Stalked Crinoid Locomotion, and its Ecological and Evolutionary Implications

In the past two decades, much direct evidence has been gathered on active crawling by stalked crinoids, a group generally thought to be sessile. Detailed descriptions of crawling mechanics of isocrinids in aquaria revealed only exceedingly slow movements (~0.1 mm sec-1). Crawling at such speeds severely restricted the range of roles that this behavior could play in stalked crinoid biology and, consequently, in its potential impact on their ecology and evolutionary history. Here, we provide evidence collected in situ by submersible near Grand Bahama Island at a depth of 420 m for a different mode of crawling in stalked crinoids. Its most striking feature is a speed two orders of magnitude greater (~10-30 mm sec-1) than previously observed. The biomechanical cause for the differences in speeds between the two crawling modes is related to the difference in the number of articulations, and thus length of the arm, involved in the power stroke. We suggest that the high speed mode may represent an escape strategy from benthic enemies such as cidaroid echinoids, which occur with stalked crinoids and have been shown to ingest them. A first-order tally of crinoid genera possessing morphological traits required for crawling is provided. Crawling may have characterized some Paleozoic taxa, such as some of the advanced cladids (a group very closely related to post-Paleozoic crinoids), but the Permo-Triassic extinction represents a major threshold between the largely sessile crinoid faunas of the Paleozoic and the increasingly dominant motile crinoids of the post-Paleozoic

A biomechanical approach to Ediacaran hypotheses: how to weed the Garden of Ediacara

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73910/1/j.1502-3931.1998.tb00494.x.pd

Urchins in the Meadow: Paleobiological and Evolutionary Implications of Cidaroid Predation on Crinoids

Deep-sea submersible observations made in the Bahamas revealed interactions between the stalked crinoid Endoxocrinus parrae and the cidaroid sea urchin Calocidaris micans. The in situ observations include occurrence of cidaroids within “meadows” of sea lilies, close proximity of cidaroids to several upended isocrinids, a cidaroid perched over the distal end of the stalk of an upended isocrinid, and disarticulated crinoid cirri and columnals directly underneath a specimen of C. micans. Guts of two C. micans collected from the crinoid meadow contain up to 70% crinoid material. Two of three large museum specimens of another cidaroid species, Histocidaris nuttingi, contain 14–99% crinoid material. A comparison of cidaroid gut contents with local sediment revealed significant differences: sediment-derived material consists of single crinoid ossicles often abraded and lacking soft tissue, whereas crinoid columnals, cirrals, brachials, and pinnulars found in the cidaroids are often articulated, linked by soft tissue, and unabraded. Furthermore, articulated, multi-element fragments often show a mode of fracture characteristic of fresh crinoid material. Taken together, these data suggest that cidaroids prey on live isocrinids. We argue that isocrinid stalk-shedding, whose purpose has remained a puzzle, and the recently documented rapid crawling of isocrinids are used in escaping benthic predators: isocrinids sacrifice and shed the distal stalk portion when attacked by cidaroids and crawl away, reducing the chance of a subsequent encounter. If such predation occurred throughout the Mesozoic and Cenozoic (possibly since the mid-Paleozoic), several evolutionary trends among crinoids might represent strategies to escape predation by slow-moving benthic predators

Taphonomy of Isocrinid Stalks: Influence of Decay and Autotomy

Stalks of isocrinid crinoids are differentiated into cirri-bearing columnals (nodals) and columnals lacking cirri (internodals). This skeletal differentiation allowed us to test whether stalk fragmentation is random or whether it occurs preferentially at a specific articulation. Our analyses indicate that the patterns of fragmentation in multicolumnal segments of extant isocrinids collected by submersible, by dredging, and in sediment samples, as well as those found as fossils, are nonrandom. The preferred plane of fragmentation corresponds to the synostosis, the articulation between a nodal and the internodal distal to it. In isocrinids this articulation has a characteristic morphology and is the site of autotomy. Although stalk shedding by autotomy may contribute to the observed patterns, decay experiments on isocrinid stalks, both in situ and in the lab, suggest that post-mortem disarticulation also results in nonrandom fragmentation. Thus both processes, autotomy and post-mortem decay, contribute to the observed pattern of fragmentation. Underlying both processes is the organization of soft tissues at synostoses

Growth, Injury, and Population Dynamics in the Extant Cyrtocrinid Holopus mikihe (Crinoidea, Echinodermata) near Roatan, Honduras

The crinoid order Cyrtocrinida is known mainly from Mesozoic fossils; its few surviving members, all from bathyal environments, are among the most peculiar living crinoids. Cyrtocrinids attributed to Holopus mikihe Donovan and Pawson, 2008, have been observed in large numbers via submersible off the western coast of Roatán, Honduras, on vertical and overhanging walls at depths between 430 and 640 m. Observations in 2012, 2013, and 2014 have permitted the first estimates of population structure, growth, and regeneration. Two size modes were observed; the flat barnacle-like “juvenile” stage resembles confamilial and co-occurring Cyathidium pourtalesiAméziane, 1999, whereas the larger “adults” elevate the crown on a stumplike calyx. The 99th percentile growth rate was 0.19 cm yr–1, giving a minimum predicted age of 16 yrs for the largest specimen and 8.7 yrs for the median specimen; the median growth rate was 0.04 cm yr–1, corresponding to 72 and 39 yrs. However, the slower rate of growth in juvenile compared to adult specimens means that these ages are underestimates; actual median age may be closer to 50 yrs. Arm regeneration rate is estimated at 0.6 cm yr–1, and 9.8% of adult individuals were visibly injured, giving an interval of about 1.4 yrs between arm loss events. No recruitment or mortality was observed, and aggregations of evenly-sized individuals were prevalent, consistent with sporadic local recruitment and mortality

Lack of Chemical Defense in Two Species of Stalked Crinoids: Support for the Predation Hypothesis for Mesozoic Bathymetric Restriction

Methanol/dichloromethane extracts of (1) the arms and pinnules, and (2) the stalk and cirri of the deep water stalked crinoids Endoxocrinus parrae (Gervais) and Neocrinus decorus (Carpenter) were imbedded at ecologically relevant volumetric concentrations in alginate food pellets containing 2% krill as a feeding stimulant and presented in situ to an assemblage of shallow-water reef fish. Experimental pellets were highly palatable to reef fish; no significant differences in pellet consumption occurred between experimental pellets containing extracts from either species of stalked crinoid or control pellets. Small pieces of cirri, stalks, calyx, arms and pinnules of both species were also tested in in situ feeding assays. While immediate consumption by fish was not apparent, Blue Headed Wrasse (Thalassoma bifasciatum (Block)) and Dusky Damselfish (Stegastes fuscus (Cuvier)) bit at pieces of each body component. Similar fish biting behaviors were also observed when two living Endoxocrinus parrae were deployed on the shallow reef. Observations indicate that neither species of stalked crinoid is chemically defended from predation by a natural assemblage of reef fish. This supports the predation hypothesis that restriction of stalked crinoids in deep-water habitats may have resulted from the Mesozoic radiation of durophagous fishes in shallow seas, resulting in a reduction of stalked crinoids from shallow water

Ability to Swim (Not Morphology or Environment) Explains Interspecific Differences in Crinoid Arm Regrowth

Regrowth of body parts occurs in almost every phylum of the animal kingdom, but variation in this process across environmental, morphological, and behavioral gradients remains poorly understood. We examined regeneration patterns in feather stars – a group known for a wide range of morphologies and behaviors and up to a forty-fold difference in arm regeneration rates – and found that the variation in arm regeneration rates is best explained by swimming ability, not temperature, food supply, morphology (total number of arms and number of regenerating arms), or degree of injury. However, there were significant interactive effects of morphology on rates of regeneration of the main effect (swimming ability). Notably, swimmers grew up to three-fold faster than non-swimmers. The temperate feather star Florometra serratissima regenerated faster under warmer scenarios, but its rates fell within that of the tropical species suggesting temperature can account for intraspecific but not interspecific differences. We urge comparative molecular investigations of crinoid regeneration to identify the mechanisms responsible for the observed interspecific differences, and potentially address gaps in stem cell research

A soluble model of evolution and extinction dynamics in a rugged fitness landscape

We consider a continuum version of a previously introduced and numerically studied model of macroevolution (PRL 75, 2055, (1995)) in which agents evolve by an optimization process in a rugged fitness landscape and die due to their competitive interactions. We first formulate dynamical equations for the fitness distribution and the survival probability. Secondly we analytically derive the $t^{-2}$ law which characterizes the life time distribution of biological genera. Thirdly we discuss other dynamical properties of the model such as the rate of extinction and conclude with a brief discussion.Comment: 6 pages LaTeX source with 2 figures. Submitted to PRL (Jan. 97

Data from: Rautangaroa, a new genus of feather star (Echinodermata: Crinoidea) from the Oligocene of New Zealand

We describe a nearly complete, and thus extremely rare, featherstar (Crinoidea, Comatulida) from Oligocene strata of North Otago/South Canterbury, New Zealand. A detailed analysis of this specimen, as well as newly recovered material and previously described fragmentary remains from nearby contemporaneous sedimentary units, in addition to relevant historical specimens, lead us to conclude that it cannot be placed in any currently established genus. A new genus, Rautangaroa, is proposed to accommodate it. This intact specimen of Rautangaroa aotearoa (Eagle, 2007), new combination, provides rare data on the morphology of arms and cirri. It represents the first example of arm autotomy and regeneration in a fossil featherstar, and thus has bearing on the importance of predation to the evolutionary history of this group

Predation as an explanation for a latitudinal gradient in arm number among featherstars

AimThe role of biotic interactions in generating broad patterns in organismal phenotypes is a central question in macroecology. We investigate global patterns in feeding morphology among featherstars, a globally widespread group of suspension‐feeding echinoderms whose evolutionary history has been demonstrably shaped by predators.LocationWorld’s oceans.TaxonCrinoidea.MethodsWe tested for global patterns in the featherstar suspension‐feeding apparatus, a filter made up of 5–200 arms which is the main interface with predators. We investigate a geospatial dataset of 23,950 occurrences in 442 species using statistical analyses including quantile regression and a new permutation‐based phylogenetic comparative approach appropriate for testing for a broad range of patterns in data with strange distributions.ResultsWe find that featherstars exhibit a latitudinal gradient in arm number: arm number is both greater on average and more variable between species at lower latitudes. This pattern holds across depths and hemispheres and is not a spurious result of either the latitudinal diversity gradient or phylogenetic autocorrelation. Tropical featherstars that conceal themselves have fewer arms, and also appear to experience less intense predation.Main conclusionsTemperature, primary productivity and substrate type do not adequately explain the latitudinal gradient in arm number. We attribute it instead to a corresponding gradient in predation intensity: many armed featherstars can withstand more intense arm loss to predators. Concealment and other alternate solutions to the problem of predation, along with reproductive costs associated with having many arms, explain why the trend is wedge‐shaped rather than linear. Our findings constitute a latitudinal gradient in functional diversity, paralleling recent findings in other taxa. The gradient may be a consequence of shallow tropical reefs; inasmuch as reefs as centres of biotic interactions promote functional richness, changes in the distribution of reefs through deep time probably entailed shifts in the global deployment of ecological diversity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163602/3/jbi13965.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163602/2/jbi13965_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163602/1/jbi13965-sup-0003-AppendixS1.pd