In the dozen years since Alvarez et al. (1980) proposed their argument for dinosaur (and other) extinctions, lengthy debate has provided no consensus and the issue remains strongly polarized. The only test that has been proposed, that of additional fieldwork that sought to fill in the “gap” at the top of the Hell Creek Formation, recently has been conducted by Sheehan et al. (1991). Although the analysis found no indication of a gradual decline through the bulk of the formation, it did not produce the distribution Alvarez sought, a random distribution of remains clear through to the iridium. A second test based on the differing taphonomic predictions of catastrophic and noncatastrophic extinctions, and a comparison with the distribution of remains in the uppermost part of the formation, gives some credence to the latter and places considerable doubt on the former.

A complete morphologic intergradation from biperforate to multiperforate specimens of Nephrolithus frequens Górka (1957) occurs in the uppermost Maastrichtian chalk at southern high-latitude ODP Holes 750A (Kerguelen Plateau, southern Indian Ocean) and 690C (Maud Rise, Weddell Sea). Previous workers have assigned taxonomic importance to the number of pores of the central area. Two subspecies, N. frequens subsp. frequens and N. frequens subsp. miniporus, were recently differentiated (Pospichal and Wise, 1990) based on this character (four or more pores and two pores, respectively). The observation of specimens of Nephrolithus frequens with three pores in the central area indicates that there is no “natural” breaking point in a progression from two to numerous pores and that specimens of N. frequens with different pore numbers should be considered morphotypes of a single species exhibiting a high intraspecific variability. In addition, our observations using the scanning electron microscope and light microscope illustrate that in well-preserved specimens each pore in the central area is surrounded by two cycles of elements. The margin consists of two cycles, with the elements of the inner cycle extending proximally about twice as far as the elements of the outer cycle.

Microforaminiferal linings assigned to 10 known genera have been recovered from Early Devonian (Lochkovian to Late Emsian) limestones from Victoria, New South Wales, and Queensland. These organic linings have been identified by comparison with normal-sized agglutinated foraminiferan genera known to occur in the associated sediments. Microforaminiferal linings with smooth walls and reticulate sculptured walls were present and the possible implications of these (diagenetic, relict structure, naked homeomorphs, or processing artifact) are discussed. Evidence is presented that Ordovicina may have a bilamellar organic wall lining.

Anthaspidellid sponges are reported from the La Laja Formation in the Chica de Zonda Range in the Precordillera Oriental, Argentina. These are generically unidentifiable fragments of trabs and more or less well-defined dendroclone spicules. They occur as skeletal elements in small transported fragments and are the only Cambrian occurrence of anthaspidellids known thus far from South America.

Walcott (1920) proposed to include an array of dissociated spicules, including triradiate prodiaenes, hexactines, and probable monactine spicules, in the genus Kiwetinokia. Assemblages tentatively identified as Kiwetinokia utahensis? Walcott, 1920, are reported from the Estancia San Martin Formation, of latest Early Cambrian and early Middle Cambrian age from San Isidro Gulch near Mendoza. Similar spicule assemblages occur in the La Laja Formation from the Chica de Zonda Range, in the Precordillera Oriental near San Juan, and in the Los Sombreros Formation in the Tontal Range of the Precordillera Occidental.

Sclerites of the sponge-like Chancelloria eros Walcott, 1920, are described from the upper Lower to lower Middle Cambrian La Laja Formation. Chancelloria sclerites are also reported here from rocks of the Middle Cambrian Glossopleura Zone in the San Isidro Formation in Empozada Gulch in the San Isidro area of the Precordillera Austral, west of Mendoza, in Mendoza Province. Sponges and chancelloriids from the Cambrian of Argentina are known basically from dissociated skeletal elements.

Several specimens of the small hexactinellid, Cyathophycus mackenziensis n. sp., were collected from pale brown, shaly mudstone of the Road River Formation. The sponges are of Wenlock age and were collected from near Avalanche Lake, Mackenzie Mountains, Northwest Territories, Canada. The small, steeply obconical sponges have skeletons in crudely ranked quadrules to at least third-order, with first-order openings generally 2 mm high and 1 mm wide. Successive orders decrease in stages approximately half that of larger elements. A moderately irregular dermal(?) layer with circular parietal gaps is suggested in some specimens. The new species is consistently finer textured than either the type species Cyathophycus reticulatus Walcott, 1879, or the later described Cyathophycus quebecensis Dawson, 1889.

The enigmatic tabulate genus Palaeacis is composed primarily of species with wedge-shaped coralla. Palaeacis walcotti Moore and Jeffords, 1945, P. kingi Jeffords, 1955, and P. cf. P. walcotti, described below from the Morrowan (Pennsylvanian) Golf Course Formation of the Ardmore Basin, south-central Oklahoma, represent a distinctive morphogroup characterized by a discoid corallum. Discoid Palaeacis ranges from the Morrowan to the Missourian and, so far, is known only from the mid-continent region of North America. The discoid shape, combined with concentric skeletal accretion, large corallite diameters, complex calice floors, and porous skeleton suggest, based on comparisons with the functional morphology of recent scleractinians, that these corals were well suited to an auto-mobile (vagile) life strategy, much as are many Recent fungiid corals. Discoid Palaeacis inhabited environments with muddy or sandy, unconsolidated substrates and was associated with low-diversity, nonencrusting faunas. This association is consistent with an auto-mobile life strategy. Auto-mobility in Palaeacis would represent the first such reported occurrence in the Tabulata, and the first in Paleozoic colonial corals of all types.

Bimuropora dendroidea, previously assigned to other genera, is described from Tennessee and B. winchelli is reported from Nevada. The occurrence of B. winchelli in Nevada extends the geographic range of the Middle Ordovician trepostome genus Bimuropora in North America. These two species share many derived characteristics with the halloporids, including a similar growth pattern and fluted zooecial walls in the endozone. This strengthens the hypothesis that the bimuroporids are a sister group to the halloporids. Sonninopora, a monospecific genus, contains these same features, and because of the presence of acanthostyles it is removed from the family Halloporidae and assigned to the family Bimuroporidae.

Colonies of the runner-like bryozoans Corynotrypa delicatula (James) and C. inflata (Hall) are common encrusters of Middle and Upper Ordovician shells and hardgrounds, especially in Cincinnatian deposits. The simplicity of their zooids contrasts with complexities in the dynamics of colonial organization. Both species have uniserial branches that bifurcate at intervals and, in addition, give rise periodically to lateral ramifications. Although angles of bifurcation and lateral ramification each average about 80°, bifurcations and lateral ramifications are fundamentally different modes of branch multiplication. In C. delicatula new lateral branches have conspicuous secondary zones of astogenetic change distinguished by elongation of successively budded zooids. Unlike bifurcations, the first zooids in lateral branches in Corynotrypa are not linked to the parent branch by a narrow basal canal, and each new lateral branch can be regarded as a distinct subcolonial unit. The ancestrula, described here for the first time in an Ordovician species of Corynotrypa, has a poorly differentiated protoecium and initiates a primary zone of astogenetic change. Colony growth in Corynotrypa was more plastic than in many other bryozoan runners. The systematics of C. delicatula and C. inflata are revised, and a lectotype is chosen for the former species.

The continuous sequence of Maastrichtian to Paleocene sediments exposed in the Sierra Dorotea area in southwestern Santa Cruz (Argentina) contains a rich molluscan fauna with many elements characteristic of the Weddellian Faunistic Province. The presence in this fauna of genera such as Taioma, Heteroterma, Fyfea, Zemacies, and Priscaphander suggests close affinities with faunas of similar age from New Zealand, further supporting the existence of continuous shallow-sea conditions along the southern margin of the Pacific Ocean during the end of the Cretaceous and beginning of the Tertiary. In this paper 25 species are described, of which six are new: Pseudofax costellatus n. sp., Taioma patagonica n. sp., Heteroterma elegans n. sp., Fyfea beui n. sp., Priscaphander sanjosensis n. sp., and Priscaphander bracaccinii n. sp.

Morphometric analysis demonstrates that Strepsidura ficus (Gabb) of Harris (1895), from the lower middle Eocene Reklaw and Queen City Formations of Texas, is specifically distinct from Whitneya ficus Gabb (1864) of the Californian Eocene. Accordingly, the new name Strepsidura harrisi is proposed for the Texas species. Strepsidura s.s. is represented in North America by S. ficus (Gabb), S. harrisi n. sp., and an unnamed species closely related to S. harrisi in the upper Paleocene Sequin Formation of Texas. Strepsidura s.s. apparently originated in the Old World Tethyan Realm during the Paleocene and subsequently spread to North America.

A new Tertiary gastropod genus, Peonza n. gen., is described, along with two new species, P. torquata from southern Argentina and P. benjamina from southern Chile. These muricacean gastropods, of uncertain familial status, occur in the late Eocene San Julián Formation and in the late Oligocene to early Miocene? Monte León Formation, Santa Cruz Province, Argentina. They also were recorded in the (probably) Oligocene Magellanian beds in Tierra del Fuego, Argentina, and in early Miocene deposits of the Tres Montes region in the Chilean Canals. In spite of the small number of specimens, Peonza n. gen. seems to have had a wide geographic and temporal distribution.

Kheraiceras Spath, 1924, is known mainly from macroconchs. Matching of dimorphic pairs at species level is difficult due to the rarity of microconchs and consequent difficulty in establishing contemporaneity. The present study reveals dimorphism within Kheraiceras cosmopolitum (Parona and Bonarelli, 1895) from the lower part of the Callovian Chari Formation, Kutch, India, where microconch closely resembles macroconch except for the size, being about three times smaller and having an aperture characterized by terminal construction. The evolution of Kheralceras from Bullatimorphites Buckman is based on macroconchs only. The discovery of coeval microconch specimens and study of known microconchs within the lineage indicate “parallel” evolution in macro- and microconchs and improves the understanding of evolutionary trends that involve complex heterochronic processes.

Three types of alimentary canals (=midgut) occur in the Annelida and non-trilobite Arthropoda: 1) a sagittal tube with metamerically paired diverticula related to the number of somites; 2) a tube that is constricted slightly between somites; and 3) a simple tubular gut that may taper slightly backwards to the anus. At least two of these three types (1 and 3) occur in the Trilobita. Pterocephalia and Olenoides share the first type with the probable sister taxon to the Trilobita, Naraoia (Nectaspida), and this is probably the plesiomorphic condition for the class. Varying feeding habits may well have made this character homoplastic within each of these groups. The preservation of parts of the alimentary tract in specimens of Upper Cambrian Pterocephalia n. sp. (McKay Group, British Columbia) was probably a function of taphonomic and/or very early diagenetic changes that resulted from the type of food preferred by that trilobite. Other trilobites from the same beds do not have their soft parts preserved. The alimentary structures are preserved in a different fashion from, apparently unattached to, and an order of magnitude larger than genal caeca that occur in this taxon. Thus, genal caeca are regarded as imprints of circulatory rather than alimentary structures.

Energy dispersive analysis of a fragment of preserved alimentary tract of Pterocephalia n. sp. showed the presence of Ca, Si, Al, Fe, P, K, Na, and Cl. These alimentary tracts are composed of a complex mixture of minerals that probably includes clays, detrital quartz, carbonates, phosphates, and oxides or hydroxides. The structure of these dark fillings is microcrystalline. The presence of detrital minerals as part of this mixture would suggest that this trilobite was a deposit feeder.

The genus Otarion Zenker, 1833, first appears in the Wenlock simultaneously with Cyphaspis Burmeister, 1843, as the oldest known species of each occur together in the southern Mackenzie Mountains of the Canadian Northwest Territories. The genera are unambiguous sister groups, a relationship supported most compellingly by a uniquely derived and distinctive pattern of juvenile cephalic spines, shared also with the Carboniferous genus Namuropyge Richter and Richter, 1939. This sister group relationship permits the development of a robust and stratigraphically correlated hypothesis of relationship among the adequately known species of Otarion, Otarion, Cyphaspis, and Namuropyge constitute the tribe Otarionini. The Mississippian genus Dixiphopyge Brezinski, 1988, may also belong to Otarionini. Namuropyge is a paedomorph, likely derived from a Degree Six or Seven meraspid of an older species of uncertain position in the Otarion–Cyphaspis clade.

Three Wenlock species of Otarion occur in stratigraphic succession in a single section in the Mackenzie Mountains. Analysis of morphological change with time, and of sequential ontogenies, suggests that the Silurian history of the genus was dominated by incidents of peramorphosis.

New species are Otarion huddyi, O. beukeboomi, and O. coppinsensis. Otarion brauni Perry and Chatterton, 1979, is revised.

Four specimens of blastozoan and crinozoan echinoderms are described from the Lower Ordovician El Paso Group in the southern Franklin Mountains just north of El Paso, west Texas. Cuniculocystis floweri n. gen. and sp., based on two partial specimens, appears to be a typical rhombiferan in most of its morphologic features except that it lacks pectinirhombs and instead has covered epispires (otherwise known only from Middle Ordovician eocrinoids) opening on most of the thecal plate sutures. The covered epispires in Cuniculocystis indicate that some early rhombiferans had alternate respiratory structures and had not yet standardized on pectinirhombs, a feature previously used as diagnostic for the class Rhombifera. Bockia? elpasoensis n. sp. is a new eocrinoid based on one poorly preserved specimen that has a small ellipsoidal theca and unbranched brachioles attached to a flat-topped spoutlike summit. It is the earliest known questionable representative of this genus and the only one that has been described from North America. Elpasocrinus radiatus n. gen. and sp. is an early cladid inadunate crinoid based on a single well-preserved calyx. It fits into a lineage of early cladids leading to the dendrocrinids and to Carabocrinus. Several additional separate plates, stem segments, and a holdfast of these and other echinoderms are also described.

Species of the late Osagean and early Meramecian advanced cladid crinoid genera (suborder Poteriocrinina) Adinocrinus, Eratocrinus, Lekocrinus n. gen., Linocrinus, Sarocrinus, and Worthenocrinus n. gen. from Illinois, Indiana, Iowa, Kentucky, and Missouri are redescribed and redefined from study of type material and museum collections. These species are considered to have advanced-grade calyces because of the substantial size reduction of the infrabasals and basals relative to the radials. Nomenclatural and systematic changes include the following: 1) Eratocrinus coxanus (Worthen, 1882) is a senior synonym of Zeacrinus keokuk Worthen, 1882; 2) E. commaticus (Miller, 1891a) is a senior synonym of Z. blairi Miller and Gurley, 1895; 3) Lekocrinus n. gen. is described and Scaphiocrinus divaricatus Hall, 1860, and Z. planobrachiatus Meek and Worthen, 1860, are assigned to this new genus; 4) Linocrinus praemorsus (Miller and Gurley, 1890a) is a senior synonym of Poteriocrinus lautus Miller and Gurley, 1896; 5) Sarocrinus kirki n. sp. is described; 6) P. varsoviensis Worthen, 1882, is assigned to Sarocrinus and is a senior synonym of P. tentaculatus Worthen, 1883, P. granilineus Miller and Gurley, 1890a, Z. pocillum Miller, 1891b, S. nitidus Kirk, 1942, and S. plenus Kirk, 1942; 7) P. asperatus Worthen, 1882, is assigned to Sarocrinus; 8) Worthenocrinus n. gen. is described and W. paterus n. sp. is assigned to this new genus; 9) Poteriocrinus iowensis Worthen, 1882, is considered a nomen dubium and placed in incertae sedis.

A previously undocumented echinoid fauna occurs in the terrigenous clastic sedimentary sequence of the Old Pera Beds (Lower Pleistocene) and the overlying Port Morant Formation (Upper Pleistocene) at Old Pera, parish of St. Thomas, southeast Jamaica. The fauna is comprised of complete tests (particularly from two horizons in the Port Morant Formation), test fragments, and radioles, and includes: Cidaris (Tretocidaris) bartletti (A. Agassiz); Eucidaris tribuloides (Lamarck); diadematoid indet. gen. and sp.; Echinometra viridis A. Agassiz; Echinometra? sp.; Clypeaster rosaceus (Linné); a juvenile C. subdepressus? (Gray); mellitid indet. gen. and sp.; clypeasteroid sp.; Schizaster doederleini Chesher; Meoma ventricosa (Lamarck); and irregular indet. gen. and sp. Schizaster doederleini is still extant in the Caribbean, but is not known to live in Jamaican waters. Schizaster doederleini and Meoma ventricosa are the first nominal spatangoids to be reported from the Jamaican Pleistocene.

Forty-seven samples of the Bromide Formation (Simpson Group) of south-central Oklahoma produced a collection of 10,216 conodonts assigned to 46 species. The conodont fauna is dominated by species of Phragmodus and Plectodina and indicates a latest Whiterockian to early Mohawkian (Black Riveran) or late Llandeilian to early Caradocian age. Five new species are named including Ansella crassa, Bryantodina aequalis, Plectodina edentula, Walliserodus declivis, and Pharagmodus ambiguus. The latter species is distinct from Phragmodus flexuosus Moskalenko, a species to which it has been assigned in past reports.

Analysis of conodont distribution with respect to the shallow-water Bromide lithofacies distinguishes shallow to deeper water conodont associations. Samples from shallower water facies contain Ansella crassa n. sp., Cahabagnathus sweeti (Bergström), Curtognathus spp., Eoplacognathus elongatus (Bergström), Erismodus typus Branson and Mehl, Oneotodus? ovatus (Stauffer), Phragmodus ambiguus n. sp., Phragmodus flexuosus, and Staufferella falcata (Stauffer). Samples from deeper water facies contain forms such as Ansella nevadensis (Ethington and Schumacher) and Baltoniodus gerdae (Bergström).

All species of North American marsupials from the Chadronian through Hemingfordian are reviewed. Most North American species of didelphids previously referred to Peratherium are allocated to Herpetotherium. Five species of Herpetotherium are recognized.

The Chadronian Peratherium donahoei Hough is synonymized with Herpetotherium valens (Lambe). The Orellan species Herpetotherium stevensoni Cope is resurrected and referred, along with the Chadronian Peratherium titanelix Matthew, to a new genus, Copedelphys. Both Copedelphys and Herpetotherium can be derived from known Duchesnean species of Peratherium from North America.

Two genera of peradectids are recognized, Nanodelphys McGrew and Didelphidectes Hough. Nanodelphys minutus is synonymized with “Herpetotherium” hunti Cope and a second species of Nanodelphys is recognized from the Arikareean, though not named.

Actinomycetes are Gram-positive prokaryotes that tend to form branching and fragmenting filaments, which in some groups form a sizable mycelium. They make up a large and important part of modern terrestrial microfloras but are not known extensively as fossils, although they have a long fossil history. Actinomycete-like fossils appear several times in the Precambrian: in the middle Precambrian Gowganda Formation of Ontario (Jackson, 1967), in the 2.0 Ga Gunflint Chert of Ontario (Lanier, 1987), and possibly in a lichen-like symbiosis in the 2.8 Ga Witwatersrand rocks of South Africa (Hallbauer and Van Warmelo, 1974), among others. Direct fossil evidence of actinomycetes is very rare in the Phanerozoic, and some “fossil” actinomycetes may be later contaminants (Knoll, 1977; Smoot and Taylor, 1983). Hyphae identified as actinomycetes are known from rod-like bodies identified as nematodes inside a decaying scorpion from the lower Carboniferous of Scotland (Stoermer, 1964), and from the interior of fern phloem cells from the Pennsylvanian (Smoot and Taylor, 1983). Unmineralized Actinomyces-like cells are known from calcite in bituminous lake-bed sediments from the early Cretaceous of Nevada (Bradley, 1963), and similar, poorly preserved fossils of a form called Actinomycites have been reported from the Jurassic of Scotland (Ellis, 1915). Actinorhizal nodules, formed by actinomycetes symbiotic with plant roots, have been described from the late Pleistocene (Baker and Miller, 1980).