IN PALAEONTOLOGY EARLY PHYLOGENY OF CRINOIDS WITHIN THE PELMATOZOAN CLADE by (original) (raw)
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Palaeontology
Phylogenetic relationships among early crinoids are evaluated by maximizing parsimonious-informative characters that are unordered and unweighted. Primarily Tremadocian–Darriwilian (Early–Middle Ordovician) taxa are analysed. Stratigraphic congruence metrics support the best phylogenetic hypothesis derived using parsimony meth- ods. This study confirms the traditionally recognized lineages of Palaeozoic crinoids and provides new information on the branching order of evolving lineages. Camerates are basal crinoids with progressively more tipward groups (from an Ordovician perspective) being protocrinoids, cladids (para- phyletic), hybocrinids and disparids. The Protocrinoida should be maintained, but the Aethocrinida should be placed within the Cladida. The results of this study identify phylo- genetic structure amongst the major early crinoid lineages and delineate the relative positions of crinoid higher taxa along a tree. Each valid higher taxon discussed herein requires a comprehensive treatment to delimit within-lineage phylogenetic relationships.
PALEOCOMMUNITY AND EVOLUTIONARY ECOLOGY OF PALEOZOIC CRINOIDS
Crinoids were a common component of Paleozoic benthic paleocommunities, yet they have been under-utilized in paleoecological analyses. Recent efforts to incorporate disarticulated ossicles into these analyses have greatly increased the robustness of paleoecological patterns noted for the Crinoidea. Analyses of crinoid functional morphology, particularly filtration dynamics, have provided testable hypotheses concerning the distribution of crinoids among benthic environments. These models predict that crinoids with dense-mesh filtration fans should be most common in high energy, shoreward paleoenvironments, whereas open-fan crinoids should be most common in low-energy, offshore paleoenvironments. Review of the Paleozoic fossil record appears to support these general predictions-from the Late Ordovician to the end of the Paleozoic, dense-fan crinoids are most abundant in nearshore paleoenvironments, whereas open-fan crinoids are most abundant offshore. The partitioning of crinoid diversity through the Paleozoic shifted through time. Beta diversity was highest in the Ordovician, implying that the early diversification of crinoids was focused on partitioning the benthic landscape among taxa. Beta diversity was quite low by the late Paleozoic, however, local and within-habitat alpha diversity was much greater than during the Ordovician. This resulted in generally higher levels of eurytopy in the late Paleozoic compared to the Ordovician. Patterns of faunal disassembly associated with regional extinctions in North America during the Ordovician and Permian underscore the differences in the paleoecology of these crinoid faunas.
Journal of Paleontology, 2017
The subclass Camerata (Crinoidea, Echinodermata) is a major group of Paleozoic crinoids that represents an early divergence in the evolutionary history and morphologic diversification of class Crinoidea, yet phylogenetic relationships among early camerates remain unresolved. This study conducted a series of quantitative phylogenetic analyses using parsimony methods to infer relationships of all well-preserved Ordovician camerate genera (52 taxa), establish the branching sequence of early camerates, and test the monophyly of traditionally recognized higher taxa, including orders Monobathrida and Diplobathrida. The first phylogenetic analysis identified a suitable outroup for rooting the Ordovician camerate tree and assessed affinities of the atypical dicyclic family Reteocrinidae. The second analysis inferred the phylogeny of all well-preserved Ordovician camerate genera. Inferred phylogenies confirm: (1) the Tremadocian genera Cnemecrinus and Eknomocrinus are sister to the Camerata; (2) as historically defined, orders Monobathrida and Diplobathrida do not represent monophyletic groups; (3) with minimal revision, Monobathrida and Diplobathrida can be re-diagnosed to represent monophyletic clades; (4) family Reteocrinidae is more closely related to camerates than to other crinoid groups currently recognized at the subclass level; and (5) several genera in subclass Camerata represent stem taxa that cannot be classified as either true monobathrids or true diplobathrids. The clade containing Monobathrida and Diplobathrida, as recognized herein, is termed Eucamerata to distinguish its constituent taxa from more basally positioned taxa, termed stem eucamerates. The results of this study provide a phylogenetic framework for revising camerate classification, elucidating patterns of morphologic evolution, and informing outgroup selection for future phylogenetic analyses of post-Ordovician camerates.
—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.
A revised macroevolutionary history for Ordovician–Early Silurian crinoids
Paleobiology, 2005
Much of what is known about the long-term history of biodiversity and rates of taxonomic evolution in the fossil record derives from literature-based compilations of fossil stratigraphic ranges. It has been suggested that taxonomic and stratigraphic errors in these compilations are randomly distributed and, therefore, introduce no significant bias to macroevolutionary patterns. Here we compare a new, comprehensive global database of Ordovician and Early Silurian crinoids to Sepkoski's global genus compendium. Approximately 44% of the crinoid genera resolved to substage in Sepkoski's compendium are taxonomically inaccurate (i.e., invalid, nomina dubia, or column genera) or have incorrect first and/ or last occurrences. Errors in Sepkoski's compendium result from incomplete coverage of existing taxonomic work and incorrect stratigraphic correlations that, in some cases, are propagated throughout the taxonomic literature. Stratigraphic range errors are nonrandomly distributed among substages in Sepkoski's compendium. The result is underestimated richness in the Early Silurian and significantly overestimated rates of extinction in the Late Ordovician. There is no similar bias in Sepkoski's substage origination rates for crinoids. At the stage-level of temporal resolution, Sepkoski's crinoid data are more accurate. In this case, only 32% of the compendium's crinoid genera contain some stratigraphic or taxonomic inaccuracy. However, errors still result in incorrect macroevolutionary patterns, particularly with respect to rate of origination in the Ashgill, which is significantly underestimated in Sepkoski's compendium. Genera described since the completion of Sepkoski's compendium have had relatively little effect on estimated rates of evolution at both stage and substage resolution. These results suggest that macroevolutionary patterns among some taxa in Sepkoski's compilation may be significantly influenced by nonrandomly distributed taxonomic inaccuracies and stratigraphic range errors. In the case of the apparent end-Ordovician mass extinction among crinoids, the revised history reveals a dramatically reduced role for extinction at the substage-level of temporal resolution. At the stage level, Sepkoski's original compilation strongly exaggerates the excess of extinction over origination in the Ashgill. Although biases inherent in the stratigraphic record remain unaccounted for, removing taxonomic and stratigraphic errors in Sepkoski's compendium substantially changes our understanding of the nature of large-scale biotic change for an important Paleozoic taxon during the end-Ordovician.
Paleobiologists must propose a priori hypotheses of homology when conducting a phylogenetic analysis of extinct taxa. The distributions of such “primary” homologies among species are fundamental to phylogeny reconstruction because they reflect a prior belief in what constitutes comparable organismal elements and are the principal determinants of the outcome of phylogenetic analysis. Problems arise when fossil morphology presents seemingly equivocal hypotheses of homology, herein referred to as antinomies. In groups where homology recognition has been elusive, such as echinoderms, these problems are commonly accompanied by the presence (and persistence) of poor descriptive terminology in taxonomic literature that confounds an understanding of characters and stymy phylogenetic research. This paper combines fossil morphology, phylogenetic systematics, and insights from evolutionary developmental biology to outline a research program in Phylogenetic Paleo-ontogeny. A “paleo” ontogenetic approach to character analysis provides a logical basis for homology recognition and discerning patterns of character evolution in a phylogenetic context. To illustrate the utility of the paleo-ontogenetic approach, I present a reassessment of historically contentious plate homologies for “pan-cladid” crinoids (Cladida, Flexibilia, Articulata). Developmental patterns in living crinoids were combined with the fossil record of pan-cladid morphologies to investigate primary posterior plate homologies. Results suggest the sequence of morphologic transitions unfolding during the ontogeny of extant crinoids are developmental relics of their Paleozoic precursors. Developmental genetic modules controlling posterior plate development in pan-cladid crinoids have likely experienced considerable constraint for over 250 million years and limited morphologic diversity in the complexity of calyx characters. Future phylogenetic analyses of pan-cladids are recommended to consider the presence of a single plate in the posterior region homologous with the radianal, rather than the anal X, as is commonly assumed.
Journal of Asian Earth Sciences, 2018
This study reports new crinoid material, which is identified as Muicrinus dawanensis new genus and new species from South China, representing the oldest known iocrinid in the world. These new fossils, which are characterized by bearing simple primibrachials and a helically coiled column, are from the lower-middle part of the Dawan Formation, which ranges from the upper Floian (Lower Ordovician) to the lower Dapingian (Middle Ordovician) (∼470 Ma). A total of 11 related taxa with 80 characters were selected to conduct phylogenetic analyses. Our results indicated that South China specimens are closely related to ones that are endemic to Laurentia. Synapomorphies shared between species in those two cratons include elongate supraradial plates and isotomous arm branching. Furthermore, the phylogenetic closeness of endemic taxa that only occurred in two cratons leads us to suggest a geographic connection between those regions during deep time. Combining biogeographic evidence reported from Cambrian studies, this study supports the "missing-link" configuration of Rodinia during the breakup phase. Based on the crinoid global biodiversity pattern updated here, the potential for discovery of new Paleozoic crinoid faunas in China is very high. Ausich, 2008; Ausich and Deline, 2012) to form the Early Paleozoic Crinoid Evolutionary Fauna (CEF) (Baumiller, 1994; Ausich et al., 1994). The oldest crinoids are from Laurentia. By the late Tremadocian crinoids are also known from Gondwana (Ubaghs, 1969; Ausich et al., 2007), and the oldest crinoids on other paleocontinents are as follows: Avalonia, Floian; Baltica, Darriwilian; Siberia, Sandbian; South China Block, Dapingian. Fig. 1 depicts the Phanerozoic biodiversity of crinoids and illustrates the three CEFs. Crinoids suffered a mass extinction at the onset of the glacial epoch responsible for Late Ordovician (Hirnantian) extinctions (Peters and Ausich, 2008), and recovery to pre-existing biodiversity level was reached by the close of the Llandovery (Peters and Ausich, 2008; Ausich and Deline, 2012). The Llandovery radiation initiated the Middle Paleozoic CEF that culminated in the "Age of Crinoids" during the lower Mississippian (Kammer and Ausich, 2006; Sallan et al., 2011). The primary extinction episode among crinoids during this interval was an end-Givetian extinction rather than the more widely recognized Frasnian-Famennian extinction (Baumiller, 1994). After crinoids from important Middle Paleozoic CEF clades became extinct at or near the close of the early Viséan, the Late Paleozoic CEF radiated with biodiversity peaks during the Serpukhovian and Artinskian (the lows between these
A sampling-adjusted macroevolutionary history for Ordovician-Early Silurian crinoids
Paleobiology, 2008
Temporal variation in sampling intensity and geologically controlled rates of fossil preservation distort macroevolutionary patterns in the fossil record. Here, we use a comprehensive, list-based compilation of taxonomically and stratigraphically vetted global crinoid genus occurrences to evaluate and correct for the effects of variable and incomplete sampling from the Ordovician through Early Silurian. After standardizing the number of occurrences or the number of biofacies used to estimate the stratigraphic ranges of genera and after adjusting rates of turnover to account for the incomplete preservation of true extinction and origination pulses, we find support for several important revisions to the macroevolutionary history of crinoids. First, in contrast to the uncorrected data, sample-standardized genus richness does not appear to increase by more than 20% after an abrupt Middle Ordovician (Harnagian) diversification. Second, the only significant short-term change in genus rich...
Early phylogeny and subclass division of the Crinoidea (Phylum Echinodermata)
Journal of Paleontology, 1998
A stepwise approach is employed to determine the phylogeny of the initial crinoid radiation during the Arenig and Llanvirn series of the Ordovician. Parsimony-based character analysis is completed first on Arenig crinoids and then for Arenig and Llanvirn crinoids combined.The topology from well-resolved trees of this early crinoid radiation indicates that the Crinoidea should be subdivided into six subclasses. A new subclass and new order, Aethocrinea and Aethocrinida, respectively, are proposed for crinoids with four circlets of plates in the aboral cup: lintels, infrabasals, basals, and radials. This aboral cup construction is best displayed byAethocrinus, one of the oldest known crinoids (?Tremadoc-Arenig). However, this primitive aboral cup construction is also present in two Llanvirn crinoids,PerittocrinusandTetracionocrinus.The Aethocrinea was a small, short-lived radiation of crinoids with this design that was different from those of other crinoids. Two families in the Aethoc...