One method of increasing the resolving power of paleontological inquiries is to assess the time distribution, or phenology, of perispeciational change. The rationale for this test is that, while concentration of morphologic change around the time of speciation is consistent with both known microevolutionary mechanisms and punctuated equilibria, punctuated equilibrium theory presupposes that most of the change occurs either before or during initial allopatry to produce morphologically static taxa. Considerable change in the initial phases of speciation could also result from known microevolutionary mechanisms, but if significant change occurs in the neosympatric phase, or at any time after the species have become differentiated, then that change is best explained by known microevolutionary mechanisms.

Amount and rate of morphologic change during each phase of the allopatric speciation process were determined for two cognate species of the radiolarian genus Eucyrtidium. In this case, morphologic change accruing to these species during the neosympatric phase was 2-3 times as great as that which occurred during the initial allopatric phase. Morphologic trends in both these species during the allopatric phase differed significantly from a random walk. The size differential that characterized this speciation event was not the product of a single large step early in the process but of a disproportionate number of small steps in one direction during neosympatry. Therefore, the hypothesis of no statistically significant change following the “first stage” of speciation, which is a major tenet of punctuated equilibrium theory, is falsified for this case.

Symbiotic relationships involving physical contact between worms and solitary rugosan polyps are recorded by the following structures in North American Late Ordovician corals: (1) Trypanites borings enclosed within septal swellings in two specimens, (2) vermiform grooves and openings along the external wall of one corallum, and (3) a chamber containing a unique brown tube within one individual. These features are indicative, respectively, of commensal boring polychaete annelids that penetrated through coralla, commensal epizoic worms of unknown taxonomic affinity that attached to the side of a polyp, and a tubicolous worm (possibly a polychaete) that was likely a parasitic endozoan. Symbionts comparable to the latter two types are also known from two specimens of Devonian solitary rugose corals.

Indirect evidence suggests that symbioses between solitary rugosans and the worms that produced Trypanites borings as dwelling structures in the sides of coralla were relatively common. However, direct evidence that the hosts were alive has been found in only two corals. In both cases, worms bored through septa within the calices and came into contact with basal surfaces of the polyps, which secreted skeletal material that sealed off the intruders. The rarity of such structures suggests that the encounters were inadvertent. If boring worms favored upcurrent portions of objects in order to maximize feeding benefits and avoid sedimentation, their locations indicate that the concave sides of curved coralla faced toward prevailing currents when in life positions.

“Opportunistic” worms are known to have attached to the sides of polyps only in rare instances when the hosts became temporarily exposed as a result of accidents or abnormalities. This indicates that coralla normally served to shield polyps from colonization by nonboring epizoans.

Worms that apparently extended up through openings in basal surfaces of polyps likely obtained sustenance parasitically within the central cavities. They could have entered the hosts through their mouths, or via the calices when parts of the polyps detached from their coralla and contracted radially. The rarity of this type of relationship in solitary Rugosa suggests that the worms entered inadvertently.

Symbioses involving physical contact between worms and polyps seem to have been rare throughout the history of solitary rugose corals. Both groups apparently tolerated such associations when they did occur, although the rugosans secreted structures in their coralla that served to isolate the symbionts. In doing so, they recorded the presence of worms not likely to be preserved as body fossils. The interpretation of such features provides information on the physiology and ethology of both organisms, on the history of symbiotic relationships, and on the diversity of soft-bodied organisms in ancient environments.

Animals evolve by changing their form and by changing the rate at which they develop. Since evolution of development through time may be directly related to the adaptation of their life histories, study of ontogeny in fossils may yield information about the ecology of extinct animals. We need to know how to measure animals' ontogeny and at what taxonomic level structural differences overshadow differences in development. Two closely related species of the Permian ostracode Cavellina were compared to determine how much of the morphological difference between them is due to differences in their ontogenies. Most of the difference is not related to ontogeny. They also differ in a way that could be explained by heterochrony, although this difference is secondary in importance to the structural difference. These findings suggest that ecological adaptation might best be studied by examining the changes in development that occur within species through time and space.

Three genera of the echinoderm class Edrioasteroidea comprise the suborder Cyathocystina; each is small, has five short straight ambulacra, few thecal plates, and commonly has a modified peripheral rim with tightly sutured or fused plates. The cyathocystids appear to have evolved by paedomorphosis; they have become sexually mature “adults” while retaining a morphology similar to juveniles of isorophid edrioasteroids. This mode of evolution may have been beneficial in colonizing shallow water, nearshore, current-swept environments.

The marine faunas of tropical America underwent substantial evolutionary turnover in the past 3 to 4 million years in response to changing environmental conditions associated with the rise of the Isthmus of Panama, but the ecological signature of changes within major clades is still poorly understood. Here we analyze the paleoecology of faunal turnover within the family Pectinidae (scallops) over the past 12 Myr. The fossil record for the southwest Caribbean (SWC) is remarkably complete over this interval. Diversity increased from a low of 12 species ca. 10–9 Ma to a maximum of 38 species between 4 and 3 Ma and then declined to 22 species today. In contrast, there are large gaps in the record from the tropical eastern Pacific (TEP) and diversity remained low throughout the past 10 Myr. Both origination and extinction rates in the SWC peaked between 4 and 3 Ma, and remained high until 2–1 Ma, resulting in a 95% species level turnover between 3.5 and 2 Ma. The TEP record was too incomplete for meaningful estimates of origination and extinction rates. All living species within the SWC originated within the last 4 Myr, as evidenced by a sudden jump in Lyellian percentages per faunule from nearly zero up to 100% during this same interval. However, faunules with Lyellian percentages near zero occurred until 1.8 Ma, so that geographic distributions were extraordinarily heterogeneous until final extinction occurred. There were also striking differences in comparative diversity and abundance among major ecological groups of scallops. Free-swimming scallops constituted the most diverse guild throughout most of the last 10 Myr in the SWC, and were always moderately to very abundant. Leptopecten and Argopecten were also highly diverse throughout the late Miocene and early Pliocene, but declined to very few species thereafter. In contrast, byssally attaching scallops gradually increased in both diversity and abundance since their first appearance in our samples from 8–9 Ma and are the most diverse group today. Evolutionary turnover of scallops in the SWC was correlated with strong ecological reorganization of benthic communities that occurred in response to declining productivity and increased development of corals reefs.

Poecilozonites (Gastrelasmus) is an important component of the endemic land snail fauna of Pleistocene Bermuda. The type species P. circumfirmatus Redfield usually occurs in sympatry with its congener P. discrepans Pfeiffer, though each species is found alone at several localities. The species are less alike morphologically where they occur together than where they are allopatric. This allopatric convergence and sympatric divergence strongly suggests the biological interaction known as character displacement, often documented for living populations. The relatively complete fossil record of Bermuda offers advantages for studying this phenomenon. Collections can be made from a variety of microhabitats occupied through time. Statistical analysis of 1,600 individuals collected from more than 100 localities indicates that interspecific variation is primarily a function of the presence or absence of a congener and depends to a lesser degree on microhabitat. P. circumfirmatus undergoes a smaller morphological change between allopatry and sympatry than does P. discrepans. Study of relative abundances suggests that P. discrepans may have been competitively inferior, though no functional bases for differences between the species are known.

The late Neogene was a time of major environmental change in Tropical America. Global cooling and associated oceanographic reorganization and the onset and intensification of glaciation in the Northern Hemisphere during the past ten million years coincided with the uplift of the Central American isthmus and resulting changes in regional oceanographic conditions. Previous analyses of patterns of taxonomic turnover and the shifting abundances of major ecological guilds indicated that the regional shallow-water marine biota responded to these environmental changes through extinction and via a restructuring of local benthic food webs, but it is not clear whether this ecological response had an effect on the diversity of molluscan assemblages in the region. Changes in regional and local diversity are often used as proxies for similar ecological response to environmental change in large-scale paleontological studies, but a clear relationship between diversity and ecological function has rarely been demonstrated in marine systems dominated by mollusks. To explore this relationship, we have compiled a data set of the stratigraphic and environmental distribution of genera of mollusks in large new collections of fossil specimens from the late Neogene and Recent of the southwestern Caribbean. Analysis of a selection of ecological diversity measures indicates that within shelf depths, assemblages from deeper water (51–200 m) were more diverse than shallow-water (<50 m) assemblages in the Pliocene. Lower diversity for shallow-water assemblages is caused by increased dominance of a few superabundant taxa in each assemblage. This implies that studies of diversity of shelf benthos need to control for relatively fine scaled environmental conditions if they are to avoid interpreting artifacts of uneven sampling as true change of diversity. For shallow-water assemblages only, there was significant increase in local and regional diversity of bivalve assemblages after the late Pliocene. No parallel increase in gastropods could be detected, but this likely is because sample size was inadequate for documenting the diversity of gastropod assemblages following a steep post-Pliocene decline of average gastropod abundance. Both the increasing bivalve diversity and the decrease in average abundance of gastropod taxa correspond to an interval of increasing carbonate deposition and reef building in the region, and are likely a result of increased fine-scale habitat heterogeneity controlled by the local distribution of carbonate buildups. Each of these results demonstrates that documenting the ecological response of tropical marine ecosystems to regional environmental change requires a large volume of fine-scaled samples with detailed paleoenvironmental control. Such data sets are rarely available from the fossil record.

Thylacoleo carnifex, or the “pouched lion” (Mammalia: Marsupialia: Diprotodontia: Thylacoleonidae), was a carnivorous marsupial that inhabited Australia during the Pleistocene. Although all present-day researchers agree that Thylacoleo had a hypercarnivorous diet, the way in which it killed its prey remains uncertain. Here we use geometric morphometrics to capture the shape of the elbow joint (i.e., the anterior articular surface of the distal humerus) in a wide sample of extant mammals of known behavior to determine how elbow anatomy reflects forearm use. We then employ this information to investigate the predatory behavior of Thylacoleo. A principal components analysis indicates that Thylacoleo is the only carnivorous mammal to cluster with extant taxa that have an extreme degree of forearm maneuverability, such as primates and arboreal xenarthrans (pilosans). A canonical variates analysis confirms that Thylacoleo had forearm maneuverability intermediate between wombats (terrestrial) and arboreal mammals and a much greater degree of maneuverability than any living carnivoran placental. A linear discriminant analysis computed to separate the elbow morphology of arboreal mammals from terrestrial ones shows that Thylacoleo was primarily terrestrial but with some climbing abilities. We infer from our results that Thylacoleo used its forelimbs for grasping or manipulating prey to a much higher degree than its supposed extant placental counterpart, the African lion (Panthera leo). The use of the large and retractable claw on the semiopposable thumb of Thylacoleo for potentially slashing and disemboweling prey is discussed in the light of this new information.

A marked retardation of dental ontogeny characterizes the family Elephantidae. As a consequence of this retardation, elephant teeth are subject to the forces of mastication, eruption, and progression while still in a developing and pliant stage. As specimens described here illustrate, the mechanical forces are often sufficient to deform the gross morphology of dentitions. Morphological variation in elephant teeth can be regarded as “fabricational noise”—revealing information about the dynamic context in which the teeth develop. Accordingly, dental variation is less species-specific in elephants than in other mammals. The fossil record may comprise fewer species of elephants than is generally believed, and trends inferred to reflect rapid evolution within this family may in fact reflect phenotypic plasticity.

Systematics, ostensibly the “old” paleontology, actually plays a central and crucial role in modern paleobiology. We argue that a revised ontology has recently clarified the nature of species and has expressly added monophyletic groups to the roster of spatiotemporally bounded entities—“individuals”—that are now seen as participants in the evolutionary process. Systematics is the study of species and monophyletic taxa, and fossils alone provide the data on the temporal boundedness of such taxa.

Cladistics (phylogenetic systematics) is explicitly geared to the recognition of monophyletic taxa. We review aspects of the core problem of character analysis in systematics, particularly addressing the still contended issue of the seemingly competitive claims of three methodologies: out-group comparison, comparative ontogeny, and the “paleontological method.” We find that these methods overlap in their basic assumptions to a significant extent, yet each retains a characteristic and distinctive flavor. They are not all “the same,” nor are they always “complementary”—and no one method is superior to the others in all circumstances.

Far from being the Victorian symbol of a moribund science, systematics lies at the very heart of modern paleobiological research, providing the central data for paleobiology's truly unique contribution, both real and potential, to evolutionary biology in general.

In this paper we analyze the laws of growth that control planktic foraminiferal shell morphology. We assume that isometry is the key toward the understanding of their ontogeny. Hence, our null hypothesis is that these organisms construct isometric shells. To test this hypothesis, geometric models of their shells have been generated with a personal computer. It is demonstrated that early chambers in log-spirally coiled structures cannot follow a strict isometric arrangement. In the real world, the centers of juvenile chambers deviate from the logarithmic growth curve. Juvenile stages are generally more planispiral and contain more chambers per whorl than adult stages. These traits are shown to be essential in order to keep volumes of consecutive chambers in geometric progression. We are convinced that the neanic stage marks the constructional bridge from a juvenile set of growth parameters to an adult one. The adult stage can be strictly isometric, that is, the effective shape is constant and the increase in volume after a chamber addition is proportional to the preexisting volume of the shell.

The shell volume is related to the biomass, the ratio of outer shell surface area to shell volume is related to the respiration rate and the ratio of the total shell surface area to shell volume is related to the total calcification effort. The influence of the parameters of the model on these relationships is investigated. Only the initial radius and the rate of radius increase affect the relationships between shell volume and surface area. The other shape parameters merely provide a fine tune-up of these relationships. Size itself plays a major role during foraminiferal development.

Polymorphism is being actively investigated by ostracode specialists because the phenomenon is widespread and may be a key to understanding speciation patterns and evolutionary processes. However, the methods for recognizing the phenomenon and the cause or causes of polymorphism are still under debate. This study presents an example of genetically controlled ostracode dimorphism in which the relationship between the two forms can be explained in terms of heterochrony. The living males as well as the females of Loxoconcha uranouchiensis in Aburatsubo Cove, central Japan, are found to be dimorphic in size, shape, and surface ornamentation of the carapace. The dimorphic forms appear concurrently in the same microhabitat, suggesting that the dimorphism is genetically rather than environmentally controlled. Although the large and the small forms are indistinguishable in their early stages, morphological differences gradually appear and become complete after the final molting, which is the seventh molting for both forms. The characters determined by the number of moltings, such as the numbers of reticules, bristles, and pores, are identical between adults of the two forms. In contrast, for characters affected by the growth condition of the epidermal-cell system, such as carapace shape and fine surface ornamentation, the small-form adult is similar to the penultimate instar of the large form. Taking the large form as a standard, the small form is paedomorphic. These two forms are reproductively isolated and should be considered different species.

Selected shell specimens of extant and fossil streamlined pectinids, which have or presumably had level-swimming ability, were examined experimentally to elucidate their hydrodynamic properties, in particular, airfoil efficiency estimated by lift-drag ratio. Using a stationary water tank for nautical engineering, lift and drag forces were measured at various attack angles. Of the examined species, Amusium japonicum, which is characterized by an unusually shiny surface, upward-cambered commissure and sharpened trailing edge, is the most efficient level swimmer and has the lowest drag coefficient and the highest value of lift-drag ratio at any attack angle. Amussiopecten praesignis from the Plio-Pleistocene may have swum horizontally because its airfoil efficiency is superior to that of a living level swimmer, Placopecten magellanicus. Although its shell shape is analogous to that of Placopecten, Camptonectes (Maclearnia) cinctus from the Lower Cretaceous shows a much inferior efficiency and a significant flow separation from the surface. Bernoulli's effect in convex-upward species may contribute to increase lift, but a certain attack angle is always required for level flight. The strategy of level swimming probably evolved independently in several pectinacean lineages in which swimming rather than shell robustness became the preferred defense against predators. One problem that must be solved is that some feedback mechanism is required to check pitching, rolling, and yawing of the shell to attain stability in level flight.

Dental microwear analyses of ungulates and other large herbivores rely on correlations of diet and microwear among extant ungulates, primarily ruminants. Microwear is considered a ‘taxon-free’ method of paleodietary analysis. The properties of food are associated with causality of microwear, but the possibility that heritable properties of the consumer (tooth morphologies, masticatory dynamics, enamel mechanical properties, digestive physiologies) may introduce bias is not considered. Using an observer blind method of light microscopy, we examined the distribution of microwear features on the molars of eight species of ruminants and perissodactyls. Grazing and browsing ruminants had statistically different numbers of scratches forming discrete data clusters. Perissodactyls differ in the numbers of scratches and pits but without discrete browser and grazer clusters. Microwear features were distributed homogeneously across ruminant molars and strongly predictive of diet from the labial edge of the molar to the lingual edge. Microwear was heterogeneously distributed across perissodactyl molars with more pits on the labial edge and more scratches on the lingual edge. In perissodactyls, microwear sampled from the labial edge was strongly predictive of diet, while microwear sampled from other areas were not. Discriminant function analyses of microwear assigned individual molars to diets (browser and grazer) and clades (ruminant and perissodactyl) with similar success (70–73%) indicating that phylogeny and diet influence microwear equally. Rhino microwear was more sensitive to clade membership while other perissodactyl microwear was more sensitive to diet. Although it is not clear what heritable variables may phylogenetically bias dental microwear, extant ruminants may not be appropriate models for the microwear of other large herbivores.

Time is so fundamental to the everyday thinking of paleobiologists and geologists that it is seldom given close critical attention. Many of the currently debated issues in evolutionary history—catastrophic extinctions and punctuated vs. gradual morphological change, for instance—include assumptions about time and rate which are seldom made explicit. Methods now exist for calibrating evolutionary patterns through estimates of time components in the fossil and sedimentological records. There is a growing realization that increased precision in defining time frameworks can greatly clarify evolutionary problems. This has helped to stimulate renewed interest in the traditional topic of time and how it is represented in the biological and geological record.

Predatory marine snails and their prey provide a unique look at many aspects of predation events, allowing behavioral inference and studies of coevolution. This study examines differential predation patterns, rates, and success of two co-occurring gastropod predator families which drill two co-occurring species of Turritella (Turritellidae: Gastropoda) in the Gulf of California. Both naticid and muricid predators, identified by the shapes of their respective boreholes, attacked the thinner-shelled Turritella leucostoma more frequently than the thicker-shelled Turritella gonostoma. Both species were drilled more frequently and more successfully by naticid, as compared to muricid, predators. Naticids drilled prey in the 40- to 70-mm size class most frequently. Prey over 100 mm in length were relatively safe from all drilling predators. Predator size (estimated by borehole diameter) in naticids was correlated with prey size in both species, but for a given-sized prey, predators on T. gonostoma were proportionally larger. There was no size correlation for muricid predators. Unsuccessful attempts (incomplete drilling) were started on the suture more often than were completed holes, for both predator families on both prey species. Naticids began drilling T. leucostoma on the suture significantly less than expected by chance. We looked for possible changes over evolutionary time by analyzing prey shells from Pleistocene and Recent storm deposits. We found no evidence of change in any aspect of implied predatory behavior over the past 100 k.y.

The theoretical framework developed here delineates the biological and paleontological circumstances under which the observed durations and diversities of fossil taxa will be significantly affected by three time-dependent sampling biases. The pull of the Recent and the loss of fossiliferous sediments shorten the observed durations of ancient taxa, as compared to the observed durations of Recent taxa. By contrast, the duration truncation mechanism lengthens the observed durations of ancient, as compared to more recent, taxa. Both the pull of the Recent and loss of fossiliferous sediments decrease the observed diversity of ancient, as compared to contemporary, communities.

This theoretical framework is built on four parameters: the extinction and origination rates q and p; the fossilization rate, v; and the fossil loss rate, h. I derive formulas for the observed durations and diversities of fossil taxa in terms of these parameters and develop a method of estimating these parameters. The estimation procedure is applied to the bivalve families, and I provide statistical evidence for the conclusion that q – p < 0 for bivalve families, and hence that bivalve diversity has been increasing through time. The theory predicts that a certain fraction of an extinct fauna will be represented by only one fossil, and hence will have an observed duration of zero. As the record becomes poorer, this fraction increases. For bivalves I assume that families known from only one stage have an observed duration of zero, and exploit this assumption to estimate h and v/p.

To evaluate the errors made in applying the model to the bivalves, I estimate several parameters in two different ways and find the estimates to be consistent. Additionally, I argue that the errors caused by the simplifying assumptions of the model are less than the sampling errors inherent in estimating p, q, h, and v.

Studies of taxonomic diversity over time commonly count and compare first- and last-appearance data (FADs and LADs) over a succession of temporal intervals, and interpret them with respect to taxon origination and extinction. Singleton taxa, which first appear and last appear in the same temporal interval, are often removed from analyses because they might result from preservational biases rather than evolutionary processes, or they might represent non-independent FADs and LADs. Should singleton taxa always be excluded? We argue that in the case of Paleozoic terebratulide brachiopods, although they may be sensitive to biases in sampling intensity, singleton genera should be included in diversity studies because they do not appear to result from more typical biases, such as Lagerstätten and temporal interval length, that arguably can result in artificially high numbers of singleton genera.

Singleton genera can be critical and effective when used to test hypotheses regarding the existence and generation of latitudinal diversity gradients. Contrary to the anti-tropical diversity pattern of modern articulated brachiopods, Paleozoic terebratulides show a latitudinal diversity gradient that peaks in the Tropics. The hypothesis that the Tropics are either a diversity source or sink can be tested by comparing FAD and LAD latitudes. For singleton genera, FAD and LAD latitudes are taken from the same data points and must be removed for statistical comparisons to be valid. We suggest that taxon age distributions can accommodate singleton data, as the taxon age metric considers origination and extinction simultaneously. We generated taxon age distributions to test the hypothesis that the observed Paleozoic diversity gradient results from a latitudinal bias in generic turnover rate. We discovered that singletons are not randomly distributed over latitude, with proportionally more singleton genera occurring in the Tropics. In this case, singleton genera may reflect rapid evolutionary turnover of taxa, rather than simply preservational bias. Methods that can accommodate singleton taxa should be used to study the diversity of Paleozoic terebratulides and possibly other well-skeletonized marine metazoans.

The Plio-Pleistocene planktic foraminiferal sequence of the Globorotalia (Globoconella) puncticulata-inflata clade in Deep Sea Drilling Project Site 588, dated at 4.36 Ma to 0.05 Ma, records the branching history of the G. inflata lineage from the ancestral G. puncticulata lineage. The gradational nature of the divergence and the enormous morphological variability inherent in the G. inflata lineage have elicited different views on taxonomy and phylogeny of this clade. A pattern recognition technique, soft independent modeling of class analog (SIMCA), was used as an objective quantitative stratophenetic methodology to reconstruct the phylogenetic history.

Typical specimens of two species, G. puncticulata and G. inflata, were identified from a stratigraphic level dated at 2.76 Ma. Principal component models were built to characterize the morphometric patterns of the two morphotypes using SIMCA. The Globoconella specimens of the next lower and higher adjacent stratigraphic levels were evaluated against the models and classified into one of the two morphotypes. The newly classified specimens were then used to build new models for further tracing of lineages in lower and upper sections, respectively. Progression of such training and classification procedures through stratigraphic intervals resulted in a reconstruction of the evolutionary patterns of the two lineages. Cladogenesis gave rise to the descendant lineage, G. inflata, at about 3.5 Ma. The two co-existing species, G. inflata and G. puncticulata, differ only in size and show similarity in most characters at the beginning of their divergence. Other characters began to diverge later, at various rates. The gradients between planktic and benthic foraminiferal δ18O values show a continuous increase during the late Pliocene. The succession from G. puncticulata to G. inflata during the same time correlates with the progressively increased vertical stratification in temperature of surface waters. Globorotalia puncticulata became extinct at 2.35 Ma when the temperature gradient further increased, corresponding to the onset of extensive glaciation in the Northern Hemisphere.

In a seminal paper in 1975, Gould proposed that postcanine occlusal area (PCOA) should scale metabolically (0.75) with body mass across mammals. By regressing PCOA against skull length in a small sample of large-bodied herbivorous mammals, Gould provided some marginal support for this hypothesis, which he then extrapolated as a universal scaling law for Mammalia. Since then, many studies have sought to confirm this scaling relationship within a single order and have found equivocal support for Gould's assertion. In part, this may be related to the use of proxies for both PCOA and body mass, small sample sizes, or the influence of a “taxon-level effect,” rendering Gould's scaling “universal” problematic.

Our goal was to test the universality of Gould's prediction and the impact of the taxon-level effect on regressions of tooth size on body mass in a large extant mammalian sample (683 species spanning 14 orders). We tested for the presence of two types of taxon-level effect that may influence the acceptance or rejection of hypothesized scaling coefficients. The hypotheses of both metabolic and isometric scaling can be rejected in Mammalia, but not in all sub-groups therein. The level of data aggregation also influences the interpretation of the scaling relationship. Because the scaling relationship of tooth size to body mass is highly dependent on both the taxonomic level of analysis and the mathematical methods used to organize the data, paleontologists attempting to retrodict body mass from fossilized dental remains must be aware of the effect that sample composition may have on their results.