The Marellomorphs are a poorly understood group of Arthropods that appeared early in the Cambrian and survived to the Devonian. They apparently lacked mineralized tissues, and therefore are only found in fossil-bearing deposits with exceptional preservation, often only with the large cephalic shield being preserved.
In a paper published in the journal Acta Palaeontologica Polonica on 4 November 2016, María Aris of the Cátedra de Paleontología and Instituto para el Estudio de la Biodiversidad de Invertebrados at the Universidad Nacional de Salta, Jose Corronca, also of the Instituto para el Estudio de la Biodiversidad de Invertebrados at the Universidad Nacional de Salta, Sebastián Quinteros of the Consejo Nacional de Investigaciones Científicas y Técnicas and Instituto de Bio y Geociencias del Noroeste Argentino at the Universidad Nacional de Salta, and Paolo Pardo, again of the Instituto para el Estudio de la Biodiversidad de Invertebrados at the Universidad Nacional de Salta, describe a new species of Marrellomorph from the Earliest Ordovician Floresta Formation of the Mojotoro Mountains in Salta Province, Argentina.
The new species is placed in the genus Mimetaster, and given the specific name florestaensis, meaning 'from Floresta', a reference to the sediments that produced the specimen from which the species is described. This specimen is an isolated cephalic shield preserved as part and counterpart on a split block. The central cephalic field of this is trapezoidal and slightly convex, and bears three pairs of elongate spines, each with a different length and orientation. This is the first Marrellomorph found in either Argentina or South America.
Marellomorph Arthropod Mimetaster florestaensis from Tremadocian of Mojotoro Mountains, Salta, Argentina. (A)–(C) Part. (A) Cephalic shield and spines. Detail of the secondary spines on mediolateral spine (A2). (B) View of the imprint of the ventral posterior margin of the cephalic shield. (C) Explanatory drawing revealing the most important morphological characters. (D) Counterpart showing detail of strong secondary spines on anterolateral spine. Arrows indicate the secondary spines. Aris et al. (2016).
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