Juliana de Moraes Leme

Reassessment of the phylogenetic position of conulariids (?Ediacaran‐Triassic) within the subphylum medusozoa (phylum cnidaria)

Synopsis Fossil taxa of uncertain phylogenetic affinities can play a crucial role in the analysis of character evolution within major extant groups. Marques & Collins (2004) concluded that conulariids (?Ediacaran‐Triassic) are an extinct group of medusozoan cnidarians most closely related to Stauromedusae. However, only six of the 87 characters used by these authors can be observed in conulariid fossils. Rescoring the character states of conulariids in a conservative manner yields a new hypothesis for the phylogenetic position of conulariids, namely that they are the sister group of the scyphozoan order Coronatae rather than Stauromedusae, which is revealed as the earliest diverging lineage of Medusozoa. This new hypothesis also implies several different sequences of character evolution within Cnidaria. Specifically, the presence of a periderm completely covering the polyp in conulariids and coronates appears to be derived within Scyphozoa. Strobilation appears to be a synapomorphy uniting conulariids, Coronatae, Rhizostomeae and Semaeostomeae. This result supports the controversial interpretation of one exceptionally preserved conulariid that potentially shows that these animals produced ephyrae by strobilation. Finally, the pelagic adult medusa stage and the giant fibre nerve net appear to be features that are derived within Medusozoa.

Insights into the Skeletonization, Lifestyle, and Affinity of the Unusual Ediacaran Fossil Corumbella

The Ediacaran fossil Corumbella is important because it is hypothesized to be a scyphozoan cnidarian, and thus might be one of the rare examples of bona fide Neoproterozoic animals. Unfortunately, its mode of life, style of skeletonization, and taxonomic affinity have been very controversial. Here, we use X-ray micro-CT, SEM, and taphonomic analysis to compare preservational modes of Corumbella, in order to better understand the symmetry, mode of construction, preservational style, and taxonomy of this group. Results suggest that articulated and disarticulated specimens of Corumbella from the Ediacaran of Brazil, Paraguay, and the United States, although sometimes preserved very differently, represent the same taxon—Corumbella werneri. Corumbellids had a thick but flexible theca and probably lived with their basalmost part anchored in the sediment, much like Conotubus. When considered together, these results suggest that Corumbella was one of the first animals to build a skeleton, employing a lamellar microfabric similar to conulariids.

Alternative Interpretations of Some Earliest Ediacaran Fossils from China

In a letter to Nature (February, 2011), Xunlai Yuan and collaborators recorded carbon compression fossils from black shales of the Lantian Formation (Ediacaran), southern Anhui Province, South China. The new fossils, described under five morphological types (Types A to E), exhibit degrees of morphological differentiation suggesting that they were multicellular eukaryotes. Some of the Lantian macrofossils were interpreted as algae, but others are of unknown affinities. For reasons noted in this discussion, Type A fossils attracted our particular attention, and we suggest an alternative interpretation of their affinities. According to our view, some of them (at least those with three faces and no globose holdfast at their base) may represent conulariid cnidarians or close medusozoan relatives. The undistorted organism probably was a three-sided cone in life. We believe that our suggested alternative interpretations of the anatomy and affinities of the fossils in question can be useful in guiding future research on the oldest currently known fossil assemblage of multicellular organisms.

Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil

The evolutionary events during the Ediacaran–Cambrian transition (~541 Myr ago) are unparalleled in Earth history. The fossil record suggests that most extant animal phyla appeared in a geologically brief interval, with the oldest unequivocal bilaterian body fossils found in the Early Cambrian. Molecular clocks and biomarkers provide independent estimates for the timing of animal origins, and both suggest a cryptic Neoproterozoic history for Metazoa that extends considerably beyond the Cambrian fossil record. We report an assemblage of ichnofossils from Ediacaran–Cambrian siltstones in Brazil, alongside U–Pb radioisotopic dates that constrain the age of the oldest specimens to 555–542 Myr. X-ray microtomography reveals three-dimensionally preserved traces ranging from 50 to 600 μm in diameter, indicative of small-bodied, meiofaunal tracemakers. Burrow morphologies suggest they were created by a nematoid-like organism that used undulating locomotion to move through the sediment. This assemblage demonstrates animal–sediment interactions in the latest Ediacaran period, and provides the oldest known fossil evidence for meiofaunal bilaterians. Our discovery highlights meiofaunal ichnofossils as a hitherto unexplored window for tracking animal evolution in deep time, and reveals that both meiofaunal and macrofaunal bilaterians began to explore infaunal niches during the late Ediacaran.Trace fossils from the Ediacaran–Cambrian transition of Brazil are interpreted as the remains of burrows made by a nematoid-like organism moving through sediment: these organisms are interpreted as the oldest known fossil meiofaunal bilaterians.

Origin and Early Diversification of Phylum Cnidaria: Key Macrofossils from the Ediacaran System of North and South America

Recent molecular clock studies place the origin of phylum Cnidaria within the Cryogenian Period (ca. 850–635 Ma), with the split between the two subphyla (Anthozoaria and Medusozoa) likewise occurring during this time interval. However, the oldest cnidarian macrofossils, all medusozoans, occur in rocks of the late Ediacaran Period (ca. 560–541 Ma). Lightly skeletonized Corumbella werneri, currently known from late Ediacaran strata of Brazil, Paraguay and Nevada (USA), has been allied with coronate and conulariid scyphozoans, but it also shares gross morphological similarities with Carinachites spinatus, a possible conulariid from Cambrian Stage 1 (China), and it may be compared with Sinotubulites and Wutubus annularis from the late Ediacaran Dengying Formation (China). The strongest evidence of affinity with coronate scyphozoans is exhibited by Paraconularia sp. from a Corumbella-bearing shale interval in the latest Ediacaran Tamengo Formation of central Brazil. Furthermore, Paraconularia sp. from this rock unit establishes conulariids as a cnidarian clade that crossed the Proterozoic-Phanerozoic boundary. Finally, Haootia quadriformis from the late Ediacaran lower Fermeuse and Trepassy formations (southeastern Newfoundland, Canada) exhibits intriguing gross morphological similarities to extant staurozoans and may represent the earliest record of metazoan musculature. Together, C. werneri and latest Ediacaran Paraconularia sp. fix the split between the medusozoan classes Cubozoa and Scyphozoa at no later than ca. 543 Ma. If H. quadriformis was indeed a staurozoan or stem staurozoan, then this fossil taxon fixes the split between the class Staurozoa and all other medusozoan cnidarians at no later than ca. 560 Ma.

Cladistics and mass extinctions: the example of conulariids (Scyphozoa, Cnidaria) and the End Ordovician Extinction Event

The End Ordovician Extinction Event (EOEE) had little impact on supra-specific diversity and disparity within the order Conulariida (Scyphozoa, Cnidaria). With two possible exceptions (Exoconularia and Glyptoconularia), all eight genera currently known from strata of middle or late Katian age survived the crisis, and nearly all of the discontinuous gross morphological features present in Ordovician and older genera are present in at least one of the surviving genera. A cladistic parsimony analysis of 17 genera, 12 of which occur in Ordovician strata, produced 3 major subclades and 7 less inclusive subclades within Conulariida. With one possible exception, the clade Anaconularia+Baccaconularia, all other monophyletic groups within Conulariida survived the EOEE. Moreover, additional, ghost lineages in the clade Climacoconus+Holoconularia+Notoconularia+Paraconularia+Reticulaconularia must have crossed the Ordovician–Silurian boundary. The minor impact of the EOEE on diversity and disparity within Conulariida probably reflects the eurytopic character and simple but efficient metabolism (possibly glycolysis-based) of this group.

O registro fossilífero de metazoários ediacaranos na América do Sul e suas implicações nos estudos sobre origem e complexificação da vida animal

The Ediacaran Period marks the first appearance of complex macroscopic organisms in the fossil record. Current evidence indicates that Ediacara biota is composed of animals, groups of extinct giant protists, algae and other organisms without proven affinities with modern groups. Fossils of this biota have been documented in at least 40 locations worldwide. In South America, ediacaran metazoan fossils are found in Brazil, Paraguay, Uruguay and Argentina. In most of these locations, are found fossils of the last moment of evolutionary ediacaran biota, capable of performing skeletogenesis, such as Cloudina and Corumbella, related to Nama assemblage. This evolutionary novelty arose probably in response to predation pressures and chemical changes in the oceans. Newly, fossils of soft-bodied organisms were found, typical of other ediacaran assembly (White Sea), in Santa Catarina (Brazil). This occurrence is of great importance since it represents the only discovery about its assemblage in South America. This work aims to compile the occurrences of the Ediacara biota in South America, as well as discussing the importance of inclusion and study these events on the world scene in the scope of one of the most important issues of Paleobiology: the origin and evolution animals on Earth.

The occurrence of Phacopida trilobites from Pimenteira Formation at João Costa, Piauí, Brazil

The marine macroinvertebrate fossils from the Devonian of the Parnaiba Basin are among the most diverse of Paleozoic of Brazil. In recent years, most revisions on these fossils involved trilobites from the Pimenteira and Cabecas formations, in the region of Picos and Pimenteiras cities, in the Piaui State. This survey reports the occurrence of Devonian trilobites from the Pimenteira Formation cropping out at Joao Costa city, in the region of Serra da Capivara National Park, southeastern Piaui State, where two species were recognized: Burmeisteria notica Clarke, 1913 and Metacryphaeus cf. australis Clarke, 1913. The wide occurrence of these genera in the Malvinokaffric Realm shows that transgressive events during part of the Devonian favored the faunal communication between the Andean, Brazilian and South African provinces through the reduction of geographical barriers. Finally, although the still preliminary character of the studies on Pimenteira Formation trilobites, this unit is already providing new paleontological data that contribute to the understanding of these fossil assemblages.

Ecological interactions in Cloudina from the Ediacaran of Brazil: implications for the rise of animal biomineralization

At the Ediacaran/Cambrian boundary, ecosystems witnessed an unparalleled biological innovation: the appearance of shelled animals. Here, we report new paleoecological and paleobiological data on Cloudina, which was one of the most abundant shelled animals at the end of the Ediacaran. We report the close association of Cloudina tubes with microbial mat textures as well as organic-rich material, syndepositional calcite and goethite cement between their flanges, thus reinforcing the awareness of metazoan/microorganism interactions at the end of the Ediacaran. The preservation of in situ tubes suggests a great plasticity of substrate utilization, with evidence of different life modes and avoidance behavior. Geochemical analysis revealed walls composed of two secondary laminae and organic sheets. Some walls presented boreholes that are here described as predation marks. Taken together, these data add further information regarding the structuring of shelled animal communities in marine ecosystems.

The “Metacryphaeus tuberculatus Group” (Trilobita, Calmoniidae) from the Devonian of the Parnaíba Basin, Brazil

Abstract. Calmoniid trilobites of the “Metacryphaeus tuberculatus group” occur in many Devonian localities within the Malvinokaffric Realm. In the Parnaíba Basin, in northeastern Brazil, the group is represented by Metacryphaeus tuberculatus Kozlowski, 1923, and M. meloi Carvalho, Edgecombe and Lieberman, 1997, from the late Eifelian—early Givetian Pimenteira Formation in the environs of the city of Picos and the early Givetian Passagem Member (Pimenteira Formation) from the vicinities of Picos and Pimenteiras in Piauí State. Based on specimens found in the region of João Costa, southeastern Piauí State, the present study reinforces data on the occurrence of M. tuberculatus in the Pimenteira Formation and reports the presence of genal spines in some individuals of M. meloi, indicating a feature previously unknown for this species.