Universal Elemental Homology in Glyptocystitoids, Hemicosmitoids, Coronoids and Blastoids: Steps Toward Echinoderm Phylogenetic Reconstruction in Derived Blastozoa

Abstract

Late Devonian to Early Carboniferous stratigraphic units within the 'Zhulumute' Formation, Honggule-leng Formation (stratotype), 'Hebukehe' Formation and the Heishantou Formation near the Boulongour Reservoir in northwestern Xinjiang are fossil-rich. The Hongguleleng and 'Hebukehe' formations are bio-stratigraphically well constrained by microfossils from the latest Frasnian linguiformis to mid-Famennian trachytera conodont biozones. The Hongguleleng Formation (96.8 m) is characterized by bioclastic argil-laceous limestones and marls (the dominant facies) intercalated with green spiculitic calcareous shales. It yields abundant and highly diverse faunas of bryozoans, brachiopods and crinoids with subordinate solitary rugose corals, ostracods, trilobites, conodonts and other fish teeth. The succeeding 'Hebukehe' Formation (95.7 m) consists of siltstones, mudstones, arenites and intervals of bioclastic limestone (e.g. 'Blastoid Hill') and cherts with radiolarians. A diverse ichnofauna, phacopid trilobites, echinoderms (crinoids and blastoids) together with brachiopods, ostracods, bryozoans and rare cephalopods have been collected from this interval. Analysis of geochemical data, microfacies and especially the distribution of marine organisms, which are not described in detail here, but used for facies analysis, indicate a deepen-ing of the depositional environment at the Boulongour Reservoir section. Results presented here concern mainly the sedimentological and stratigraphical context of the investigated section. Additionally, one Late Devonian palaeo-oceanic and biotic event, the Upper Kellwasser Event is recognized near the section base.

Testing for homologies in the axial skeleton of primitive echinoderms

“…In glyptocystitoid rhombiferans, the first, horseshoe-shaped, brachiole facet is developed to the left (as viewed in the direction of growth) in all ambulacra (Fig. 3) and is shared by one of the peri-orals (PO1-PO5) and the plates labeled L ("first left ambulacral floor plates" of Sumrall and Waters, 2012). Thereafter, each brachiole facet is supported by a smaller adoral ambulacral flooring plate and a larger distal flooring plate.…”

New insights concerning homology of the oral region and ambulacral system plating of pentaradial echinoderms

“…(1, 3, 6, 9) after Sumrall (2008); (2) after Sumrall and Deline (2009); (4) after (7, 8) after Sumrall and Waters (2012); (10) after Frest and Strimple (1982); (11) after Sheffield and Sumrall (2015).…”

“…The abradial floor plates of blastoids are also positioned epithecally upon the lancet plate of the theca (Sumrall and Waters, 2012). The ambulacral floor plates (called side plates in blastoid terminology) in most cases form the main food groove along the parradial suture.…”

“…In Paleozoic echinoderms, assessing homology is particularly challenging because: (1) the process of evolution often masks homology via character transformation, and (2) a striking proliferation of taxonomic 'classes' based on unique combinations of morphological characters has emphasized differences rather than underlying similarities. Unfortunately, many of these classes have unique sets of terminology, which apply different names to homologous structures or identical names to nonhomologous structures (Sumrall, 2010;Sumrall and Waters, 2012). Recently, the universal elemental homology (UEH) model provided a morphologic framework to facilitate the identification of individual echinoderm skeletal elements associated with the mouth region and ambulacral system (Sumrall, 2010(Sumrall, , 2015Sumrall and Waters, 2012;Kammer et al, 2013;Ausich and Kammer, 2016).…”

“…Unfortunately, many of these classes have unique sets of terminology, which apply different names to homologous structures or identical names to nonhomologous structures (Sumrall, 2010;Sumrall and Waters, 2012). Recently, the universal elemental homology (UEH) model provided a morphologic framework to facilitate the identification of individual echinoderm skeletal elements associated with the mouth region and ambulacral system (Sumrall, 2010(Sumrall, , 2015Sumrall and Waters, 2012;Kammer et al, 2013;Ausich and Kammer, 2016). With this model based on detailed anatomy, symmetry, and development, evolved differences in plate relationships, morphology, and presence/absence of plates can be identified with high precision and utilized to construct useful phylogenetic characters.…”