The occurrence of zooxanthellae in Recent scleractinian corals is strongly correlated with their growth form, corallite size, and degree of morphological integration of corallites. The great majority of zooxanthellate corals are multiserial with small, highly integrated corallites, whereas most corals lacking zooxanthellae are solitary or uniserial colonial forms with large, poorly integrated corallites. Beginning in the Jurassic, fossil scleractinian faunas are morphologically similar to Recent faunas dominated by zooxanthellate species, strongly implying that most scleractinians contained zooxanthellae by that time. Evidence for Siluro–Devonian tabulates and Triassic scleractinians is equivocal but still suggests the presence of zooxanthellae in these corals. In contrast, morphological evidence suggests that rugosan corals lacked zooxanthellae.

Most populations of Recent zooxanthellate corals contribute to reef formation, but many do not. Similarly, fossil corals interpreted to contain zooxanthellae on morphological grounds did not always form reefs. Recent reef formation depends upon a host of environmental factors that have little to do with the possession of zooxanthellae per se. Coral morphology should be a better predictor of the presence of zooxanthellae in fossil corals than their association with reefs.

Distributional patterns of late Osagean (Mississippian) crinoids from the east-central United States are examined using multivariate analysis of crinoid species diversity and species abundance data. We confirm previous hypotheses that three well-defined crinoid associations existed during the late Osagean. These associations were dominated, respectively, by 1) monobathrid camerates preserved in carbonate packstones; 2) poteriocrine inadunates in higher-energy siltstones and sandstones; and 3) disparid inadunates, cyathocrine inadunates, and flexibles in mudstones where neither monobathrids nor poteriocrines dominated. In conjunction with petrologic data on the enclosing sediments, the analyses suggest that these associations occurred along a spectrum of increasing current velocity at the seafloor. Camerates, poteriocrine inadunates, and flexibles are interpreted to display preferences for specific environmental conditions, whereas disparid and cyathocrine inadunates are inferred to be environmental generalists.

The different environmental distributions of the major crinoid groups are interpreted to be a function of the mode or modes of aerosol filtration feeding used by each group. This inference is possible through functional morphologic and morphometric studies of crinoid arms, because the skeletal elements of the arms, which are commonly preserved, are directly involved in feeding.

The morphology of the tarsi, hindlimbs, and pelves of the earliest crocodilians and their nearest relatives, Hallopus and the “sphenosuchians,” indicates that these animals had adaptations for erect posture. The widespread distribution of apparently homologous adaptations for erect gait among the archosaurs with crocodile-normal tarsi suggests that those structures are plesiomorphic for this group, which comprises the Aetosauria, “rauisuchians,” “sphenosuchians,” Hallopus, and the Crocodylia. Adaptations for erect posture are seen most clearly in the structure of the proximal tarsus (astragalus and calcaneum).

An important implication of this argument is that the most primitive crocodylomorphs, comprising the “protosuchian” crocodiles, the “sphenosuchians,” and Hallopus, had an erect stance and gait. The sprawling stance and associated gait used by modern crocodilians during swimming and upon entering the water can be viewed as secondary adaptations to an aquatic existence. The environments of deposition and faunal associations of “sphenosuchians” and “protosuchian” crocodiles are consistent with primarily terrestrial habits. Living crocodilians have two types of step cycles, sprawling and erect; the sprawling pattern is overprinted onto the inferred ancestral “high-walk,” and onto the gallop sometimes used by juvenile crocodilians.

The unique holotype of the Triassic reptile Sharovipteryx (initially Podopteryx) mirabilis has been reexamined and redescribed, correcting the original account. It is a small lizard-like reptile with an elongate head and densely tubular femur and tibia each longer than the (estimated) intergirdle distance. (Part of the pectoral region has been lost and the remnants remain encased in the matrix.) The matrix retains the impression of portions of the integument, including a patagium that reached from the hindlimbs to the base of the tail. Unlike the original account, the patagium did not extend to the pectoral limbs. Experiments with models indicate that Sharovipteryx could have maintained a shallow glide if the femora were held at a shallow angle to the vertebral column and the tibia and feet extended out at right angles to it, thus stretching the integument. The pectoral limbs (with or without a fringing membrane) might have produced a variable canard; alternatively vertical bending of the tail could have applied drag, each making the glide more stable.

Using Sepkoski's compendium of fossil marine families (1982a, and updates), we have analyzed the changing pace of familial origination and extinction within 55 extinct and 44 extant higher taxa of marine organisms. Eight different metrics were calculated, and least-squares regression analysis was used to identify within-taxon trends in the data. All metrics and analyses gave essentially the same results. Origination metrics decline significantly with time during the histories of higher taxa, while extinction metrics increase significantly. The number of statistically significant declines of origination metric, however, substantially and invariably exceeds the number of statistically significant increases of extinction metric for each pair of corresponding metrics analyzed. It follows, therefore, that temporal trends in the pace of origination and extinction within higher taxa are highly asymmetrical.

Further analysis shows that truncating data from temporal endpoints has little effect upon the intensity of origination trends, implying that declining pace of origination is a sustained property of the long term histories of taxa. Such truncation, however, reduces the intensity of extinction trends to statistical insignificance and confirms Van Valen's (1985a) suggestion that extinction behaves largely as a stationary process. If the histories of higher taxa are characterized by substantial declines in the pace of origination while the pace of extinction remains largely stationary, it follows that declining pace of origination is an important controlling factor in long term taxic evolution.

Before one can study evolutionary rates one must reject the null model of symmetric random walk. for which the requisite quantity does not exist. As random walks reliably simulate all the features we find so compelling in the fossil record—jumps, trends, and irregular cycles—rejection of this irritating hypothesis is much more difficult than one might hope. This paper reviews principal theorems from the mathematical literature of random walk and shows how they may be applied to empirical data by scaling net changes according to the square root of elapsed time. The notorious pair of “opposite” findings, equilibrium and anagenesis, may be construed as deviations from random walk in opposite directions. Malmgren's data on Globorotalia tumida, previously interpreted as an example of punctuated anagenesis, are consistent with a random walk showing neither punctuation nor anagenesis, but instead varying in speed over four subsequences.

Periodicity has recently been reported in the extinction rates of fossil marine families since the Permian. The analysis used appears particularly sensitive to parameter estimation techniques, particularly in the definition of mass extinctions. It also fails to incorporate autocorrelation in the fossil record into its null hypothesis and rests on an inappropriate a posteriori comparison to the null hypothesis. An alternative analysis, examining the time-lags between periods of high extinction rates, produces no evidence of a cycle.

Stanley's (1979) method of estimating taxonomic longevity from Lyellian curves differs from Kurtén's (1960) because of different underlying assumptions. Kurtén's model supposes that taxon richness and longevity are stochastically invariate over the period used for the Lyellian estimate. Both Kurtén and Stanley seek to calculate the average longevity of a taxon, when the temporal stratigraphic ranges are known after and before a given time datum. Under the exponential decay model used by Kurtén, mean taxonomic longevity is indeed approximately 2.89 half-lives, as he maintained. Stanley's estimate is based on the unrealistic assumptions of uniform longevity and evenly-spaced origins of fossil taxa. This leads to an estimate of longevity as exactly two half-lives.

The mean taxon duration, , and the 50 percent point of the Lyellian curve, T50, are directly proportional to one another: . However, there is a disagreement in the literature over the correct value of the proportionality constant, C. Various authors have claimed that C ≈ 1.44, C = 2.00 and C ≈ 2.89. I critically examine the assumptions underlying these three choices of C and argue that C ≈ 1.44, which is based on an exponential model of survivorship, is more widely applicable than the other values of C.