A quantitative study was made of the orientation of corals and stromatoporoids in reef core, flank, and interreef rocks representing three geological periods at eight sites, including the Florida Keys (Pleistocene), Ridgemount, Ontario (Devonian), and Pekin, New York, Maumee and Rockford, Ohio, and Bluffton and Delphi, Indiana (Silurian). Orientation, width, and height were measured for each fossil as seen in outcrop.

Fossils in Pleistocene and Silurian reef core facies have pronounced upward orientation, suggesting that most fossils are in growth location, or that the reefs were moved to their present location without appreciable tilting. Silurian distal flank facies have approximately random coral orientations, while the proximal (near-core) Silurian flank facies at Rockford has coral orientations with some upward bias. Coral width is greater than or equal to coral height (on outcrop) for 79% of the corals at all flank sites, and for 80% of the corals at the interreef site, an indicator of transport when taken with orientation data. This study permits reef facies differentiation and illustrates that fossil orientation is a useful technique for studying reefs.

A two meter stratigraphic interval within the Chowan River Formation of North Carolina contains a thicket of branching coral, Septastrea crassa (Holmes), associated with a diverse macrofaunal assemblage. The thicket modified a local shelf habitat by providing protection and feeding opportunities for certain vagrant epifaunal species. Faunal adjustments wrought by the thicket and thicket growth represent autogenic succession. Coral growth rates and preservation suggest a time span of about 100–300 years for thicket development.

Bottom shoaling, associated with a eustatic regression, caused movement of a depth controlled environmental gradient during thicket growth. As the habitat changed, a plane bottom macrofaunal assemblage replaced the thicket assemblage by reordering abundances of intergradational species and introducing a few new species. Faunal density, diversity, trophic structure, and modes of life of component species were altered during replacement.

Observed temporal community changes are best explained as gradual faunal adjustments along a shelf stress gradient. Short term allogenic or autogenic events may temporarily perturb gradual changes. Changes associated with thicket development are interpreted as a brief autogenic perturbation of long term community replacement.

Although Nuculoidea corbuliformis (Hall and Whitfield) is the most widespread Devonian nuculid species in North America, the hinge and internal morphology have not been adequately described. A newly excavated hinge shows the dentition and resilifer to be fundamentally similar to those of other species of Nuculoidea, while the resilifer morphology and shell shape more closely link N. corbuliformis to post-Devonian nuculid species. An internal mold of a probable N. corbuliformis found among Hall's original syntypes (here restudied) shows typical nuculid interior morphology. These new data allow the problematic genus Nuculoidea Williams and Breger to be further clarified.

Comparisons with N. corbuliformis suggest that N. aquisgranensis (Beushausen), N. herzeri (Nettleroth), N. neda (Hall and Whitfield), N. niotica (Hall and Whitfield), N. trigona (Spriestersbach), N. macrorhyncha (Spriestersbach), and N. subtrigona (Simpson) are subjective junior synonyms.

The Protocardiinae is represented by 11 valid species of Protocardia and one species of Nemocardium in the Lower Cretaceous of the Gulf of Mexico. These taxa appeared in the Caribbean Province through a combination of immigration and evolution from the local stock. One species group, Protocardia texana-Protocardia salinaensis-Protocardia subspinigera, developed as geographically and environmentally distinct populations that migrated in space and time. Another group, Protocardia roanokensis-Protocardia prosogyrata-Protocardia nutans-Protocardia denisonensis, differentiated through time by dichotomous branching. These species occupied sand to mud substrates. The coarseness of their shell ornament is positively related to substrate grain size. The geographic and stratigraphic distributions of these species illustrate that diversity is positively correlated with the extent of distribution and that endemism develops during transgression.

As first designated by Böse, the Albian-Cenomanian (Lower Cretaceous-Upper Cretaceous) boundary in northern Mexico and Texas is selected at the base of the ammonite zone of Plesioturrilites brazoensis (Römer). This boundary seems to best agree with boundaries selected for North Africa and Europe, but in North America it may not be the optimum boundary for paleontologists working with foraminiferans.

The marine Bajocian Taberna Formation of west-central Oaxaca consists mainly of shale, intercalated siltstone, and frequent iron concretions with ammonites. This formation overlies the continental Zorrillo Formation and is overlain by the continental to subcontinental Simon and Otatera formations. The best outcrops are in the area of Mixtepec and Diquiyú-Yutatio.

Two new ammonite biozones are distinguished: Duashnoceras floresi Range Zone (≃ upper Humphriesianum-lower Subfurcatum standard zones), and Parastrenoceras zapotecum Assemblage Zone (≃ Subfurcatum Standard Zone). The biogeographic affinities are principally with the Mediterranean Province, and also with both the East-Pacific Andean and North Cordilleran provinces. A high percentage of species is endemic. The Stephanoceratinae, mainly Duashnoceras, are dominant in the D. floresi Zone, which also includes Subcollina lucretia, Strigoceras (Liroxyites), Stephanoceras, Phaulostephanus, Stephanosphinctes, and Oppelia. Parastrenoceras and Leptosphinctes are dominant in the P. zapotecum Zone, whereas Oppelia and Strigoceras are less abundant.

Stephanosphinctes n. gen., type species S. buitroni n. sp., is intermediate between the Stephanoceratinae and Leptosphinctinae. The species Phaulostephanus burckhardti is also new.

The genus Physaster was erected by Pomel (1883, p. 47) for Holaster inflatus of Agassiz and Desor (1847, p. 28) which d'Orbigny had first (1854, p. 89, Pl. 814, figs. 4, 5) maintained in Holaster but later (1855, p. 171, Pl. 903, figs. 1–8) transferred to Echinospatangus. Physaster inflatus (Agassiz and Desor) is the type species by monotypy. Inflataster Anthula, 1899, is an objective junior synonym derived tautologically from the same type species.

Oligocene landscapes of New Mexico were dominated by andesite stratovolcanoes and resurgent domes of ash-flow tuff (ignimbrite) cauldrons (Smith et al., 1985). This pervasive volcanism produced volcanic and volcaniclastic rocks that have been neglected by vertebrate paleontologists, so that, until now, no Oligocene vertebrate fossils have been discovered in New Mexico. This documents the initial results of vertebrate paleontological investigations of Oligocene rocks in New Mexico, a lower jaw of the oromerycid artiodactyl Montanatylopus matthewi, the first Oligocene mammal from the state. In this paper, CM = Carnegie Museum of Natural History and UNM = University of New Mexico.

The genus Merychippus was erected by Leidy (1857), who named as the type species Merychippus insignis. The type specimen of M. insignis is an immature and incomplete maxilla containing a broken dp2 and a dp3. The type comes from the Bijou Hills of South Dakota, probably from the Barstovian (middle Miocene) Fort Randall Formation of South Bijou Hill in Charles Mix County (Skinner and Taylor, 1967), but possibly from the overlying undifferentiated Ogallala Formation, or possibly from North Bijou Hill in Brule County. Despite this enigmatic type, the species M. insignis has frequently been identified in the fossil record, and the genus Merychippus has grown to include all mesodont horses (Stirton, 1940). Conceptually, the taxon Merychippus is considered a horizontal grade rather than a vertical clade (Simpson, 1945, p. 18). As a horizontal concept, the genus Merychippus derived importance as the ancestral group for the many Mio-Pliocene lineages of hypsodont horses. Today, as horse classification is remodeled along cladistic lines, the taxon Merychippus derives importance from its early naming. Several distinctive horse clades extend upward from a middle Miocene radiation (Stirton, 1940; Quinn, 1955). If M. insignis can be placed within one of these clades, then it is likely that the clade will bear the generic nomen Merychippus because of the antiquity of the name.