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New anomalocaridid appendages from the Burgess Shale, Canada
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology. (Palaeobiology)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology. (Palaeobiology)
2010 (English)In: Palaeontology, ISSN 0031-0239, E-ISSN 1475-4983, Vol. 53, no 4, 721-738 p.Article in journal (Refereed) Published
Abstract [en]

The complex history of description of the anomalocaridids has partly been caused by the fragmentary nature of these fossils. Frontal appendages and mouth parts are more readily preserved than whole-body assemblages, so the earliest work on these animals examined these structures in isolation. After several decades of research, these disarticulated elements were assembled together to reconstruct the anomalocaridid body plan, and a total of three Burgess Shale genera, Anomalocaris, Laggania, and Hurdia, were described in full.  Here we present new frontal appendage material of additional anomalocaridid taxa from the ‘Middle’ Cambrian (Series 3) Burgess Shale Formation in Canada, showing that the diversity of anomalocaridids in this locality is even higher than previously thought. Material includes Amplectobelua stephenensis sp. nov., the first known occurrence of this genus outside of China; Caryosyntrips serratus gen. et sp. nov., which is similar to the Anomalocaris appendage but has a straighter outline and a different arrangement of spines; and an appendage that may be either the Laggania appendage or a third morph of the Hurdia appendage. The new anomalocaridid material is contemporaneous with the previously described taxa Anomalocaris, Laggania, and Hurdia, and the differences in morphology between the frontal appendages may reflect different feeding strategies. The stratigraphically lowest locality, S7 on Mount Stephen, yields material from all anomalocaridid taxa, but the assemblages in the younger quarries on Fossil Ridge are dominated by Anomalocaris and Hurdia only.

Place, publisher, year, edition, pages
2010. Vol. 53, no 4, 721-738 p.
Keyword [en]
anomalocaridids, appendages, Burgess Shale, Canada, Cambrian
National Category
Earth and Related Environmental Sciences
Research subject
Historical Geology and Paleontology
Identifiers
URN: urn:nbn:se:uu:diva-114188DOI: 10.1111/j.1475-4983.2010.00955.xISI: 000280127500004OAI: oai:DiVA.org:uu-114188DiVA: diva2:293429
Available from: 2010-02-11 Created: 2010-02-11 Last updated: 2010-12-08Bibliographically approved
In thesis
1. The morphology and evolutionary significance of the anomalocaridids
Open this publication in new window or tab >>The morphology and evolutionary significance of the anomalocaridids
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Approximately 600 to 500 million years ago, a major evolutionary radiation called the “Cambrian Explosion” gave rise to nearly all of the major animal phyla known today. This radiation is recorded by various fossil lagerstätten, such as the Burgess Shale in Canada, where soft-bodied animals are preserved in exquisite detail. Many Cambrian fossils are enigmatic forms that are morphologically dissimilar to their modern descendants, but which still provide valuable information when interpreted as stem-group taxa because they record the actual progression of evolution and give insight into the order of character acquisitions and homologies between living taxa. One such group of fossils is the anomalocaridids, large presumed predators that have had a complicated history of description. Their body has a trunk with a series of lateral lobes and associated gills, and a cephalic region with a pair of large frontal appendages, a circular mouth apparatus, stalked eyes and a cephalic carapace. Originally, two taxa were described from the Burgess Shale, Anomalocaris and Laggania, however data presented herein suggests that the diversity of the anomalocaridids was much higher. Newly collected fossil material revealed that a third Burgess Shale anomalocaridid, Hurdia, is known from whole-body specimens and study of its morphology has helped to clarify the morphology and systematics of the whole group. Hurdia is distinguished by having mouthparts with extra rows of teeth, a unique frontal appendage, and a large frontal carapace. Two species, Hurdia victoria and Hurdia triangulata were distinguished based on morphometric shape analysis of the frontal carapace. A phylogenetic analysis placed the anomalocaridids in the stem lineage to the euarthropods, and examination of Hurdia’s well-preserved gills confirm the homology of this structure with the outer branches of limbs in upper stem-group arthropods. This homology supports the theory that the Cambrian biramous limb formed by the fusion of a uniramous walking limb with a lateral lobe structure bearing gill blades. In this context, new evidence is present on the closely allied taxon Opabinia, suggesting that it had lobopod walking limbs and a lateral lobe structure with attached Hurdia-like gills. The diversity of the anomalocaridids at the Burgess Shale is further increased by two additional taxa known from isolated frontal appendages. Amplectobelua stephenensis is the first occurrence of this genus outside of the Chengjiang fauna in China, but Caryosyntrips serratus is an appendage unique to the Burgess Shale. To gain a better understanding of global distribution, a possible anomalocaridid is also described from the Sirius Passet biota in North Greenland. Tamisiocaris borealis is known from a single appendage, which is similar to Anomalocaris but unsegmented, suggesting this taxon belongs to the arthropod stem-lineage, perhaps in the anomalocaridid clade. Thus, the anomalocaridids are a widely distributed and highly diverse group of large Cambrian presumed predators, which provide important information relevant to the evolution of the arthropods.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 40 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 714
Keyword
anomalocaridids, Cambrian, Burgess Shale, exceptional preservation, palaeontology
National Category
Geology
Research subject
Historical Geology and Paleontology
Identifiers
urn:nbn:se:uu:diva-114102 (URN)978-91-554-7723-3 (ISBN)
Public defence
2010-03-26, Hambergsalen, Villavägen 16, Institutionen för geovetenskaper, 10:00 (English)
Opponent
Supervisors
Available from: 2010-03-03 Created: 2010-02-10 Last updated: 2010-03-03Bibliographically approved

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