Abstract: Frustule fragmentation is one of the major taphonomic factors affecting diatom preservation in Pampean shallow lakes. Although this has been demonstrated by taphonomic studies conducted on extant and fossil material, little is known about the causes of frustule breakage and its environmental significance. Field studies along modern environmental gradients showed a low but significant correlation between dissolution and fragmentation. Reworking of sediments by wind action has also been suggested as a plausible explanation for the fragmentation patterns observed in the field. To evaluate the relative importance of chemical and physical causes of diatom fragmentation, three laboratory experiments were conducted to test for (1) the effect of physical agitation; (2) the effect of chemical dissolution; and (3) the joint effect of both variables on diatom fragmentation. Diatom samples were subjected to physical agitation with a reciprocating shaker at 250 rpm for 20 days. Chemical dissolution was tested by mixing diatom assemblages with solutions of different concentrations of NaCl and NaHCO3, and pH 10 for 20 days. The joint effect of both processes was tested by dissolving diatom assemblages in salt solutions and subjecting them simultaneously to agitation for 20 days at 250 rpm. In all cases, aliquots of each assemblage were sampled at initial and final experimental times and their preservation analyzed via the application of fragmentation and dissolution indices. Significant and similar differences in fragmentation indices were observed in both dissolution alone and combined experiments, but no differences were found in samples subjected to agitation alone. In all cases, dissolution and fragmentation indices were correlated, suggesting a causal relationship between them. Overall, our results suggest that the debilitation of the diatom frustule by chemical dissolution may be the main cause of the fragmentation patterns observed in surface sediments of Pampean shallow lakes.
{"title":"EXPERIMENTAL TAPHONOMY OF FRESHWATER DIATOMS: DISCRIMINATING BETWEEN CHEMICAL AND PHYSICAL CAUSES OF FRUSTULE FRAGMENTATION","authors":"G. Hassan, M. Díaz","doi":"10.2110/palo.2021.047","DOIUrl":"https://doi.org/10.2110/palo.2021.047","url":null,"abstract":"Abstract: Frustule fragmentation is one of the major taphonomic factors affecting diatom preservation in Pampean shallow lakes. Although this has been demonstrated by taphonomic studies conducted on extant and fossil material, little is known about the causes of frustule breakage and its environmental significance. Field studies along modern environmental gradients showed a low but significant correlation between dissolution and fragmentation. Reworking of sediments by wind action has also been suggested as a plausible explanation for the fragmentation patterns observed in the field. To evaluate the relative importance of chemical and physical causes of diatom fragmentation, three laboratory experiments were conducted to test for (1) the effect of physical agitation; (2) the effect of chemical dissolution; and (3) the joint effect of both variables on diatom fragmentation. Diatom samples were subjected to physical agitation with a reciprocating shaker at 250 rpm for 20 days. Chemical dissolution was tested by mixing diatom assemblages with solutions of different concentrations of NaCl and NaHCO3, and pH 10 for 20 days. The joint effect of both processes was tested by dissolving diatom assemblages in salt solutions and subjecting them simultaneously to agitation for 20 days at 250 rpm. In all cases, aliquots of each assemblage were sampled at initial and final experimental times and their preservation analyzed via the application of fragmentation and dissolution indices. Significant and similar differences in fragmentation indices were observed in both dissolution alone and combined experiments, but no differences were found in samples subjected to agitation alone. In all cases, dissolution and fragmentation indices were correlated, suggesting a causal relationship between them. Overall, our results suggest that the debilitation of the diatom frustule by chemical dissolution may be the main cause of the fragmentation patterns observed in surface sediments of Pampean shallow lakes.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":"38 1","pages":"125 - 135"},"PeriodicalIF":1.6,"publicationDate":"2023-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43880180","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Matias Do Nascimento Ritter, Fernando Erthal, R. S. Horodyski
MATIAS DO NASCIMENTO RITTER, FERNANDO ERTHAL, AND RODRIGO SCALISE HORODYSKI Centro de Estudos Costeiros, Limnológicos e Marinhos, Campus Litoral Norte, Universidade Federal do Rio Grande do Sul, Imbé, RS, CEP 95625-000, Brazil (ORCID: MNR; 0000-0001-8150-4443) Programa de Pós-Graduação em Geociências, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, CEP 91501-970, Brazil Departamento de Paleontologia e Estratigrafia, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, CEP 91501-970, Brazil (ORCID: FE; 0000-0001-8036-192X) Geology Graduate Program, Unisinos University, São Leopoldo, Brazil (ORCID: RSH; 0000-0001-7195-2170). email: matias.ritter@ufrgs.br
MATIAS DO NASCIMENTO RITTER, FERNANDO ERTHAL和RODRIGO SCALISE HORODYSKI海岸、湖泊和海洋研究中心，北海岸校区，里约热内卢Grande DO Sul联邦大学，imbe, RS, CEP 95625-000，巴西(ORCID: MNR;南大联邦大学地球科学研究所地球科学研究生项目，阿雷格里港，RS, CEP 91501-970，巴西南大联邦大学地球科学研究所古生物与地层学系，阿雷格里港，RS, CEP 91501-970，巴西(ORCID: FE;美国地质学会地质研究生项目，Unisinos大学，sao Leopoldo，巴西(ORCID: RSH;0000 -0001 -7195 -2170)。电子邮件:matias.ritter@ufrgs.br
{"title":"THE PRESENT IS THE KEY TO THE PAST: ACTUALISTIC TAPHONOMY IN SOUTH AMERICA","authors":"Matias Do Nascimento Ritter, Fernando Erthal, R. S. Horodyski","doi":"10.2110/palo.2023.008","DOIUrl":"https://doi.org/10.2110/palo.2023.008","url":null,"abstract":"MATIAS DO NASCIMENTO RITTER, FERNANDO ERTHAL, AND RODRIGO SCALISE HORODYSKI Centro de Estudos Costeiros, Limnológicos e Marinhos, Campus Litoral Norte, Universidade Federal do Rio Grande do Sul, Imbé, RS, CEP 95625-000, Brazil (ORCID: MNR; 0000-0001-8150-4443) Programa de Pós-Graduação em Geociências, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, CEP 91501-970, Brazil Departamento de Paleontologia e Estratigrafia, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, CEP 91501-970, Brazil (ORCID: FE; 0000-0001-8036-192X) Geology Graduate Program, Unisinos University, São Leopoldo, Brazil (ORCID: RSH; 0000-0001-7195-2170). email: matias.ritter@ufrgs.br","PeriodicalId":54647,"journal":{"name":"Palaios","volume":"38 1","pages":"109 - 110"},"PeriodicalIF":1.6,"publicationDate":"2023-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43114639","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
ABSTRACT: Rapana venosa (Valenciennes, 1846) is an invasive gastropod, the arrival of which in the Río de La Plata estuary 22 years ago is well-documented. Rapana venosa shells were collected during two sampling events from four beaches with different substrate types and wave energy regimes to compare the taphonomic attributes under different environmental conditions. We analyzed the samples by comparing frequencies of taphonomic attributes. Our results show that intermediate-reflective beaches with rocky substrates were dominated by intermediate- to highly fragmented specimens, with high corrasion, intermediate to high bioerosion, low bioencrustation, and medium to large sizes. In contrast, intermediate-dissipative beaches with sandy substrate, mobile stones, and occasional consolidated sediments were dominated by less fragmented shells, high to intermediate corrasion, scarcer bioerosion, low bioencrustation, and small- to medium-sized specimens. Results suggest that significant taphonomic differences arise within two decades under natural conditions. These findings imply that paleoenvironmental signals derived from the taphonomic attributes of fossil assemblages emerge much faster than the potential duration of time averaging of shelly fossils in shallow marine settings.
{"title":"TAPHONOMIC SIGNATURES IN DEAD SHELLS OF THE INVASIVE GASTROPOD RAPANA VENOSA (VALENCIENNES, 1846) AFTER TWO DECADES IN THE RÍO DE LA PLATA, URUGUAY","authors":"María Cecilia Gómez-Maduro, A. Rojas, S. Martínez","doi":"10.2110/palo.2021.070","DOIUrl":"https://doi.org/10.2110/palo.2021.070","url":null,"abstract":"ABSTRACT: Rapana venosa (Valenciennes, 1846) is an invasive gastropod, the arrival of which in the Río de La Plata estuary 22 years ago is well-documented. Rapana venosa shells were collected during two sampling events from four beaches with different substrate types and wave energy regimes to compare the taphonomic attributes under different environmental conditions. We analyzed the samples by comparing frequencies of taphonomic attributes. Our results show that intermediate-reflective beaches with rocky substrates were dominated by intermediate- to highly fragmented specimens, with high corrasion, intermediate to high bioerosion, low bioencrustation, and medium to large sizes. In contrast, intermediate-dissipative beaches with sandy substrate, mobile stones, and occasional consolidated sediments were dominated by less fragmented shells, high to intermediate corrasion, scarcer bioerosion, low bioencrustation, and small- to medium-sized specimens. Results suggest that significant taphonomic differences arise within two decades under natural conditions. These findings imply that paleoenvironmental signals derived from the taphonomic attributes of fossil assemblages emerge much faster than the potential duration of time averaging of shelly fossils in shallow marine settings.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":"38 1","pages":"136 - 147"},"PeriodicalIF":1.6,"publicationDate":"2023-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43045583","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
ABSTRACT: Premortem and postmortem processes significantly influence the formation of the molluscan fossil record in freshwater environments. Despite their importance for paleoenvironmental studies, they remain poorly understood. In Pampean shallow lakes, Holocene shell deposits of the euryhaline snail Heleobia parchappii show a relation with salinity, as preservation seems to be favored by brackish-saline water conditions. To explore if this pattern may respond to ecological (i.e., differential survival and reproduction) or taphonomic processes acting differently in freshwater and brackish-saline environments, we conducted a field-based study comparing premortem (abundance, length, width/length ratio, and crushing resistance in living and dead shells) and postmortem (fragmentation, fine-scale surface alteration, and loss of periostracum of dead shells) attributes along a modern lacustrine salinity gradient (0.5–40 ppt) in the Pampa plain of Argentina. Snails from saline lakes were smaller and more rotund than those from freshwater lakes, exhibiting higher abundances and resistances in death assemblages. They showed the highest fidelity in shell length and the best states of preservation, which were similar to values recorded in fossil shells. We concluded that shells deposited in saline lakes are better preserved than those deposited in freshwater lakes, giving rise to highly abundant shell concentrations, analogues to those shell-rich fossil levels recorded in Pampean lakes. Such abundance does not reflect the natural abundances of living snails, but rather is the result of the combined influence that less destructive environments and better shell intrinsic properties have on preservation.
{"title":"SALINITY-RELATED PRESERVATION OF MOLLUSKS IN SHALLOW LAKES: IMPLICATIONS FOR THE UNDERSTANDING OF THE LACUSTRINE PAMPEAN FOSSIL RECORD","authors":"Claudio G. De Francesco, G. Hassan","doi":"10.2110/palo.2021.048","DOIUrl":"https://doi.org/10.2110/palo.2021.048","url":null,"abstract":"ABSTRACT: Premortem and postmortem processes significantly influence the formation of the molluscan fossil record in freshwater environments. Despite their importance for paleoenvironmental studies, they remain poorly understood. In Pampean shallow lakes, Holocene shell deposits of the euryhaline snail Heleobia parchappii show a relation with salinity, as preservation seems to be favored by brackish-saline water conditions. To explore if this pattern may respond to ecological (i.e., differential survival and reproduction) or taphonomic processes acting differently in freshwater and brackish-saline environments, we conducted a field-based study comparing premortem (abundance, length, width/length ratio, and crushing resistance in living and dead shells) and postmortem (fragmentation, fine-scale surface alteration, and loss of periostracum of dead shells) attributes along a modern lacustrine salinity gradient (0.5–40 ppt) in the Pampa plain of Argentina. Snails from saline lakes were smaller and more rotund than those from freshwater lakes, exhibiting higher abundances and resistances in death assemblages. They showed the highest fidelity in shell length and the best states of preservation, which were similar to values recorded in fossil shells. We concluded that shells deposited in saline lakes are better preserved than those deposited in freshwater lakes, giving rise to highly abundant shell concentrations, analogues to those shell-rich fossil levels recorded in Pampean lakes. Such abundance does not reflect the natural abundances of living snails, but rather is the result of the combined influence that less destructive environments and better shell intrinsic properties have on preservation.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":"38 1","pages":"111 - 124"},"PeriodicalIF":1.6,"publicationDate":"2023-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45078185","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Ritter, Fernando Erthal, M. Kosnik, M. Kowalewski, J. Coimbra, F. Caron, D. Kaufman
Abstract: Surficial shell accumulations from shallow marine settings are typically averaged over centennial-to-millennial time scales and dominated by specimens that died in the most recent centuries, resulting in strongly right-skewed age-frequency distributions (AFDs). However, AFDs from modern offshore settings (outer shelf and uppermost continental slope) still need to be explored. Using individually dated shells (14C-calibrated amino acid racemization), we compared AFDs along an onshore-offshore gradient across the southern Brazilian shelf, with sites ranging from the inner shelf, shallow-water (< 40 m) to offshore, deep-water (> 100 m) settings. The duration of time averaging is slightly higher in deeper water environments, and the AFD shapes change along the depositional profile. The inner shelf AFDs are strongly right-skewed due to the dominance of shells from the most recent millennia (median age range: 0–3 ka). In contrast, on the outer shelf and the uppermost continental slope, AFDs are symmetrical to left-skewed and dominated by specimens that died following the Last Glacial Maximum (median age range: 15–18 ka). The onshore-offshore changes in the observed properties of AFDs—increased median age and decreased skewness, but only slightly increased temporal mixing—likely reflect changes in sea level and concurrent water depth-related changes in biological productivity. These results suggest that on a passive continental margin subject to post-glacial sea-level changes, the magnitude of time-averaging of shell assemblages is less variable along the depositional profile than shell assemblage ages and the shapes of AFDs.
{"title":"ONSHORE-OFFSHORE TRENDS IN THE TEMPORAL RESOLUTION OF MOLLUSCAN DEATH ASSEMBLAGES: HOW AGE-FREQUENCY DISTRIBUTIONS REVEAL QUATERNARY SEA-LEVEL HISTORY","authors":"M. Ritter, Fernando Erthal, M. Kosnik, M. Kowalewski, J. Coimbra, F. Caron, D. Kaufman","doi":"10.2110/palo.2021.041","DOIUrl":"https://doi.org/10.2110/palo.2021.041","url":null,"abstract":"Abstract: Surficial shell accumulations from shallow marine settings are typically averaged over centennial-to-millennial time scales and dominated by specimens that died in the most recent centuries, resulting in strongly right-skewed age-frequency distributions (AFDs). However, AFDs from modern offshore settings (outer shelf and uppermost continental slope) still need to be explored. Using individually dated shells (14C-calibrated amino acid racemization), we compared AFDs along an onshore-offshore gradient across the southern Brazilian shelf, with sites ranging from the inner shelf, shallow-water (< 40 m) to offshore, deep-water (> 100 m) settings. The duration of time averaging is slightly higher in deeper water environments, and the AFD shapes change along the depositional profile. The inner shelf AFDs are strongly right-skewed due to the dominance of shells from the most recent millennia (median age range: 0–3 ka). In contrast, on the outer shelf and the uppermost continental slope, AFDs are symmetrical to left-skewed and dominated by specimens that died following the Last Glacial Maximum (median age range: 15–18 ka). The onshore-offshore changes in the observed properties of AFDs—increased median age and decreased skewness, but only slightly increased temporal mixing—likely reflect changes in sea level and concurrent water depth-related changes in biological productivity. These results suggest that on a passive continental margin subject to post-glacial sea-level changes, the magnitude of time-averaging of shell assemblages is less variable along the depositional profile than shell assemblage ages and the shapes of AFDs.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":"38 1","pages":"148 - 157"},"PeriodicalIF":1.6,"publicationDate":"2023-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48541700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
F. R. Branco, F. Callefo, M. A. Zezzi Arruda, Gustavo De Sousa Pessôa, Alcina Magnólia Franca Barreto, A. Ghilardi, Lara Maldanis, Luiz Ricardo Da Silva Lóbo Do Nascimento
ABSTRACT: Early diagenesis of fossil plants, especially of their reproductive structures, provides essential information about the evolution of the group. In this study, we describe the morphology and early fossil diagenesis of isolated eudicot seeds collected in neosols (entisols) derived from limestones of Romualdo Formation, Araripe Basin, Brazil. They were studied using scanning electron microscopy, X-ray microtomography, and laser ablation inductively coupled plasma mass spectrometry in the imaging mode. The seeds were three-dimensionally preserved with volumes ranging from 10.16 to 18.57 mm3. The morphology and anatomy are described, and the specimens are identified as Fabidae seeds. It is known that Fabidae arose in the mid-late Cretaceous, so the seeds were considered diachronic to the paleobiota from the Romualdo Formation, not belonging to this stratigraphy. Based on the spectrometric intensities of the mapped elements, such as C, Fe, Si, and Cu, intensity images were elaborated on these elements on the surface and inside the seeds. The maps indicated higher intensities of C, Fe, Si, and Cu in the seed tissues than those in modern seeds, suggesting an early stage of diagenesis. The calcareous sandstones of the Romualdo Formation may have contributed charged ions carried by meteoric water and groundwater, and they later precipitated in the organic tissues, triggering the start of diagenesis in the soil.
{"title":"EARLY DIAGENESIS OF SEEDS ASSOCIATED WITH LIMESTONES SOILS","authors":"F. R. Branco, F. Callefo, M. A. Zezzi Arruda, Gustavo De Sousa Pessôa, Alcina Magnólia Franca Barreto, A. Ghilardi, Lara Maldanis, Luiz Ricardo Da Silva Lóbo Do Nascimento","doi":"10.2110/palo.2021.053","DOIUrl":"https://doi.org/10.2110/palo.2021.053","url":null,"abstract":"ABSTRACT: Early diagenesis of fossil plants, especially of their reproductive structures, provides essential information about the evolution of the group. In this study, we describe the morphology and early fossil diagenesis of isolated eudicot seeds collected in neosols (entisols) derived from limestones of Romualdo Formation, Araripe Basin, Brazil. They were studied using scanning electron microscopy, X-ray microtomography, and laser ablation inductively coupled plasma mass spectrometry in the imaging mode. The seeds were three-dimensionally preserved with volumes ranging from 10.16 to 18.57 mm3. The morphology and anatomy are described, and the specimens are identified as Fabidae seeds. It is known that Fabidae arose in the mid-late Cretaceous, so the seeds were considered diachronic to the paleobiota from the Romualdo Formation, not belonging to this stratigraphy. Based on the spectrometric intensities of the mapped elements, such as C, Fe, Si, and Cu, intensity images were elaborated on these elements on the surface and inside the seeds. The maps indicated higher intensities of C, Fe, Si, and Cu in the seed tissues than those in modern seeds, suggesting an early stage of diagenesis. The calcareous sandstones of the Romualdo Formation may have contributed charged ions carried by meteoric water and groundwater, and they later precipitated in the organic tissues, triggering the start of diagenesis in the soil.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":"38 1","pages":"158 - 171"},"PeriodicalIF":1.6,"publicationDate":"2023-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48583541","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Riley C. Morton, Reed A. Myers, M. Gingras, J. Zonneveld
ABSTRACT: An array of trace fossils have been ascribed to brittle-star behaviors including locomotion traces such as Biformites. Brittle-star locomotion has been well described but little work has been done to link modern brittle-star behavior to the trace fossil record. To draw this connection, a brittle star was kept in an aquarium and isolated in a “walking” tank with a fine glass-bead substrate. The animal was left in the walking tank for 30 minutes then the substrate was examined for traces. A digital camera was used to record the animal's movements and to document the resulting traces. Photographs were processed with photogrammetry software to produce digital models in order to acquire high-resolution images. Walking traces were described in detail and two morphologies were identified, which correspond with the ‘rowing’ and ‘reverse-rowing’ modes of brittle-star locomotion. Interestingly, traces similar to Biformites were not formed although some Biformites characters are observed. Morphological similarities include elongated lobate depressions and bioglyphs. Trackway dissimilarities include a repeating, paired, symmetrical pattern observed in the lab contrasting with Biformites that is often expressed as a texture of dense and overlapping, or isolated imprints. Another dissimilarity is the expression of bioglyphs in the lab as striae compared to the positive protuberances observed in Biformites. This study illustrates the utility of using actualistic observations to: (1) refine interpretations of locomotory mechanisms, such as rowing and reverse rowing, for a better understanding of walking behavior, and (2) to expand recognition criteria for ophiuroid (and other taxa) tracks in the fossil record.
{"title":"AQUARIA-BASED OBSERVATIONS OF THE OPHIUROID OPHIOLEPIS SUPERBA AND THE TRACKWAYS IT PRODUCES","authors":"Riley C. Morton, Reed A. Myers, M. Gingras, J. Zonneveld","doi":"10.2110/palo.2022.035","DOIUrl":"https://doi.org/10.2110/palo.2022.035","url":null,"abstract":"ABSTRACT: An array of trace fossils have been ascribed to brittle-star behaviors including locomotion traces such as Biformites. Brittle-star locomotion has been well described but little work has been done to link modern brittle-star behavior to the trace fossil record. To draw this connection, a brittle star was kept in an aquarium and isolated in a “walking” tank with a fine glass-bead substrate. The animal was left in the walking tank for 30 minutes then the substrate was examined for traces. A digital camera was used to record the animal's movements and to document the resulting traces. Photographs were processed with photogrammetry software to produce digital models in order to acquire high-resolution images. Walking traces were described in detail and two morphologies were identified, which correspond with the ‘rowing’ and ‘reverse-rowing’ modes of brittle-star locomotion. Interestingly, traces similar to Biformites were not formed although some Biformites characters are observed. Morphological similarities include elongated lobate depressions and bioglyphs. Trackway dissimilarities include a repeating, paired, symmetrical pattern observed in the lab contrasting with Biformites that is often expressed as a texture of dense and overlapping, or isolated imprints. Another dissimilarity is the expression of bioglyphs in the lab as striae compared to the positive protuberances observed in Biformites. This study illustrates the utility of using actualistic observations to: (1) refine interpretations of locomotory mechanisms, such as rowing and reverse rowing, for a better understanding of walking behavior, and (2) to expand recognition criteria for ophiuroid (and other taxa) tracks in the fossil record.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":"38 1","pages":"98 - 108"},"PeriodicalIF":1.6,"publicationDate":"2023-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48174205","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract: The type material of Tisoa siphonalis de Serres, 1840 is lost but nearly complete specimens occur at the herein designated type locality Hameau de Valz (Department of Gard, France), where Tisoa is present in dark Pliensbachian organic-rich mudrock. The upper part of the trace is encased in a concretion. The concretion's carbonate content implies 65% initial porosity, a value typical of soft mud. Such a consistency is also indicated by shallowly produced biodeformational structures that dominate the fabric; in association with small traces they are diagnostic of low-oxygenated bottom water and anoxic conditions just below the seafloor. At its type locality, Tisoa represents a nearly vertical protrusive spreite burrow, exceeding 2 m in length and having nearly parallel limbs 0.1–1.5 cm apart. The spreite is only weakly expressed; the inter-limb material was apparently not processed during deepening of the U-tube but placed directly in the spreite or pressed aside. Tisoa deviates slightly but consistently from a vertical orientation and commonly shows a low-amplitude helicoidal course. The U-tube exhibits a thick pyrite lining implying the former presence of mucus. The steep chemical gradient between oxygenated water in the U-tube and anoxic host sediment evidently fostered microbial activity. The extraordinary penetration depth of Tisoa suggests exploitation of extreme redox conditions such as could be found in the methanogenesis zone. The Tisoa producer probably deepened the U-tube incrementally, continuing when the chemical gradient between tube and host sediment declined due to circulation of the oxygenated water used for respiration. The Tisoa producers might have fed on suspended material, microbes flourishing along the tube wall, or acquired nutrition via chemosymbionts.
摘要1840年Tisoa siphonalis de Serres的模式材料丢失，但在本文指定的模式地点Hameau de Valz(法国加尔省)发现了几乎完整的标本，Tisoa存在于黑暗的pliensbachia富有机质泥岩中。痕迹的上部包裹在一种固结物中。固结物的碳酸盐含量意味着65%的初始孔隙度，这是软泥的典型值。这种一致性也体现在主导织物的浅层生物变形结构上;与少量痕迹相联系，它们可以诊断低氧的底部水和海底以下的缺氧条件。在其类型位置，Tisoa代表一个近垂直的突出的spite洞穴，长度超过2 m，四肢几乎平行，相距0.1-1.5 cm。精灵只是弱表达;在u型管加深过程中，肢间材料显然没有被加工，而是直接放置在积雪中或压在一边。Tisoa稍微偏离垂直方向，但始终如一，通常表现为低振幅螺旋轨迹。u型管有一层厚的黄铁矿衬里，表明以前有粘液存在。u型管中含氧水和缺氧宿主沉积物之间的陡峭化学梯度明显促进了微生物的活动。二氧化钛非同寻常的渗透深度表明，利用了甲烷生成带中可能发现的极端氧化还原条件。Tisoa生产者可能会逐渐加深u型管，当管和宿主沉积物之间的化学梯度由于用于呼吸的含氧水的循环而下降时，u型管继续加深。Tisoa生产者可能以悬浮物质、沿着管壁生长的微生物为食，或者通过化学共生体获得营养。
{"title":"THE TRACE FOSSIL TISOA SIPHONALIS IN ITS TYPE AREA—CHARACTERISTICS AND ENVIRONMENTAL SIGNIFICANCE","authors":"A. Wetzel, J. Blouet","doi":"10.2110/palo.2022.036","DOIUrl":"https://doi.org/10.2110/palo.2022.036","url":null,"abstract":"Abstract: The type material of Tisoa siphonalis de Serres, 1840 is lost but nearly complete specimens occur at the herein designated type locality Hameau de Valz (Department of Gard, France), where Tisoa is present in dark Pliensbachian organic-rich mudrock. The upper part of the trace is encased in a concretion. The concretion's carbonate content implies 65% initial porosity, a value typical of soft mud. Such a consistency is also indicated by shallowly produced biodeformational structures that dominate the fabric; in association with small traces they are diagnostic of low-oxygenated bottom water and anoxic conditions just below the seafloor. At its type locality, Tisoa represents a nearly vertical protrusive spreite burrow, exceeding 2 m in length and having nearly parallel limbs 0.1–1.5 cm apart. The spreite is only weakly expressed; the inter-limb material was apparently not processed during deepening of the U-tube but placed directly in the spreite or pressed aside. Tisoa deviates slightly but consistently from a vertical orientation and commonly shows a low-amplitude helicoidal course. The U-tube exhibits a thick pyrite lining implying the former presence of mucus. The steep chemical gradient between oxygenated water in the U-tube and anoxic host sediment evidently fostered microbial activity. The extraordinary penetration depth of Tisoa suggests exploitation of extreme redox conditions such as could be found in the methanogenesis zone. The Tisoa producer probably deepened the U-tube incrementally, continuing when the chemical gradient between tube and host sediment declined due to circulation of the oxygenated water used for respiration. The Tisoa producers might have fed on suspended material, microbes flourishing along the tube wall, or acquired nutrition via chemosymbionts.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":"38 1","pages":"76 - 97"},"PeriodicalIF":1.6,"publicationDate":"2023-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42756183","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract: This study is based on the analysis of burrow casts of three species of armadillos from central Argentina: Chaetophractus villosus, Chaetophractus vellerosus, and Zaedyus pichiy (Chlamyphoridae: Euphractinae). The aim of this work was to identify key ichnologic signatures of Euphractinae armadillo burrows for application to the paleoecological and behavioral interpretation of fossil examples. A total of 15 active burrows from different biogeographic provinces were casted with polyurethane foam and then excavated. About two hundred uncasted burrows and foraging pits were also measured at the same localities. Euphractinae burrows are clearly distinguished from Chlamyphorinae burrows by its filling, surface ornamentation, and size. It is suggested that fossil armadillo (Euphractinae) burrows would be characterized by a single ramp with one entrance and massive or laminated fill, horizontal diameter larger than 100 mm, strongly marked sets of three claw traces that are arranged oblique to the ramp axis, and absence of feces or plant remains. The distinctive surface ornamentation present in the casted burrows is tentatively linked to a particular excavation mechanism involving rotation of the body along the antero-posterior axis. Burrow systems with a chamber are interpreted as permanent burrows, whereas those lacking chamber are considered as temporary/shelter burrows. Armadillo burrow systems (either temporary or permanent) are longer, less inclined, and have lower relative diameter indices (RDI) than armadillo foraging pits. Euphractinae burrows are linked to producers with solitary, fossorial, opportunistic omnivorous habits that excavate several burrows during their lives. They are left open after abandonment, and preferably located in xeric shrub lands and grasslands. The described morphological features of the burrows systems can be useful for the interpretation of fossil (post-Eocene) burrows.
{"title":"NEOICHNOLOGY OF ARMADILLOS: KEYS FOR THE PALEOECOLOGICAL AND BEHAVIORAL INTERPRETATION OF FOSSIL TETRAPOD BURROWS","authors":"M. C. Cardonatto, Ricardo Néstor Melchor","doi":"10.2110/palo.2022.034","DOIUrl":"https://doi.org/10.2110/palo.2022.034","url":null,"abstract":"Abstract: This study is based on the analysis of burrow casts of three species of armadillos from central Argentina: Chaetophractus villosus, Chaetophractus vellerosus, and Zaedyus pichiy (Chlamyphoridae: Euphractinae). The aim of this work was to identify key ichnologic signatures of Euphractinae armadillo burrows for application to the paleoecological and behavioral interpretation of fossil examples. A total of 15 active burrows from different biogeographic provinces were casted with polyurethane foam and then excavated. About two hundred uncasted burrows and foraging pits were also measured at the same localities. Euphractinae burrows are clearly distinguished from Chlamyphorinae burrows by its filling, surface ornamentation, and size. It is suggested that fossil armadillo (Euphractinae) burrows would be characterized by a single ramp with one entrance and massive or laminated fill, horizontal diameter larger than 100 mm, strongly marked sets of three claw traces that are arranged oblique to the ramp axis, and absence of feces or plant remains. The distinctive surface ornamentation present in the casted burrows is tentatively linked to a particular excavation mechanism involving rotation of the body along the antero-posterior axis. Burrow systems with a chamber are interpreted as permanent burrows, whereas those lacking chamber are considered as temporary/shelter burrows. Armadillo burrow systems (either temporary or permanent) are longer, less inclined, and have lower relative diameter indices (RDI) than armadillo foraging pits. Euphractinae burrows are linked to producers with solitary, fossorial, opportunistic omnivorous habits that excavate several burrows during their lives. They are left open after abandonment, and preferably located in xeric shrub lands and grasslands. The described morphological features of the burrows systems can be useful for the interpretation of fossil (post-Eocene) burrows.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":"38 1","pages":"57 - 75"},"PeriodicalIF":1.6,"publicationDate":"2023-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48117580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Tomassini, M. D. Marin-Monfort, Sara García-Morato, C. I. Montalvo, D. Barasoain, E. M. Zaracho, M. L. Chatellenaz, M. Garrone, A. Zurita, Y. Fernández-Jalvo
Abstract: Diverse modifications of the original morphological features occur throughout the taphonomic history of osteological remains, which may lead in erroneous interpretations about the formation of an accumulation as well as taxonomic misidentifications. Here, we present a neo-taphonomic study in order to analyze and interpret the modifications generated by digestion on osteoderms of the armadillo Dasypus novemcinctus obtained from scats produced by Puma concolor. Results reveal intense breakage and modifications of the articular and broken edges, dorsal surface, bone tissues, and ornamentation pattern of the osteoderms. This work describes for the first time the modifications caused by digestion in armadillo osteoderms, improving the knowledge of preservation of this type of skeletal element and providing a modern analog that can be used to distinguish archeological and paleontological accumulations formed by predators from those generated by other processes. The recognition that digestion modifies the original ornamentation pattern is particularly significant because ornamentation features are used in nearly all taxonomic and phylogenetic studies of fossil cingulates. We use this new information to re-evaluate osteoderms recovered from carnivore coprolites of the classic Middle Miocene La Venta site (Colombia), which formed the basis for recognizing and characterizing the dasypodid species Nanoastegotherium prostatum. We highlight the importance of knowing with certainty the origin and taphonomic history of remains since, in the particular case of cingulates, taxonomic identification also has important biostratigraphic, paleoecological, paleoenvironmental, and paleobiogeographical implications.
{"title":"ARMADILLO OSTEODERMS ALTERED BY DIGESTION AND HOW TAPHONOMY CAN HELP TAXONOMY","authors":"R. Tomassini, M. D. Marin-Monfort, Sara García-Morato, C. I. Montalvo, D. Barasoain, E. M. Zaracho, M. L. Chatellenaz, M. Garrone, A. Zurita, Y. Fernández-Jalvo","doi":"10.2110/palo.2022.040","DOIUrl":"https://doi.org/10.2110/palo.2022.040","url":null,"abstract":"Abstract: Diverse modifications of the original morphological features occur throughout the taphonomic history of osteological remains, which may lead in erroneous interpretations about the formation of an accumulation as well as taxonomic misidentifications. Here, we present a neo-taphonomic study in order to analyze and interpret the modifications generated by digestion on osteoderms of the armadillo Dasypus novemcinctus obtained from scats produced by Puma concolor. Results reveal intense breakage and modifications of the articular and broken edges, dorsal surface, bone tissues, and ornamentation pattern of the osteoderms. This work describes for the first time the modifications caused by digestion in armadillo osteoderms, improving the knowledge of preservation of this type of skeletal element and providing a modern analog that can be used to distinguish archeological and paleontological accumulations formed by predators from those generated by other processes. The recognition that digestion modifies the original ornamentation pattern is particularly significant because ornamentation features are used in nearly all taxonomic and phylogenetic studies of fossil cingulates. We use this new information to re-evaluate osteoderms recovered from carnivore coprolites of the classic Middle Miocene La Venta site (Colombia), which formed the basis for recognizing and characterizing the dasypodid species Nanoastegotherium prostatum. We highlight the importance of knowing with certainty the origin and taphonomic history of remains since, in the particular case of cingulates, taxonomic identification also has important biostratigraphic, paleoecological, paleoenvironmental, and paleobiogeographical implications.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":"38 1","pages":"31 - 42"},"PeriodicalIF":1.6,"publicationDate":"2023-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44552668","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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