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Exceptionally Preserved Cambrian Lophotrochozoa: Taxonomy, Systematics and Taphonomy of Chengjiang and Indian Springs Lophophorates
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology. (Earth Sciences, Palaeobiology)
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The origin and evolution of Lophotrochozoa can be traced to the plethora of lower Cambrian scleritome taxa.  We aim to determine the character suites linking these stem-Lophotrochozoa to their extant crown relatives, in particular the small shelly tommotiids and the stem-group brachiopods. Tracing the origin of morphological characters from these fossils informs the evolution and construction of lophotrochozoan body plans associated with the Cambrian Explosion. This is achieved by comparing records of exceptional preservation, most conspicuously Burgess Shale type Lagerstätten with more widespread Cambrian stem-brachiopods and small shelly fossils with their purported extant relatives, for example. Determining morphological character homologies is crucial to reconstructing the brachiopod stem-group and in polarising character changes associated with the putative transition from scleritome organisms to crown-group brachiopods. In this thesis arguments for a common origin of specific shell structures and exceptionally preserved soft-tissues are investigated. New records of enigmatic stem-group lophotrochozoans are described from two localities, the Indian Springs and Chengjiang Lagerstätte. Comprising the stem-brachiopod Mickwitzia cf. occidens, a putative stem-group entoproct Cotyledion tylodes and an enigmatic agglutinated tubular lophophorate possessing an unusual combination of phoronid, brachiopod and tommotiid characters, Yuganotheca elegans gen. et sp. nov. The interplay of bauplan, microbial activity and environmental factors resulting in such incidences of exceptional soft tissue preservation is also examined critically. Consequently, the evolution of through-gut bearing bilaterians is suggested as the reason for why the Cambrian hosts such a plethora of Lagerstätten. The closure of this taphonomic window is then associated with increased bioturbation following the Cambrian substrate revolution.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214
Keyword [en]
Brachiopoda, Chengjiang, Lagerstätte, Cambrian Explosion, palaeobiology, stem-group, entoproct, phoronid, tommotiid, exceptional preservation.
National Category
Evolutionary Biology Geology Other Earth and Related Environmental Sciences
Research subject
Earth Science with specialization in Historical Geology and Palaeontology
Identifiers
URN: urn:nbn:se:uu:diva-216363OAI: oai:DiVA.org:uu-216363DiVA: diva2:689788
Presentation
2014-02-19, Geo/Gm116 Norrland II, Geocentrum, Villavägen 16B, Uppsala, 13:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2014-02-06 Created: 2014-01-21 Last updated: 2014-02-06Bibliographically approved
List of papers
1. Exceptionally-preserved Mickwitzia from the Indian Springs Lagerstätte.
Open this publication in new window or tab >>Exceptionally-preserved Mickwitzia from the Indian Springs Lagerstätte.
(English)In: Journal of Paleontology, ISSN 0022-3360, E-ISSN 1937-2337Article in journal (Other academic) Accepted
Abstract [en]

A new assemblage of the early Cambrian stem group brachiopod Mickwitzia is described from the Indian Springs Lagerstätte possessing exceptionally preserved mantle setae. Critical analysis of shell structure and mantle setae from these specimens with those from additional sites with variable diagenetic history reveals the extent of taphonomic alteration and further sheds light on the phylogenetic position of the mickwitziids. A morphometric approach to shell outline and growth landmarks within these specimens reveals a clear species level discriminant signal of Nevada Mickwitzia in comparison to M. monlifera from Sweden. Detailed electron micrographs allow revision of the genus diagnosis for Mickwitzia based on presence of inward pointing phosphatic cones and tangential setae bearing tubes. We also conclude the inward pointing cone structures are not consistent with setal bearing structures as previously thought, but rather represent an endopunctae-like structure. A tommotiid-like shell architecture and presence of acrotretid columns in the dorsal juvenile shell of M. cf. occidens further strengthens the proposed close relationship between stem-group brachiopods and tommotiids.

Keyword
Brachiopoda, Mickwitzia, shell penetrating setae, lower Cambrian, Indian Springs
National Category
Other Earth and Related Environmental Sciences Geology Evolutionary Biology
Research subject
Earth Science with specialization in Historical Geology and Palaeontology
Identifiers
urn:nbn:se:uu:diva-216149 (URN)
Funder
Swedish Research Council, 2009-4395, 2012-1658
Available from: 2014-01-21 Created: 2014-01-19 Last updated: 2017-12-06
2. The role of microbes in decay and preservation: a Cambrian Explosion of animals and Lagerstätten.
Open this publication in new window or tab >>The role of microbes in decay and preservation: a Cambrian Explosion of animals and Lagerstätten.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The abrupt appearance of animals in the early Cambrian has been interpreted either as an explosive biological diversification or, alternatively, as an artefact resulting from a sudden increase in the probability of animal remains becoming fossilised. We attempt to reconcile these competing interpretations in exceptionally-preserved biota, which provide a vital part of our knowledge of the disparity and diversity of the Cambrian fauna. We assess the factors influencing the potential for exceptional fossil preservation using the brine shrimp Artemia salina as our experimental model. Following gut wall rupture, but prior to cuticle failure, internal, gut-derived microbes spread into the body cavity and formed pseudomorphs of tissues. Gut-derived microbes were shown to be the main factor mediating both decay and biofilm replacement and tissue stabilisation. This pattern of preservation is consistent with results from other experimental studies and with the nature of Burgess Shale type fossil remains. Thus, the evolution of a through-gut may have not only underpinned the ecological revolution that bilaterian diversification represents, but also catalysed the exceptional preservation of early bilaterian fossils.

Keyword
Cambrian Explosion, palaeobiology, taphonomy, bilateria, metazoa
National Category
Other Earth and Related Environmental Sciences Evolutionary Biology Geology
Research subject
Earth Science with specialization in Historical Geology and Palaeontology
Identifiers
urn:nbn:se:uu:diva-216151 (URN)
Available from: 2014-01-21 Created: 2014-01-19 Last updated: 2014-02-06
3. A sclerite-bearing stem group entoproct from the early Cambrian and its implications
Open this publication in new window or tab >>A sclerite-bearing stem group entoproct from the early Cambrian and its implications
Show others...
2013 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, 1066- p.Article in journal (Refereed) Published
Abstract [en]

The Lophotrochozoa includes disparate tentacle-bearing sessile protostome animals, which apparently appeared in the Cambrian explosion, but lack an uncontested fossil record. Here we describe abundant well preserved material of Cotyledion tylodes Luo et Hu, 1999, from the Cambrian (Series 2) Chengjiang deposits, reinterpreted here as a stem-group entoproct. The entoproct affinity is supported by the sessile body plan and interior soft anatomy. The body consists of an upper calyx and a lower elongate stalk with a distal holdfast. The soft anatomy includes a U-shaped gut with a mouth and aboral anus ringed by retractable marginal tentacles. Cotyledion differs from extant entoprocts in being larger, and having the calyx and the stalk covered by numerous loosely-spaced external sclerites. The description of entoprocts from the Chengjiang biota traces the ancestry of yet another lophotrochozoan phylum back to the Cambrian radiation, and has important implications for the earliest evolution of lophotrochozoans.

National Category
Natural Sciences
Research subject
Earth Science with specialization in Historical Geology and Palaeontology
Identifiers
urn:nbn:se:uu:diva-194748 (URN)10.1038/srep01066 (DOI)000313650900001 ()
Funder
Swedish Research Council, 2012–1658
Available from: 2013-03-13 Created: 2013-02-19 Last updated: 2017-12-06Bibliographically approved
4. An early Cambrian agglutinated tubular lophophorate with brachiopod characters
Open this publication in new window or tab >>An early Cambrian agglutinated tubular lophophorate with brachiopod characters
2014 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, 4682- p.Article in journal (Refereed) Published
Abstract [en]

The morphological disparity of lophotrochozoan phyla makes it difficult to predict the morphology of the last common ancestor. Only fossils of stem groups can help discover the morphological transitions that occurred along the roots of these phyla. Here, we describe a tubular fossil Yuganotheca elegans gen.et sp. nov. from the Cambrian (Stage 3) Chengjiang Lagerstätte (Yunnan, China) that exhibits an unusual combination of phoronid, brachiopod and tommotiid (Cambrian problematica) characters, notably a pair of agglutinated valves, enclosing a horseshoe-shaped lophophore, supported by a lower bipartite tubular attachment structure with a long coelomic pedicle providing anchorage. The discovery has important implications for the early evolution of lophotrochozoans, suggesting rooting of brachiopods into the sessile lophotrochozoans and the origination of their bivalved bauplan preceding the biomineralization of shell valves in crown brachiopods.

National Category
Geology Other Earth and Related Environmental Sciences Evolutionary Biology
Research subject
Earth Science with specialization in Historical Geology and Palaeontology
Identifiers
urn:nbn:se:uu:diva-216152 (URN)10.1038/srep04682 (DOI)000335885800001 ()
Funder
Swedish Research Council, 2009-4395, 2012-1658
Available from: 2014-01-21 Created: 2014-01-19 Last updated: 2017-12-06Bibliographically approved

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