Size distributions, based on molar length, are presented for various groups of living and fossil primates. I examine (1) the extent to which particular taxonomic groups with distinctive morphological and behavioral attributes are characterized by distinctive size ranges or distributions and (2) the way in which size ranges and distributions are affected by the presence or absence of other primates within the same geographical area and time. Distinctive behavioral and ecological “adaptive zones” are characterized by distinctive size ranges and behavioral and morphological parallelism or convergence among living and fossil primate taxa usually results in similar size distributions.

The megafauna and associated behavioral traces of two deep-sea benthic environments, the central Arctic and Antarctic, with a surface primary productivity differential of 104 were compared to assess the role of food availability in foraging strategy and community structure. Bottom photographs, analyzed for megafauna and trace density and diversity at comparable depths in the Arctic Canada Basin and the Antarctic Bellingshausen Basin, indicated that trace frequency was inversely proportional to organism density but that trace diversity directly reflected organism diversity. Those traces identified in the fossil record to represent efficient foraging strategies, i.e., the Nereites facies, were conspicuously absent at all depths in the Arctic and present at all depths in the Antarctic, in contradiction of the paradigm of increasing behavioral complexity and sediment exploitation as food availability decreases. Presence or absence of surface-grazing organisms seems to exert a greater influence on trace diversity than depth or nutrient supply. Trace density, however, may reflect episodic sedimentation events which intermittently influence the deep-sea trophic regime.

If the dinosaurs Protoceratops grangeri and Hypselosaurus sp. grew at rates predicted for their body size from extant reptiles, their expected ages at reproductive maturity would be about 20 and 62 yr respectively. This calculation assumes that dinosaurs grew at ectothermic rates which are about an order of magnitude slower than those of endothermic vertebrates of the same body size. Such delayed reproductive maturity may have set a premium on selection for high juvenile survivorship that is reflected in the relatively large eggs of these dinosaurs and in their only moderately large clutch sizes compared to modern reptiles.

Shotwell's method of paleoecological reconstruction attempts to define community membership of mammals represented within paleontological assemblages. Analysis of the measure of community membership upon which the method is based (relative skeletal completeness) shows this measure to be a function of sample size. A method for controlling for the effects of sample size upon measures of relative skeletal completeness is needed. A method is suggested which employs ratios of numbers of individuals to numbers of specimens, and a specific correction of Shotwell's method is proposed.

Arcoid bivalves occupy an intermediate position, in terms both of morphology and of adaptive range between the Pterioida and the Veneroida. The range and limits of arcoid adaptations are related to the growth patterns of their shells. Both the arcoid hinge and ligament grow by the serial repetition of simple structures, in contrast with the development of more specialized, complex structures in other groups. These simple growth patterns place significant mechanical constraints on the range of possible shell forms. Most arcoids live in moderately unstable environments, where they are liable to be excavated or detached from their substrates. Many employ recovery strategies, being adapted to regain their life positions. However, a variety of specialized forms, convergent on other groups of bivalves, have become adapted to avoid being dislodged in the first place. Thus, intrinsic growth patterns and substrate relationships have been the major factors in the evolution of the Arcoida.

Limestone beds in the Middle Ordovician (Trentonian) Bobcaygeon Formation, exposed near Kirkfield, Ontario, exhibit irregular, bored and encrusted surfaces indicative of early lithification. These hardgrounds were formed in extensively burrowed carbonate sediments and their hummocky surface topographies were inherited, in part, from a pre-existing pattern of burrow tunnels. A diverse community, including bryozoans, brachiopods, crinoids, edrioasteroids, and paracrinoids, colonized these hard substrates. In addition, most surfaces are riddled with small, cylindrical boreholes (Trypanites) which represent dwellings of soft-bodied organisms. Some hardground surfaces were inhabited by multiple generations of organisms. Remains of the older generations of encrusters were strongly abraded and nearly obliterated. Superimposed upon these worn remnants are well-preserved remains of rather fragile organisms, e.g. complete hybocystitid crinoids and edrioasteroids. Evidently, certain hardground surfaces were rapidly buried by muds, resulting in the in situ preservation of the last generation of attached organisms.

Slightly differing subcommunities of organisms inhabited various microhabitats provided by the irregular hardground surfaces. Thus, the relative abundance of bryozoans and echinoderms encrusting the roofs of small crevices differs from that on the exposed upper surfaces of the hardgrounds. This is the geologically oldest known hardground community in which microhabitat subdivision can be recognized. However, polarity between the subcommunities is not as pronounced as in geologically younger hard substrate faunas.

Shells of 375 sexed specimens of Nautilus cf. N. pompilius trapped at 300–700 ft (90–215 m) depth off Mutremdiu Point and Ngemelis Island, Palau, exhibit distinctive dimorphism in shell proportion and overall size. Of 221 mature animals, males have larger shells (mean diameter = 209 mm), a broader aperture (mean maximum width = 99 mm; mean width at apertural salient = 92 mm) and greater weight (mean shell + body weight = 1426 gm). Female shells are smaller (mean diameter = 198 mm), narrower (mean maximum width = 91 mm; mean apertural salient width = 81 mm) and the overall weight is less (mean = 1157 gm). Dimorphic differences are not apparent in young shells (less than 180 mm diameter), but develop during the final ½ to ¼ whorl. This is accompanied by development of the spadix in males, indicating that shell dimorphism reflects sexual maturity. Of 375 animals trapped, 28% were female; no depth segregation was apparent. Traditional identification of larger fossil dimorphic cephalopods as females and smaller forms as males is the reverse of observed dimorphism in Nautilus and should be discontinued in favor of macroconch and microconch designations.

Mark and Flessa (1977) have argued that the evolutionary equilibrium hypothesis requires that there should be significant correlation between generic origins and extinctions, and they presented data on Phanerozoic brachiopods and Cenozoic mammals. Their data are re-examined and the correlations are found not to support their version of the evolutionary equilibrium hypothesis. We argue that the equilibrium hypothesis may not be falsifiable using paleontological data.

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.

Cowen and Stockton (1978) seem to agree with one of our main conclusions (Mark and Flessa 1977, p. 21): “Problems of ecological classification, taxonomic consistency and temporal and geographic scale need resolution before evolutionary equilibrium models can be more than heuristic.” Their discussion points out other difficulties with hypotheses of evolutionary equilibrium and with tests for their validity.

Life-sized scale models and a flume were used to observe simulated feeding and hydrodynamics of the Paleozoic camerate crinoid, Pterotocrinus. Three orientations of the crown and filtration fan (downcurrent, upcurrent, upright) in a gentle (3.5 cm/sec) current were used. Maximum baffling of the current and eddying of water into feeding areas occurred where models were oriented like most living stalked crinoids, with a parabolic filtration fan perpendicular to the current and ambulacral side downcurrent. Facing the ambulacral side of the fan upcurrent reduced time available for entrapment of potential food particles. Calyx shape was important in modifying the nature of the filtration fan baffle. Overlapping (36%) of the pinnulate arms increased the baffling effect of the filtration fan. Conspicuous tegminal structures, the Pterotocrinus wing plates, only had a baffling effect where the fan was in an upright position or the arms were infolded between the wing plates. Species of Pterotocrinus possessing blade-like wing plates could have fed effectively in several different orientations. Evolutionary success of Pterotocrinus species with blade-like wing plates probably resulted from dual feeding and protective functions of the wing plates.

Applications of the species-area equation to studies of fluctuations in Phanerozoic diversity have great promise but can involve questionable assumptions. Sepkoski's (1976) analysis of marine diversity throughout the Phanerozoic record assumes that total rock volume is a sufficient measure of sampling efficiency and that an isomorphous equation is appropriate for all of Phanerozoic time. The area of marine sedimentary rock and the area of continental seas are not independent variables. Residual variation in diversity (that which remains after subtracting the effects of rock volume) might be explained by either the species-area relationship or by another component of sampling efficiency. A species-area equation in which the slope (z) and intercept (k) are assumed constant receives mixed support from arguments based on Recent terrestrial and aquatic organisms. Observed z-values cluster near a value of 0.30 despite a wide taxonomic range, but are generally below those found for the Phanerozoic record. Temporal fluctuations in k values, in response to changes in the area of continental seas, may produce elevated estimates of z.

The trophic role assumed by an animal taxon in a community is best understood when the structure of the community is viewed in historical perspective (Whittaker 1977). In many environments it is not physical and behavioral limitations which guide a group's evolutionary potential, but the opportunity to exploit available adaptive zones, which, because of the nature of the fauna, were open (Hecht 1975, p. 248). [The term adaptive zone is used as defined by Van Valen (1971, p. 421) … “the niche of any taxon, especially a supraspecific one.” Van Valen distinguished adaptive zones from the “ways of life” of taxa. Adaptive zones are part of the environment and exist independently of taxa that exploit them.] It is often assumed or implied that a systematic group can, in its adaptive radiation, fill most of the available niches within a particular adaptive zone (Hecht 1975, p. 247). This type of “taxocene” analysis (Whittaker 1972, p. 218; Levandowsky and White 1977, p. 133), which promotes these views, has obvious shortcomings. It is now evident that mammals, for example, were unable to equally exploit and partition all available adaptive zones on every continent. The failure of carnivorous mammals to do this to a complete degree in Australia (see Hecht 1975, p. 247) and in South America (see Marshall 1977, p. 709) has some historical basis in the development of the stratification of the vertebrate fauna.

The published fossil record has significant bias in favor of common and biostratigraphically important taxa when compared with data obtained from a thorough examination of several hundred collections from the Western Interior of North America. Overall species diversity is underestimated by a factor of 3 to 4, and bivalve and gastropod diversity by a factor of 5. The proportion of bivalves increased from 40 to 56% of the fauna, and the proportion of ammonites decreased from 28 to 18%. Thirteen published reports listed 65 species from 203 reported occurrences. Data from all sources showed 170 species for 1050 occurrences. By using abundance data and assuming a log-normal distribution, as many as 200 fossilizable mollusc species may have inhabited the Western Interior during the uppermost biozone of the Cenomanian. The importance of this study is that it quantifies the bias in the published fossil record relative to the potential fossil record for an unusually well studied interval of geologic time. The bias would be greater for less well studied strata.

In their “alternative interpretation” Marshall and Hecht raise two interesting questions:

1. I) Is “Taxocene Analysis” a permissible approach to community evolution, and if so under what conditions?

2. II) What really happened to the ten South American ungulate genera that vanished during the Early Pleistocene?

As these are fundamentally different questions, I shall consider each separately.