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The morphology and evolutionary significance of the anomalocaridids
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology. (Palaeobiology)
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. , p. 40
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 714
Keywords [en]
anomalocaridids, Cambrian, Burgess Shale, exceptional preservation, palaeontology
National Category
Geology
Research subject
Historical Geology and Paleontology
Identifiers
URN: urn:nbn:se:uu:diva-114102ISBN: 978-91-554-7723-3 (print)OAI: oai:DiVA.org:uu-114102DiVA, id: diva2:293051
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
List of papers
1. The Burgess Shale Anomalocaridid Hurdia and Its Significance for Early Euarthropod Evolution
Open this publication in new window or tab >>The Burgess Shale Anomalocaridid Hurdia and Its Significance for Early Euarthropod Evolution
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2009 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 323, no 5921, p. 1597-1600Article in journal (Refereed) Published
Abstract [en]

As the largest predators of the Cambrian seas, the anomalocaridids had an important impact in structuring the first complex marine animal communities, but many aspects of anomalocaridid morphology, diversity, ecology, and affinity remain unclear owing to a paucity of specimens. Here we describe the anomalocaridid Hurdia, based on several hundred specimens from the Burgess Shale in Canada. Hurdia possesses a general body architecture similar to Anomalocaris and Laggania, including the presence of exceptionally well-preserved gills, but differs from those anomalocaridids by possessing a prominent anterior carapace structure. These features amplify and clarify the diversity of known anomalocaridid morphology and provide insight into the origins of important arthropod features, such as the head shield and respiratory exites.

Place, publisher, year, edition, pages
Washington, DC: American Association for the Advancement of Science, 2009
National Category
Earth and Related Environmental Sciences
Research subject
Historical Geology and Paleontology
Identifiers
urn:nbn:se:uu:diva-114185 (URN)10.1126/science.1169514 (DOI)000264342300036 ()
Available from: 2010-02-11 Created: 2010-02-11 Last updated: 2017-12-12Bibliographically approved
2. New anomalocaridid appendages from the Burgess Shale, Canada
Open this publication in new window or tab >>New anomalocaridid appendages from the Burgess Shale, Canada
2010 (English)In: Palaeontology, ISSN 0031-0239, E-ISSN 1475-4983, Vol. 53, no 4, p. 721-738Article 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.

Keywords
anomalocaridids, appendages, Burgess Shale, Canada, Cambrian
National Category
Earth and Related Environmental Sciences
Research subject
Historical Geology and Paleontology
Identifiers
urn:nbn:se:uu:diva-114188 (URN)10.1111/j.1475-4983.2010.00955.x (DOI)000280127500004 ()
Available from: 2010-02-11 Created: 2010-02-11 Last updated: 2017-12-12Bibliographically approved
3. Morphology and systematics of the anomalocaridid arthropod Hurdia from the Middle Cambrian of British Columbia and Utah
Open this publication in new window or tab >>Morphology and systematics of the anomalocaridid arthropod Hurdia from the Middle Cambrian of British Columbia and Utah
2013 (English)In: Journal of Systematic Palaeontology, ISSN 1477-2019, E-ISSN 1478-0941, Vol. 11, no 7, p. 743-787Article in journal (Refereed) Published
Abstract [en]

In Cambrian fossil Lagerstätten like the Burgess Shale, exceptionally preserved arthropods constitute a large part of the taxonomic diversity, providing opportunities to study the early evolution of this phylum in detail. The anomalocaridids, large presumed pelagic predators, are particularly relevant owing to their unique combination of morphological characters and basal position in the arthropod stem lineage. Although isolated elements and fragmented specimens were first discovered over 100 years ago, subsequent findings of more complete bodies ofAnomalocaris and Peytoia, especially in the 1980s, allowed for a better understanding of these enigmatic forms. Their evolutionary significance as stem group arthropods was further clarified by the recent discovery of a third anomalocaridid taxon, Hurdia. Here, examination of hundreds ofHurdia specimens from different stratigraphical layers within the Burgess Shale and Stephen Formation, combined with statistical analyses, provides a detailed description of the taphonomy, morphology and diversity of the genus and further elucidates anomalocaridid systematics. Hurdiais distinguished from other anomalocaridids in having mouthparts with extra rows of teeth, a large frontal carapace complex and diminutive swimming flaps with prominent setal structures. The two original species, H. victoria Walcott, 1912 and H. triangulata Walcott, 1912, are confirmed based on morphometric outline analyses of the frontal carapace components combined with stratigraphical evidence; a third species, Hurdia dentata Simonetta & Delle Cave, 1975, is synonymized with H. victoria. Morphology, preservation and stratigraphical distribution suggest that H. victoria and H. triangulata share the same type of frontal appendage; a second type of appendage, previously assigned to Hurdia (Morph A), belongs to Peytoia nathorsti. These and other morphological differences between the anomalocaridids may reflect different feeding strategies. Appendages and mouthparts of Hurdia indet. sp. are also identified from the Spence Shale Member of Utah, making Hurdia and Anomalocaris the most common and globally distributed anomalocaridid taxa.

Keywords
Cambrian, Burgess Shale, Radiodonta, arthropods, multivariate statistics, taxonomy
National Category
Geology
Identifiers
urn:nbn:se:uu:diva-114195 (URN)10.1080/14772019.2012.732723 (DOI)000326860800001 ()
Available from: 2010-02-11 Created: 2010-02-11 Last updated: 2017-12-12Bibliographically approved
4. A possible anomalocaridid from the Cambrian Sirius Passet lagerstätte, North Greenland
Open this publication in new window or tab >>A possible anomalocaridid from the Cambrian Sirius Passet lagerstätte, North Greenland
2010 (English)In: Journal of Paleontology, ISSN 0022-3360, E-ISSN 1937-2337, Vol. 84, no 2, p. 352-355Article in journal (Refereed) Published
Abstract [en]

The Sirius Passet biota of North Greenland is one of the oldest Cambrian lagerstätten, and although it is dominated by non-mineralized arthropods and lobopods, anomalocaridids have never been identified. Based on a single specimen, we herein describe for the first time an appendage with possible anomalocaridid affinities as suggested by an overall gross morphology similar to that of the frontal appendage of Anomalocaris from other localitites. Tamisiocaris borealis n. gen. and n. sp. has an elongated appendage with paired spines along one margin, and differs from the frontal appendage of Anomalocaris in that segment boundaries are absent and ventral spines are relatively long and spineless. These differences may be taphonomic, but the entire surface of the appendage is covered in a fine fabric, making it unlikely that this appendage was originally segmented or sclerotized. The taxon is tentatively placed within Radiodonta, but this systematic placement cannot be confirmed while complete body specimens are lacking.

National Category
Geology
Research subject
Earth Science with specialization in Historical Geology and Palaeontology
Identifiers
urn:nbn:se:uu:diva-114191 (URN)10.1666/09-136R1.1 (DOI)000275689000014 ()
Available from: 2010-02-11 Created: 2010-02-11 Last updated: 2017-12-12Bibliographically approved
5. The lobes and lobopods of Opabinia regalis from the middle Cambrian Burgess Shale
Open this publication in new window or tab >>The lobes and lobopods of Opabinia regalis from the middle Cambrian Burgess Shale
2012 (English)In: Lethaia: an international journal of palaeontology and stratigraphy, ISSN 0024-1164, E-ISSN 1502-3931, Vol. 45, no 1, p. 83-95Article in journal (Refereed) Published
Abstract [en]

Despite many papers devoted to it, the morphology of the Burgess Shale animal Opabinia regalis continues to excite controversy. In particular, the trunk region remains incompletely understood, leading to several recent attempts to interpret the fossil in radically different ways. New material of Opabinia from the Royal Ontario Museum and the Smithsonian collection, together with the recent description of comparative material of the Burgess Shale anomalocaridid Hurdia, help clarify details of its morphology, in particular with regards to the lateral lobes and setal blades. A recent reconstruction of the trunk lobes is rejected, and further evidence for the presence of trunk limbs is presented. Despite disagreements over its morphology, the phylogenetic placement of Opabinia is now relatively uncontroversial, although various derived aspects of its morphology complicate placing it precisely.

Keywords
Biramous limb, Burgess Shale, exceptional preservation, Opabinia regalis
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-114193 (URN)10.1111/j.1502-3931.2011.00264.x (DOI)000298301900009 ()
Available from: 2010-02-11 Created: 2010-02-11 Last updated: 2017-12-12Bibliographically approved

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Citation style
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  • Other style
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