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A new mobergellan (small shelly fossils) from the early middle cambrian of morocco and its significance

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Abstract

A new mobergellan genus and species,Tateltella ranoculata, is described from the early Middle Cambrian (Agdzian Stage) of Morocco. The new taxon is characterized by only four pairs of muscle scars and is furthermore distinguished from other mobergellans by its strongly concave shape and its distally rising muscle scars. The individual specimens ofTateltella ranoculata distinctly vary in size and display different ontogenetic stages. Juvenile, intermediate, and adult stages can be distinguished by means of the development of the muscle scars that differ in Position relative to the apex, size, and distinctness between individual stages. The shell ofT. ranoculata is composed of a succession of thin phosphatic lamellae separated by interlamellar gaps, presumably originally filled by organic material. The interlamellar gaps may be divided by septum-like structures producing discrete cavities. The specimens are the youngest mobergellans known so far and correlation of their stratigraphic position suggests a correspondence with the lower part of the Amgan stage of the Siberian Platform. In addition, they are the first reported mobergellans from the present day continent Africa. Other mobergellan taxa and mobergellan-like species are briefly reviewed and the genusHippoklosma Missarzhevsky, previously assigned to the Mobergellidae, is excluded from the family due to its different shell structure. An evolutionary trend of reduction in the number of muscle scars from 14 in the early Early Cambrian to only eight in the early Middle Cambrian is apparent among mobergellans.

Kurzfassung

Eine neue Gattung und Art der Familie Mobergellidae (incertae sedis),Tateltella ranoculata, wird aus dem unteren Mittelkambrium (Agdzium-Stufe) von Marokko beschrieben. Das neue Taxon ist durch seine einzigartige Kombination von Merkmalen von anderen Repräsentanten der Familie unterschieden. Lediglich vier Paar nach distal ansteigende Muskelabdrücke und eine stark konvexe Form kennzeichnen seine Schale. Die einzelnen Exemplare vonT. ranoculata variieren stark in ihrer Größe und repräsentieren unterschiedliche ontogenetische Stufen. Es können eine juvenile, eine intermediäre und eine adulte Entwicklungsphase unterschieden werden, die durch die unterschiedliche Ausprägung und Position der Muskelabdrücke gekennzeichnet sind. Die Schale vonT. ranoculata besteht aus einer Abfolge von dünnen, phosphatischen Lagen („lamellae“), die durch vermutlich primär mit organischen Material gefüllten Zwischenräume voneinander getrennt sind. Diese Zwischenräume können durch Septeneinschaltungen in einzelne Kammern untergliedert sein. Das stratigraphische Niveau der gefunden Exemplare korreliert mit der unteren Amga-Stufe der Sibirischen Tafel und stellt somit das jüngste bislang bekannte Niveau für Mobergelliden dar. Weitere Vertreter der Mobergelliden werden kurz besprochen, und die bislang zur Familie gezählte GattungHippoklosma Missarzhevsky wird aufgrund ihrer andersartigen Schalenstruktur von der Familie ausgeschlossen.

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  1. Christian B. Skovsted

    Present address: Centre for Ecostratigraphy and Palaeobiology, Macquarie University, 2109, NSW, Australia

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  1. Institute of Earth Sciences, Palaeobiology, University of Uppsala, Norbyvägen 22, SE-752 36, Uppsala, Sweden

    Michael Streng & Christian B. Skovsted

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Correspondence to Michael Streng.

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Streng, M., Skovsted, C.B. A new mobergellan (small shelly fossils) from the early middle cambrian of morocco and its significance. Paläontol Z 80, 209–220 (2006). https://doi.org/10.1007/BF02988437

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