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Controls on gut phosphatisation: the trilobites from the Weeks Formation Lagerstätte (Cambrian; Utah).

Lerosey-Aubril R, Hegna TA, Kier C, Bonino E, Habersetzer J, Carré M - PLoS ONE (2012)

Bottom Line: We hypothesize that the gut provided a microenvironment where special conditions could develop and harboured a source of phosphorus.However, in some specimens from the Weeks Formation, the phosphatisation extends to the entire digestive system, suggesting that trilobites might have had some biological particularities not observed in modern arthropods.We speculate that one of them might have been an increased capacity for ion storage in the gut tissues, related to the moulting of their heavily-mineralised carapace.

View Article: PubMed Central - PubMed

Affiliation: Department of Palaeontology and Historical Geology, Senckenberg Research Institute, Frankfurt am Main, Germany.

ABSTRACT
Despite being internal organs, digestive structures are frequently preserved in Cambrian Lagerstätten. However, the reasons for their fossilisation and their biological implications remain to be thoroughly explored. This is particularly true with arthropods--typically the most diverse fossilised organisms in Cambrian ecosystems--where digestive structures represent an as-yet underexploited alternative to appendage morphology for inferences on their biology. Here we describe the phosphatised digestive structures of three trilobite species from the Cambrian Weeks Formation Lagerstätte (Utah). Their exquisite, three-dimensional preservation reveals unique details on trilobite internal anatomy, such as the position of the mouth and the absence of a differentiated crop. In addition, the presence of paired pygidial organs of an unknown function is reported for the first time. This exceptional material enables exploration of the relationships between gut phosphatisation and the biology of organisms. Indeed, soft-tissue preservation is unusual in these fossils as it is restricted to the digestive structures, which indicates that the gut played a central role in its own phosphatisation. We hypothesize that the gut provided a microenvironment where special conditions could develop and harboured a source of phosphorus. The fact that gut phosphatization has almost exclusively been observed in arthropods could be explained by their uncommon ability to store ions (including phosphorous) in their digestive tissues. However, in some specimens from the Weeks Formation, the phosphatisation extends to the entire digestive system, suggesting that trilobites might have had some biological particularities not observed in modern arthropods. We speculate that one of them might have been an increased capacity for ion storage in the gut tissues, related to the moulting of their heavily-mineralised carapace.

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Arthropods bearing phosphatised digestive structures from the Middle Cambrian Weeks Formation.All specimens are complete and preserved dorsal side up, with head to top of image. A–E, Meniscopsia beebei. A, BPM 1017. B, BPM 1000. C, BPM 1001. D, BPM 1020. E, BPM 1018. F, Coosella kieri, BPM 1002. G, Geneviella granulatus, UU 11071.01. H, undetermined arthropod, BPM 1019. Scale bars: 5 mm.
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pone-0032934-g001: Arthropods bearing phosphatised digestive structures from the Middle Cambrian Weeks Formation.All specimens are complete and preserved dorsal side up, with head to top of image. A–E, Meniscopsia beebei. A, BPM 1017. B, BPM 1000. C, BPM 1001. D, BPM 1020. E, BPM 1018. F, Coosella kieri, BPM 1002. G, Geneviella granulatus, UU 11071.01. H, undetermined arthropod, BPM 1019. Scale bars: 5 mm.

Mentions: The House Range of central Utah is home to three Cambrian Konservat-Lagerstätten: the Marjum Formation, the Weeks Formation, and the Wheeler Shale. The Weeks Formation has received the least scientific attention of the three while paradoxically being well-known to amateur palaeontologists for its well-preserved and complete trilobites. The unit is a 300 m thick sequence of thin-bedded lime mudstones, locally enriched in siliciclastic sediments [5]. It is interpreted as a shallowing-upward sequence, transitional between the outer-shelf shale and lime mudstones of the underlying Marjum Formation and the shallow subtidal carbonates of the overlying Big Horse Limestone Member of the Orr Formation. Boundaries between the three units are conformable. A Guzhangian age (Cambrian, Series 3) can be proposed for most, if not the entirety of the Weeks Formation [5]. Laurentian Cambrian Lagerstätten were all deposited on the inner portion of the outer shelf [3], which likely explains the important similarities of their faunas. In this regard, the Weeks formation may be of particular interest, since it probably represents a shallower palaeoenvironment. However, the most remarkable feature of the Weeks Formation Lagerstätte is the quality of arthropod digestive system preservation. Digestive structures belonging to diverse arthropods are preserved in three dimensions (Figures 1A–H) and are best exemplified by the trilobites, which are discussed below.


Controls on gut phosphatisation: the trilobites from the Weeks Formation Lagerstätte (Cambrian; Utah).

Lerosey-Aubril R, Hegna TA, Kier C, Bonino E, Habersetzer J, Carré M - PLoS ONE (2012)

Arthropods bearing phosphatised digestive structures from the Middle Cambrian Weeks Formation.All specimens are complete and preserved dorsal side up, with head to top of image. A–E, Meniscopsia beebei. A, BPM 1017. B, BPM 1000. C, BPM 1001. D, BPM 1020. E, BPM 1018. F, Coosella kieri, BPM 1002. G, Geneviella granulatus, UU 11071.01. H, undetermined arthropod, BPM 1019. Scale bars: 5 mm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3303877&req=5

pone-0032934-g001: Arthropods bearing phosphatised digestive structures from the Middle Cambrian Weeks Formation.All specimens are complete and preserved dorsal side up, with head to top of image. A–E, Meniscopsia beebei. A, BPM 1017. B, BPM 1000. C, BPM 1001. D, BPM 1020. E, BPM 1018. F, Coosella kieri, BPM 1002. G, Geneviella granulatus, UU 11071.01. H, undetermined arthropod, BPM 1019. Scale bars: 5 mm.
Mentions: The House Range of central Utah is home to three Cambrian Konservat-Lagerstätten: the Marjum Formation, the Weeks Formation, and the Wheeler Shale. The Weeks Formation has received the least scientific attention of the three while paradoxically being well-known to amateur palaeontologists for its well-preserved and complete trilobites. The unit is a 300 m thick sequence of thin-bedded lime mudstones, locally enriched in siliciclastic sediments [5]. It is interpreted as a shallowing-upward sequence, transitional between the outer-shelf shale and lime mudstones of the underlying Marjum Formation and the shallow subtidal carbonates of the overlying Big Horse Limestone Member of the Orr Formation. Boundaries between the three units are conformable. A Guzhangian age (Cambrian, Series 3) can be proposed for most, if not the entirety of the Weeks Formation [5]. Laurentian Cambrian Lagerstätten were all deposited on the inner portion of the outer shelf [3], which likely explains the important similarities of their faunas. In this regard, the Weeks formation may be of particular interest, since it probably represents a shallower palaeoenvironment. However, the most remarkable feature of the Weeks Formation Lagerstätte is the quality of arthropod digestive system preservation. Digestive structures belonging to diverse arthropods are preserved in three dimensions (Figures 1A–H) and are best exemplified by the trilobites, which are discussed below.

Bottom Line: We hypothesize that the gut provided a microenvironment where special conditions could develop and harboured a source of phosphorus.However, in some specimens from the Weeks Formation, the phosphatisation extends to the entire digestive system, suggesting that trilobites might have had some biological particularities not observed in modern arthropods.We speculate that one of them might have been an increased capacity for ion storage in the gut tissues, related to the moulting of their heavily-mineralised carapace.

View Article: PubMed Central - PubMed

Affiliation: Department of Palaeontology and Historical Geology, Senckenberg Research Institute, Frankfurt am Main, Germany.

ABSTRACT
Despite being internal organs, digestive structures are frequently preserved in Cambrian Lagerstätten. However, the reasons for their fossilisation and their biological implications remain to be thoroughly explored. This is particularly true with arthropods--typically the most diverse fossilised organisms in Cambrian ecosystems--where digestive structures represent an as-yet underexploited alternative to appendage morphology for inferences on their biology. Here we describe the phosphatised digestive structures of three trilobite species from the Cambrian Weeks Formation Lagerstätte (Utah). Their exquisite, three-dimensional preservation reveals unique details on trilobite internal anatomy, such as the position of the mouth and the absence of a differentiated crop. In addition, the presence of paired pygidial organs of an unknown function is reported for the first time. This exceptional material enables exploration of the relationships between gut phosphatisation and the biology of organisms. Indeed, soft-tissue preservation is unusual in these fossils as it is restricted to the digestive structures, which indicates that the gut played a central role in its own phosphatisation. We hypothesize that the gut provided a microenvironment where special conditions could develop and harboured a source of phosphorus. The fact that gut phosphatization has almost exclusively been observed in arthropods could be explained by their uncommon ability to store ions (including phosphorous) in their digestive tissues. However, in some specimens from the Weeks Formation, the phosphatisation extends to the entire digestive system, suggesting that trilobites might have had some biological particularities not observed in modern arthropods. We speculate that one of them might have been an increased capacity for ion storage in the gut tissues, related to the moulting of their heavily-mineralised carapace.

Show MeSH
Related in: MedlinePlus