Crinoids Aweigh: Experimental Biomechanics of Ancyrocrinus Holdfasts

Plotnick, Roy E.; Bauer, Jennifer E.

doi:10.1007/978-94-017-8721-5_1

Cited by 3 publications

(7 citation statements)

References 30 publications

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“…This problem is usually described as avoiding sinking (foundering) into sediments of low strength, accomplished by such means as becoming flat or developing spines. For organisms such as crinoids, however, the challenge is avoiding being pulled out of the sediment or being toppled as a result of drag on the crown (Plotnick & Bauer ).…”

Section: Biomechanics Of Eucalyptocrinites Holdfastsmentioning

confidence: 99%

“…For small plants that lack a stiff stem, the relevant forces are tensional, such as might be produced by an animal browsing on it. Similarly, for crinoids with very flexible stalks, the drag on the crown would produce tension on the stalk that would be transferred to the holdfast (Plotnick & Bauer ).…”

Section: Biomechanics Of Eucalyptocrinites Holdfastsmentioning

confidence: 99%

“…Forces required to pull the models out of the sediment were measured using a Chatillon DFIS‐10 digital force gauge, mounted on a Chatillon TCM‐200 motorized test stand (Plotnick et al . ; Plotnick & Bauer ). One set of experiments were carried out pulling straight up, using the four‐ and five‐root models (three‐root models interfered with the side of the sediment container).…”

Section: Biomechanics Of Eucalyptocrinites Holdfastsmentioning

confidence: 99%

“…One set of experiments were carried out pulling straight up, using the four‐ and five‐root models (three‐root models interfered with the side of the sediment container). An additional set of experiments were run attaching the top of model column to a fishing line run around a pulley to the force gauge, to measure horizontal uprooting forces (see Plotnick & Bauer for illustrations of the setup). Three‐ and four‐root models were oriented in two directions (Table ): for the four‐root models, orientation A was with one pair of roots parallel to the direction of pull and one pair perpendicular and orientation B was with the pairs turned 45 o ; for the three‐root models, orientation C was with one root parallel and opposed to the direction of pull and orientation D was with one root parallel and towards to the direction of pull.…”

Section: Biomechanics Of Eucalyptocrinites Holdfastsmentioning

confidence: 99%

“…Research on specific genera is less common, with most of the attention on unusual forms such as scyphocrinitid ‘loboliths’ and Ancyrocrinus Hall (Ehrenberg ; Haude ; Ausich et al . ; Plotnick & Bauer ). This situation is beginning to change, with studies on the holdfasts of Gilbertsocrinus Phillips and Barycrinus Meek & Worthen (Hollis & Ausich , ) and on the role of holdfasts in the life history of upper Ordovician crinoids (Brett et al .…”

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confidence: 99%

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A radicle solution: morphology and biomechanics of the Eucalyptocrinites ‘root’ system

Plotnick

Ebey

Zinga

2016

LET

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Eucalyptocrinites is one the most common and familiar mid‐Palaeozoic crinoids and is the exemplar of a form with dendritic radicular holdfasts. American museums have hundreds of specimens of Eucalyptocrinites holdfasts from the Silurian Waldron Shale of Indiana and Kentucky, USA. The radix (‘root’) system of Eucalyptocrinites can be described as comprised of links (branches) that meet at nodes. Measured values include the x‐ and y‐coordinates of the nodes, the distances of the nodes from the stem, the angles between branches, branch length and branch width. Rose diagrams show clearly that the root systems are not isotropic but have preferred orientations. Branch angles are highly variable, but cluster around 60 degrees. Branch lengths and distal branch widths are relatively constant, but branch width increases variably towards the column. The branching pattern can be modelled as a self‐similar (‘fractal’) structure. Several specimens labelled as Eucalyptocrinites show a distinct fivefold symmetry without branching and very likely represent a different taxon. The Eucalyptocrinites radix system, along with the probably stiff dististele, most likely functioned as a rigid plate that resisted rotational forces due to currents acting on the crown. Upstream radicles experienced tension, whereas downstream roots were compressed. This force distribution may explain the observed anisotropies in radix morphology. The ‘roots’ of Eucalyptocrinites and other crinoids have long been compared with the root systems of plants. Although there are superficial similarities, there are fundamental differences.

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Section: Biomechanics Of Eucalyptocrinites Holdfastsmentioning

confidence: 99%

Section: Biomechanics Of Eucalyptocrinites Holdfastsmentioning

confidence: 99%

Section: Biomechanics Of Eucalyptocrinites Holdfastsmentioning

confidence: 99%

Section: Biomechanics Of Eucalyptocrinites Holdfastsmentioning

confidence: 99%

mentioning

confidence: 99%

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A radicle solution: morphology and biomechanics of the Eucalyptocrinites ‘root’ system

Plotnick

Ebey

Zinga

2016

LET

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Redescription, paleogeography, and experimental paleoecology of the Silurian phyllocaridGonatocaris

Collette¹,

Plotnick²

2020

J. Paleontol.

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Gonatocaris decora (Clarke, 1901) is an unusual, highly ornamented Silurian phyllocarid from the Pittsford Shale Member of the Vernon Formation, Salina Group of New York, that has been allied with Emmelezoe in the past due to the possession of an ‘optic tubercle.’ The systematic positions of Gonatocaris and Emmelezoe have been difficult to assess due to the lack of complete remains, attributions based on spurious characters, and missing and unfigured specimens. Relatively recent collections of Gonatocaris decora, along with a relocation of the original type material of Emmelezoe, have allowed a reexamination of all relevant genera and a more robust systematic placement for G. decora. Characters of generic importance for Gonatocaris include a greatly elongated abdomen; an acute angle of the ventral carapace margin separating distinct anteroventral and posteroventral margins from each other; and distinctive, multiscale horizontal ridge-like ornament of the carapace valves. Growth was found to be isometric. Experimental work done using a model of the scale-like ornament and multiple grain sizes of substrate indicates that cuticle ornament may have served to increase friction between the animal and a fine sand substrate, although resistance to predation is the currently favored hypothesis. Because Gonatocaris species are currently known only from the eastern margin of Laurentia and northern South China, it is likely that this genus was nektonic. Accumulations of similarly sized carapaces and other disarticulated sclerites in shallow-water settings may indicate spawning events following molting en masse.

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Ecological novelty at the start of the Cambrian and Ordovician radiations of echinoderms

Novack‐Gottshall,

Purcell,

Sultan

et al. 2024

Palaeontology

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The Cambrian and Ordovician radiations marked the origins of all major echinoderm clades and established their Phanerozoic ecological blueprint. Recent claims of modest innovation of early echinoderms and other animals suggest constraints on novelty during the origins of phyla. Here, we document the life‐habit richness, body size, tiering, habitat usage, mobility, diet and foraging habits of 366 Cambrian–Ordovician echinoderm genera across a time‐scaled phylogeny to identify the timing and impact of novelty. Most early echinoderms were sedentary, filter‐feeding microbivores, and their body sizes, diets and modes of locomotion were largely unchanged through time, despite major volatility in taxonomic composition. Cambrian echinoderms lived close to the seafloor, with stylophorans first evolving semi‐infaunality. Many Ordovician echinoderms lived farther from the seafloor, with more complex filter‐feeding organs and tiering structure, often using other organisms as substrates. Mobile carnivores and mass‐feeders emerge then, too, across diverse asterozoans and echinozoans. Most of these novelties coincide with the origins of individual clades during the early and late Cambrian (Terreneuvian/Series 2 and Furongian), and 10–20 million years pass before most become ecologically important. Life‐habit evolution within most taxa involved new variations in these traits, with crinoids and asterozoans better able to shift strategies. The Ordovician radiation records more new variability in pre‐existing Cambrian life habits rather than radical re‐invention, with important novelties (like mobile carnivory and mass‐feeding, increased height off the seafloor, and biotic substrates) becoming ecologically more impactful. Taxa with these strategies were those best able to capitalize on the newly heterogeneous Ordovician world.

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Crinoids Aweigh: Experimental Biomechanics of Ancyrocrinus Holdfasts

Cited by 3 publications

References 30 publications

A radicle solution: morphology and biomechanics of the Eucalyptocrinites ‘root’ system

A radicle solution: morphology and biomechanics of the Eucalyptocrinites ‘root’ system

Redescription, paleogeography, and experimental paleoecology of the Silurian phyllocaridGonatocaris

Ecological novelty at the start of the Cambrian and Ordovician radiations of echinoderms

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