Analysis of stratigraphically separated collections of Late Ordovician fossilized marine invertebrates suggests that our understanding of faunal changes through time may be enhanced by considering them in terms of a successional framework. The faunal succession in the Nicolet River Valley, St. Lawrence Lowlands, Quebec, began with the initial colonization of an offshore barren mud by two or three presumably opportunistic deposit-feeding species. Diversity, both of species and of trophic types, increased gradually, peaked, and then decreased slightly with some faunal shifts, especially in the numerical predominance of the epifaunal element. A three-fold repetition of this quiet-water succession seems in each case to have been terminated by an external physical perturbation. There also appears to be a second, separate successional sequence which became localized on a somewhat coarser-grained and perhaps less stable substratum as the paleoshoreline was approached, due to sediment filling of the basin.

Succession involves changes in a community through time, whether internally or externally controlled. As succession progresses, niche specialization, species diversity (variety and equitability), complexity of food chains, and pattern diversity increase; net production and species growth rate decrease. We apply the succession concept to three types of ancient community sequences: 1) fossil reefs (Ordovician—Cretaceous in age), 2) short-term successions occurring through thin stratigraphic intervals, and 3) long-term successions occurring through thicker stratigraphic intervals. Ancient reefs show four vertical zones: (1) a basal stabilization zone (autogenic), 2) the overlying colonization zone (autogenic, pioneer stage), 3) the diversification zone, the bulk of most reefs (diversification culminating in climax), and 4) the uppermost domination zone. The first three zones represent autogenic succession but the final stage may involve allogenic succession. Short-term succession usually occurs where periodic allogenic catastrophes wipe out the community which is rebuilt through autogenic succession. Opportunistic pioneer species are important and in our examples (Ordovician, Silurian, and Cretaceous) are species which pave soft substrata. Paleozoic strophomenid brachiopods filled this role, and inoceramid pelecypods served the function in the Mesozoic. The succession which begins with opportunists progresses to a climax community of equilibrists. Repetition of catastrophe-succession couplets produces a cyclic stratigraphic record. Long-term successions are recorded in thicker stratigraphic sequences, and are of two types: 1) autogenic succession in unchanging physical environments and 2) allogenic succession in changing physical environments. Our examples of these are from the Devonian Haragan-Bois D'Arc formations of Oklahoma and the Lime Creek Formation of Iowa. This type of succession represents a temporal-spatial mosaic. The Haragan data (unchanging environments) indicate characteristic, intergrading, and ubiquitous species in the brachiopod communities. Most ubiquitous species in the pioneer community were eurytopic opportunists. The Lime Creek data allows testing of the prediction that environmental changes cause regression to an earlier succession stage. The brachiopod communities after environmental changes have more ubiquitous and intergrading eurytopic species. These represent an earlier stage in the succession.

Quantitative systems for describing naticid borehole position in bivalve and gastropod prey are presented. Pleistocene nassariid prey were bored at 53% of the distance up the shell and 8° to the right of the columella. A similar stereotyped position was found for Recent prey. The longitudinal shell axis and the aperture of the gastropod shell are proposed as primary cues in orienting prey for boring.

Studies of the internal anatomy of Mississippian camerate crinoids have revealed the presence and plan of groove and ridge networks here interpreted as evidence of former nervous systems in these animals. The inner thecal surfaces of hollow specimens and surfaces of internal chert molds possess radiating networks of grooves and ridges in both the dorsal cup and tegmen that resemble the plan of the aboral and hyponeural nervous systems, respectively, of modern crinoids. The aboral network of camerates radiates from the basal region of the dorsal cup at the point of stem attachment and provides one radially positioned nerve trunk per arm. In addition to the radial trunks, branches are present in each of the five interrays; the pattern in the CD (i.e., posterior) interray is different from the others. Two ring commissures interconnect the radial and interradial nerve trunks. The hyponeural nerve network in the tegmen originates from a ring commissure located near the upper part of the tegmen. From the ring commissure radiate radial and interradial nerve trunks that divide to produce two nerve trunks per arm as in modern crinoids. Raised ridges that define the hyponeural nerve network on the inner tegminal surface are separate from impressions representing the water vascular network.

By analogy to living crinoids, the aboral nerve center in camerates was located in the base of the dorsal cup. The radial portion of the aboral nervous system is judged to have functioned as the main motor network in camerates, innervating arm flexor muscles, pinnules, and arm epidermis, thus controlling the “display” of arms to form an effective filtration baffle. The interradial aboral nerves may have been sensory nerves which were part of an active balance system in these stalked echinoderms. The hyponeural system in camerates, as in living forms, probably acted as a sensory system by innervation of the lateral walls of the tube feet and arms. A third system, the ectoneural system, which lines the ciliated food grooves and gut of living crinoids has not been detected in fossil camerates; however, due to its functional significance, its presence in camerates was very probable.

Geological data show that high Andean habitats have been available for plant colonization only since the end of the Tertiary. The manner in which plant species moved into these habitats, the times during which, and the methods by which they differentiated during the Pleistocene varied altitudinally and latitudinally along the tropical Andes. The process of speciation in all areas, however, was the same as that in temperate environments, namely, geographic isolation and subsequent divergence. Except on the Altiplano, most plant species expanded their ranges during glacial periods when vegetation zones were lowered. In the northern paramos at elevations above treeline, colonization was greatest during glacial periods but has always occurred in a manner similar to that of oceanic islands. At lower elevations in the northern Andes, and along the Eastern Cordillera, direct migration was possible in glacial times because of increased contiguity of upper montane forest habitats. On the upper slopes of the west coast of Perú, glacial-age plant migrations were fostered more by changes in precipitation than by the lowering of vegetation belts. In all of these areas, interglacial periods were, and are, times of isolation and differentiation. Across the Altiplano in contrast, glacial periods were times of population fragmentation accompanied by differentiation and/or speciation.

The cranial structure of anteosaurid and many tapinocephalid dinocephalians became modified in a manner consistent with Geist's hypothesis that they used their heads for pushing and ramming during intraspecific combat. These modifications are most pronounced in certain tapinocephalids by the evolution of a strong dorsal head shield supported by a massive arch network suitable for receiving and supporting blows delivered to the dorsal surface of the head. The position of the occipital condyle reduced the torque created by such blows at the craniocervical joint. Evidence also indicates that the head was reoriented into a position suitable for butting. The cranial architecture displayed by dinocephalians suspected of headbutting differs from that of living mammalian rammers. The differences can be directly attributed to the modification, in the former, of a reptilian skull with its relatively unexpanded braincase into a ramming instrument.

Amecystis Ulrich and Kirk is a rhombless rhombiferan cystoid exhibiting adaptation to an active mode of life in the bilaterally symmetrical, dorso-ventrally compressed theca and to an active mode of respiration suggested by the lack of pore rhombs and greatly enlarged periproct. Like other members of the Pleurocystitidae, Amecystis probably wriggled along the bottom, but may have adopted a temporarily sessile habit by pushing the distal stele into the substrate or by grasping. Evolution of the genus began in the Middle Ordovician, probably as a development from Pleurocystites. General trends in the stratigraphic succession of recognized morphospecies: A. raymondi Parsley, A. woodi n.sp., and A. laevis (Raymond) show a reduction in angularity of thecal outline and obsolescence of surface features on the thecal plates. The use of the periproct as a pumping organ in respiration is regarded as an advanced trend that was probably utilized by many rhomb-bearing cystoids as an accessory respiratory mode; alone, it proved to be an unsuccessful adaptation in Amecystis.

Lysorophus, a serpentiform, nearly limbless, aquatic Paleozoic amphibian was described in detail by Sollas in 1920. Although Sollas did not discuss cranial kinesis, his original reconstructions suggest that Lysorophus had an unusually kinetic skull for an amphibian. We have reexamined the skull of Lysorophus and find that kinesis, if present, was slight. The maxillae, premaxillae, and vomers might have moved in limited protraction and retraction, with the premaxillae rotating about their contacts with the nasals. There is a possibility of small medio-lateral movements of the lacrimal and maxilla as a unit at the lacrimal-prefrontal joint. The skull of Lysorophus shows many features convergent with the skulls of burrowing reptiles, such as amphisbaenians. Modifications in the skull of Lysorophus from a more primitive tetrapod condition seem associated with burrowng in a soft substratum rather than with kinesis per se.