852 1
Journal of Paleontology 91(4):847–857
Pentremites godoni Deltoblastus permicus Diploblastus glaber Ellipticoblastus ellipticus Granatocrinus granulatus Globoblastus norwoodi Cryptoblastus melo Monoschizoblastus rofei Stephanocrinus angulatus
2
Pentremites godoni Deltoblastus permicus Diploblastus glaber Ellipticoblastus ellipticus Granatocrinus granulatus Globoblastus norwoodi Monoschizoblastus rofei Cryptoblastus melo Stephanocrinus angulatus
Figure 5. (1) Strict consensus tree of seven most parsimonious trees with tree lengths of 52 without the addition of hydrospire data (CI 0.645, RI 0.486, RC 0.309). (2) Strict consensus tree of one most parsimonious tree with the addition of hydrospire data with a length of 60 (CI 0.650, RI 0.488, RC 0.317).
characters were removed and the analysis was performed again without hydrospire data in the matrix (Fig. 5.1). An additional analysis was then performed on this matrix with the hydrospire data included (Fig. 5.2). The tree topology without the hydrospire data (Fig. 5.1) is
largely unresolved with a polytomy at the base in the strict consensus of the nine equally most parsimonious trees, with several small groupings of taxa but relatively little resolution. Pentremites godoni and D. permicus form a sister pair, but their relationship to other taxa is unresolved. Ellipticoblastus ellipticus, G. granulatus (Roemer, 1851), and G. norwoodi (Owen and Shumard, 1850) form a smaller polytomy with a sister taxon of C.
melo.Both D. glaber and M. rofei are in an unresolved relationship with these two groupings of taxa. The addition of hydrospire data does not significantly alter
tree topology (Fig. 5.2) but does provide resolution within the smaller groupings of taxa. The pairing of P. godoni and D. permicus is now sister group to D. glaber, united by the number of respiratory fields. The pairing of P. godoni and D. permicus is further supported by the shared reduction of hydrospire folds in the anal area. The grouping of E. ellipticus, G. norwoodi, G. granulatus,and M. rofei is supported by the ambulacra being in line with surrounding thecal plates, the number of respiratory folds per field, and the transitions from hydrospire fold to spiracle. The wide hydrospire folds of E. ellipticus support its separation fromthe pairing ofG. norwoodi and G. granulatus. The clade of G. granulatus, G. norwoodi, M. rofei,and E. ellipticus is sister group to M. rofei in the analysis containing hydrospire data rather than C. melo in the data set
lacking hydrospire data. This shows that the addition of hydrospire data can support novel relationships that are not supported by external data alone. This preliminary analysis provides support that the incorporation of internal character data aids in understanding
evolutionary relationships among blastoid taxa. Although only five additional internal characters were added to the amended character matrix of 29 characters, these characters appear to provide additional resolution both within and between group- ings of blastoids and, in one case, novel relationships.
Future directions
Respiratory structures of blastozoan echinoderms have been long considered synapomorphies for clades and often are used to delineate species (Sprinkle, 1973). While internal character data have previously been successfully incorporated into phylogenetic inference for fossil taxa (Leighton and Maples, 2002; Wright and Stigall, 2013, 2014; Bauer and Stigall, 2016), this study is the first to do so with Blastoidea. Although the internal anatomical models used in this study are currently limited, we provided evidence that respiratory structures provide further resolution to a phylogenetic hypothesis because they bring more data to bear in the inferred phylogeny. With more complete taxonomic coverage of blastoid hydrospire structure, the inferred blastoid phylogeny will provide a basis to support or reject the groupings of Fissiculata and Spiraculata, a framework for taxonomic revision, and a basis for testing evolutionary questions throughout the Paleozoic. In addition to the hydrospires being identifiable in serial
sections, thecal plate boundaries can be clearly outlined in the peels (Fig. 4.3, 4.6, 4.9, 4.12, 4.15, 4.18). Plates of particular interest for internal anatomy include the lancet, which can occur exposed or concealed along the length of the ambulacra by the side plates. The lancet and adjacent side plates are important as the hydrospire pores are often found along the plate sutures. Questions concerning plate origination and persistence throughout the theca can be examined. Incorporation of all morphological details will provide a fuller understanding of early echinoderm relationships. Data derived from the evolu- tionary history of the blastoids can therefore be applied to other echinoderm groups to aid in inferring the relationships among members of this diverse clade.
Systematic paleontology
Remarks.—Descriptions are based on the modeled hydrospire structures and acetate peel images. As the data set was a legacy collection, the descriptions are based on the peels available for study. The extent of the peels through the specimens was at the discretion of those that generated the peels (A. Breimer), resulting in several models being incomplete (noted in the following). Although it is a variation on normal systematic descriptions, the authors feel that a thorough examination and description of the structures is necessary and provides the framework for understanding subtle similarities and differences between species. The objective, therefore, is to provide descriptions relating the internal anatomy to the external expression of the respiratory structures. These models are
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