ALBERT

Description: Knowing the structure and branching order of the evolutionary tree is essential to many studies of the evolutionary process and the history of life. Most attempts to reconstruct evolutionary trees are based on rectangular matrices, in which coded states are assigned for each character and each taxon under study. Everyone who has tried to infer the pattern of evolution from such character-taxon matrices is confronted with a great deal of “noise” and uncertainty. Often, there are multiple “most parsimonious trees” (those requiring the fewest evolutionary steps), which often differ significantly in topology; and many nodes in such trees are poorly supported; that is, there are contradictions and inconsistencies in the data. Some of this noise arises for reasons well known to phylogeneticists. Character states may arise multiple times, evolve in parallel, or reverse (homoplasy); taxa vary insufficiently among themselves; and diversification may be so rapid that data are insufficient to detect the order of branching. Polytomies are regarded as a nuisance rather than as real information. Characters may be coded inappropriately, so that there are too many redundancies, inapplicable character states, and multistate characters, as well as dependence among characters. Moreover, it is highly debatable whether evolution is parsimonious, and there are conflicts about how to establish the polarity of characters (primitive vs. derived). (For reviews and discussion see Sober 1988; Huelsenbeck and Crandall 1997.)

Description: Two intervals of the Phanerozoic stand out as times of biosphere-scale revolution in the sense that biogeochemical cycles came under increased control by organisms. These are the early Paleozoic (extending from just before the Cambrian to the Middle Ordovician, a duration of about 100 m.y.), characterized by the appearance of predators, burrowers, and mineralized skeletons, and by the subsequent diversification of planktonic animals and suspension-feeders; and the later Mesozoic (latest Triassic to mid-Cretaceous, a duration of somewhat more than 100 m.y.), marked by a great diversification of predators and burrowers and by the rise of mineralized planktonic protists. This paper explores the economic conditions that make such revolutions possible.I argue that opportunities for innovation and diversification are enhanced when raw materials and energy are supplied at increasing rates, or when organisms gain greater access to these commodities through rising temperatures and higher metabolic rates. Greater per capita availability of resources enables populations to grow; lessens or alters ecological constraints on functional improvement; makes possible the evolution of high metabolic rates (large incomes), which in turn permit improvement in each of several otherwise incompatible functions; and favors the establishment and spread of daughter species arising through founder speciation. Reductions in productivity reinforce adaptational constraints and may bring about extinctions.Massive submarine volcanism, together with its associated phenomena of warming, sea-level rise, and widening of warm-weather zones, is proposed to be the chief extrinsic trigger for the Phanerozoic revolutions. The later Mesozoic was characterized by continental rifting, which accompanied massive submarine volcanic eruptions that produced large quantities of nutrients and carbon dioxide. This activity began in the Late Triassic and peaked in the mid- to Late Cretaceous. The Early Cambrian was also a time of rifting and may likewise have been marked by large-scale submarine volcanism. Continental and explosive volcanism, weathering, and upwelling are other potential means for increasing evolutionary opportunity, but their effects are either local or linked directly or indirectly with cooling. Intense chemical weathering in the Early Cambrian, however, may have contributed to the early Paleozoic revolution.The extrinsic stimulus was greatly amplified through positive feedback by the evolution of higher metabolic rates and other means for acquiring, trading, retaining, and recycling resources more rapidly and from a wider range of environments. Because these novelties usually require a high and predictable supply of resources, their evolution is more likely when extrinsically controlled supplies increase rather than when per capita availability is low.In the view adopted here, the microevolutionary and microeconomic market forces of competition and natural selection operate against a backdrop of macroeconomic supply and demand. Resources are under both extrinsic and intrinsic control. Positive and negative feedbacks link processes at the micro- and macroeconomic levels. This view complements the genealogical and hierarchical conception of evolution by emphasizing that the pattern of descent is influenced by resources and by market forces operating at all scales of space and time.

Description: The intensity of drilling predation was studied on samples of fossil and Recent species of Turritella, a soft-bottom mesogastropod mollusc. Our data and records in the literature show that the frequency of drilling has remained about the same from the Eocene to the present. There may have been less predation by drilling during the Late Cretaceous. Among living Turritella, there is a sharp increase in intensity of drilling predation from the temperate zones to the tropics. This latitudinal trend is paralleled by an equatorward increase in number of species of drilling gastropods. Strong spiral ribs of some Eocene, Miocene, and Recent species of Turritella confer protection against drilling, but the mechanism of this immunity remains unclear.

Description: Tertiary and Recent marine gastropods include in their ranks a complement of mechanically sturdy forms unknown in earlier epochs. Open coiling, planispiral coiling, and umbilici detract from shell sturdiness, and were commoner among Paleozoic and Early Mesozoic gastropods than among younger forms. Strong external sculpture, narrow elongate apertures, and apertural dentition promote resistance to crushing predation and are primarily associated with post-Jurassic mesogastropods, neogastropods, and neritaceans. The ability to remodel the interior of the shell, developed primarily in gastropods with a non-nacreous shell structure, has contributed greatly to the acquisition of these antipredatory features.The substantial increase of snail-shell sturdiness beginning in the Early Cretaceous has accompanied, and was perhaps in response to, the evolution of powerful, relatively small, shell-destroying predators such as teleosts, stomatopods, and decapod crustaceans. A simultaneous intensification of grazing, also involving skeletal destruction, brought with it other fundamental changes in benthic community structure in the Late Mesozoic, including a trend toward infaunalization and the disappearance or environmental restriction of sessile animals which cannot reattach once they are dislodged. The rise and diversification of angiosperms and the animals dependent on them for food coincides with these and other Mesozoic events in the marine benthos and plankton.The new predators and prey which evolved in conjunction with the Mesozoic reorganization persisted through episodes of extinction and biological crisis. Possibly, continental breakup and the wide extent of climatic belts during the Late Mesozoic contributed to the conditions favorable to the evolution of skeleton-destroying consumers. This tendency may have been exaggerated by an increase in shelled food supply resulting from the occupation of new adaptive zones by infaunal bivalves and by shell-inhabiting hermit crabs.Marine communities have not remained in equilibrium over their entire geological history. Biotic revolutions made certain modes of life obsolete and resulted in other adaptive zones becoming newly occupied.

Description: In the Recent biota, species of the hipponicid gastropod genus Sabia that excavate characteristic pits on the outer surfaces of shells of reef-dwelling gastropods and hermit crabs occur only in the tropical Indo-West Pacific region and in adjacent warm-temperate parts of Japan and Australia. I report the discovery of Sabia pits in reef-associated gastropod shells from the Cercado (late Miocene) and Gurabo (early Pliocene) Formations of the Dominican Republic. The likely culprit was Hipponix otiosa Pilsbry and Johnson, 1917, a species here reassigned to Sabia Gray, 1840. Pliocene extinction, which was far more severe in the Caribbean and elsewhere in the western Atlantic than in the Indo-West Pacific, selectively eliminated Sabia and its commensalism from Atlantic reef ecosystems. This case is one of several examples indicating the vulnerability of specialized associations to extinction-causing disturbances.