We offer an alternative interpretation of the Kingdom Vendobionta as a monophyletic sister group to the Eumetazoa. We hypothesize that the Vendobionta are cnidarian-like organisms that lacked cnidae. Cnidarians are held to have arisen by acquisition of cnidae by symbiosis with a microsporidian. Our analysis differs from existing interpretations of the Ediacaran fossils as ancestors of extant cnidarians in that we do not regard any of these forms as either polypoid or medusoid. This interpretation requires the erection of a new metazoan phylum, the Vendobionta.

The same three subtypes of derived multiserial Hunter-Schreger bands are found in the incisor enamel of African phiomorph rodents from the late Eocene-early Oligocene and the oldest South American Caviomorpha from the Deseadan (late Oligocene). The synapomorphies contained therein, especially arrangement and orientation of interprismatic matrix, make an African origin of the Caviomorpha very probable. A North American origin of the Caviomorpha is thus rejected, as only primitive pauciserial Hunter-Schreger bands have been observed in possible ischyromyoid caviomorph ancestors. A multiserial Schmelzmuster apparently never evolved in the North American rodent fauna.

Benthic foraminifera have attained gigantic sizes many times throughout geologic history. To understand the selective processes underlying foraminiferal gigantism, we used a computer-based, three-dimension, solid finite element model to analyze the mechanical strength of different discoid forms, including two of the largest living foraminifera—Cycloclypeus carpenteri Brady and Marginopora vertebralis Quoy and Gaimard. These two species enlarge by cyclic, planar growth, resulting in slightly biconvex (C. carpenteri) and slightly biconcave (M. vertebralis) forms. As the tests enlarge, the maximum stresses induced by a standard bending moment decrease in both species. Such stress-reducing growth plans apparently allow growth to extraordinarily large sizes and allow volume to increase with minimal lowering of the surface-to-volume ratio, a critical functional factor in ensuring increased surface area for photosynthesis by endosymbionts contained within the tests and for chemical exchange by the foraminifera with the external environment. Of the two species, M. vertebralis has a stronger construction and a lower surface-to-volume ratio. These features indicate optimal constructional solutions to environmental constraints (degree of turbulence and light availability) in their disparate natural habitats: M. vertebralis in the mechanically rigorous inter- to subtidal, and C. carpenteri on the light-minimal and hydraulically quieter, deeper sea beds. We conclude that morphological design in larger foraminifera is constrained by a biomechanical factor, and that gigantism and biomechanical optimization are demonstrably related.

Arm autotomy was induced in a living specimen of Metacrinus rotundus (Echinodermata: Crinoidea). An arm was autotomized at a ligamentary articulation known as a cryptosyzygy, following incision by scissors distal to the break point. Although sessile stalked crinoids cannot entirely escape from a predatory attack by arm autotomy and they do not have an active defense, arm autotomy at cryptosyzygies reduces damage and arm loss by effective distribution, and by minimizing trauma and facilitating subsequent regeneration.

The paradigmatic distribution of cryptosyzygies in which arm loss is set at a minimum, compared with the actual distribution, shows that these two patterns are similar and that actual specimens successfully reduce arm loss by the effective distribution of cryptosyzygies. The crinoid branching pattern also affects arm loss, and two different paradigms are discussed: anti-predatory and harvesting. Arm branching patterns of various isocrinids have tended toward the anti-predatory configuration from the Jurassic to the Recent, suggesting that the isocrinids have coped with increased predation. Shallow-water comatulids generally adopt the anti-predatory paradigm in their branching pattern, whereas many deep-water, stalked crinoids adopt a harvesting paradigm, reflecting that shallow-water comatulids receive more predatory attacks than do deep-water crinoids.

Specimens of Nautilus species caught in the wild show a marked increase in oxygen isotopic composition between embryonic and postembryonic septa. The significance of this increase in terms of the early life history of Nautilus has been unclear. To help explain this pattern, we analyzed the isotopic composition of the septa of three specimens of Nautilus belauensis raised in aquariums under controlled temperature conditions. Our results indicate that both embryonic and postembryonic septa are secreted with the same temperature-dependent fractionation of aragonite relative to water as that of other aragonite-secreting molluscs (Grossman and Ku 1986). The δ18O values of the septa thus provide a reliable means of determining the water temperature in which the septa form. Calculated temperatures based on oxygen isotopic data from specimens caught in the wild reveal that embryonic development occurs at 22°-24° corresponding to a depth of 100-200 m depending on the location. The increase in δ18O in postembryonic septa reflects a migration into colder, deeper water after hatching. In Cretaceous nautilids, a systematic shift in δ18O is not present, indicating that these animals probably did not change their habitat after hatching. This is consistent with the likelihood that they lived in shallower environments than that of modern Nautilus.

The Plio-Pleistocene planktic foraminiferal sequence of the Globorotalia (Globoconella) puncticulata-inflata clade in Deep Sea Drilling Project Site 588, dated at 4.36 Ma to 0.05 Ma, records the branching history of the G. inflata lineage from the ancestral G. puncticulata lineage. The gradational nature of the divergence and the enormous morphological variability inherent in the G. inflata lineage have elicited different views on taxonomy and phylogeny of this clade. A pattern recognition technique, soft independent modeling of class analog (SIMCA), was used as an objective quantitative stratophenetic methodology to reconstruct the phylogenetic history.

Typical specimens of two species, G. puncticulata and G. inflata, were identified from a stratigraphic level dated at 2.76 Ma. Principal component models were built to characterize the morphometric patterns of the two morphotypes using SIMCA. The Globoconella specimens of the next lower and higher adjacent stratigraphic levels were evaluated against the models and classified into one of the two morphotypes. The newly classified specimens were then used to build new models for further tracing of lineages in lower and upper sections, respectively. Progression of such training and classification procedures through stratigraphic intervals resulted in a reconstruction of the evolutionary patterns of the two lineages. Cladogenesis gave rise to the descendant lineage, G. inflata, at about 3.5 Ma. The two co-existing species, G. inflata and G. puncticulata, differ only in size and show similarity in most characters at the beginning of their divergence. Other characters began to diverge later, at various rates. The gradients between planktic and benthic foraminiferal δ18O values show a continuous increase during the late Pliocene. The succession from G. puncticulata to G. inflata during the same time correlates with the progressively increased vertical stratification in temperature of surface waters. Globorotalia puncticulata became extinct at 2.35 Ma when the temperature gradient further increased, corresponding to the onset of extensive glaciation in the Northern Hemisphere.

Allometric analysis of the size-shape relationships in the Pliocene-Pleistocene planktic foraminiferal Globorotalia (Globoconella) puncticulata-inflata plexus reveals several heterochronic modes underlying the morphological evolution of the clade. The ancestral lineage, G. puncticulata, is a peramorphocline, showing a pre-displacement mode of heterochrony between 3.5 Ma and 3.0 Ma and an acceleration mode from 3.0 to 2.7 Ma. A different peramorphosis process, isometric giantism (hypermorphosis), in the ontogeny of the ancestral stocks of Globoconella occurred at about 3.5 Ma and gave rise to the G. inflata lineage. The descendant lineage, G. inflata, appears to have adopted a paedomorphosis trend by delaying the onset of the neanic stage in ontogeny during the period of 3.5 to 2.35 Ma, resulting in a series of transposition allometries. During the interval of 2.4 to 1.73 Ma, the allometries shifted to the opposite direction, signifying a pre-displacement trend. Evolutionary stasis marks the evolution during 1.73 to 0.25 Ma. Neoteny concluded the final evolutionary stage of the G. inflata lineage during the latest Quaternary (0.26 to 0.05 Ma). The enormous plasticity and fluctuations in morphology of G. inflata are attributed to the highly positive allometric growth during the ontogeny and the wide-range transposing allometries in the phyletic history. The major changes in heterochronic mode coincide with paleoceanographic events, suggesting that the morphological evolution in the Globoconella clade has been modulated by changes in paleoceanographic conditions.