| 1. |
- Lagebro, Linda
(författare)
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The Arthropod Assemblage of the Upper Devonian Strud locality and its Ecology
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Devonian (419-359 million years ago) is the geological period when the terrestrial biota fully established. Early representatives from a terrestrial and continental aquatic biota have previously been reported from the Upper Devonian (Famennian) Strud quarry in Belgium, in the shape of seed-bearing plants and vertebrates (fish and early tetrapods). The palaeoenvironment is interpreted as a floodplain with slow accumulation of sediment in the river channels and adjacent shallow pools, subject to seasonal flooding and desiccation. This thesis presents the upper Famennian Strud ecosystem with representatives from the largest animal phylum – the Arthropoda. Pancrustaceans are dominating the arthropod assemblage by two eumalacostracans (previously described), three groups of branchiopods, and a putative insect, all collected in fine shales likely deposited in the shallow pools. The branchiopods from Strud comprise new members from all three extant clades, i.e. notostracans, anostracans, and spinicaudatan diplostracans. The notostracan Strudops goldenbergi is remarkable for its close resemblance with the extant genus Triops by the overall body plan and telson morphology. A phylogenetic analysis including modern and extinct notostracans and anostracans was performed, where Strudops appears as the earliest undisputed notostracan ever found. In addition, new genera of Anostraca (Haltinnaias serrata) and Spinicaudata (Gesvestheria pernegrei) are described herein. The insect Strudiella devonica consists of a single specimen and is interpreted to have been a nymph due to its minute size and wingless appearance. The chelicerates are represented by one or several species of eurypterids. So far unnamed juvenile eurypterid remains have also been found within the pool strata, and fragments of adult individuals in the coarser river deposits. The branchiopod community displays a unique insight to the ecosystem that these crustaceans inhabited. This is partly because of their co-occurrence, but mainly because they are preserved in close association to draught-resistant encysted eggs, in the same manner as modern day branchiopods do to survive and disperse during periods of drought and freezing. Altogether, the arthropod assemblage offers insight to Late Devonian freshwater ecosystems, and provides further understanding of the evolution of respective groups.
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| 2. |
- Larsson, Cecilia M
(författare)
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Early Cambrian Problematic Lophotrochozoans and Dilemmas of Scleritome Reconstructions
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The emergence and radiation of metazoan body plans around the Precambrian/Cambrian boundary, some 500-600 million years ago, seems to be concordant with the appearance and diversification of preservable hard parts. Several Precambrian soft-bodied, multicellular organisms most likely represent stem-group bilaterians, but their fossil record is rather sparse. In contrast, the Cambrian fossil record is comparably rich – comprising hard part, trace fossil and delicate soft tissue preservation – and most animal phyla that we know of today had evolved by the end of the Cambrian. Consequently, this time represents an important period in the early evolution of metazoan life forms. Most skeletal remnants of invertebrate organisms from this period are preserved in incomplete, disarticulated sclerite assemblages, and the true architecture of the original skeletal structure, the scleritome, may therefore be hard to discern. Many scleritomous taxa have been suggested to be members of the lophotrochozoan clade, while their exact position within this group remains unclear. Such taxa are often referred to as Problematica. This thesis deals with some problematic scleritomous early Cambrian lophotrochozoans, and as such also addresses the dilemmas of scleritome reconstructions. In the first part, completely disarticulated calcareous sclerites from the lower Cambrian of North Greenland are described as Trachyplax arctica. Hypothetical scleritome reconstruction alternatives and comparisons to other scleritome-bearing taxa are discussed, but the lack of articulated material obscures any satisfactory conclusions regarding phylogenetic affinities and the original morphology of the organism. The other part of the thesis focuses on some minute, organophosphatic scleritomous metazoans, tommotiids, found in lower Cambrian limestone successions in South Australia – Paterimitra pyramidalis and Kulparina rostrata – their scleritome architecture and their phylogenetic relationship with paterinid brachiopods. The oldest brachiopod from South Australia, Askepasma saproconcha, and the slightly younger Askepasma toddense are also described and discussed. Based on articulated specimens, recently described partial scleritomes of the tommotiid Eccentrotheca helenia and similarities in shell ultrastructure with both Eccentrotheca and Askepasma, Paterimitra is interpreted as a stem-group brachiopod and reconstructed as a bilaterally symmetrical, sessile, filter feeder with a tubular/conical scleritome. The morphological similarities with Paterimitra point in the same direction for the slightly older Kulparina.
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| 3. |
- Stein, Martin, 1976-
(författare)
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Evolution and taxonomy of Cambrian arthropods from Greenland and Sweden
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 4. |
- Egerquist, Eva, 1945-
(författare)
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Ordovician (Billingen and Volkhov stages) Brachiopod Faunas of the East Baltic
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lower-Middle Ordovician (Arenig) successions in the East Baltic have been investigated for more than one hundred and fifty years. Nevertheless detailed sampling still yields new species and better knowledge of the environment in which these organisms lived. The successions are well suited for bed by bed sampling because of the lack of tectonic disturbance and because the sequences are well documented. This study analyses collections of Billingen-Volkhov age mainly from the St. Petersburg region, but also from Estonia. A great deal of the material was obtained from the marly to clayey, soft sediment that intercalates the compact packstones and wackestones in the succession. Twenty-nine of these clay horizons were used for diversity estimates on the fauna through the succession. The most thoroughly investigated groups for this investigation were rhynchonelliformean brachiopods, conodonts and ostracodes. The results indicate that variances in diversity and abundance levels for these groups were not correlated, either to each other or to the small-scale sea level fluctuations that have been suggested for the region. However, diversity dynamics of brachiopods and ostracodes confirm the large-scale upward shallowing of the basin into the Upper Volkhov. Comparison with fossils from the limestones did not reveal any differences in faunal composition between the two preservation modes. The detailed sampling, coupled with sampling of the recently described mud mounds that occur in several outcrops, yielded large numbers of specimens. This enabled revision of earlier poorly known rhynchonelliformean genera such as Ujukella Andreev, as well as better known genera such as Porambonites Pander. In total the examined faunas include 31 genera assigned to 53 species of rhynchonelliformean brachiopods. Of these Leoniorthis and Eoporambonites are defined as new genera, and the following new species are described: Neumania paucicostata, Ranorthis rotunda, Orthidium gambolovensis, Orthidium lavensis, Skenidioides minutus, Tetralobula peregrina, Idiostrophia prima and Idiostrophia tenuicostata.
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| 5. |
- Lindström, Anna, 1970-
(författare)
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Shell repair as a response to attempted predation in some Palaeozoic and younger gastropods
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Traces of unsuccessful predatory attacks can be found in the hard parts of shell-bearing organisms as repaired shell injuries and are often preserved in the fossil record. These repaired shell injuries can help to deduce the relationship between predator and prey in the past. Gastropods afford an excellent opportunity for study since their shells are easily recognized from the Cambrian onwards, and usually preserve a full record of their life history. Predation is a phenomenon which has led to a great variety of adaptations among prey organisms in their quest to avoid being eaten. Increased predation pressure seems to have been one of the factors that has fueled the evolution of predation-resistant shell morphologies.Individual case studies examine the frequency of shell repair in assemblages of Palaeozoic gastropods from different geological periods. The Silurian species Poleumita discors showed a shell repair frequency of 10 %, while only 4 % of the Devonian species Praenatica gregaria have been repaired. The Palaeozoic bilaterally symmetrical bellorphontiform molluscs also showed low levels of shell repair.Similar shell morphologies in the long-lived group of pleurotomarioid gastropods were examined and shell repair frequenceis calculated to investigate potential variation through geological time. The Palaeozoic species showed repair frequencies of 17.1 % and 4.2 %. The frequency increased in the Mesozoic to between 28.8 % and 46.6 %, while all shells of Recent pleurotomarioids in the study showed repaired injuries. The repaired injuries found do not change in appearance through time, which is probably a reflection of the presence of the slit in the apertural margin. Which type of injury is the most abundant can be seen to change with time, and there is also an increase in size with time. This may be a defensive strategy taken up by the pleurotomarioids as a response to more abundant predators.
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| 6. |
- Skovsted, Christian B., 1974-
(författare)
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The Early Cambrian Fauna of North-East Greenland
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Small shelly fossils are common in sediments of Early Cambrian age and include the earliest common representatives of metazoan animals with mineralized hard parts. The group includes fossils of very different morphology, composition and ultrastructure. They seem to represent skeletal remains of numerous animal groups, the biological affinities of which are largely unresolved. However, the wide geographic range of many forms has the potential to enhance biostratigraphic and palaeogeographic resolution in the Early Cambrian. The late Early Cambrian sequence of North-East Greenland has yielded an assemblage of more than 88 species of small shelly fossils, brachiopods and trilobites, indicative of a middle Dyeran age (Botoman equivalent). The recovered fossils include a number of species that are known from other Early Cambrian palaeocontinents, and particularly strong ties to late Early Cambrian faunas of Australia are documented. The many cosmopolitan taxa thus identified suggests a close juxtaposition of palaeocontinents at this time. The systematic affinity of many of these small shelly fossils is poorly understood, partly because of their fragmentary nature and poor preservation. However, new data from North-East Greenland improves our understanding of the function and biological affinity of certain taxa. Collections of the problematic fossil Mongolitubulus from North and North-East Greenland exhibit characters indicative of a defensive function as spines of bivalved arthropods, while species of the problematic genus Triplicatella represent the opercula of an unknown tubular shell, probably related to orthothecid hyoliths. The bivalved fossil Mickwitzia from North-East Greenland combines characters of linguliform brachiopods and sclerites of Micrina, a non-bivalved problematic form (halkieriid) from Australia. The combination suggests that Mickwitzia is a stem group brachiopod and strengthens arguments for a halkieriid ancestry of the brachiopod phylum.
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