Forest J. Gahn

Post-Paleozoic crinoid radiation in response to benthic predation preceded the Mesozoic marine revolution

It has been argued that increases in predation over geological time should result in increases in defensive adaptations in prey taxa. Recent in situ and laboratory observations indicate that cidaroid sea urchins feed on live stalked crinoids, leaving distinct bite marks on their skeletal elements. Similar bite marks on fossil crinoids from Poland strongly suggest that these animals have been subject to echinoid predation since the Triassic. Following their near-demise during the end-Permian extinction, crinoids underwent a major evolutionary radiation during the Middle–Late Triassic that produced distinct morphological and behavioral novelties, particularly motile taxa that contrasted strongly with the predominantly sessile Paleozoic crinoid faunas. We suggest that the appearance and subsequent evolutionary success of motile crinoids were related to benthic predation by post-Paleozoic echinoids with their stronger and more active feeding apparatus and that, in the case of crinoids, the predation-driven Mesozoic marine revolution started earlier than in other groups, perhaps soon after the end-Permian extinction.

Infestation of Middle Devonian (Givetian) camerate crinoids by platyceratid gastropods and its implications for the nature of their biotic interaction

One of the classic examples of biotic interactions preserved in the fossil record is that between crinoids and infesting platyceratid gastropods. This relationship, spanning an interval from the Middle Ordovician to the end of the Permian, is recognized by the firm attachment and positioning of platyceratids over the anal vent of their hosts. Several hypotheses have been proposed to explain this interaction; the most widely accepted is that the gastropods were coprophagous commensals, feeding on crinoid excrement without any significant detriment to their hosts. The purpose of this investigation was to test this hypothesis. Two species of Middle Devonian camerate (Monobathrida, Compsocrinina) crinoids, Gennaeocrinus variabilis Kesling & Smith 1962 and Corocrinus calypso (Hall 1862), were used in this investigation. The data consisted of 426 individuals of G. variabilis collected near Rockport, Michigan, 30 of which were infested, and 188 individuals of C. calypso collected near Arkona, Ontario, Canada, of which 25 were infested. Length and volume were measured for each crinoid to determine whether a significant difference existed in the size of infested versus uninfested individuals. The results indicated that for both species of crinoids individuals infested by snails were significantly smaller than uninfested individuals (p < 0.05). We explored a variety of scenarios to explain this pattern and conclude that they falsify the null hypothesis that the crinoid-gastropod relationship was strictly commensal. The smaller size of the infested crinoids is interpreted as a consequence of nutrient-stealing by the parasitic gastropods, a strategy that finds analogs in modern seas. Moreover, the absence of platyceratids on the largest crinoids suggests that large size may have inferred immunity from lasting infestation.

Predation on Crinoids

Over the last 25 years a conceptual shift has occurred in paleobiologists’ view of the importance of predation as an ecological and evolutionary force. The importance of predation pressure on crinoids and its effects on morphological evolution and on biogeographic patterns of this group serves as a clear illustration of this shift: whereas prior to the 1970’s crinoids were generally thought to be immune from predation, since then predation has been invoked as a probable cause of: (a) the success of extant stalkless crinoids, the comatulids, in shallow water settings (Meyer, 1977 and Macurda, 1977); (b) the retreat of isocrinids, a group of stalked crinoids, into deeper water since the Cretaceous that culminated in their present bathymetric distribution (Meyer, 1977 and Macurda, 1977; Meyer, 1985; Oji, 1996); (c) trends in arm morphology of isocrinids and comatulids (Oji, 1994 and Okamoto, 1994); (d) trends in cup plate thickness and spinosity in Devonian and post-Devonian crinoids (Signor, 1984 and Brett, 1984); (e) evolution of the cladid and disparid anal sac as an anti-predatory device (Lane, 1984); and (f) evolution of morphological and behavioral escape strategies among articulate crinoids (Baumiller, 2000), among others. In this chapter we will illustrate this conceptual shift using examples from the literature that span the interval of time during which this shift occurred, review some of the studies that present evidence of predation on crinoids and argue for its importance to their ecology and evolution, and, finally, provide additional data on predation from a couple of Paleozoic examples of regeneration.

Arm regeneration in Mississippian crinoids: evidence of intense predation pressure in the Paleozoic?

Abstract Although direct predator-prey interactions are unobservable in the fossil record, predation has been used to explain many evolutionary trends. Evidence of predation supporting such hypotheses is often presented as isolated instances of preserved sublethal damage, and less commonly, as the frequency of such injuries. For instance, numerous morphological and ecological trends and innovations observed in Phanerozoic crinoids have been causally linked to predation, and whereas the high frequency of arm regeneration in living crinoids is generally assumed to represent intense predation, attempts to assess regeneration frequency and patterns in paleontological samples are few. Can the frequency of fossil injuries be assessed to test hypothesized predation-driven trends, or are such data unavailable? To address this question, we analyzed regeneration in crinoids from the lower Mississippian (Kinderhookian) Maynes Creek Formation near Le Grand, Iowa, a locality renowned for the preservation of thousands of crinoids in tangled masses of crowns, stalks, and holdfasts. Nine percent of the specimens that we examined contained at least one regenerating arm; however, whereas some species lacked evidence of regeneration, others preserved up to 27% arm regeneration. Furthermore, we observed specimens with all arms regenerating, multiple adjacent arms regenerating from the same place along the arm, and a specimen with a damaged and regenerated primaxil and anal sac. The highest regeneration frequency was observed in the most abundant species, Rhodocrinites kirbyi, a significantly higher value than expected under a model of no taxonomic selectivity (binomial: p < 0.05). Furthermore, bootstrapped simulations of the probable number of regenerated individuals suggest that the number of regenerated arms observed in our sample is two to three times less than what existed in the living population. Rhodocrinites kirbyi constituted over 40% of the individuals in the Le Grand crinoid fauna and had the longest stalk of the studied species. In addition, regeneration in R. kirbyi is size related, with individuals above median dorsal cup height (7 mm) displaying nearly 50% regeneration, and smaller individuals only 2% (a statistically significant difference; χ2 test: p < 0.001). The regeneration patterns in R. kirbyi are consistent with predatory attacks that target the most apparent prey. Moreover, this study suggests that predation is the most likely explanation for the regeneration patterns observed in Le Grand crinoids, and that the fossil record potentially provides a valuable, yet overlooked, data source for testing hypotheses pertinent to the role of predation in the evolution of Phanerozoic marine life.

A Bootstrap Analysis for Comparative Taphonomy Applied to Early Mississippian (Kinderhookian) Crinoids from the Wassonville Cycle of Iowa

Abstract Morphological and environmental taphonomic gradient analysis provides insights into morphological, behavioral, and environmental influences on the preservation of fossil organisms. This paper explores morphological and environmental taphonomic gradients in six crinoid morphotypes (diplobathrids, monobathrids, dichocrinids, platycrinitids, cladids, and flexibles) from three stratigraphic units (the Maynes Creek Formation and the Starrs Cave and “Ollie” Members of the Wassonville Formation) representing distinct depositional environments along an onshore–offshore transect within the Early Mississippian (Kinderhookian) Wassonville Cycle of southeast Iowa. Taphonomic differences in stalk, calyx, and arm disarticulation, calyx compression, and arm orientation were categorized independently and subjected to a non-parametric ranking test with bootstrapping (rather than a parametric approach, due to the non-additive nature of the data analyzed herein) to explore taphonomic patterns. The results suggest that the disarticulation of the stalk, calyx, and arms behave independently, although patterns of arm disarticulation may be influenced by the disarticulation of the calyx. In general, preservational integrity in fossil crinoids appears to be a function of the relative proportion of articular to non-articular surface area, skeletal innovations, tissue type and properties, survival response behavior, and thickness and rapidity of burial. Furthermore, these results demonstrate a general decrease in preservational integrity from onshore to offshore environments in the Wassonville Cycle and that sedimentation dynamics associated with episodic events are more influential than background deposition in determining preservation in fossil Lagerstätten. The methodology employed herein also could be used effectively to identify morphological, behavioral, and environmental taphonomic influences on other fossil organisms.

The cladid crinoid Barycrinus from the Burlington Limestone (early Osagean) and the phylogenetics of Mississippian botryocrinids

Abstract All species of Barycrinus from the early Osagean Burlington Limestone of the United States midcontinent are reviewed. Burlington Barycrinus species include: B. rhombiferus (Owen and Shumard, 1852); B. magister (Hall, 1858); B. spurius (Hall, 1858); B. crassibrachiatus (Hall, 1860); B. scitulus (Meek and Worthen, 1860) n. combination; and B. sampsoni Miller and Gurley, 1896. Cyathocrinus latus Hall, 1861a, is here considered a junior synonym of B. rhombiferus. The stratigraphic practice of dividing the Burlington into upper and lower parts, for purposes of reporting species ranges, is evaluated. Morphologic data from these Burlington species are combined with data from late Osagean and Meramecian botryocrinid species of Barycrinus and Meniscocrinus, plus four species of Devonian and Mississippian Costalocrinus in a parsimony-based phylogenetic analysis of Mississippian botryocrinids. Results of this analysis indicate that 1) species of Barycrinus form a monophyletic clade that radiated rapidly during the Osagean; 2) B. rhombiferus may have been ancestral to all other Barycrinus species; and 3) M. magnitubus forms a clade with the Mississippian C. cornutus (Owen and Shumard, 1850) and the Devonian C. rex McIntosh, 1984.

Evolutionary History of Regeneration in Crinoids (Echinodermata)

The fossil record indicates that crinoids have exhibited remarkable regenerative abilities since their origin in the Ordovician, abilities that they likely inherited from stem-group echinoderms. Regeneration in extant and fossil crinoids is recognized by abrupt differences in the size of abutting plates, aberrant branching patterns, and discontinuities in carbon isotopes. While recovery is common, not all lost body parts can be regenerated; filling plates and overgrowths are evidence of non-regenerative healing. Considering them as a whole, Paleozoic crinoids exhibit the same range of regenerative and non-regenerative healing as Recent crinoids. For example, Paleozoic and extant crinoids show evidence of crown regeneration and stalk regrowth, which can occur only if the entoneural nerve center (chambered organ) remains intact. One group of Paleozoic crinoids, the camerates, may be an exception in that they probably could not regenerate their complex calyx-plating arrangements, including arm facets, but their calyxes could be healed with reparative plates. With that exception, and despite evidence for increases in predation pressure, there is no compelling evidence that crinoids have changed though time in their ability to recover from wounds. Finally, although crinoid appendages may be lost as a consequence of severe abiotic stress and through ontogenetic development, spatiotemporal changes in the intensity and frequency of biotic interactions, especially direct attacks, are the most likely explanation for observed patterns of regeneration and autotomy in crinoids.

Using platyceratid gastropod behaviour to test functional morphology

During the Mississippian (Tournaisian), numerous crinoid genera of the subclass Camerata evolved exaggerated anal tubes, cylindrical extensions of the tegmen with the anus at the distal end. Additionally, camerates exhibit higher frequency of platyceratid gastropod infestation than any other crinoid clade leading some researchers to speculate that anal tubes evolved in response to platyceratid parasitism. To test the infestation avoidance role of anal tubes, platyceratid distribution was analyzed among 636 tubed and 675 tubeless crinoids from Mississippian strata in North America. Results demonstrate significantly higher infestation frequency in tubeless crinoids. Rather than attach to the anal vent, as is typical for platyceratids, the gastropods that infested tubed crinoids are always found at the tube base and acquired nutrients from their hosts via drilling. It is likely that infesting tubeless crinoids was a more cost effective trophic strategy than drilling tubed crinoids.

Reconstructing predation pressure on crinoids: estimating arm-loss rates from regenerating arms

Abstract The regeneration abilities of crinoids not only are important to understanding crinoid ecology, but also can serve as the basis for assessing the pressure exerted on crinoids by predators both in the Recent and in the geologic past. This is especially true of regenerating arms, because arm loss, and subsequent regeneration, is thought to result from interactions with predators, primarily fish. However, the commonly used regeneration-based proxy for predation pressure (proportion of individuals with regenerating arms) does not provide a measure of the rate at which those events occurred. Here we present a method for reconstructing the arm-loss rate per individual, a more direct proxy of predation pressure. This metric accounts for differences in arm length, arm number, and branching pattern, features highly variable among taxa, among environments, and through geologic time. Normalizing for those characters permits the transformation of observed proportions of regenerating arms to rates that can be...

PRIMITIVE CLADID CRINOIDS FROM THE EARLY OSAGEAN BURLINGTON LIMESTONE AND THE PHYLOGENETICS OF MISSISSIPPIAN SPECIES OF CYATHOCRINITES

Abstract All 19 known species of the primitive cladid crinoid genera Atelestocrinus, Cyathocrinites, Goniocrinus, Parisocrinus, Pellecrinus, and Zygotocrinus from the early Osagean Burlington Limestone of the North American midcontinent are reviewed and redescribed or, where necessary, redefined. Nine of these species are illustrated for the first time herein. Sixteen are considered valid, including C. deroseari n. sp. Of the remaining three species, one is left in open nomenclature, and two are considered nomen dubia. Pellecrinus is recognized for the first time from the Burlington Limestone, although the specimens can not be identified to the species level and are left in open nomenclature. Cyathocrinites ranges from the Middle Silurian to at least the Middle Mississippian. During the Early Mississippian Cyathocrinites experienced an evolutionary radiation with a maximum diversity of nine species in the Burlington Limestone. Phylogenetic relationships were investigated in a parsimony-based phylogenetic analysis by combining morphologic data from the Burlington species with data from the four other species of Cyathocrinites from the late Osagean and early Meramecian of the east-central United States. The Kinderhookian C. chouteauensis (Miller and Gurley, 1896) served as the outgroup. A phylogenetic analysis of 14 species of Mississippian Cyathocrinites yielded a single most parsimonious tree with a length of 28 steps (C. I. = 0.607, H. I. = 0.392, R. I. = 0.718, R. C. = 0.436). Results of this analysis suggest that at least two major clades existed within Mississippian Cyathocrinites. One clade contains C. sampsoni (Miller, 1891b), C. gilesi (Wachsmuth and Springer, 1878), C. farleyi (Meek and Worthen, 1866), and C. barydactylus (Wachsmuth and Springer, 1878). The second clade contains C. iowensis, C. kelloggi (White, 1862), C. barrisi (Hall, 1861a), C. rigidus, C. deroseari n. sp., C. asperrimus (Springer, 1911), C. lamellosus (White, 1863), and C. harrodi (Wachsmuth and Springer, 1880). Cyathocrinites multibrachiatus forms a polytomy with these two clades. Members of the first clade exhibit a unique overall morphology present only during the Mississippian, suggesting the clade arose during this time. Members of the second clade, plus C. multibrachiatus, exhibit some characters present in Cyathocrinites species as old as the Middle Silurian and, thus, may have its roots among Silurian and Devonian species.