Small fossils are preserved as phosphatic (carbonate fluorapatite) micro-steinkerns (, 0.5 mm dia... more Small fossils are preserved as phosphatic (carbonate fluorapatite) micro-steinkerns (, 0.5 mm diameter) in Upper Ordovician beds of the Cincinnati area. Mollusks are common, along with bryozoan zooecia, echinoderm ossicles, and other taxa. Similar occurrences of Ordovician micromorphic mollusks have been interpreted as ecologically dwarfed and adapted to oxygen-starved conditions, an interpretation with implications for ocean anoxia. An alternative explanation for small phosphatic steinkerns is taphonomic. Stable carbonate fluorapatite selectively filled small voids, thus preserving small fossils, including larval/young mollusks. Reworking concentrated small phosphatic steinkerns from multiple generations while larger, unfilled calcareous shells were destroyed, resulting in small fossils progressively replacing larger fossils. With thin sections and insoluble residues, we document evidence that many of these steinkerns are incomplete (" teilsteinkerns ") recording small parts of larger, normal-sized animals, or juveniles, along with smaller species. This find‐ ing suggests that these fossil assemblages are taphonomically, not ecologically, size-limited. Based on the ecology of modern oxygen minimum zones in which shelled mollusks are rare, the presence of abundant shelled organisms actually argues against severe oxygen stress. Our results also imply that the process by which the " small shelly fossils " of the Cambrian were preserved continued into the Ordovician.
The distinctly non-random diversity of organis-mal form manifests itself in discrete clusters of ... more The distinctly non-random diversity of organis-mal form manifests itself in discrete clusters of taxa that share a common body plan. As a result, analyses of disparity require a scalable comparative framework. The difficulties of applying geometric morphometrics to disparity analyses of groups with vastly divergent body plans are overcome partly by the use of cladistic characters. Character-based disparity analyses have become increasingly popular, but it is not clear how they are affected by character coding strategies or revisions of primary homology statements. Indeed, whether cla-distic and morphometric data capture similar patterns of morphological variation remains a moot point. To address this issue, we employ both cladistic and geometric morpho-metric data in an exploratory study of disparity focussing on caecilian amphibians. Our results show no impact on relative intertaxon distances when different coding strategies for cla-distic characters were used or when revised concepts of homology were considered. In all instances, we found no statistically significant difference between pairwise Euclidean and Procrustes distances, although the strength of the correlation among distance matrices varied. This suggests that cla-distic and geometric morphometric data appear to summarize morphological variation in comparable ways. Our results support the use of cladistic data for characterizing organismal disparity.
The phylogenetic relationships between major groups of plesiomorphic pentaradial echinoderms, the... more The phylogenetic relationships between major groups of plesiomorphic pentaradial echinoderms, the Paleozoic crinoids, blastozoans, and edrioasteroids, are poorly understood because of a lack of widely recognized homologies. Here, we present newly recognized oral region homologies, based on the Universal Elemental Homology model for skeletal plates, in a wide range of fossil taxa. The oral region of echinoderms is mainly composed of the axial, or ambulacral, skeleton, which apparently evolved more slowly than the extraxial skeleton that forms the majority of the body. Recent phylogenetic hypotheses have focused on characters of the extraxial skeleton, which may have evolved too rapidly to preserve obvious homologies across all these groups. The axial skeleton conserved homologous suites of characters shared between various edrioasteroids and specific blastozoans, and between other blastozoans and crinoids. Although individual plates can be inferred as homologous, no directly overlapping suites of characters are shared between edrioasteroids and crinoids. Six different systems of mouth (peristome) plate organization (Peristomial Border Systems) are defined. These include four different systems based on the arrangement of the interradially-positioned oral plates and their peristomial cover plates, where PBS A1 occurs only in plesiomorphic edrioasteroids, PBS A2 occurs in plesiomorphic edrioasteroids and blastozoans, and PBS A3 and PBS A4 occur in blastozoans and crinoids. The other two systems have radially-positioned uniserial oral frame plates in construction of the mouth frame. PBS B1 has both orals and uniserial oral frame plates and occurs in edrioasterid and possibly edrioblastoid edrioasteroids, whereas PBS B2 has exclusively uniserial oral frame plates and is found in isorophid edrioasteroids and imbricate and gogiid blastozoans. These different types of mouth frame construction offer potential synapomorphies to aid in parsimony-based phylogenetics for exploring branching order among stem groups on the echinoderm tree of life.
A sea urchin placed on the sea floor near an active brine seep was recovered after 13 years with ... more A sea urchin placed on the sea floor near an active brine seep was recovered after 13 years with detailed soft-tissue preservation. Growth of an amorphous calcium carbonate solid with small amounts of the mineral bassa-nite occurred on the spines and test. The solid also exhibits striations at both the macro-and microscopic scales that preserve the muscle texture of the sea urchin. Such soft-tissue replacement and mineralization could lead to exquisite fossilization. Soft-tissue mineralization has been previously replicated in controlled laboratory conditions; however, this is the first report of the lithologic replication of soft tissues in an open marine experiment. Examples of extraordinary fossil preservation, or Lagers€ atten, give a distinct snapshot of the past and have led to a greater understanding of the history of life. Soft-tissue lithification occurs in special circumstances in which local chemical conditions (often mediated by decay or bacterial factors) promote early dia-genetic mineralization, the first steps of which are observed in this instance. The preservation of articulated skeletons, especially within echinoderms, is normally attributed to rapid burial, but that may not be necessary given that this urchin was at or very near the sediment–water interface for 13 years.
The end-Katian (Late Ordovician) crinoid mass extinction triggered the change from the Early to t... more The end-Katian (Late Ordovician) crinoid mass extinction triggered the change from the Early to the Middle Pa-leozoic crinoid evolutionary faunas (CEFs). This was a change from diplobathrid camerate-disparid-hybocrinid dominated faunas to faunas dominated by monobathrid camerate, cladid, and flexible crinoids. All clades suffered extinctions at the end-Katian event, but diplobathrid camerates, disparids, and hybocrinids suffered higher rates of extinction. The primary amount of diversification occurred in clades that would become dominant during the Silurian. However, the formation of the characteristic Middle Paleozoic CEF was protracted beyond the Late Ordovician extinction event. Monobathrid camerates and flexibles diversified through the Llandovery, but both dendrocrinid and cyathocrinid cladids did not diversify until later. Monobathrid camerate genera and families diversified, the flexible diversification was largely at the genus level, cyathocrine diversification was largely among families, and dendrocrinids did not diversify significantly until after the Llandovery. Overall disparity decreased during the end-Katian extinction by reducing the disparity within each clade. Disparity remained fairly constant during the Hirnantian but increased significantly during the Llandovery by both increasing disparity within clades and expanding the morphospace of the disparids due to the radiation of families with new morphologies. North America was the biogeographic center of origination for the families that survived to become dominant Silurian clades.
—Interpretations of morphologic radiations and macroevolutionary patterns are dependent on a prio... more —Interpretations of morphologic radiations and macroevolutionary patterns are dependent on a priori choices of taxonomic and geographic scales of study. The results of disparity analysis at varying taxonomic (species and genus) and geographic (regional, biofacies, and community) scales are examined in a study of Ordovician though Early Silurian crinoids. Using discrete morphologic characters, we examined the disparity of 421 crinoids from 65 Laurentian biofacies. Crinoid disparity differs when analyzed at the regional and biofacies levels. Regardless of fluctuations in regional crinoid disparity, average within-biofacies disparity was static throughout the Ordovician, deviating only during the Silurian because of the proliferation of the morphologically aberrant myelodactylid crinoids. The choice of taxonomic level does not have an effect at the biofacies level. However, at the regional level, the two taxonomic scales (genus and species) can produce different results because of variation in the number of species per genus through time and the amount of morphologic variation within individual genera. Weighting disparity by abundance provides a metric combining morphology and community structure. Average weighted disparity at the community level showed patterns similar to that of the biofacies-level disparity curve, but this metric has a greater degree of variation between biofacies. Biofacies with a low ratio of weighted to unweighted disparity display the distinctive community structure (based on aerosol filtration theory) that is often reported in crinoid assemblages.
A new species of camerate crinoid, Para-diabolocrinus teres, is described from the Upper Ordovici... more A new species of camerate crinoid, Para-diabolocrinus teres, is described from the Upper Ordovician (Soudleyan-Marshbrookian), Curdsville member of the Lexington Limestone (Central Kentucky, USA). This new cri-noid lacks the prominent ornamentation that defines other species within the genus. This species yields new information regarding the morphology of the genus preserving the first intact crown and proximal stem. In addition, apparent ontogenetic patterns observed within P. teres strength the position of P. stel-latus within this genus.
—Studies of crinoid morphology have been pivotal in understanding the constraints on the range of... more —Studies of crinoid morphology have been pivotal in understanding the constraints on the range of morphology within a clade as well as the patterns of disparity throughout the Phanerozoic. Newly discovered and described faunas and recent study of early Paleozoic crinoid diversity provide an ideal opportunity to reanalyze Ordovician through Early Silurian crinoid disparity with more complete taxonomic coverage and finer stratigraphic resolution. Using the coarse stratigraphic binning of Foote (1999), the updated morphologic data set has a similar disparity pattern to those previously reported for the early Paleozoic. However, with the more resolved stratigraphic binning used by Peters and Ausich (2008), a significant difference exists between the original and current data sets. Both data sets have a pronounced disparity high during the late Middle Ordovician. However, the updated disparity curve has a much higher initial disparity during the Early Ordovician and a pronounced rise in disparity during the Silurian recovery. Examination of differential sampling, proportions of the crinoid orders through time, and methods of coding characters indicate these factors have little effect on the pattern of crinoid disparity. The Silurian morphospace expansion occurs primarily within disparids and coincides with the origination of the myelodactylids. These findings corroborate the rapid expansion of morphospace during the Ordovician. However, crinoid disparity did not remain static and, although less frequent than during the initial radiation, new body plans evolved following the Ordovician Extinction (e.g., the myelodactylids). These results are consistent with the hypothesis of ecology constraining the limits on morphologic disparity at the class level.
—Understanding the relationships between morphological disparity and environment, geography , and... more —Understanding the relationships between morphological disparity and environment, geography , and scale require examination at the local level. Even with disparity metrics that are inherently sample size independent, the nature of rare species and the segregation of common and rare species within morphospace can create substantial sampling issues. Eight well-sampled, Late Ordovician crinoid assemblages were examined for potential biases in the study of local disparity. Disparity is based on the ordination of discrete characters. The rare and common species within these assemblages contributed equally to disparity. In spite of this pattern, rare species in some localities occupy a different area of morphospace, causing disparity to vary greatly with sampling intensity. Morphological rarefaction based on the number of specimens shows that disparity weighted by abundance is constant past a sample size of approximately 30 individuals. This metric is dependent on the evenness within an assemblage as well as the abundance within subgroups in morphospace. Disparity weighted according to abundance gives a view of the functional disparity of an assemblage, which is more applicable in studies of local disparity, though unweighted disparity is still preferred in regional-scale studies and in investigations of morphospace filling through a clade's history.
Unusually fine preservation of soft anatomy in the fossil record, often referred to as Lagersta¨t... more Unusually fine preservation of soft anatomy in the fossil record, often referred to as Lagersta¨tte deposits, has led to great advances in understanding the evolution of life. An understanding of the potential environments of deposition that might lead to exquisite preservation may help to reconstruct the effects of the taphonomic filter and thereby better interpret the completeness of fossil Lagersta¨tten. Seafloor brines are potential environments leading to exceptional preservation. The Shelf and Slope Experimental Taphonomy Initiative (SSETI) placed mollusc shells, decapod crustaceans, sea urchins, and wood into a Gulf of Mexico seafloor brine pool environment to study the rates and modes of skeletal and soft tissue decay. We found that skeletons, soft tissue, and wood placed directly in the sulfidic anoxic brine were essentially not degraded or discolored over nearly a decade. Where the brine mixed with overlying seawater in a brine stream, the taphonomic signature was quite different. Calcium-carbonate shell and urchin tests underwent severe dissolution, whereas terrestrial plant remains were unaltered. Farther from the brine, shell and urchin carbonate was only slightly dissolved, wood was completely consumed by xylophagus animals, and decapods were reduced to claw parts only. From these experiments, we conclude that the taphonomic signature of a brine seep can be recognized by a unique juxtaposition of preservation styles that varies across phyla. The central area of the anoxic brine would promote exquisite preservation of carbonate, soft-animal tissue, and cellulose. The central area would be ringed by a zone of near total loss of shell carbonate, but paradoxically would promote the preservation of organic tissue such as shell periostracum and ligament, wood, nuts, and cones. Where seawater salinity is normal, the taphonomic signature would return to a seafloor assemblage appropriate to the depth and depositional environment. Brine seep systems may provide a mechanism for maintaining unaltered organism remains at the sediment-water interface long enough to become buried with soft anatomy intact and undisturbed. The very important fossil deposit known as the Burgess Shale exhibits preservation styles and patterns that might be explained by presence of brine. Our experimental work in a modern brine system may shed some light on the taphonomic conditions that led to preservation known as the ''Burgess Shale type.''
Drillholes are common in many different echinoderm classes, but have yet to be reported in homalo... more Drillholes are common in many different echinoderm classes, but have yet to be reported in homalozoans. A borehole in the Late Ordovician echinoderm Enoploura is the first evidence of drilling in Stylophora. The level of preservation and environ− mental setting suggest this drilling occurred while the organ− ism was alive, thus supporting a predatory or parasitic inter− pretation.
Examination of a bulk sample of the Mississippian orthide brachiopod Perditocardinia cf. P. dubia... more Examination of a bulk sample of the Mississippian orthide brachiopod Perditocardinia cf. P. dubia revealed borings in 25.8% of the 259 specimens. The drillholes are small (0.13^0.80 mm in diameter), round, and each brachiopod has been drilled only once. Normally, Paleozoic brachiopods are drilled at a low frequency (6 5%) and the placement of the drillhole is directly over the viscera of the animal. The majority of the specimens of P. cf. P. dubia in this sample, however, are drilled directly on the anterior margin; this is the first documentation of Paleozoic edge-drilling on brachiopods. The high frequency of boring and especially the location of drillholes near the margin, suggest either a different predatory/parasitic organism or a different feeding behavior than is commonly associated with Paleozoic brachiopods. These drillholes may represent a behavior analogous to modern capulid gastropods that parasitize bivalves by positioning themselves along the host's commissure and sometimes drilling the shell. It could also represent a behavior similar to modern naticid gastropods, which drill along the commissure of its bivalve prey. Regardless, this example further illustrates that the Paleozoic was characterized by a broader repertoire of drilling behaviors than has been previously recognized.
Small fossils are preserved as phosphatic (carbonate fluorapatite) micro-steinkerns (, 0.5 mm dia... more Small fossils are preserved as phosphatic (carbonate fluorapatite) micro-steinkerns (, 0.5 mm diameter) in Upper Ordovician beds of the Cincinnati area. Mollusks are common, along with bryozoan zooecia, echinoderm ossicles, and other taxa. Similar occurrences of Ordovician micromorphic mollusks have been interpreted as ecologically dwarfed and adapted to oxygen-starved conditions, an interpretation with implications for ocean anoxia. An alternative explanation for small phosphatic steinkerns is taphonomic. Stable carbonate fluorapatite selectively filled small voids, thus preserving small fossils, including larval/young mollusks. Reworking concentrated small phosphatic steinkerns from multiple generations while larger, unfilled calcareous shells were destroyed, resulting in small fossils progressively replacing larger fossils. With thin sections and insoluble residues, we document evidence that many of these steinkerns are incomplete (" teilsteinkerns ") recording small parts of larger, normal-sized animals, or juveniles, along with smaller species. This find‐ ing suggests that these fossil assemblages are taphonomically, not ecologically, size-limited. Based on the ecology of modern oxygen minimum zones in which shelled mollusks are rare, the presence of abundant shelled organisms actually argues against severe oxygen stress. Our results also imply that the process by which the " small shelly fossils " of the Cambrian were preserved continued into the Ordovician.
The distinctly non-random diversity of organis-mal form manifests itself in discrete clusters of ... more The distinctly non-random diversity of organis-mal form manifests itself in discrete clusters of taxa that share a common body plan. As a result, analyses of disparity require a scalable comparative framework. The difficulties of applying geometric morphometrics to disparity analyses of groups with vastly divergent body plans are overcome partly by the use of cladistic characters. Character-based disparity analyses have become increasingly popular, but it is not clear how they are affected by character coding strategies or revisions of primary homology statements. Indeed, whether cla-distic and morphometric data capture similar patterns of morphological variation remains a moot point. To address this issue, we employ both cladistic and geometric morpho-metric data in an exploratory study of disparity focussing on caecilian amphibians. Our results show no impact on relative intertaxon distances when different coding strategies for cla-distic characters were used or when revised concepts of homology were considered. In all instances, we found no statistically significant difference between pairwise Euclidean and Procrustes distances, although the strength of the correlation among distance matrices varied. This suggests that cla-distic and geometric morphometric data appear to summarize morphological variation in comparable ways. Our results support the use of cladistic data for characterizing organismal disparity.
The phylogenetic relationships between major groups of plesiomorphic pentaradial echinoderms, the... more The phylogenetic relationships between major groups of plesiomorphic pentaradial echinoderms, the Paleozoic crinoids, blastozoans, and edrioasteroids, are poorly understood because of a lack of widely recognized homologies. Here, we present newly recognized oral region homologies, based on the Universal Elemental Homology model for skeletal plates, in a wide range of fossil taxa. The oral region of echinoderms is mainly composed of the axial, or ambulacral, skeleton, which apparently evolved more slowly than the extraxial skeleton that forms the majority of the body. Recent phylogenetic hypotheses have focused on characters of the extraxial skeleton, which may have evolved too rapidly to preserve obvious homologies across all these groups. The axial skeleton conserved homologous suites of characters shared between various edrioasteroids and specific blastozoans, and between other blastozoans and crinoids. Although individual plates can be inferred as homologous, no directly overlapping suites of characters are shared between edrioasteroids and crinoids. Six different systems of mouth (peristome) plate organization (Peristomial Border Systems) are defined. These include four different systems based on the arrangement of the interradially-positioned oral plates and their peristomial cover plates, where PBS A1 occurs only in plesiomorphic edrioasteroids, PBS A2 occurs in plesiomorphic edrioasteroids and blastozoans, and PBS A3 and PBS A4 occur in blastozoans and crinoids. The other two systems have radially-positioned uniserial oral frame plates in construction of the mouth frame. PBS B1 has both orals and uniserial oral frame plates and occurs in edrioasterid and possibly edrioblastoid edrioasteroids, whereas PBS B2 has exclusively uniserial oral frame plates and is found in isorophid edrioasteroids and imbricate and gogiid blastozoans. These different types of mouth frame construction offer potential synapomorphies to aid in parsimony-based phylogenetics for exploring branching order among stem groups on the echinoderm tree of life.
A sea urchin placed on the sea floor near an active brine seep was recovered after 13 years with ... more A sea urchin placed on the sea floor near an active brine seep was recovered after 13 years with detailed soft-tissue preservation. Growth of an amorphous calcium carbonate solid with small amounts of the mineral bassa-nite occurred on the spines and test. The solid also exhibits striations at both the macro-and microscopic scales that preserve the muscle texture of the sea urchin. Such soft-tissue replacement and mineralization could lead to exquisite fossilization. Soft-tissue mineralization has been previously replicated in controlled laboratory conditions; however, this is the first report of the lithologic replication of soft tissues in an open marine experiment. Examples of extraordinary fossil preservation, or Lagers€ atten, give a distinct snapshot of the past and have led to a greater understanding of the history of life. Soft-tissue lithification occurs in special circumstances in which local chemical conditions (often mediated by decay or bacterial factors) promote early dia-genetic mineralization, the first steps of which are observed in this instance. The preservation of articulated skeletons, especially within echinoderms, is normally attributed to rapid burial, but that may not be necessary given that this urchin was at or very near the sediment–water interface for 13 years.
The end-Katian (Late Ordovician) crinoid mass extinction triggered the change from the Early to t... more The end-Katian (Late Ordovician) crinoid mass extinction triggered the change from the Early to the Middle Pa-leozoic crinoid evolutionary faunas (CEFs). This was a change from diplobathrid camerate-disparid-hybocrinid dominated faunas to faunas dominated by monobathrid camerate, cladid, and flexible crinoids. All clades suffered extinctions at the end-Katian event, but diplobathrid camerates, disparids, and hybocrinids suffered higher rates of extinction. The primary amount of diversification occurred in clades that would become dominant during the Silurian. However, the formation of the characteristic Middle Paleozoic CEF was protracted beyond the Late Ordovician extinction event. Monobathrid camerates and flexibles diversified through the Llandovery, but both dendrocrinid and cyathocrinid cladids did not diversify until later. Monobathrid camerate genera and families diversified, the flexible diversification was largely at the genus level, cyathocrine diversification was largely among families, and dendrocrinids did not diversify significantly until after the Llandovery. Overall disparity decreased during the end-Katian extinction by reducing the disparity within each clade. Disparity remained fairly constant during the Hirnantian but increased significantly during the Llandovery by both increasing disparity within clades and expanding the morphospace of the disparids due to the radiation of families with new morphologies. North America was the biogeographic center of origination for the families that survived to become dominant Silurian clades.
—Interpretations of morphologic radiations and macroevolutionary patterns are dependent on a prio... more —Interpretations of morphologic radiations and macroevolutionary patterns are dependent on a priori choices of taxonomic and geographic scales of study. The results of disparity analysis at varying taxonomic (species and genus) and geographic (regional, biofacies, and community) scales are examined in a study of Ordovician though Early Silurian crinoids. Using discrete morphologic characters, we examined the disparity of 421 crinoids from 65 Laurentian biofacies. Crinoid disparity differs when analyzed at the regional and biofacies levels. Regardless of fluctuations in regional crinoid disparity, average within-biofacies disparity was static throughout the Ordovician, deviating only during the Silurian because of the proliferation of the morphologically aberrant myelodactylid crinoids. The choice of taxonomic level does not have an effect at the biofacies level. However, at the regional level, the two taxonomic scales (genus and species) can produce different results because of variation in the number of species per genus through time and the amount of morphologic variation within individual genera. Weighting disparity by abundance provides a metric combining morphology and community structure. Average weighted disparity at the community level showed patterns similar to that of the biofacies-level disparity curve, but this metric has a greater degree of variation between biofacies. Biofacies with a low ratio of weighted to unweighted disparity display the distinctive community structure (based on aerosol filtration theory) that is often reported in crinoid assemblages.
A new species of camerate crinoid, Para-diabolocrinus teres, is described from the Upper Ordovici... more A new species of camerate crinoid, Para-diabolocrinus teres, is described from the Upper Ordovician (Soudleyan-Marshbrookian), Curdsville member of the Lexington Limestone (Central Kentucky, USA). This new cri-noid lacks the prominent ornamentation that defines other species within the genus. This species yields new information regarding the morphology of the genus preserving the first intact crown and proximal stem. In addition, apparent ontogenetic patterns observed within P. teres strength the position of P. stel-latus within this genus.
—Studies of crinoid morphology have been pivotal in understanding the constraints on the range of... more —Studies of crinoid morphology have been pivotal in understanding the constraints on the range of morphology within a clade as well as the patterns of disparity throughout the Phanerozoic. Newly discovered and described faunas and recent study of early Paleozoic crinoid diversity provide an ideal opportunity to reanalyze Ordovician through Early Silurian crinoid disparity with more complete taxonomic coverage and finer stratigraphic resolution. Using the coarse stratigraphic binning of Foote (1999), the updated morphologic data set has a similar disparity pattern to those previously reported for the early Paleozoic. However, with the more resolved stratigraphic binning used by Peters and Ausich (2008), a significant difference exists between the original and current data sets. Both data sets have a pronounced disparity high during the late Middle Ordovician. However, the updated disparity curve has a much higher initial disparity during the Early Ordovician and a pronounced rise in disparity during the Silurian recovery. Examination of differential sampling, proportions of the crinoid orders through time, and methods of coding characters indicate these factors have little effect on the pattern of crinoid disparity. The Silurian morphospace expansion occurs primarily within disparids and coincides with the origination of the myelodactylids. These findings corroborate the rapid expansion of morphospace during the Ordovician. However, crinoid disparity did not remain static and, although less frequent than during the initial radiation, new body plans evolved following the Ordovician Extinction (e.g., the myelodactylids). These results are consistent with the hypothesis of ecology constraining the limits on morphologic disparity at the class level.
—Understanding the relationships between morphological disparity and environment, geography , and... more —Understanding the relationships between morphological disparity and environment, geography , and scale require examination at the local level. Even with disparity metrics that are inherently sample size independent, the nature of rare species and the segregation of common and rare species within morphospace can create substantial sampling issues. Eight well-sampled, Late Ordovician crinoid assemblages were examined for potential biases in the study of local disparity. Disparity is based on the ordination of discrete characters. The rare and common species within these assemblages contributed equally to disparity. In spite of this pattern, rare species in some localities occupy a different area of morphospace, causing disparity to vary greatly with sampling intensity. Morphological rarefaction based on the number of specimens shows that disparity weighted by abundance is constant past a sample size of approximately 30 individuals. This metric is dependent on the evenness within an assemblage as well as the abundance within subgroups in morphospace. Disparity weighted according to abundance gives a view of the functional disparity of an assemblage, which is more applicable in studies of local disparity, though unweighted disparity is still preferred in regional-scale studies and in investigations of morphospace filling through a clade's history.
Unusually fine preservation of soft anatomy in the fossil record, often referred to as Lagersta¨t... more Unusually fine preservation of soft anatomy in the fossil record, often referred to as Lagersta¨tte deposits, has led to great advances in understanding the evolution of life. An understanding of the potential environments of deposition that might lead to exquisite preservation may help to reconstruct the effects of the taphonomic filter and thereby better interpret the completeness of fossil Lagersta¨tten. Seafloor brines are potential environments leading to exceptional preservation. The Shelf and Slope Experimental Taphonomy Initiative (SSETI) placed mollusc shells, decapod crustaceans, sea urchins, and wood into a Gulf of Mexico seafloor brine pool environment to study the rates and modes of skeletal and soft tissue decay. We found that skeletons, soft tissue, and wood placed directly in the sulfidic anoxic brine were essentially not degraded or discolored over nearly a decade. Where the brine mixed with overlying seawater in a brine stream, the taphonomic signature was quite different. Calcium-carbonate shell and urchin tests underwent severe dissolution, whereas terrestrial plant remains were unaltered. Farther from the brine, shell and urchin carbonate was only slightly dissolved, wood was completely consumed by xylophagus animals, and decapods were reduced to claw parts only. From these experiments, we conclude that the taphonomic signature of a brine seep can be recognized by a unique juxtaposition of preservation styles that varies across phyla. The central area of the anoxic brine would promote exquisite preservation of carbonate, soft-animal tissue, and cellulose. The central area would be ringed by a zone of near total loss of shell carbonate, but paradoxically would promote the preservation of organic tissue such as shell periostracum and ligament, wood, nuts, and cones. Where seawater salinity is normal, the taphonomic signature would return to a seafloor assemblage appropriate to the depth and depositional environment. Brine seep systems may provide a mechanism for maintaining unaltered organism remains at the sediment-water interface long enough to become buried with soft anatomy intact and undisturbed. The very important fossil deposit known as the Burgess Shale exhibits preservation styles and patterns that might be explained by presence of brine. Our experimental work in a modern brine system may shed some light on the taphonomic conditions that led to preservation known as the ''Burgess Shale type.''
Drillholes are common in many different echinoderm classes, but have yet to be reported in homalo... more Drillholes are common in many different echinoderm classes, but have yet to be reported in homalozoans. A borehole in the Late Ordovician echinoderm Enoploura is the first evidence of drilling in Stylophora. The level of preservation and environ− mental setting suggest this drilling occurred while the organ− ism was alive, thus supporting a predatory or parasitic inter− pretation.
Examination of a bulk sample of the Mississippian orthide brachiopod Perditocardinia cf. P. dubia... more Examination of a bulk sample of the Mississippian orthide brachiopod Perditocardinia cf. P. dubia revealed borings in 25.8% of the 259 specimens. The drillholes are small (0.13^0.80 mm in diameter), round, and each brachiopod has been drilled only once. Normally, Paleozoic brachiopods are drilled at a low frequency (6 5%) and the placement of the drillhole is directly over the viscera of the animal. The majority of the specimens of P. cf. P. dubia in this sample, however, are drilled directly on the anterior margin; this is the first documentation of Paleozoic edge-drilling on brachiopods. The high frequency of boring and especially the location of drillholes near the margin, suggest either a different predatory/parasitic organism or a different feeding behavior than is commonly associated with Paleozoic brachiopods. These drillholes may represent a behavior analogous to modern capulid gastropods that parasitize bivalves by positioning themselves along the host's commissure and sometimes drilling the shell. It could also represent a behavior similar to modern naticid gastropods, which drill along the commissure of its bivalve prey. Regardless, this example further illustrates that the Paleozoic was characterized by a broader repertoire of drilling behaviors than has been previously recognized.
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