Cole—Phylogeny and evolution of Ordovician camerate crinoids
the family Reteocrinidae Wachsmuth and Springer, 1885 relative to Camerata. The genera Reteocrinus Billings, 1859,Gaurocrinus Miller, 1883, Cnemecrinus Guensburg and Sprinkle, 2003, and Quechuacrinus Guensburg and Waisfeld, 2015 are currently assigned to Reteocrinidae, which has traditionally been considered a family of diplobathrid camerates. The Reteocrinidae, however, lack some of the typical camerate characters and possess others that are idiosyncratic. Morphological traits that are atypical for most Ordovician camerates but variably possessed by reteocrinids include apinnulation, irregularly plated interrays that are not ankylosed, pentameric stems, and more than two fixed primibra- chials (Table 1). Similarities have been noted between Reteocrinus andboththe cladid Dendrocrinus Hall, 1852 and the disparid Iocrinus Hall, 1866 (Moore and Laudon, 1943a). On the basis of these characters, it has been suggested that reteocrinids do not belong within Camerata (Kelly, 1986; Donovan and Cope, 1989), although this proposal has not been tested quantitatively. Two of the reteocrinid genera, Cnemecrinus and Quechuacrinus, are Early Ordovician in age, making them taxa of interest for the outgroup selection analysis of early camerates. Fortuitously, the preliminary phylogenetic analysis conducted for outgroup selection also offers the opportunity to address this secondary question—affinity of family Reteocrinidae—with a single analysis.
Preliminary analysis.—The preliminary phylogenetic analysis included twenty-six genera sampled from early blastozoans (six genera), cladids (four genera), protocrinoids (two genera), monobathrid camerates (five genera), non-reteocrinid diploba- thrid camerates (six genera), and reteocrinids (three genera; Table 2). Taxa were coded for the preliminary analysis following the same methods used for the comprehensive analysis (see the following). The characters and character states used for the preliminary analysis were identical to those used for the comprehensive analysis, with the exception of five additional characters that were coded to encompass morpho- logical variation of the additional taxonomic groups sampled (Supplemental Data 1). Of the 117 characters coded in total, 90 proved parsimony-informative. The six blastozoan taxa were designated as the outgroups for the analysis. A parsimony analysis was conducted in PAUP* v. 4.0a147 (Swofford, 2003) using a heuristic search with 1,000 random addition sequence replicates with tree bisection reconnection (TBR), holding 10 trees at each step and collapsing all branches with a maximum branch length of zero. Values for the consistency index (CI) and retention index (RI) were recorded for the recovered trees, and bootstrap values and Bremer support were calculated using PAUP*.
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Results and discussion.—Twelve most parsimonious trees were recovered from the phylogenetic analysis with a tree length of 360 steps each and CI and RI values of 0.528 and 0.592, respectively. The strict consensus of these trees is well resolved with only small local polytomies (Fig. 1). Three monophyletic groups form that are respectively comprised of the four cladid genera, the two protocrinoid genera, and all genera traditionally considered camerates, including Cnemecrinus, Eknomocrinus, Reteocrinus, Quechuacrinus, and all other included mono- bathrids and diplobathrids. Although the order of branching relationships of these clades differs somewhat from the topology of Ausich et al. (2015), the tree recovers the fundamental basal split between camerate and non-camerate crinoids. Within the camerate clade, Eknomocrinus and Cnemecrinus are the first to diverge, forming a clade that is well-supported by bootstrap and Bremer support values. Two reteocrinids, Reteocrinus and Quechuacrinus, form another well-supported clade. The remaining camerate taxa are not clearly divided into mono- bathrid and diplobathrid groups. Based on the low taxonomic sampling of camerates in this analysis and low support values for most nodes within the camerate clade, interpretations of relationships among Ordovician camerates should be made based on the subsequent analysis (see below) rather than on this preliminary analysis. Results indicate: (1) members of family Reteocrinidae are
more closely related to camerate crinoids than to protocrinoids or cladids and thus should maintain status as camerate taxa, and (2) Eknomocrinus and Cnemecrinus form the sister group to the rest of Camerata and thus are the most suitable taxa for rooting the camerate tree.
Materials and methods
Taxon sampling and data collection.—The comprehensive analysis considered all currently named Ordovician camerate genera, which includes 38 diplobathrids and 17 monobathrids (Table 3). At the outset of the study, the monobathrids Schizocrinus Hall, 1847 and Habrotecrinus Guensburg and Sprinkle, 2003 were excluded due to poor preservation (<50% of characters preserved), and the incertae sedis monobathrid (?) Delgadocrinus Ausich, Sá, and Gutiérrez-Marco, 2007 was excluded due to its uncertain assignment to the Camerata. Thus, 52 genera in total, 38 diplobathrids and 14 monobathrids, were included in the analysis. A representative species was selected for each genus and coded using museum specimens available at the Smithsonian National Museum of Natural History, the London Natural History Museum, the Chicago Field Museum,
Table 1. Morphological features of genera in family Reteocrinidae. Character states of the typical camerate condition are marked with a ‘0’; character states of the ‘reteocrinid’ condition are marked with a ‘1.’ Character states are as follows: Pinnulation: 0 = pinnulate, 1 = apinnulate; Interray plating: 0 = regular, 1 = irregular; Interray suturing: 0 = ankylosed, 1 = flexible; Stem: 0 = holomeric, 1 = pentameric; Primibrachials: 0 = 2, 1 = greater than or equal to three. Ordovician camerates sharing reteocrinid-like features are listed.
Taxa Pinnulation Interray plating Interray suturing Stem
Reteocrinus 111 1 Quechuacrinus 111 1 Cnemecrinus 100 1 Gaurocrinus 011 0 Xenocrinus
Other Ordovician camerates with 'reteocrinid' (state 1) condition
Eknomocrinus Adelphicrinus
Canistrocrinus Adelphicrinus
Primibrachials 1
1 0 0
Bromidocrinus Cotylacrinna Eknomocrinus Adelphicrinus
Eknomocrinus Adelphicrinus
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