Widespread concern about environmental pollution is putting a new question to the fossil record: How has the biosphere reacted to chemical changes in the past? Monera and Protoctista might be expected to provide valuable clues in this quest since their biomineral remains are generally formed in conditions closely related to the environment. But why do unicells biomineralize at all? It was with such questions in mind that an international symposium of the Systematics Association on “Biomineralization in Lower Plants and Animals” was held at Birmingham on April 15–19, 1985. Monerans, protoctistans, lichens, calcareous algae, and bryozoans were discussed in 36 papers, of which 23 are to be published in a volume by Oxford University Press. This volume, edited by Leadbeater and Riding (1986), will form a natural sequel to the papers in Miller et al. (1984) on mineral phases in biology and in Westbroek and de Jong (1983) on biomineralization and biological metal accumulation.

Siwalik rocks of Pakistan are a virtually continuous, continental sedimentary sequence, extending in age from 18 to 1 ma b.p. This paper describes taphonomic features of late Miocene mammalian assemblages from a highly fossiliferous interval about 400 m thick, based on field documentation of sedimentary environments at 42 fossil localities and systematic fossil collection of 21 localities.

Within a broadly fluvial system, I recognize four sedimentary environments of bone accumulation, distinguished by lithology, unit-thickness, unit-geometry, contacts, sedimentary structures, and relationship to adjacent units. Each environment corresponds to an association of lithofacies. Facies Association I is interpreted as the persistent, major channel bodies of a meandering fluvial system; Facies Association II as coarse-grained flood deposits, such as crevasse splays, deposited beyond the main channels; Facies Association III as channel margins, including levees and swales; and Facies Association IV as predominantly subaerial floodplains.

Taphonomic features of bone assemblages from each facies association include skeletal-element composition, surface distribution of specimens, degree of articulation, hydraulic equivalence between organic and inorganic sedimentary particles, frequency of juvenile remains, size distribution of fauna, and an estimate of duration of accumulation of individual fossil localities. The distribution of these features among the four facies associations suggests that bone assemblages in Facies Associations I and II accumulated by the action of currents in river channels or floods, whereas bone assemblages in Facies Associations III and IV accumulated through concentration by biological agents and/or attrition at a repeatedly used site of predation.

Inclusion in fluvial accumulations depends on initial availability of skeletal remains and hydraulic characteristics of individual skeletal elements, but not taxonomic identity per se. For biological accumulations, however, taxonomic composition reflects the preferences of the individual agents of accumulation. The probability of preservation of taxa in fluvial accumulations is probably mainly a function of body size, as reflected in the sizes of isolated skeletal elements. Thus, in this Siwalik system, bone assemblages that experienced fluvial transport are better representations of original community composition than bone assemblages created by biological agents or passive accumulation.

Recent theoretical results demonstrate that a phenotypic version of Wright's shifting balance theory generates the dynamical pattern of punctuated equilibria. Thus, classical mechanisms of random genetic drift and selection for multiple adaptive peaks produce geologically long periods of relative stasis interrupted occasionally by very brief intervals of rapid change. A simple extension of this theory is made here to encompass developmental constraints between quantitative characters, manifested as phenotypic and genetic correlations between characters. Developmental constraints do not qualitatively alter the dynamical pattern of phenotypic evolution produced by selection and random genetic drift. A quantitative definition of stasis is proposed, based on a common taxonomic practice for recognizing subspecies. From this it is concluded that stasis is not the rule for quantitative measurements of detailed sequences for fossil species throughout most of their existence. Instead, periods of relative stasis are interspersed with gradual fluctuating trends, short intervals of rapid change, and discontinuities of subspecific magnitude.

The lack of tools for teasing genetic information out of the fossil record has been a source of frustration to both neontologists and paleontologists, both of whom would like to know more about what was happening genetically in association with such evolutionarily significant events as cladogenesis and extinction. The dearth of such information has been a factor contributing to the current schism between population geneticists and paleontologists over interpretations of historical patterns of evolution (Gould and Eldredge 1977; Stanley 1979; Charlesworth et al. 1982; Levinton 1983; Turner 1983), a schism which seems unbridgeable without at least some insight into paleontological patterns of genetic variation. Several recent papers, however, have documented a negative correlation between the level of fluctuating asymmetry (small, random, right-left differences between otherwise bilaterally symmetrical characters) and the level of heterozygosity in a variety of organisms. Whatever its underlying cause may be, this correlation raises a flicker of hope that a tool may exist for inferring whether some populations of fossil taxa were more variable genetically than others.

Four basic types of skeletal concentrations are modeled in terms of changes in sedimentation rate alone. The model categorizes fossil concentrations on the relatively objective basis of their bed contacts, and uses this criterion to infer directional shifts in net sedimentation. This radical simplification of accumulation histories, in which hardpart input is held constant, yields a surprisingly powerful model capable of predicting a broad spectrum of taphonomic and paleobiologic phenomena. Type I concentrations grade from less fossiliferous sediments and terminate in omission surfaces; if hardpart supply is held constant, they record a slowdown from positive to zero net sedimentation. Type II concentrations are the same as Type I but terminate in erosion surfaces (slowdown to negative net sedimentation), and Type III and IV concentrations are characterized by basal erosion or omission surfaces, respectively, grade upward into less fossiliferous sediments, and record increases in net sedimentation from negative or zero rates to positive rates. According to the model, samples collected from successive horizons within any of these shell beds will differ in the degree and type of post-mortem bias owing to differing histories of hardpart exposure at the depositional interface. Moreover, because rates of sediment accumulation govern the abundance of hardparts at the depositional interface and thus many of the physical characteristics of the benthic habitat, the dynamics of fossil accumulation have direct consequences for the structure of benthic communities (taphonomic feedback) and for ecologically controlled species morphometry.

The model is highly robust to fluctuations in hardpart input, as judged by its ability to correctly infer modes of formation of concentrations in synthetic stratigraphic sections. In addition, field examples of Type I–IV concentrations show independent evidence of formation during intervals of reduced net sedimentation, and many exhibit trends in taphonomic and paleobiologic features expected from the postulated changes in net sedimentation. The model thus provides a testable working hypothesis for the accumulation of fossil material in a wide range of environments, and should be applicable to concentrations of any taxonomic composition, state of preservation, or geologic age. The power and robustness of this heuristic model in fact argue that fossil-rich and fossil-poor strata provide fundamentally different records of past conditions, and that sedimentation rather than hardpart input is the primary control on the nature of the fossil record.

Experiments were conducted to test the hypothesis that biomechanical constraints determine the morphology of regular echinoids. Hard-bottom-dwelling Tripneustes gratilla elatensis were transferred to an artifical sandy habitat to evaluate whether the change in substrate affects their height to diameter ratio (H/D). Within 1–2 months their H/D ratio increased significantly. This change was shown to be reversible to some extent. Surgical damage to the ambulacral system of one ray caused inactivation of tubefeet and atrophy of injured ambulacra. Test shape was also affected: the damaged ray was lower, and the nondamaged ambulacra deflected toward the treated one, producing bilateral symmetry as in recorded cases of teratology. Study of T. g. elatensis tetramers showed that while “perfect” tetramery was apparently associated with genetic aberration, “imperfect” tetramery results from mechanical injury at an early ontogenetic stage. Micromorphological study shows that in the longitudinal sutures, normally under tension, long and slender trabeculae develop, associated with long and well-aligned collagenous sutural fibers, while the latitudinal trabeculae and fibers are short and less organized. A mechanical effect is suggested by the oval cross-section of the fiber-anchoring trabeculae. Further, echinoid plates interact like soap bubbles, whereas the entire test behaves like a balloon, fastened to the substrate by the ambulacral tubefeet. All these observations support earlier hypotheses on the biomechanical control of echinoid test growth. A model is proposed in which the expansion of the inner mass, counteracted by the mechanical activity of the ambulacral tubefeet, mesenterial threads, and lantern muscles, affects sutural growth, thus controlling echinoid morphogenesis.

A morphometric survey among regular echinoids reveals an inverse relationship between ambulacral width and relative ambital height. Although both increase of ambulacral width and lowering of ambitus-line are evolutionary trends, it is suggested that they are a response to a mechanical effect. H/D ratio was not related to ambulacral width on the phylogenetic level. It is therefore suggested that the latter correlation is ontogenetically controlled. Aspects of irregular echonoid evolution, such as bilateral symmetry, flattening, and formation of the ambulacral petaloid, also are explained by this model.

The evolution of body size in fossil horses is frequently depicted as a gradual, progressive trend toward increased body size (Cope's Law). Body size (actually body mass) was estimated for 40 species of fossil horses using dental and skeletal characters and regression equations derived from the same characters in extant species of Equus with known body mass. After body sizes were estimated, rates of morphological evolution, in darwins (d), were calculated between known ancestral and descendant fossil horse species. For the first half of horse evolution (from ca. 57 to 25 ma) body mass remained relatively static between about 25 and 50 kg with very slow evolutionary rates of 0.003–0.04 d. During the early–middle Miocene (from ca. 25 to 10 ma) there was a major diversification of body mass to about 75–400 kg and consistently higher evolutionary rates between 0.04 and 0.24 d. Since the late Miocene, body mass has generally increased with a maximum seen (in natural populations) in Equus scotti (ca. 500 kg) during the middle Pleistocene. Therefore, for horses, the traditional interpretation of gradual increase in body size through time is oversimplified because: (1) although the exception to the rule, 5 of 24 species lineages studied are characterized by dwarfism; and (2) the general trend seems to have been a long period (32 ma) of relative stasis followed by 25 ma of diversification and progressive (although not necessarily gradual) change in body size.

The evolutionary bootstrap is a new approach to the analysis of patterns of taxonomic diversity. In general, the evolutionary bootstrap works by surveying the diversity history of a taxon, learning its dynamic properties, and then generating randomly large numbers of artificial diversity histories based upon what was learned. The distribution of artificial—or bootstrapped—diversity histories approximates the distribution of diversity histories that were possible for taxa with the dynamic properties of the real taxon, and serves as a paleontological null hypothesis for studying statistically the diversity history of the real taxon.

Two null hypotheses were established, the additive and the multiplicative. The additive null hypothesis assumes that the amount of diversity change that occurs in a higher taxon during an interval of time is independent of the number of member subtaxa present at the beginning of the interval. The multiplicative null hypothesis, in contrast, assumes that the amount of diversity change that occurs is dependent upon the number of member subtaxa present at the start. Thus the two null hypotheses represent end members of a diversity-independent/diversity-dependent continuum of possibilities.

Detailed analyses using the evolutionary bootstrap, in conjunction with the clade statistics of Gould et al. (1977), show that several of the 17 higher taxa studied have diversity histories that are statistically significantly different from the random expectation under one or both null hypotheses. Analyses of multiple taxa in aggregate also reveal several properties of diversity histories that are statistically significantly different from random. Real taxa tend to have higher uniformities and lower maximum diversities than expected under the multiplicative null hypothesis. They have lower uniformities, higher maximum diversities, and longer durations than expected under the additive null hypothesis. And, they have lower centers of gravity than expected under either null hypothesis. Overall, the results provide a possible statistical verification of the process of taxonomic (traditionally, adaptive) radiation and suggest the need to consider deterministic explanations for observed diversity patterns.

Bones of mammals exhibit progressive stages of weathering during their time of subaerial exposure. Consequently, the study of bone weathering in fossil assemblages may help to assess the period represented by an accumulation of bones. Stages of bone decomposition due to subaerial weathering have been identified in assemblages of fossil macromammals from Olduvai Gorge, Tanzania. A modern bone assemblage collected by spotted hyenas is used to devise a method for recognizing attritional accumulations of bones from weathering characteristics. This method, which involves study of long bone diaphyses, is applied to Plio-Pleistocene faunal assemblages from Olduvai, 1.70–1.85 ma old. Previous work indicates that early hominids had an important role in the collection of fauna at five of the six sites studied. It is shown that animal bones were accumulated at each site over a period of probably 5–10 yr or more. The length of this period, along with other taphonomic evidence, suggests that the processes of bone aggregation at these sites differed from those at the short-term campsites of modern, tropical hunter-gatherers.

Body mass is estimated for extinct species of Sigmodon. These data are then used in appropriate equations derived among Recent mammals to estimate a suite of physiological and ecological variables which are followed through almost 4 ma of cotton rat history. A statistical trend towards large size is documented. Despite large swings in population size and other parameters, hypothetical values of population metabolism remain virtually constant, suggesting negligible population energetic benefit to size change in either direction. Studies of extant cotton rats and unrelated taxa sharing the same adaptive zone suggest that there is now, and has been in the past, negligible thermoregulatory advantage to modification of cotton rat body mass. Large size appears to be associated in Sigmodon with heightened aggression to the point that two species, particularly if of dichotomous size, cannot coexist in the same microhabitat. At least with regard to cotton rats, this conclusion represents a challenge to the comfortable hypotheses of coevolution and character displacement. The overall trend toward large size during Pleistocene time is considered then as the interplay of selection acting to favor large size in areas of sympatry and stochastic processes originating cotton rat populations of different body size. Because morphology and ecological strategies are stable within the cotton rat adaptive zone for millions of years, it is suggested that mammalian speciation events that result in exploitation of a new adaptive zone are uncommon and occasionally cross higher taxonomic categories. These events are defined as first-order speciation events, in contrast to second-order events that occur in clades within the same adaptive zone.

Mammalian species often exhibit clinal geographic variation in body size: individuals tend to be larger in areas with lower mean annual temperature. Climatic change involving increasing or decreasing mean annual temperature may cause clines to shift geographically, resulting in a phenotypic shift at all affected locales within a species' range. I assess the potential of shifting geographic clines to produce morphological trends in the fossil record. Five extant North American mammalian species (Didelphis virginiana, Mephitis mephitis, Odocoileus virginianus, Scalopus aquaticus, and Sciurus carolinensis) are examined to quantify size change along latitudinal clines and to estimate the geographic range and temperature difference commonly associated with a given difference in body size. Relative to body size, the observed size range of skeletal characters within each of these five species is comparable to that seen in a much larger sample of North American mammals. Thus patterns of variation documented for the five species may be used to assess the likelihood of dine translocation as an explanation of size change in the mammalian fossil record. As a case study, I examine three lineages from the Early Eocene of the Bighorn Basin, Wyoming. I determine that size change in these chronoclines represents evolutionary change and is not merely the result of shifting geographic clines.

The dominance of Paleozoic articulate brachiopods in once-muddy environments may be explained by an array of mechanisms and structures that reject nonfood particles, in some cases without interruption of feeding: (1) behavioral flexibility of the lophophore and its individual filaments; (2) persistent, variable-speed rejection currents on the mantle, which sometimes concentrate pseudofeces in topographically controlled vortices; (3) costae and alae (which have many other probable functions); (4) inhalant currents elevated above substrate; (5) marginal setae.

Some mantle currents parallel (and presumably augment) lophophore feeding currents; others diverge up to 90° to provide rejection while feeding continues. Contrary to previous reports, the lateral cilia seem to be involved in rejection and may reverse.

Repeated claims for the superiority of the gill of suspension-feeding bivalves over the “weak” individual filaments of the lophophore are probably false. In suspension-feeding bivalves, simultaneous feeding and rejection are likely to be hindered by fused gill elements and mucus-trapping of food. The energetically efficient articulates are predicted to have a competitive advantage over suspension-feeding bivalves when oxygen or food is limiting, as, for example, after a bolide impact.

Morphometric examination of cladogenesis and phyletic evolution in two late Neogene sister lineages of marine microfossils (Pterocanium prismatium and P. charybdeum, Radiolaria) from two equatorial Pacific sediment cores was undertaken to better understand the rate of cladogenesis and its relation to subsequent phyletic change. The origin of P. prismatium from P. charybdeum ∼4 ma ago has been estimated to take place over an interval of ∼500,000 yr. Results show that the speciation event consists of two distinct phases. The first phase, cladogenesis, occurred relatively rapidly (on the order of 50,000 yr). A second phase of relatively rapid divergent phyletic evolution away from the common ancestral state followed in both descendant branches and continued for at least 500,000 yr after completion of the cladogenetic event. Net evolutionary rates over the next 2 ma appear to be much lower. Individual characters change by as much as 2 population standard deviations during cladogenesis, and by a total of approximately 3 standard deviations over 2.5 ma of phyletic evolution. Up to 5 population standard deviations of change during ≦ 50,000 yr of cladogenesis, and 7 additional standard deviations of phyletic change over 500,000 yr are observed in multivariate (discriminant function) indices of morphologic difference. The measured pattern does not appear to be either strictly “punctuated” or strictly “gradual,” but instead shows features of both hypotheses.

Biometric analyses of the ontogenies of 31 species of fossil echinoids support a hypothesized relationship between regulatory gene changes and environmental stability. In 15 of 17 pairs of related species, the larger species, undergoing slower (neotenic) and/or prolonged (hypermorphic) growth, apparently inhabited the stabler environment. If true, this relationship connects biological processes at a number of levels and explains or agrees with some important macroevolutionary observations, such as onshore evolutionary innovation and Cope's Rule.

Numerical cladistic analysis of 73 cranial and postcranial characters has resulted in a highly corroborated hypothesis describing the phylogenetic pattern of early avian evolution. Using “non-avian theropod” dinosaurs as a comparative outgroup and root for the tree, the analysis confirmed Archaeopteryx to be the sister-group of all remaining avian taxa, or Ornithurae. This latter taxon is subdivided into two lineages, the Hesperornithiformes and the Carinatae. The carinates, in turn, were also resolved into two sister-groups, the Ichthyornithiformes and the modern birds, or Neornithes. This paper provides morphological data corroborating the divergence of the two basal clades of the Neornithes: the Palaeognathae (tinamous and ratites) and Neognathae (all other modern birds). The phylogenetic relationships of four important Cretaceous taxa were also investigated, but these fossil taxa were too fragmentary to determine their phylogenetic position unambiguously. Alexornis and Ambiortus are both carinates, but their relationships cannot be resolved in greater detail. The relationships of the Enantiornithes may lie within the Carinatae or these two taxa may be sister-groups. Gobipteryx is a neornithine and possibly the sister-group of the Palaeognathae.

This analysis indicates that major patterns of morphological change took place at the time of origin of the ancestors of the Ornithurae and the Carinatae. Ornithurine innovations included major changes throughout the skeleton, whereas those of the carinates, while substantial, were primarily restricted to the pectoral girdle and forelimb. The phylogenetic results, in conjunction with the known ages of fossil taxa, indicate that the early lineages of birds very likely arose in the Jurassic. The early cladistic events within the neornithine lineage are also more ancient than generally recognized, and may well extend back to the early Cretaceous.

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.

Inadequacies in stratigraphic resolution or completeness can make true rates of morphologic change through geologic time impossible to estimate precisely. However, relative rates may be sufficient to test whether the tempo of change within species can account for morphologic differences across species boundaries, and hence to distinguish between gradual and punctuated patterns of evolution. The conditions under which these patterns can be distinguished statistically are explored by simulating varying degrees of within-species rate variability relative to across-species morphologic difference. The statistical methods are then applied to multiple-character morphologic data from closely spaced sequential populations of the Neogene bryozoan Metrarabdotos, using discriminant analysis to compare overall morphologies. In nine comparisons of ancestor-descendant species pairs, all show within-species rates of morphologic change that do not vary significantly from zero, hence accounting for none of the across-species difference. In all cases the ratio of within-species fluctuation to across-species difference is low enough to allow the punctuated pattern to be distinguished with virtual certainty. In at least seven of the cases, ancestor species persisted after giving rise to descendants, in conformity with the punctuated equilibrium mode of evolution.

Tiering is the vertical distribution of organisms within the benthic boundary layer. Primary tierers are suspension-feeding organisms with a body or burrow that intersects the seafloor. Secondary tierers are suspension-feeders that maintain positions above or below the sediment-water interface as either epizoans on primary tierers and plants or by living in the burrows of primary tierers. Different primary tierers from soft substrata, nonreef, shallow subtidal shelf and epicontinental sea settings have had different tiering histories, resulting largely from contrasting constructional and phylogenetic constraints. Primary colonial tierers generally occupied lower epifaunal tiers during the Paleozoic and Mesozoic, but since the Cretaceous they have been dominant in the highest tier (+ 20 to +50 cm). Primary echinoderm tierers have been almost exclusively epifaunal, and from the Paleozoic through the Jurassic they were present throughout the epifaunal tiered structure. Although primary bivalve tierers have been both epifaunal and infaunal, they have occupied only lower epifaunal tiers, whereas they have adapted to all levels of the infaunal tiering structure, particularly from the late Paleozoic through the Recent. Brachiopods have lived primarily in tiers directly above or below the water-sediment interface and have not contributed significantly to tiering complexity.

Of the numerous physical and biotic processes and constraints that affect shallow marine benthos, a few have contributed more significantly to changes in tiering patterns. Trends for increasing body size could have accounted for most of the development of tiering complexity up to +50 cm and down to –12 cm. Development of tiering above +50 cm could have been due to processes which would have yielded greater feeding capability, such as competitive interactions for a place from which to feed or adaptations to velocity gradients in the hydrodynamic boundary layer. The most significant process for development of infauanl tiering below –12 cm appears to have been as an adaptive response for predator avoidance.

Unlike infaunal tiering, which never declined after it developed, epifaunal tiering has undergone a general reduction twice. Reduction in epifaunal tiering at the end of the Paleozoic appears to have been the result of the mass extinction at this time, whereas long-term biotic processes seem to have been more important for the tiering decline at the end of the Mesozoic. Tiering structure through the Phanerozoic was thus produced through interactions of a number of physical and biotic factors, tempered by constructional and phylogenetic constraints of each primary tierer group.

A range of specialized burrowing sculptures evolved convergently in at least one lingulid and in several obolid and lingulasmatid genera. The sculptures in Lingula punctata (Ordovician) indicate a burrowing process with the pedicle trailing behind the shell, similar to that of Recent Lingulidae. In the Obolidae and Lingulasmatidae, the orientation of the sculptures indicates a burrowing process with the pedicle oriented downward in the sediment. A burrowing mechanism in which the valves alternated in functioning as anchors, without active participation of the pedicle, is proposed for these forms. Infaunal life habits for several obolid genera are further indicated by the shell morphology and by the distribution of repaired shell damage.

The burrowing Obolidae are likely to have been adapted to relatively high-energy environments, which required frequent reburrowing in addition to escape (upward) burrowing. The increase in bioturbation in these environments in the Middle Paleozoic may have contributed to their extinction. The Lingulidae, instead, being mostly adapted to extreme environmental conditions, could survive in marginal niches which were not intensively exploited by actively burrowing organisms.

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.