Previously unreported silicified trilobite faunas occur in a narrow stratigraphic interval of the Upper Cambrian (Sunwaptan) St. Charles Formation in the Bear River Range of southeastern Idaho. The faunas occur in four closely spaced rudstones and trilobite packstones indicating deposition in a shallow subtidal setting above storm wave base. At least 23 species are represented, included two undescribed genera and several undescribed species. The faunas are notable for their high trilobite abundance and pervasive silicification. Most coeval faunas have been described on the basis of small numbers of "crack-out" specimens, and the new material reveals many details of anatomy, including knowledge of most exoskeletal sclerites. The four trilobite-yielding beds contain markedly different taxon-abundance profiles, yet most species are shared between them. This suggests multiple, taphonomically-controlled samples of a similar underlying distribution, though true ecological variation cannot be discounted.

Submitted by Alberto Vieira (martins_vieira@ibest.com.br) on 2017-10-18T22:33:43Z No. of bitstreams: 1 618442.pdf: 5192820 bytes, checksum: 022b0b6c5ae216bd511524dc4969c626 (MD5) / Made available in DSpace on 2017-10-18T22:33:43Z (GMT). No. of bitstreams: 1 618442.pdf: 5192820 bytes, checksum: 022b0b6c5ae216bd511524dc4969c626 (MD5) Previous issue date: 2004-03 / Foram identificadas quatorze espécies de trilobitas da Formação Maecuru e uma da Formação Ererê (Devoniano, Bacia do Amazonas), coletadas no Estado do Pará, Brasil, Dessas, oito foram submetidas a uma análise morfofuncional por apresentarem céfalo e/ou hipostômios preservados, e agrupadas em três morfotipos. O morfotipo I – Homalonotus derbyi – apresenta glabela e lobo frontal pouco inflados e sulcos glabelares rasos. O morfotipo II – Phacopina brasiliensis, “Dalmanites” (gen. nov. aff. Fenestraspis) maecurua, “D.”(gen. nov. aff. Vogesina) galeus, “D.”(gen. nov. aff. Malvinella) tumilobus e Eldredgeia paituna (da qual foi descrito pela primeira vez um exemplar inteiro) – apresenta glabelas moderadamente infladas, lobo frontal bem diferenciado, sulcos glabelares mais profundos, olhos de tamanho médio e hipostômio fixo contérmino. O morfotipo III – “Malvinella” australis e “Palpebrops” goeldii – apresenta glabela e lobo frontal bastante inflados, sulcos glabelares rasos a moderadamente rasos e olhos de tamanho médio, aproximadamente na altura da glabela. Os três morfotipos apresentam características de hábito alimentar predador/necrófago. Os morfotipos I e II apresentam adaptação para escavação, mais desenvolvida no morfotipo I, para o qual é sugerido uma atitude semi–endobentônica, provavelmente usada para alimentação ou proteção contra predadores e distúrbios ambientais. O morfotipo III, de hábito predominantemente epibentônico, possui uma maior cavidade estomacal, sendo provavelmente um predador mais ávido. A Formação Maecuru apresenta duas concentrações fossilíferas distintas. Os bioclastos do ponto OAD 3 podem ter sido depositados por ondas de tempestade e seriam parautócnes. Os dos pontos rio Maecuru, OAD 4 e 4A podem indicar eventos deposicionais diferentes, mistura temporal e associações parautóctones e/ou alóctones. A Formação Ererê apresenta concentrações parautócnes e/ou alóctones nos arenitos e autóctones a parautócnes no folhelho. / Fourteen species of trilobites were identified from the Maecuru Formation and one from Ererê Formation (Devonian, Amazon Basin), sampled at Pará State, Brazil. Seven species from the Maecuru Formation and the species from the Ererê Formation were submitted to the morph functional analysis, because the presence of cephalous and/or hypostome well–preserved. These species were grouped into three morphotypes: morphotype I – Homalonotus derbyi – presents glabella, with shallow glabellar furrows, and glabellar frontal lobe weakly inflated; morphotype II – Phacopina brasiliensis, “Dalmanites” (gen. nov. aff. Fenestraspis) maecurua, “D.” (gen. nov. aff. Vogesina) galeus, “D.” (gen. nov. aff. Malvinella) tumilobus and Eldredgeia paituna (a complete specimen, described here, at the first time) – presents a fixed conterminant hypostome, medium size eyes, glabella moderately inflated, glabellar frontal lobe differentiated from the others and glabellar furrows deeper than morphotype I; morphotype III – “Malvinela” australis and “Palpebrops” goeldii – presents glabella and glabellar frontal lobe strongly inflated, glabellar furrows shallow to moderately shallow, and medium size eye, approximately in the same height of the glabella. All morphotypes shows predator/scavenger feeding habits. The morphotypes I and II present burrow adaptations, more developed in the morphotype I, and therefore suggests a semiinfaunistic mode of life. These adaptations were used probably to feeding and protection against predators and environmental disturbances. The morphotyape III is characterized by predominantly epifaunistic habits and shows greater stomach cavity, and were probably more voracious predators than the others morphotypes. The Maecuru Formation presents two different fossiliferous concentrations: the bioclasts of the point OAD 3, which were probably parautochthonous and deposited by storm waves; and the blioclasts from the Maecuru River, OAD 4 and OAD 4A points, which could indicate different depositional events, time averaging and allochthonous and/or parautochthonous assemblages. The Ererê Formation presents allochthonous and/or parautochthonous concentrations at the sandstone beds and autochthonous to parautochthonous at the shale beds.

No description available.

<p>Small shelly fossils are common in sediments of Early Cambrian age and include the earliest common representatives of metazoan animals with mineralized hard parts. The group includes fossils of very different morphology, composition and ultrastructure. They seem to represent skeletal remains of numerous animal groups, the biological affinities of which are largely unresolved. However, the wide geographic range of many forms has the potential to enhance biostratigraphic and palaeogeographic resolution in the Early Cambrian. </p><p>The late Early Cambrian sequence of North-East Greenland has yielded an assemblage of more than 88 species of small shelly fossils, brachiopods and trilobites, indicative of a middle Dyeran age (Botoman equivalent). The recovered fossils include a number of species that are known from other Early Cambrian palaeocontinents, and particularly strong ties to late Early Cambrian faunas of Australia are documented. The many cosmopolitan taxa thus identified suggests a close juxtaposition of palaeocontinents at this time. </p><p>The systematic affinity of many of these small shelly fossils is poorly understood, partly because of their fragmentary nature and poor preservation. However, new data from North-East Greenland improves our understanding of the function and biological affinity of certain taxa. Collections of the problematic fossil <i>Mongolitubulus</i> from North and North-East Greenland exhibit characters indicative of a defensive function as spines of bivalved arthropods, while species of the problematic genus <i>Triplicatella</i> represent the opercula of an unknown tubular shell, probably related to orthothecid hyoliths. The bivalved fossil <i>Mickwitzia</i> from North-East Greenland combines characters of linguliform brachiopods and sclerites of <i>Micrina</i>, a non-bivalved problematic form (halkieriid) from Australia. The combination suggests that <i>Mickwitzia</i> is a stem group brachiopod and strengthens arguments for a halkieriid ancestry of the brachiopod phylum.</p>

Small shelly fossils are common in sediments of Early Cambrian age and include the earliest common representatives of metazoan animals with mineralized hard parts. The group includes fossils of very different morphology, composition and ultrastructure. They seem to represent skeletal remains of numerous animal groups, the biological affinities of which are largely unresolved. However, the wide geographic range of many forms has the potential to enhance biostratigraphic and palaeogeographic resolution in the Early Cambrian. The late Early Cambrian sequence of North-East Greenland has yielded an assemblage of more than 88 species of small shelly fossils, brachiopods and trilobites, indicative of a middle Dyeran age (Botoman equivalent). The recovered fossils include a number of species that are known from other Early Cambrian palaeocontinents, and particularly strong ties to late Early Cambrian faunas of Australia are documented. The many cosmopolitan taxa thus identified suggests a close juxtaposition of palaeocontinents at this time. The systematic affinity of many of these small shelly fossils is poorly understood, partly because of their fragmentary nature and poor preservation. However, new data from North-East Greenland improves our understanding of the function and biological affinity of certain taxa. Collections of the problematic fossil Mongolitubulus from North and North-East Greenland exhibit characters indicative of a defensive function as spines of bivalved arthropods, while species of the problematic genus Triplicatella represent the opercula of an unknown tubular shell, probably related to orthothecid hyoliths. The bivalved fossil Mickwitzia from North-East Greenland combines characters of linguliform brachiopods and sclerites of Micrina, a non-bivalved problematic form (halkieriid) from Australia. The combination suggests that Mickwitzia is a stem group brachiopod and strengthens arguments for a halkieriid ancestry of the brachiopod phylum.