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The stem crustacean Oelandocaris oelandica re-visited
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
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2008 (English)In: Acta Palaeontologica Polonica, ISSN 0567-7920, Vol. 53, no 3, 461-484 p.Article in journal (Refereed) Published
Abstract [en]

The arthropod Oelandocaris oelandica from the upper Middle Cambrian “Orsten” of Sweden was recently recognized as a member of the early phase of crustacean evolution based on additional morphological detail from new specimens. Here we present a detailed investigation of all available material. It includes the description of a 400 μm long specimen probably representing an early developmental stage. Variation in size correlated with variation of trunk−segment numbers allowed recognition of different instars. The largest specimens do not exceed an estimated length of about 1 mm, indicating that our material may consist only of immature specimens. The characteristic, extremely long antennula of O. oelandica branches into three long rods. It may have served as the major structure to sweep in food, aided by the two subsequent appendages. These and the more posterior limbs were also responsible for locomotion. Minute pores on the outer edges of the posterior limbs and on the trunk tergites possibly contained sensilla originally, which may have served as water−current detectors. The presence of a minute proximal endite only on the third head appendage suggests a rather basal position of this species within Crustacea, because comparable developmental stages of other known stem crustaceans have such an endite on more of their appendages. Reconstruction of O. oelandica and its life attitudes (referred to the largest instar known) benefited from the application of 3D modelling. These helped, e.g., in identifying the combination of the plesiomorphic feeding function of the antennulae and the specialisation of the exopods of the next two appendages as a step toward the development of a sweep−net mode of feeding, one of the key novelties in the evolution of Crustacea. Such a mode of feeding coupled with locomotion of the three anterior appendages is still practiced in the naupliar and metanaupliar phases of many extant eucrustaceans, and even some adults.

Place, publisher, year, edition, pages
2008. Vol. 53, no 3, 461-484 p.
Keyword [en]
Crustacea, Arthropoda, morphology, life habits, sweep−net feeding, evolution, phylogeny, stem lineage, computer−aided 3D modelling
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:uu:diva-97595ISI: 000259830000008OAI: oai:DiVA.org:uu-97595DiVA: diva2:172600
Available from: 2008-09-29 Created: 2008-09-29 Last updated: 2009-08-27Bibliographically approved
In thesis
1. Evolution and taxonomy of Cambrian arthropods from Greenland and Sweden
Open this publication in new window or tab >>Evolution and taxonomy of Cambrian arthropods from Greenland and Sweden
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Arthropods have a rich fossil record spanning the Phanerozoic. Biomineralized forms such as the extinct trilobites are particularly common and are proven index fossils for biostratigraphy. Forms with an unmineralized cuticle are more rare, preserved only in so called konservat lagerstätten. Cambrian strata of Greenland have yielded rich trilobite faunas with potential for intercontinental correlation of Cambrian strata, but also an exceptionally preserved fauna, the Sirius Passet Lagerstätte. The first part of this thesis is concerned with trilobite biotratigraphy of the provisional Cambrian Series 2 in Greenland. The second part is concerned with exceptionally preserved arthropods from the Sirius Passet Lagerstätte, but also from 'Orsten' deposits from the Cambrian of Sweden.

Perissopyge phenax occurs in the Henson Gletscher and Paralleldal formations spanning the Series 2 and 3 boundary interval in North Greenland. It also occurs in the Sekwi Formation of Yukon Territory, demonstrating that the species may hold potential for correlation within Laurentia. An indeterminate species of Perissopyge is shown to occur in the Ella Island Formation of North-East Greenland together with Olenellus cf. hanseni, which is similar to Olenellus cf. truemani described from the Henson Gletscher Formation. If this correlation is further corroborated it would offer a first tie-point for the An t'Sron Formation of North-West Scotland which yields Fritzolenellus lapworthi, herein reported for the first time from the Bastion Formation which underlies the Ella Island Formation.

Oelandocaris oelandica from ‘Orsten’ deposits in the Cambrian series 3 and 4 boundary interval in Sweden is an early representative of the Crustacean stem lineage. Kiisortoqia avannaarsuensis is a new arthropod from the Sirius Passet Lagerstätte with robust antennulae strikingly similar to the 'raptorial' limb of the problematic anomalocaridids. The ventral morphology of the 'bivalved' Isoxys volucris is described for the first time and compared with other species assigned to Isoxys from Cambrian lagerstätten around the world. Finally, Siriocaris trolla, is a new arthropod that similarities with trilobites and certain ‘trilobitomorphs’ but seems to lack important synapomorphies of these taxa, though this may be due to preservational limitations in the material at hand.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 35 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 558
Cambrian, Arthropods, Trilobites, Evolution, Greenland, Sweden
National Category
urn:nbn:se:uu:diva-9301 (URN)978-91-554-7302-0 (ISBN)
Public defence
2008-10-31, the lecture theatre, Museum of Evolution (Palaeontology), Norbyvägen 22, 75236 Uppsala, 10:00
Available from: 2008-09-29 Created: 2008-09-29 Last updated: 2011-01-12Bibliographically approved

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