Tomasz K. Baumiller

Experimental disintegration of regular echinoids: Roles of temperature, oxygen, and decay thresholds

Laboratory experiments on regular echinoids indicate that low water temperatures retard organic decomposition far more effectively than anoxia, and that the primary role of anoxia in the preservation of articulated multi-element calcareous skeletons may be in excluding scavenging organisms. When tumbled at 20 rpm, specimens that were first allowed to decay for two days in warm seawater (30°C) disintegrated more than six times faster than specimens treated at room temperature (23°C) and more than an order of magnitude faster than specimens treated in cool water (11°C). In contrast, the effects of aerobic versus anerobic decay on disintegration rates were insignificant. The longer the period that specimens were allowed to decay before tumbling, the greater the rate at which specimens disintegrated, until a threshold time that appears to mark the decomposition of collagenous ligaments. This required a few days at 30°C, about two weeks at 23°C, and more than 4 weeks at 11°C for Strongylocentrotus . Up until this threshold, coronas disintegrate by a combination of cross-plate fractures and separation along plate sutures; cross-plate fractures thus can be taphonomic in origin and are not necessarily related to predation. Specimens decayed for longer-than-threshold periods of time disintegrate virtually instantaneously upon tumbling by sutural separation only. Undisturbed coronas can remain intact for months, sufficient time for epibiont occupation. Rates of disintegration were documented semi-quantitatively by recognizing seven stages of test disarticulation, and quantitatively by tensometer measures of test strength and toughness. The effects of temperature and oxygen on decay and the existence of a decay threshold in disintegration should apply at least in a qualitative sense to many other animals whose skeletons consist of multiple, collagen-bound elements. Regular echinoids should still be perceived as taphonomically fragile organisms, but our results suggest the potential for latitudinal as well as bathymetric gradients in the preservation of fossil echinoid faunas. Echinoid preservation under any given set of conditions should also be a function of taxonomic differences in test construction (particularly stereom interlocking along plate sutures) as suggested by previous workers, although our experiments indicate that these effects should only be significant among post-threshold specimens. A survey of regular echinoids from Upper Cretaceous white chalk facies of Britain substantiates the basic experimental patterns, yielding examples of all disarticulation stages and significant taxonomic differences in quality of preservation. A diverse array of borers and encrusters on fossil coronas also corroborates the post-mortem persistence of some tests on mid-latitude seafloors.

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.

Species longevity as a function of niche breadth: Evidence from fossil crinoids

High-resolution stratigraphic and taxonomic data indicate that species longevities among Paleozoic (Mississippian) crinoids (Echinodermata) were affected by differences in niche breadth. A strong positive relationship exists between niche breadth, measured as the number of environments occupied by a species, and stratigraphic range. The robustness of this pattern is verified by a variety of rarefaction and statistical techniques confirming the long-held supposition that among animals ecological “generalists” have greater species longevities than ecological “specialists.” The results also support the hypothesis that specialist clades have higher species richness.

Selective extinction among Early Jurassic bivalves: A consequence of anoxia

Analyses of taxonomically standardized data sets demonstrate several statistically robust extinction patterns in Early Jurassic bivalve species from northwest Europe and the Andean basins of South America. In both regions, extinction intensities were significantly enhanced in late Pliensbachian and early Toarcian time as compared to all other time intervals. The same intervals (except for the early Toarcian of South America) also represent times of unusual extinction selectivity, with infaunal taxa suffering distinctly more than epifaunal forms. As infaunal suspension feeders are extremely rare components of Early Jurassic oxygen-controlled macrofaunas, these results are entirely compatible with sedimentological and geochemical data suggesting that widespread anoxia was a principal cause of the diversity crisis. Although many biotic traits that enhance survivorship during background times seem to be irrelevant during major mass extinctions, patterns of survivorship selectivity may provide more distinct clues to the causes of less severe mass extinctions.

Demise of the middle Paleozoic crinoid fauna: a single extinction event or rapid faunal turnover?

Macroevolutionary change from the Middle to the Late Paleozoic crinoid fauna was not the result of mass extinction. The presumption that the decline of the middle Paleozoic crinoid fauna was from a single mass extinction event was tested using seriation, multidimensional scaling (MDS), binomial analysis, and bootstrapping simulations on a data set which is a comprehensive revision of old faunal lists. The data for these analyses were based on temporal distributions of 214 species from 69 late Osagean and early Meramecian localities from the midcontinental United States. The time under consideration is subdivided into seven informal intervals using MDS in conjunction with biostratigraphy. Seriation of species ranges into these intervals results in a gradual pattern of faunal turnover, and sampling bias can be eliminated as a cause for this more gradual pattern. MDS analysis of the crinoid range data is similar to MDS simulations using data with continuous, mono- tonic species turnover and dissimilar to a simulated mass extinction. Binomial analysis and boot- strapping demonstrate that the observed number of extinctions at the putative extinction boundary were not unusually high. All methods agree that extinctions throughout this time were high but spanned several time intervals and that rapid, monotonic faunal turnover describes the data better than mass extinction. Macroevolutionary processes other than mass extinction and microevolution- ary processes must have dictated the character and composition of this remarkable faunal transition among the Crinoidea.

Taphonomic Inferences on Boring Habit in the Richmondian Onniella meeki Epibole

Abstract Shell boring is one of the few quantifiable, well-preserved biotic interactions in the fossil record. While some workers have used boring intensity as a proxy for predation pressure in both Recent and fossil assemblages, others have warned that taphonomic and other effects can alter the boring intensity and lead to paleoecological misinterpretation. When the biocoenosis is known, however, taphonomic effects can be “undone” a posteriori. Because the valve ratio of any bivalved organism must be 1:1 in the biocoenosis, strengths of between-valve taphonomic biases can be calculated directly for any disarticulated assemblage of bivalved fossils. By back-calculating the biocoenotic boring intensities, improved estimates of boring stereotypy may be obtained. These “restored” boring intensities can provide more accurate paleoecological interpretations of boring habit while remaining numerically conservative. Taphonomic analysis of a bored Ordovician brachiopod assemblage shows that (1) the assemblage had experienced negligible differential transport; and (2) convex (pedicle) valves have been preferentially crushed in place. Comparing the taphonomy of the assemblage to a set of laboratory taphonomic regimes reveals that valve-valve contact may be of great consequence in skeletal taphonomy. In particular, valve-valve contacts appear to promote (1) preferential destruction of convex valves; and (2) subequal destruction of bored vs. unbored valves. Taking into account these taphonomic effects, numerous hypotheses of boring habit—including mixed-motive boring—have been tested using a probabilistic model. The model herein presented indicates a likely contribution of 10–15% predatory boring in the assemblage. The usefulness of probabilistic models for providing simultaneous, realistic tests of multiple hypotheses is emphasized.

Boreholes in Mississippian spiriferide brachiopods and their implications for Paleozoic gastropod drilling

Abstract Bored specimens of the spiriferide brachiopod genera Brachythyris and Spirifer from several localities of the Mississippian Fort Payne Formation (Kentucky, USA) represent 7.0% of the total sampled population. The boreholes are typically single, complete, circular in plan view, and with their long axes perpendicular to the valve. These traits and stereotypy with respect to the pedicle valve and the fold and sulcus are consistent with a predatory/parasitic origin of the holes. The presence of platyceratid gastropods in the Fort Payne localities with bored brachiopods, the previously documented drilling abilities of these gastropods, and the occurrence of a platyceratid snail attached to specimen of a bored Devonian brachiopod, Atrypa, argue for platyceratids as the most probable culprits.

Boreholes in the Middle Devonian blastoid Heteroschisma and their implications for gastropod drilling

Abstract Boreholes in over 100 specimens of the Devonian blastoid Heteroschisma and the presence of the gastropod Platyceras (Orthonychia) sp. attached to a specimen of Heteroschisma subtruncatus (Hall 1858) suggest that platyceratid gastropods were capable of drilling their hosts at least as early as the Middle Devonian and thus represent the first known gastropods to have evolved this ability. The presence of similar holes in numerous other Devonian and Mississippian blastoids and the occurrence of several additional examples of platyceratids attached to blastoids indicate that the interaction between gastropods and blastoids was not infrequent; as in the case of the gastropod/crinoid interaction, this relationship is interpreted as having been parasitic rather than predatory. The parasitic, drilling platyceratids may have been a factor in the Paleozoic precursor of the Mesozoic marine revolution: some of the anti-predatory defenses of crinoids described from the Late Paleozoic may have been strategies of avoiding platyceratid infestation.

Urchins in the meadow: paleobiological and evolutionary implications of cidaroid predation on crinoids

Abstract 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.

Invention by evolution: functional analysis in paleobiology

Abstract Functional analysis of fossils is and should remain a key component of paleobiological research. Despite recently expressed doubts, conceptual and methodological developments over the past 25 years indicate that robust and testable claims about function can be produced. Functional statements can be made in at least three different hierarchical contexts, corresponding to the degree of structural information available, the position in the phylogenetic hierarchy, and the degree of anatomical specificity. The paradigm approach, which dominated thinking about function in the 1960s and 1970s, has been supplanted with a methodology based on biomechanics. Paleobiomechanics does not assume optimality in organismal design, but determines whether structures were capable of carrying out a given function. The paradigm approach can best be viewed as a way of generating, rather than testing, functional hypotheses. Hypotheses about function can also be developed and supported by well-corroborated phylogenetic arguments. Additional functional evidence can be derived from studies of trace fossils and of taphonomy. New computer techniques, including “Artificial Life” studies, have the potential for producing far more detailed ideas about function and mode of life than have been previously possible. Functional analysis remains the basis for studies of the history of adaptation. It is also an essential component of many paleoecological and paleoenvironmental studies.