The pattern of differential species longevities among five Osagean–Meramecian crinoid clades is analyzed for its evolutionary significance. Differences in mean species longevity between clades may have resulted from species sorting based on eurytopy (niche breadth). In order to test the relationship between longevity and eurytopy it was first necessary to recognize generalists (eurytopes) vs. specialists (stenotopes) objectively. Three different approaches were used: (1) the “Eurytopy Index” (EI), which is a measure of mean number of facies per species; (2) analysis of crinoid functional morphology; and (3) use of canonical discriminant analysis to analyze species distributions between facies in order to separate generalists from specialists. Mean species longevity for each clade was evaluated by four different approaches: (1) rarefaction was used to control for differences in sample size, including both species richness and number of occurrences, between clades; (2) potential facies control of species longevity was evaluated by a bootstrap that compared the observed data to a null model where species longevity was limited only by the actual occurrences of each species known facies through time; (3) uniformity of clade species richness through time was evaluated by the “Index of Uniformity for Species Richness” based on the standard deviation of clade species richness across the time intervals; and (4) potential species range truncations were evaluated by a biostratigraphic gap analysis based on the binomial distribution.

The general order of increasing longevity and eurytopy is (from least to most): flexibles, advanced cladids, camerates, disparids, and primitive cladids. In general the pinnulate crinoids (advanced cladids and camerates) were specialists with lower mean species longevity, and the non-pinnulate crinoids (disparids and primitive cladids) were generalists with higher mean species longevity. Pinnulate crinoids were specialized for feeding in high-energy currents and, thus, were limited in their facies distribution and presumably more extinction-prone. The non-pinnulates could feed in both low- and high-energy currents and, thus, were less limited in their facies distribution and presumably less extinction-prone. The flexibles were the exception in that they were non-pinnulate but had the lowest mean species longevity, apparently because they were specialized for deeper-water clastic environments.

On average, generalist clades have mean species longevities that at a minimum are up to 45% (≈1.0 ± 0.7 m.y.) longer than specialist clades. However, greater mean species longevity did not necessarily confer long-term advantages to a clade. The specialist advanced cladids became the dominant crinoid clade of the late Paleozoic and gave rise to the articulate crinoids of the post-Paleozoic. This may have resulted from the more rapid species turnover of stenotopes creating adaptive evolutionary novelties for their clade. Alternatively, it could simply be the result of stochastic processes.

The finer subdivision of niche space by specialists has led previous workers to predict that specialist clades should have higher species richness than generalist clades. The present study supports this prediction.

An understanding of several macroevolutionary trends has been greatly advanced in recent years by a focus on disparity (morphological variety) rather than taxic diversity. A seminal issue has been the nature of the Cambrian Radiation, and the question of whether problematical Cambrian fossils embody a range of anatomical design far exceeding that observed thereafter. Arthropods have hitherto furnished the only case study, revealing comparable levels of Cambrian and Recent disparity. The generality of this observation needs to be tested in other groups, and the priapulid worms provide a well-documented example. Cladistic analysis of morphological characters for priapulids reveals a paraphyletic series of Cambrian taxa below a crown-group of post-Cambrian genera. However, one extant family (the Tubiluchidae) may be more closely related to Cambrian forms or resolve basally. Character-based morphospace analysis demonstrates greater disparity amongst Recent taxa than amongst their Cambrian counterparts. There is relatively little overlap between the regions of morphospace occupied by Cambrian and Recent genera (contrasting with the situation in arthropods). The Tubiluchidae are morphologically intermediate between Cambrian and other Recent families using several measures of phenetic proximity, and they inhabit environments more comparable with their Cambrian cousins. This work confirms the extensive morphological diversification of major clades by the Cambrian but lends no support to models of a post-Cambrian “decimation” of disparity.

A new hypothesis concerning the evolutionary origin of pentameral symmetry in echinoderms is presented. The BA-A-BA pattern of Lovén's law in echinoids and the 2-1-2 symmetry of the edrioasteroid Stromatocystites appear to be morphogenetically related, and this pattern appears to be locked into development. This pattern may have originated from a unirayed 0-1-0, —A—, ancestor. I propose that a duplication of the uniray occurred and resulted in the addition of a pair of rays that followed Bateson's rules of symmetry to form a three-rayed 0-1-2, —A-BA, construction. This change occurred on the side that corresponds to the left side of the organism. This event made the individual asymmetric with respect to its anterior-posterior axis. Therefore I propose that morphogenetic regulation of bilaterality of the organism then led to homeotic expression of a mirror-image pair of rays on the opposite side. These two morphogenetic steps achieved the 2-1-2, BA-A-BA pattern. “Appendage status” of rays is assumed necessary to invoke the Batesonian mirror-image duplications of the model.

Three robust morphological characters emerge from the “rays-as-appendages” model: (1) 2-1-2, BAo-A-BA, organization; (2) “locked-in” pentamerism; and (3) a 2-3 pattern of right and left rays. Results based on ray homology research are presented for echinoids, asteroids, ophiuroids, edrioasteroids, ophiocistioids, and holothurians. I speculate that helicoplacoids may have 0-1-2 triradiate construction, and that solutes may have 0-1-0 uniray construction. The model has limits; it does not explain 1-1, or 2-1, or 2-2 or 1-1-1 organization of ambulacra.

To a first approximation, the logarithmic spiral is a close fit to the biconvex lateral outline of three terebratellid genera from Australasia. Investigation of spiral parameters confirms the value of the biconvex morphospace of McGhee (1980), but not the method for estimating the spiral itself. Deviations from the estimated spiral are episodic and consistent with Rudwick's (1959) observations of allometry in brachiopod growth. Morphospace location is postulated to be indicative of a species' substrate and lifestyle. The logarithmic spiral offers much opportunity for gaining better understanding of external shape and its cause in articulate brachiopods.

The Scleractinia, which are one of the most important builders of modern reefs, have been considered to have first appeared in the Middle Triassic. Recently, Paleozoic scleractiniamorphs have been reported from both the Ordovician and the Permian, suggesting that the scleractinian-like body plan was already established in the Paleozoic. Those Paleozoic scleractiniamorphs are considered either unsuccessful skeletonized offshoots (extinct experiments) or Paleozoic progenitors of the post-Paleozoic Scleractinia. Permian scleractiniamorphs are characterized by “ancestral” features and have no specific morphologies that deny scleractinian affinities. Molecular phylogenetics also indicate that extant scleractinians are monophyletic and originated long before their Triassic appearance. A Paleozoic origin for the Scleractinia is supported by morphological and molecular phylogenetic data. On the other hand, there is no positive evidence to show that different groups of scleractinians had separate soft-bodied precursors.

The Paleozoic scleractinians evolved within the framework of their basic body plan, and a direct derivation of the Scleractinia from the Rugosa is not probable. The Anthozoa are characterized by a bilaterally symmetrical body plan, which is traditionally considered to have been derived from other radially symmetrical Cnidaria. The problem of the origin of scleractinian body plan may provide a key for deciphering the early anthozoan radiation within the Bilateria. Other examples of Paleozoic Scleractinia and scleractiniamorphs will be found, probably in shallow-water reefal facies or deeper-water communities, bridging the stratigraphic gaps in occurrence and elucidating the origin of the Scleractinia and their body plan.

Evidence that can be used to interpret the life habits of extinct organisms usually takes three forms: functional analysis, analogy with living organisms, and geological evidence. Independent quantitative tests for habit are rarely available. A theory of optimum eye design originally derived for living aquatic arthropods provides quantitative data that are used to test previous suppositions about the life habits of two Ordovician pelagic trilobites: that the telephinid trilobite Carolinites was epipelagic while the cyclopygid Pricyclopyge was mesopelagic. Optimum compound eye design theory uses measured lens diameters and interommatidial angles to determine the “eye parameter” (p), which can be used to gauge approximate optimum level of illumination for the eyes of these trilobites. The eye parameter provides an independent test for their relative paleobathymetry. Values of the eye parameter measured in the dorso-ventral direction across two eyes of Carolinites killaryensis utahensis were found to have medians of 2.13 and 3.24. Values measured in the antero-posterior direction have medians of 3.17 and 4.86 for the two eyes. Values measured in the dorso-ventral direction across two eyes of Pricyclopyge binodosa have medians of 4.23 and 4.98, while values measured in the antero-posterior direction have medians of 7.06 and 8.31. Eye parameters are higher in Pricyclopyge than in Carolinites, the difference statistically significant at p = 0.05. The eyes of Pricyclopyge are optimally designed for lower levels of illumination than are those of Carolinites. This accords with the previous interpretations of the former trilobite as mesopelagic and the latter as epipelagic.

The origin of mammals has been characterized as a gradual process, a claim based primarily on a well-preserved series of extinct nonmammalian synapsids (“mammal-like reptiles”) that span some 200 million years. In contrast to the origin of many other higher taxa, the origin of mammals from within cynodont-grade therapsids is not considered to coincide with a major morphological change, but rather to be simply the culmination of a series of more and more mammal-like transitional forms. To test these assertions, an asymmetrical cladogram extending from primitive “pelycosaurs” to morganucodontid mammaliaforms was created. Three different methodologies were then used to compare the amount of morphological change between nodes on this cladogram with the minimum missing time interval between each node, as inferred from sister taxon-based ghost lineages. In general, a statistically significant positive relationship was found, indicating that greater numbers of derived features tend to be correlated with longer ghost lineages. A significant correlation between the number of accumulated apomorphies and branching events was also found. Although the rate of character change was variable, in no case was a long ghost lineage associated with few apomorphies. These correlations are consistent with the hypothesis that rapid accumulation of derived features occurred relatively infrequently within the synapsid lineage leading toward mammals and that gradual character evolution predominated.

Carbon (δ13C) and oxygen (δ18O) isotopic results are presented from 42 tooth enamel carbonate samples of rhinos (Family Rhinocerotidae) from a sequence of Florida Neogene localities between 9.5 and 4.5 Ma. These data are used to interpret ancient diets and test previous hypotheses of terrestrial/aquatic adaptations of two sympatric rhinos, Aphelops and Teleoceras. The long-limbed, shorter-crowned Aphelops traditionally has been reconstructed as an open-country browser (similar to the modern black rhino), whereas short-limbed, higher-crowned Teleoceras traditionally has been reconstructed as an amphibious grazer (similar to the modern hippo). Between about 9. 5 and 7 Ma the δ13C values (all <−11.0‰) from Florida Aphelops and Teleoceras indicate that both rhinos were feeding on C3 plants. This diet probably included a combination of browse and C3 grasses, although the exact proportions for each genus cannot be distinguished isotopically. In contrast, after the late Miocene global carbon shift as represented at 4.5 Ma in Florida, Aphelops was a browser (mean δ13C = −11.9‰), whereas Teleoceras was a mixed feeder/C4 grazer (mean δ13C = −7.0‰). Oxygen isotopic values indicate that neither Aphelops nor Teleoceras was principally aquatic. Given these new isotopic data, more plausible modern analogs for these two extinct rhinos are, respectively, the terrestrial browsing black rhino (Diceros bicornis) and the terrestrial grazing white rhino (Ceratotherium simum), which are sympatric today in Africa.