830


Journal of Paleontology 91(4):829–846


Gauthier, 1994; Brochu and Sumrall, 2001). Under a phylogeny-based system of classification, groups of taxa are organized by their patterns of shared common ancestry rather than diagnostic traits. This is a particularly useful aspect of phylogenetic taxonomy: if named evolutionary units are defined by their history of common ancestry, they do not change if new information comes to light that necessitates modification of taxonomic diagnoses. For example, new fossil discoveries and/ or more nuanced understandings of phylogenetic relationships may alter the distribution of synapomorphies among members of a clade but do not alter the definition of the clade. Moreover, by naming taxa on the basis of cladogram topologies, phylo- genetic taxonomy can provide a precise definition for groups previously difficult to diagnose by a unique combination of synapomorphies, such as the Articulata (Simms, 1988; Webster and Jell, 1999; Rouse et al., 2013). To avoid potential instability in taxonomic nomenclature and/or the proliferation of clade names, we advocate that major changes in crinoid systematics should: (1) be based on well-supported phylogenetic hypotheses inferred using rigorous and repeatable quantitative techniques, and (2) employ widely used names and/or names with historical precedence if available. In this paper, we propose a series of stem-based and node-


based clade definitions to help standardize nomenclature for crinoid higher taxa. The clade definitions proposed herein are informed by a series of recent phylogenetic analyses (Ausich et al., 2015; Cole, 2017; Wright, 2017) and represent the first attempt to classify crinoids using the principles of phylogenetic taxonomy (de Queiroz and Gauthier, 1992, 1994). Although Linnaean classifications lack rigorous criteria for


assigning ranks, they can nevertheless provide useful (if coarse) reflections of phylogenetic relatedness and divergence among taxa, particularly in paleontology (Smith, 1984; Potter and Freudenstein, 2005; Jablonski and Finarelli, 2009; Soul and Friedman, 2015). Given the widespread use of rank-based classifications among invertebrate paleontologists in both alpha taxonomy and paleobiological studies, it is prudent to present a phylogenetically informed revision of the rank-based classifi- cation of the Crinoidea. These revisions modify the existing Linnaean classification of crinoids to better represent the set of nested hierarchies implied by phylogenetic trees (Ausich et al., 2015; Cole, 2017; Wright, 2017). In their review of progress made in crinoid research during


the twentieth century, Ausich and Kammer (2001, p. 1167) stated the “immediate challenge for the [twenty-first century] study of crinoids is to establish a phylogenetic classification for the entire class.” It is our hope that the dual classification systems presented herein will provide a foundation for future studies employing phylogenetic nomenclature in crinoid research and promote the use of an improved classification system among researchers who choose to work with the Linnaean system.


The dredge and the hammer: a brief history of crinoid classification


The whole history of the attempts to classify the Crinoidea shows… the gradual emancipation from the older habit


of lumping forms together because they are alike in structure without considering how the likeness arose.


–F.A. Bather (1898, p. 339)


Formal scientific description and classification of crinoids began in 1821 when J.S. Miller recognized fossilized stalked echino- derms from the “environs of Bristol” as a distinct group. Although he did not include comatulids in his original concep- tion of the Crinoidea, he anticipated that they were crinoids: “The combination of these results with those from the Crinoidea made me anxious to examine the Comatulae…an animal which would be defined with sufficient precision as a Pentacrinus destitute of the column” (Miller, 1821, p. 127). Further, he judged Marsupites ornatus Miller, 1821 (an unstalked crinoid of Cretaceous age) to be the ‘link’ between comatulids and his Crinoidea (Miller, 1821, p. 139). Extant stalked crinoids were unknown until the mid- to late 1860s, when their discovery during oceanic dredging expeditions provided fodder for early debates regarding the efficacy of Darwin’s (1859) then recently proposed theory of natural selection (see Alaniz, 2014; Etter and Hess, 2015). Thus, the original description, definition, and diagnosis of the Crinoidea relied entirely on fossil remains. Despite the morphological diversity and deep phylogenetic divergences among groups of extant species, the inclusion of living crinoids with fossil forms has not fundamentally altered Miller’s (1821) concept. Following subsequent inclusion of the comatulids and extant stalked crinoids with fossil forms, the Crinoidea has withstood nearly 200 years of scrutiny as a distinct group within the Echinodermata. In contrast with their long-term recognition as a clade, the


classification of taxa within the Crinoidea has been widely debated since the nineteenth century (Müller, 1841; Angelin, 1878; Wachsmuth and Springer, 1897; Bather, 1899; Springer, 1913; Jaekel, 1918).With few exceptions, debates on crinoid classifica- tion have primarily been based on disagreements over phylo- genetic affinities among taxa rather than systematic practices among researchers (see Bather, 1899 for a counter example). The intensity of early debates over crinoid classification is best epitomized by the frequent yet acrimonious exchanges between Wachsmuth and Springer (e.g., 1885, 1891, 1897) and Bather (e.g., 1898, 1899, 1900). Attempts to resolve these debates among nineteenth-century systematists have largely shaped the last ~70 years of crinoid research (Ausich and Kammer, 2001). In their seminal work Evolution and Classification of


Paleozoic Crinoids, Moore and Laudon (1943) presented a classification that incorporated aspects of both Frank Springer’s and Francis Bather’s ideas (see discussion in Ausich and Kammer, 2001). With few modifications, Moore and Laudon’s (1943) publication formed the basis of the Treatise on Invertebrate Paleontology (Moore and Teichert, 1978). Following publication of the 1978 Treatise, the classification of crinoids entered a protracted yet frail era of nomenclatural stability. Although few authors have advanced major revisions or comprehensive modifications, many have voiced contention with the Treatise classification (Kelly, 1982, 1986; Kolata, 1982; McIntosh, 1984, 1986, 2001; Ausich, 1986, 1998a, 1998b; Donovan, 1988; Simms, 1988; Simms and Sevastopulo, 1993; Brower, 1995; Webster and Jell, 1999; Guensburg and Sprinkle, 2003; Hess and Messing, 2011; Guensburg, 2012;


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