A re‐interpretation of the ambulacral system of <i>Eumorphocystis</i> (Blastozoa, Echinodermata) and its bearing on the evolution of early crinoids

Sheffield, Sarah L.; Sumrall, Colin D.

doi:10.1111/pala.12396

Cited by 14 publications

(32 citation statements)

References 38 publications

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“…Recently, the discovery that early crinoids express what could also be considered a tripartite pattern (Guensburg and Sprinkle, 2009) formed the basis for a reinterpretation that Eumorphocystis "arm" anatomy is homologous to that of early crinoids (Sheffield and Sumrall, 2019a). In this paper, however, we add descriptive data and imagery that enhance our understanding of, and provide a basis for, interpretation of Eumorphocystis "arms" that is in agreement with the original suggestion that Eumorphocystis is of strictly blastozoan affinity (Parsley, 1982).…”

Section: Introductionsupporting

confidence: 78%

Evolutionary significance of the blastozoanEumorphocystisand its pseudo-arms

Guensburg¹,

Sprinkle²,

Mooi³

et al. 2020

J. Paleontol.

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Twelve specimens of Eumorphocystis Branson and Peck, 1940 provide the basis for new findings and a more informed assessment of whether this blastozoan (a group including eocrinoids, blastoids, diploporites, rhombiferans) constitutes the sister taxon to crinoids, as has been recently proposed. Both Eumorphocystis and earliest-known crinoid feeding appendages express longitudinal canals, a demonstrable trait exclusive to these taxa. However, the specimen series studied here shows that Eumorphocystis canals constrict proximally and travel within ambulacrals above the thecal cavity. This relationship is congruent with a documented blastozoan pattern but very unlike earliest crinoid topology. Earliest crinoid arm cavities lie fully beneath floor plates; these expand and merge directly with the main thecal coelomic cavity at thecal shoulders. Other associated anatomical features echo this contrasting comparison. Feeding appendages of Eumorphocystis lack two-tiered cover plates, podial basins/pores, and lateral arm plating, all features of earliest crinoid ‘true arms.’ Eumorphocystis feeding appendages are buttressed by solid block-like plates added during ontogeny at a generative zone below floor plates, a pattern with no known parallel among crinoids. Eumorphocystis feeding appendages express brachioles, erect extensions of floor plates, also unknown among crinoids. These several distinctions point to nonhomology of most feeding appendage anatomy, including longitudinal canals, removing Eumorphocystis and other blastozoans from exclusive relationship with crinoids. Eumorphocystis further differs from crinoids in that thecal plates express diplopores, respiratory structures not present among crinoids, but ubiquitous among certain groups of blastozoans. Phylogenetic analysis places Eumorphocystis as a crownward blastozoan, far removed from crinoids.

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Section: Introductionsupporting

confidence: 78%

Evolutionary significance of the blastozoanEumorphocystisand its pseudo-arms

Guensburg¹,

Sprinkle²,

Mooi³

et al. 2020

J. Paleontol.

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“…However, observation of 10 Eumorphocystis specimens other than the single example used in Sheffield and Sumrall (2019a) to hypothesize the existence of this homology indicates that these similarities are superficial. Most important among this evidence is that the specimen studied by Sheffield and Sumrall (2019a) provides incomplete information regarding putative coeloms. As preserved, the arms of this specimen do not reveal a situation in which these longitudinal appendage cavities are contiguous with the thecal cavity.…”

Section: Origin Of the Crinoid Armmentioning

confidence: 99%

Athenacrinusn. gen. and other early echinoderm taxa inform crinoid origin and arm evolution

Guensburg¹,

Sprinkle²,

Mooi³

et al. 2019

J. Paleontol.

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Intermediate morphologies of a new fossil crinoid shed light on the pathway by which crinoids acquired their distinctive arms. Apomorphies originating deep in echinoderm history among early nonblastozoan pentaradiate echinoderms distinguish Tremadocian (earliest Ordovician) crinoid arms from later taxa. The brachial series is separated from the ambulacra, part of the axial skeleton, by lateral plate fields. Cover plates are arrayed in two tiers, and floor plates expressed podial basins and pores. Later during the Early Ordovician, floor plates contacted and nestled into brachials, then were unexpressed as stereom elements entirely and cover plates were reduced to a single tier. Incorporation of these events into a parsimony analysis supports crinoid origin deep in echinoderm history separate from blastozoans (eocrinoids, ‘cystoids’). Arm morphology is exceptionally well-preserved in the late Tremadocian to early Floian Athenacrinus broweri new genus new species. Character analysis supports a hypothesis that this taxon originated early within in the disparid clade. Athenacrinus n. gen. (in Athenacrinidae new family) is the earliest-known crinoid to express what is commonly referred to as ‘compound’ or ‘biradial’ morphology. This terminology is misleading in that no evidence for implied fusion or fission of radials exists, rather it is suggested that this condition arose through disproportionate growth.UUID: http://zoobank.org/b383e039-3298-4472-a7e3-e81684f87cfe

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“…; Thuy & Stöhr , ; Bauer et al . ; Sheffield & Sumrall ) that have been complemented by analyses of extant echinoderms (e.g. Rouse et al .…”

mentioning

confidence: 99%

Phylogeny and evolutionary history of diplobathrid crinoids (Echinodermata)

Cole

2018

Palaeontology

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Order Diplobathrida is a major clade of camerate crinoids spanning the Ordovician–Mississippian, yet phylogenetic relationships have only been inferred for Ordovician taxa. This has hampered efforts to construct a comprehensive tree of life for crinoids and develop a classification scheme that adequately reflects diplobathrid evolutionary history. Here, I apply maximum parsimony and Bayesian phylogenetic approaches to the fossil record of diplobathrids to infer the largest tree of fossil crinoids to date, with over 100 genera included. Recovered trees provide a framework for evaluating the current classification of diplobathrids. Notably, previous suborder divisions are not supported, and superfamily divisions will require significant modification. Although numerous revisions are required for families, most can be retained through reassignment of genera. In addition, recovered trees were used to produce phylogeny‐based estimates of diplobathrid lineage diversity. By accounting for ghost lineages, phylogeny‐based richness estimates offer greater insight into diversification and extinction dynamics than traditional taxonomy‐based approaches alone and provide a detailed summary of the ~150 million‐year evolutionary history of Diplobathrida. This study constitutes a major step toward producing a phylogeny of the Crinoidea and documenting crinoid diversity dynamics. In addition, it will serve as a framework for subsequent phylogeny‐based investigations of macroevolutionary questions.

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A re‐interpretation of the ambulacral system of Eumorphocystis (Blastozoa, Echinodermata) and its bearing on the evolution of early crinoids

Cited by 14 publications

References 38 publications

Evolutionary significance of the blastozoanEumorphocystisand its pseudo-arms

Evolutionary significance of the blastozoanEumorphocystisand its pseudo-arms

Athenacrinusn. gen. and other early echinoderm taxa inform crinoid origin and arm evolution

Phylogeny and evolutionary history of diplobathrid crinoids (Echinodermata)

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