The Mesozoic-Cenozoic coral Order Scleractinia has been suggested to have originated or evolved (1) by direct descent from the Paleozoic Order Rugosa or (2) by the development of a skeleton in members of one of the anemone groups that probably have existed throughout Phanerozoic time. In spite of much work on the subject, advocates of the direct descent hypothesis have failed to find convincing evidence of this relationship. Critical points are:

(1) Rugosan septal insertion is serial; Scleractinian insertion is cyclic; no intermediate stages have been demonstrated. Apparent intermediates are Scleractinia having bilateral cyclic insertion or teratological Rugosa.

(2) There is convincing evidence that the skeletons of many Rugosa were calcitic and none are known to be or to have been aragonitic. In contrast, the skeletons of all living Scleractinia are aragonitic and there is evidence that fossil Scleractinia were aragonitic also. The mineralogic difference is almost certainly due to intrinsic biologic factors.

(3) No early Triassic corals of either group are known. This fact is not compelling (by itself) but is important in connection with points 1 and 2, because, given direct descent, both changes took place during this only stage in the history of the two groups in which there are no known corals.

Previous descriptions and interpretations of the Cycadeoidea pollen organ are followed by a new interpretation based upon its presumed neotenous condition. The sexually mature pollen organ represents a juvenile morphological condition that persisted into the adult stage of the organism and was inherited ultimately from a seed fern ancestor. The neotenous organ is considered to have come into existence abruptly and the altered morphology to have been achieved without an intervening series of intermediates. Abrupt establishment of higher taxa by heterochrony constitutes a mechanism capable of decoupling microevolutionary processes from macrevolutionary differences and poses a distinct challenge to current evolutionary theory.

Cameral water in the shell of the cephalopod Nautilus physically supports each septum while it is being formed; it also provides a reservoir of liquid ballast which is extracted to balance the increase in weight in seawater due to shell and tissue growth. It is not used as an aid to vertical movement. In adults, the sole function of cameral water is ballast in order to maintain Nautilus' slight weight in seawater.

Barnacles living along rocky shores provide the classic example of competitive dominance in the marine ecosystem: by means of firm attachment and rapid growth, balanoid barnacles commonly undercut and overgrow the genus Chthamalus, which is thereby restricted to the upper fringe of the intertidal zone, where balanoids are physiologically incapable of living. Today, after perhaps less than 50 Myr of evolution, balanoid barnacles are in the midst of rampant adaptive radiation, being represented by about 273 species, of which about half are free-living species of intertidal or shallow subtidal habitats. Chthamaloid barnacles, in contrast, are on the decline, having originated at least 70 Myr ago but today comprising only about 53 living species, approximately 40 of which occupy the uppermost intertidal. The remainder persist as localized, relict, and often disjunct populations. Through competitive exclusion, balanoid barnacles have apparently caused the ecological restriction and decline of the chthamaloids. The balanoids have an advanced feeding mechanism, but the most important adaptive breakthrough leading to their competitive success was probably the origin of a tubiferous wall structure, which affords rapid skeletal growth for the efficient monopolization of free space and for the destruction of chthamaloids.

Geographic distribution, species duration, and population size of 41 bivalve species which coexisted during the uppermost biozone (Sciponoceras gracile zone) of the Cenomanian were measured. Average species duration and correlation between geographic distribution, species duration, and population size were computed for five groups: total, infaunal, epifaunal, cemented epifaunal, and uncemented epifaunal bivalves.

Average species duration for all bivalves is less than 2 Myr. Infaunal bivalves averaged slightly higher, epifaunal slightly lower. Positive correlation was measured between species duration and geographic distribution for all five groups and statistical significance of the relationships was demonstrated for all but infaunal forms. In general no correlation was found between species duration and population size, and between population size and geographic distribution with the following exceptions: species duration and population size were significantly correlated for infaunal bivalves and uncemented epifaunal bivalves, and population size and geographic distribution were correlated for uncemented bivalves. Because these 41 fossil species coexisted at the same time and were distributed in the same space, differences in the relationships of species duration, geographic distribution and population among the various life habits indicate differences in ecological strategy and the evolutionary consequences of that difference.

The Lower Tertiary Gulf Coast was subjected to repeated transgressive-regressive cycles of varying rate and extent which had a marked effect on species longevities. In some neogastropods dispersal and geographic distribution played important roles in species longevities. Species with planktic larval stages that inhabited broad areas of the Gulf Coast could maintain their distributions even during regressive phases when delta building was strong. Wide distributions, free gene flow, and resistance to isolation gave planktic species an evolutionary stability that resulted in greater species longevity. Species with nonplanktic development could attain wide geographic ranges when barriers were minimized, but they were unable to maintain their distributions in the face of regressive progradation. Thus their populations were isolated, and extinction and speciation accelerated, giving them lesser evolutionary longevity. Although planktic volutids tend to be widespread, planktic fasciolariids and mitrids were often restricted in distribution and therefore probably stenotopic. If dispersal and environmental tolerance are considered as separate forces, they seem to act in combination to produce very long, very short or intermediate species longevities.

The Upper Jurassic Morrison Formation has yielded one of the richest dinosaur faunas of the world. Morrison sediments are distributed over more than a million square kilometers in the western United States and represent a mosaic of riverine, lacustrine and floodplain environments developed on a vast alluvial plain nourished by debris from the ancestral Rocky Mountains. Plant productivity must have been reasonably high to support abundant large-bodied herbivores, but the absence of coals, scarcity of small aquatic vertebrates, the abundance of oxidized sediments, and presence of calcretes lead us to believe that water was periodically in short supply. A strongly seasonal climate may have necessitated annual large-scale movements of large herbivores, accounting in part for their remarkably broad and uniform geographic distribution. Dinosaur diversity is lower in the Morrison than in the Late Cretaceous, and taphonomic alteration is higher. Massed accumulations of thousands of bones are characteristic of the Morrison. Morrison dinosaurs were not confined to specific depositional environments but were distributed across the complete spectrum of available habitats, from lakes to dry floodplains; this type of distribution is similar to that of large terrestrial mammals such as elephants and rhinos and is different from that of hippos and crocodiles. Common Morrison taxa were Camarasaurus, Apatosaurus, Diplodocus, Allosaurus and Stegosaurus; these genera probably constituted a true dinosaur community. Stegosaurus may have been partially segregated from the other genera, and Camptosaurus more strongly so. Camarasaurus and Diplodocus were gregarious, with juveniles and subadults of the former particularly common; Apatosaurus was less abundant and more solitary in its habits. Juveniles and subadults are known for a number of dinosaurs.