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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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Reconstructions of the digestive systems of a trilobite and a remipedian.A, digestive system of the trilobite Meniscopsia beebei in dorsal, right lateral, and ventral views (from left to right). B, digestive system of the remipedian Speleonectes gironensis in dorsal, right lateral, and ventral views (from left to right; reconstruction based on [65], [66]). In both reconstructions, the foregut and hindgut are in bright pink, the midgut tract in blue-violet, and the midgut caeca/glands in lavender. Scale bars: 5 mm for (A) and 1 mm for (B).
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pone-0032934-g004: Reconstructions of the digestive systems of a trilobite and a remipedian.A, digestive system of the trilobite Meniscopsia beebei in dorsal, right lateral, and ventral views (from left to right). B, digestive system of the remipedian Speleonectes gironensis in dorsal, right lateral, and ventral views (from left to right; reconstruction based on [65], [66]). In both reconstructions, the foregut and hindgut are in bright pink, the midgut tract in blue-violet, and the midgut caeca/glands in lavender. Scale bars: 5 mm for (A) and 1 mm for (B).

Mentions: The outstanding quality of the preservation allows previously unrecorded details of the digestive system of trilobites to be observed [8] (for detailed descriptions of each specimen, see Text S1). This is particularly true for M. beebei, where DS are known from seven specimens, which permits a complete description of the species's digestive system (Figure 4A). It is composed of a central tract and three cephalic and seven thoracic digestive caeca (Dc; Figures 1A, 2A, B, 3A, B). Anteriorly, the tract bears a short but broad sagittal depression, giving a bilobate appearance (Figures 2A, D). Uniformly wide (c. 25% of the maximum width of the glabella [transverse, tr.]) beneath the glabella, it tapers posteriorly until the seventh thoracic segment (c. a half of cephalic width), and then remains roughly constant in width in its posterior portion (Figures 1A, B). The paired Dc are similar in shape but decrease in size posteriorly. Their insertions occur dorso-laterally on the digestive tract and they are wide (exsagittally, exs.), especially those of the first four pairs (Figure 3A). The anterior halves (exs.) of the Dc project abaxially and slightly anteriorly for a distance equal to half the width (tr.) of the tract. The best-preserved specimen (BPM 1017) displays a shallow sagittal furrow dorsally along the caeca-bearing portion of the tract (Figure 3D), which might have hosted the dorsal heart. On the posterior portion of the tract (e.g. BPM 1000), fine, grossly transversal furrows are visible. Three specimens exhibit a dark stain behind the posterior tip of the pygidial axis (Figures 3E–G), which may represent material exuded from the anus after death. In addition, one specimen (BPM 1017) possesses a pair of rounded structures under the pygidial pleurae (Figure 1A). Microradiograph of specimen BPM 1017 shows ventral structures beneath the anteriormost portion of the dorsal tract (Figures 3B, C). These are tentatively interpreted as the oesophagus and posteriorly-facing mouth, with the surrounding material probably exuded from the mouth after death. This observation confirms the presence of a J-shaped gut in trilobites. The mouth is just in front of the first of pair of Dc, which corresponds to a short distance behind the anterior wings of the hypostome, which are visible in in situ position.


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)

Reconstructions of the digestive systems of a trilobite and a remipedian.A, digestive system of the trilobite Meniscopsia beebei in dorsal, right lateral, and ventral views (from left to right). B, digestive system of the remipedian Speleonectes gironensis in dorsal, right lateral, and ventral views (from left to right; reconstruction based on [65], [66]). In both reconstructions, the foregut and hindgut are in bright pink, the midgut tract in blue-violet, and the midgut caeca/glands in lavender. Scale bars: 5 mm for (A) and 1 mm for (B).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0032934-g004: Reconstructions of the digestive systems of a trilobite and a remipedian.A, digestive system of the trilobite Meniscopsia beebei in dorsal, right lateral, and ventral views (from left to right). B, digestive system of the remipedian Speleonectes gironensis in dorsal, right lateral, and ventral views (from left to right; reconstruction based on [65], [66]). In both reconstructions, the foregut and hindgut are in bright pink, the midgut tract in blue-violet, and the midgut caeca/glands in lavender. Scale bars: 5 mm for (A) and 1 mm for (B).
Mentions: The outstanding quality of the preservation allows previously unrecorded details of the digestive system of trilobites to be observed [8] (for detailed descriptions of each specimen, see Text S1). This is particularly true for M. beebei, where DS are known from seven specimens, which permits a complete description of the species's digestive system (Figure 4A). It is composed of a central tract and three cephalic and seven thoracic digestive caeca (Dc; Figures 1A, 2A, B, 3A, B). Anteriorly, the tract bears a short but broad sagittal depression, giving a bilobate appearance (Figures 2A, D). Uniformly wide (c. 25% of the maximum width of the glabella [transverse, tr.]) beneath the glabella, it tapers posteriorly until the seventh thoracic segment (c. a half of cephalic width), and then remains roughly constant in width in its posterior portion (Figures 1A, B). The paired Dc are similar in shape but decrease in size posteriorly. Their insertions occur dorso-laterally on the digestive tract and they are wide (exsagittally, exs.), especially those of the first four pairs (Figure 3A). The anterior halves (exs.) of the Dc project abaxially and slightly anteriorly for a distance equal to half the width (tr.) of the tract. The best-preserved specimen (BPM 1017) displays a shallow sagittal furrow dorsally along the caeca-bearing portion of the tract (Figure 3D), which might have hosted the dorsal heart. On the posterior portion of the tract (e.g. BPM 1000), fine, grossly transversal furrows are visible. Three specimens exhibit a dark stain behind the posterior tip of the pygidial axis (Figures 3E–G), which may represent material exuded from the anus after death. In addition, one specimen (BPM 1017) possesses a pair of rounded structures under the pygidial pleurae (Figure 1A). Microradiograph of specimen BPM 1017 shows ventral structures beneath the anteriormost portion of the dorsal tract (Figures 3B, C). These are tentatively interpreted as the oesophagus and posteriorly-facing mouth, with the surrounding material probably exuded from the mouth after death. This observation confirms the presence of a J-shaped gut in trilobites. The mouth is just in front of the first of pair of Dc, which corresponds to a short distance behind the anterior wings of the hypostome, which are visible in in situ position.

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