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Journal of Paleontology 91(4):815–828


phylogeny to identify monophyletic groups, relative branching order, and patterns of morphologic evolution in early camerate crinoids. The recovered trees provide a detailed view of early evolutionary relationships among camerate crinoids and serve as a phylogenetic framework for subsequent systematic work. The recovered phylogeny of Ordovician camerates indicates systematic revision is needed at the suprageneric level. Because this study focused on Ordovician camerates, it is best suited for assessing questions related to evolutionary relationships at the base of the camerate tree of life, such as the affinity of Reteocrinidae with Camerata and the monophyly of orders Monobathrida and Diplobathrida. For this reason, the primary emphasis is on systematic revisions at the suprageneric level. Ongoing analyses of post-Ordovician Diplobathrida and Monobathrida (Cole, 2015) are expected to further inform evolutionary relationships within these clades, and thus a com- prehensive systematic revision will be postponed until more inclusive phylogenetic analyses are completed for the Camerata.


Implications for systematic revision of the Camerata.—On the basis of both the preliminary analysis presented herein and the analysis of Ausich et al. (2015), Camerata is recognized as a monophyletic group.As such, it should be maintained as a subclass and is formally defined byWright et al. (2017). In the phylogeny of the Ordovician Camerata presented herein, the majority of taxa fall within one of two clades. These clades correspond closely to Monobathrida and Diplobathrida as historically defined, and thus, these orders should be retained based on the results of this analysis. Minor revisions, primarily reassignment of genera from each order to other groups, are required to redefine both orders as mono- phyletic. Formal phylogeny-based definitions are provided for Monobathrida andDiplobathrida by Wright et al. (2017). The terms ‘Monobathrida’ and ‘Diplobathrida’ will be used for the remainder of this discussion to refer only to taxa that belong to these clades, as identified based on the phylogenetic inferences presented herein. The remaining taxa that are not containedwithinMonobathrida and Diplobathrida occupy a basal position in the tree with respect to these two clades and are therefore identified as ‘stem taxa.’ Because members of the monobathrid and diplobathrid clades are more closely related to each other than to the stem taxa, it is fitting that a new term be erected to reflect evolutionary relationships between camerates and to maintain clarity in taxonomic communication. The term ‘Eucamerata’ is proposed to designate the clade contain- ing all members ofMonobathrida and Diplobathrida; stem taxa are excluded from this group. In Figure 2, Eucamerata is represented by Node B and all of its descendents. Formal definition of ‘Eucamer- ata’ is given by Wright et al. (2017). Consequently, the stem taxa identified herein are informally designated as stem eucamerates. The term ‘stem’ is here used to indicate a paraphyletic assemblage of early diverging camerate lineages with the Eucamerata as their nearest outgroup. Taxa recognized as stem eucamerates include Eknomocrinus,


Cnemecrinus, Adelphicrinus, Reteocrinus, and Quechuacrinus. Although these genera are all currently assigned to either the Monobathrida or Diplobathrida, their phylogenetic position as stem taxa indicates they should not be assigned to either of these orders. Based on the preliminary analysis, members of the Reteocrinidae are more closely related to camerates than to other crinoid groups and thus should maintain their classification


as camerate taxa. Not all genera currently assigned to the Reteocrinidae form a cohesive family, however. Reteocrinus and Quechuacrinus form a clade of stem eucamerates, whereas Cnemecrinus is an independent stem lineage, and Gaurocrinus occupies a position within Eucamerata. Retention of Reteocrinus and Quechuacrinus as reteocrinids and removal of the other genera from this family would be the best approach to amend Reteocrinidae to represent a monophyletic group. The stem eucamerates form an evolutionary grade, and as such, a suite of diagnostic traits is difficult to assemble that applies to all stem eucamerates. There are several traits, however, that are commonly shared by stem eucamerates, the most notable of which include variable location of the primaxil, apinnulation, rectilinear uniserial brachials, and pentameric stems. All these traits differ between eucamerates and stem eucamerates. As traditionally defined, most previously recognized


Ordovician diplobathrid families are not supported by the tree produced in this study. The family Rhodocrinitidae, a heterogeneous group to which more than 40% of all diplobathrid genera are assigned, appears to represent a morphological grade rather than a clade. In part, this is likely because the characters used to diagnose rhodocrinitids are not unique to this family (Kolata, 1982; Ausich, 1986). One morphological character that is widely employed as a distinguishing feature of the Rhodocrinitidae is the separation of the radials in all interrays. However, several other diplobathrid families possess this character, including the Anthracocrinidae and Anthemocrinidae, both of which first appeared during the Ordovician. In this study, the largest clade within Diplobathrida comprises anthracocrinids in addition to rhodocrinitids, and most other clades include a combination of rhodocrinitid genera and genera from other families. This confirms previous suggestions that systematic revisions at the family level (Brower and Veinus, 1974; Kolata, 1982), and of the Rhodocrinitidae in particular (Ausich, 1986), are in order. It should be noted that several diplobathrid families, such as Dimerocrinitidae and Anthemocrinidae, have low generic diversity in the Ordovician, and thus their placement within this analysis should presently be treated with caution pending analyses that include a broader sample of post-Ordovician taxa. Similarly, the division of suborders Eudiplobathrina and Zygodiplobathrina and the superfamilies Rhodocrinitacea and Dimerocrinitacea requires sampling of post-Ordovician taxa to adequately test the validity of these groups. As traditionally defined, the 14 Ordovician monobathrid


genera included in this study are assigned to nine different families. Most of these families are representedby onlya single Ordovician genus, and thus the present analysis does little to resolve the details of family-level classification. However, some family-level divisions are represented by closely related taxa, including PeriglyptocrinusWachsmuth and Springer, 1897 andGlyptocrinus Hall, 1847 (Glyptocrinidae); Canistrocrinus Wachsmuth and Springer, 1885 and XenocrinusMiller, 1881 (Tanaocrinidae); and Eopatelliocrinus Brower, 1973 and Macrostylocrinus Hall, 1852 (Patelliocrinidae). Likewise, the suborder Compsocrinina is represented by only two Ordovician genera, preventing confident assessment of the division between the monobathrid suborders Compsocrinina and Glyptocrinina. Ordovician monobathrids are less diverse than diplobathrids and did not become significant


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