and Hystricurus, and several species of Symphysurina. Micragnostus chiushuensis (Kobayashi, 1931) is rare, as are Chasbellus sp., Clelandia sp., and Lunacrania?. The presence of several Symphysurina species places the Antiklinalbugt Formation within the Symphysurina Zone. Chasbellus indicates the upper (lower Ordovician) part of the Symphysurina Zone for the lower upper Antiklinalbugt Formation. Conodonts place the middle lower formation in the Cordylodus intermedius conodont Biozone, the lower upper part in the Cordylodus angulatus conodont Biozone and the uppermost part in the Rossodus manitouensis conodont Biozone. This combined fauna is characteristic of the upper Skullrockian Stage of the Ibexian Series, with the lower part of the Antiklinalbugt Formation lying within the uppermost Cambrian of North America, and the upper part within the lower Ordovician. The entire formation lies within the global Tremadocian Stage of the early Ordovician.

Catalog of Organisms on Bobble-nosed Trilobites

While most fossil invertebrates manage to completely fly under the radar when it comes to popular culture (it's not as if we're drowning under cartoon depictions of euthycarcinoids or eldoniids), one group that will often get a passing nod is the trilobites. Any depiction of early animal life worth its salt is going to feature a couple of these crunchy bugs scurrying about. Nevertheless, the range of varieties of trilobite shown will generally be low, and will usually be something similar to Olenellus or Elrathia. Seeing as trilobites persisted for hundreds of millions of years, it should be no surprise that their actual diversity was much higher.

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a 3d Video Reconstruction of a 410 million Year old Pragian/Lochkovian Devonian Arachnid

Researchers from The University of Manchester and the Museum für Naturkunde, Berlin, used exceptionally preserved fossils from the Natural History Museum in London to create the video showing the most likely walking gait of the animal; the study is published in a special issue of the Journal of Paleontology today (Wednesday).

The scientists used the fossils - thin slices of rock showing the animal's cross-section - to work out the range of motion in the limbs of this ancient, extinct early relative of the spiders. From this, and comparisons to living arachnids, the researchers used an open source computer graphic program called Blender to create the video showing the animals walking.

"When it comes to early life on land, long before our ancestors came out of the sea, these early arachnids were top dog of the food chain," said author Dr Russell Garwood, a palaeontologist in the University of Manchester's School of Earth, Atmospheric and Environmental Sciences. "They are now extinct, but from about 300 to 400 million years ago, seem to have been more widespread than spiders. Now we can use the tools of computer graphics to better understand and recreate how they might have moved – all from thin slivers of rock, showing the joints in their legs."

Co-author Jason Dunlop, a curator at the Museum für Naturkunde, Berlin, said: "These fossils – from a rock called the Rhynie chert – are unusually well-preserved. During my PhD I could build up a pretty good idea of their appearance in life. This new study has gone further and shows us how they probably walked. For me, what's really exciting here is that scientists themselves can make these animations now, without needing the technical wizardry – and immense costs – of a Jurassic Park-style film.

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Explaining the Behaviour and Niches of Trilobites

The palaeoecology of trilobites

Author:

Fortey

Abstract:

Trilobites comprise a major group of extinct marine arthropods, which thrived in a variety of habitats surrounding the Palaeozoic palaeocontinents. The evidence that can be used to infer their ecology is reviewed, including functional anatomy, field occurrence and geology in comparison with living arthropods and palaeogeography. Where different lines of evidence are consistent with one interpretation, the inferred life habits are considered well supported, but there remain some intriguing enigmas. Trilobites occupied many of the ecological niches available to living marine arthropods, including the pelagic realm. Benthic species included predator/scavengers, grazers and particle feeders, and specialist filter feeders. Different contemporaneous natural assemblages of trilobites occupied different habitats ranging from shallow water to deep environments, which are characterized by distinctive suites of genera (biofacies). Such differentiation was already well established in the Cambrian. Dispersed palaeocontinents through much of the Palaeozoic further encouraged the evolution of endemics and distinct suites of taxa in relation to palaeolatitude. Taken together, these factors go some way towards explaining the great variety of species that evolved during more than 250 million years of their history.

Crustaceans Just Before the Permian Extinction

Evolution of Crustaceans at the edge of the end-Permian crisis: Ichnonetwork analysis of the fluvial succession of Nurra (Permian–Triassic, Sardinia, Italy)

Authors:

Baucon et al

Abstract:

Decapod crustaceans are among the most efficient ecosystem engineers 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 a well-preserved 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.

Phylogeny of Cambrian Spiny Trilobites

Phylogenetic analysis of the spiny oryctocephalids (Trilobita, Corynexochida?, Oryctocephalidae), Cambrian

Author:

Sundberg

Abstract:

Phylogenetic analyses of the Cambrian spiny oryctocephalids support the elevation to familiar rank of Oryctocephalidae Beecher, 1897 and indicate that the family can be divided into two clades, here designated as the subfamilies Oryctocephalinae Beecher, 1897 and Lancastriinae Kobayashi, 1935. Curvoryctocephaliinae Zhao and Yuan in Yuan et al., 2002 is considered here a junior synonym of Lancastriinae. Oryctocephalinae have tapered or parallel sided glabella and is composed of species of Oryctocephalus Walcott, 1886. The subgenera Oryctocephalus (Oryctocephalus) and O. (Eoryctocephalus) Zhao and Yuan in Yuan et al., 2002 do not form separate clades and are here rejected.

The genera of the Lancastriinae have expanding glabellae. The subfamily is composed of a broad variety of genera that can be divided into three major subclades: Lancastria, Protoryctocephalus, and Oryctocephalites. The Lancastria subclade is composed of Lancastria Kobayashi, 1935, Changaspis Lee in Chien, 1961, and Goldfieldia Palmer, 1964 occurring at the base of the Lancastriinae. Goldfieldia and Lancastria form a sister group to Changaspis. The long branches in the phylograms indicated significant differences between these taxa; thus, the genus Goldfieldia is maintained. The Protoryctocephalus subclade is monogeneric and forms a sister group to the Oryctocephalites subclade. The Oryctocephalites subclade consists of several species of this genus and the more derived forms Metabalangia Qian and Yuan in Zhang et al., 1980 and Tonkinella Mansuy, 1916. Oryctocephaloides Yuan in Zhang et al., 1980 is considered a junior synonym of Oryctocephalites Resser, 1939. The subgenera Oryctocephalites (Oryctocephalites) and O. (Parachangaspis) Zhao and Yuan in Yuan et al., 2002 do not form separate clades. The later subgenus occurs in the basal portion of the Oryctocephalites subclade indicating that it is a paraphyletic taxon.

Opsiosoryctocephalus Sundberg, 1994, Oryctocephalops Lermontova, 1940, and Curvoryctocephalus Zhao and Yuan in Yuan et al., 2002 are not consistent in their placement within the phylogenetic analyses, although they always occur in the Lancastriinae. As a result they are not placed within a subclade within Lancastriinae.

The type species Goldfieldia pacifica Palmer, 1964 was based solely on cranidia. This species is redescribed using topotype material that includes cranidia, librigenae, hypostomes, thorax, and pygidia.

Were There Arthropods in the Ediacaran?

The Ediacaran biota has been touted as one of the great mysteries of palaeontology. Comprising the latest part of the Precambrian era, the Ediacaran is generally believed to have given us the earliest known animal fossils. However, palaeontologists have disagreed on just how the Ediacaran fossils relate to modern animals (see McCall 2006 for an exhaustively detailed review). Some see the Ediacarans as including the ancestors of groups that remain with us today: jellyfish, corals, comb jellies, sponges. Others see Ediacarans as outside the modern lineages: ancient animal groups that were swept aside by more modern animals at the beginning of the Cambrian. And some have even questioned whether the Ediacarans were even animals at all, suggesting links instead to fungi or Foraminifera, or even that they were an entirely independent lineage unrelated to any modern multicellular organisms.

In 1996, Benjamin Waggoner proposed the name 'Cephalata' for a clade uniting the arthropods with two groups of Ediacaran organisms: the Sprigginidae and the Vendiamorpha. These are among the most undeniably animal-like of the Ediacarans. The sprigginids (including Spriggina shown at the top of the post) have an undivided 'head' followed by a long segmented body. The vendiamorphs are shield-like organisms that also show evidence for segment-like divisions behind the 'head', such as branching internal structures that may represent side-branches of an internal gut.

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