816


Journal of Paleontology 91(4):815–828


that considered all currently recognized Ordovician camerate genera to explore evolutionary relationships within the Camerata, assess the monophyly of higher camerate taxa, and evaluate the congruence of the traditional classification scheme with phylogeny. This is the first quantitative phylogenetic study to focus specifically on the Ordovician Camerata. As a result, it provides insight into a significant period in camerate evolutionary history and elucidates evolutionary relationships and patterns of morphologic evolution at the base of the crinoid tree of life. In addition to informing systematic revision of the group, the recovered trees provide a phylogenetic framework for the study of macroevolutionary patterns within the subclass Camerata.


Previous work on camerate phylogeny


The relationship of camerates to other major crinoid groups has, until recently, remained uncertain. Systematists responsible for establishing camerate classificationmade little attempt to infer the relationship of camerates to other crinoid groups (Moore, 1952; Moore and Laudon, 1943a; Ubaghs, 1978). Since then, a number of studies have considered the relationships among the major crinoid groups, including the Camerata, on the basis of either quantitative phylogenetic analyses or qualitative study of cladograms. The major hypotheses that have been proposed for camerates are summarized by Cole and Ausich (2015, fig. 1) and include past suggestions that they are most closely related to disparids (Simms, 1993) or cladids (Ausich, 1998a, 1998b) or are sister to a clade comprised of disparids and cladids (Guensburg, 2012). The most recent and comprehensive quantitative analysis, which considered Early–Middle Ordovician crinoid taxa, concluded that the Camerata: (1) form amonophyletic group, and (2) were the first clade to diverge from the rest of the Crinoidea (Ausich et al., 2015). It should be noted that the first point, the monophyly of the Camerata, has been supported by previous phylogenetic analyses by Ausich (1998a, 1998b) for all camerate taxa included and by Guensburg (2012) with the exception of Eknomocrinus Guensburg and Sprinkle, 2003. Although the relationship of camerates to other crinoid clades


has now been established, few quantitative phylogenetic analyses have been conducted at lower taxonomic levels, and as a result, evolutionary relationships at the taxonomic rank of order and below remain poorly understood. Themonophyly of ordersDiplobathrida and Monobathrida have been implicitly assumed yet have never been substantiated through quantitative testing. Qualitative family- level cladograms have represented the monobathrid–diplobathrid relationship as a simple basal divergence (Moore, 1952) or left the relationship between orders largely ambiguous (Ubaghs, 1978; Simms, 1993; Cole and Ausich, 2015, fig. 2). In the most com- prehensive phylogeny of Ordovician camerates, which considered Arenig to Caradoc taxa, all monobathrids and most diplobathrids were left unresolved on a polytomy, and thus the monophyly of the orders could not be established (Ausich, 1998b). Our poor understanding of evolutionary relationships


within the Camerata, which has been repeatedly acknowledged (Ubaghs, 1978; Simms, 1993), is reflected in the classification of subordinal taxa. For example, the diplobathrid suborder Zygodiplobathrina (Ubaghs, 1953, 1978) is thought to represent a polyphyletic grouping although its status as a clade has never


been tested through phylogenetic analysis. Similarly, the phylogenetic reality of superfamilies Dimerocrinitacea and Rhodocrinitacea have been questioned (Brower, 1973; Frest and Strimple, 1981), and revisions of many camerate families to better reflect phylogeny have been proposed (Brower and Veinus, 1974; Kolata, 1982; Ausich, 1985, 1986; Rhenberg et al., 2015). These long-suspected systematic issues highlight the need for comprehensive camerate phylogenies to inform systematic revision and amend non-monophyletic groups.


Preliminary analysis and outgroup selection


Rooting the camerate tree.—Before inferring the phylogeny of Ordovician camerates, a preliminary analysis with two primary objectives was conducted. The first goal of this preliminary analysis was to identify a suitable outgroup for the camerate phylogeny. Outgroup selection is important in phylogenetic analysis for rooting the tree and determining character polarity, which in turn may affect branching order, inferred relationships, and interpretations of morphological change within the ingroup. Using distant outgroups can result in an incorrect topology that is spuriously rooted on a long branch, and thus, the outgroup(s) selected should ideally be as closely related to the ingroup as possible to break up long branches and differentiate ancestral states from derived character states (Wheeler, 1990; Smith et al., 1992; Smith, 1994a, 1994b). Rooting the crinoid tree of life has proven one of the most


challenging aspects of inferring phylogeny of the clade. This is due in part to its rapid early radiation and long-uncertain evolutionary origins, both of which complicate rooting


phylogenies (Shavit et al., 2007; Smith and Zamora, 2009). The first appearance of crinoids in the fossil record (LowerOrdovician, Tremadocian) is marked by the occurrence of representatives from several major groups, including camerates, protocrinoids, cladids, and disparids. This diversity of crinoid taxa at their first appearance precludes rooting the tree with a single crinoid taxon based on stratigraphic appearance alone. Because Camerata was the earliest recognized clade to diverge fromthe rest of Crinoidea, it is similarly plagued by this issue of outgroup selection (Ausich et al., 2015). Recent phylogenetic analyses of pelmatozoans have


suggested crinoids are nested within blastozoan clades such as diploporoids, eocrinoids, and glyptocystitoids (Sumrall, 2014, 2015). This relationship has been further corroborated by organic molecules recovered from fossil echinoderms (O’Malley et al., 2016). Because the potential sister group to crinoids is nested within the Blastozoa, representatives from these clades have been successfully utilized as outgroups for analyses of early crinoids (Ausich, 1998a, 1998b; Ausich et al., 2015). For this study, however, the paucity of unequivocally homologous characters shared between blastozoan outgroups and camerate crinoids makes it difficult to determine character polarizationwith certainty and avoid spurious rooting of the ingroup. Consequently, it was deemed advantageous to conduct a preliminary analysis of early camerates and other representative clades to identify an outgroup taxon that is more closely related to the camerate ingroup.


Affinities of family Reteocrinidae.—The second goal of the preliminary analysis was to identify the phylogenetic position of


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