A newly discovered assemblage of archaeocyathans, dominated by the unusual genus Retilamina, occurs in outcrops of the upper Harkless Formation in Esmeralda County, Nevada. These rock units have been correlated with the Saline Valley Formation in the Bonnia–Olenellus Zone (late Early Cambrian) of eastern California, making this the youngest known occurrence of archaeocyathans in the White–Inyo region.

Although the assemblage contains a variety of different organisms (including the alga Renalcis, trilobite and echinoderm debris, bivalves?, and Chancelloria spines), it is dominated by archaeocyathans. Diplocyathellus, a conical form with a complex inner wall, is the only genus of regular archaeocyathan in the assemblage. The irregular archaeocyathans Arrythmocricus and Metaldetes exhibit dendroid branching and cylindroconical morphologies, respectively. A third irregular, Retilamina debrennei n. sp., is an atypical archaeocyathan with a sheetlike or shallow convex dome morphology. Retilamina formed natural cavities that sheltered cryptobionts. Unlike coelobiont communities reported from other Lower Cambrian cavities where the diversity of the supported biota is relatively high, the Harkless cavities contain only the alga Renalcis. While the undersurfaces of Retilamina are consistently encrusted by Renalcis, the upper, exposed surfaces typically lack epibionts. Similar morphologies and associations for Retilamina have been reported from bioherms and biostromes from southern Labrador and western Newfoundland. Unlike most archaeocyathans, Retilamina had a solitary, free-lying life habit. Retilamina's broad base and low profile provided stability in episodically turbulent conditions or on biologically disturbed substrates.

This occurrence demonstrates that the disappearance of archaeocyathans from the stratigraphic record of the southern Great Basin in the late Early Cambrian is a paleoecological artifact. Archaeocyathans were extant in the region in the late Early Cambrian but the habitats conducive to archaeocyathan growth or preservation are, for the most part, not represented in the preserved strata.

The new thin-walled vasiform dictyospongid hexactinellid, Tiddalickia manitobensis, is described from the Ordovician Red River Formation at McBeth Point on Lake Winnipeg, Manitoba. Vertical spicule bundles are an outer? part of the wall and horizontal spicule bundles an inner? different level within the wall. Bundle quadrules are only half the size of those in Tiddalickia quadrata Rigby and Webby, 1988. A complete anthaspidellid lithistid, Aulocopella winnipegensis Rauff, 1895, is described from a glacial erratic recovered from near Reston, Manitoba.

In the El Castro Formation, cropping out on the Asturian coast of northern Spain, two fossiliferous horizons have been studied. Above the basal one, containing the Llandeilian brachiopods Tissintia cf. T. convergens and Howellites? sp., a new horizon of estimated Ashgillian age has been identified that has yielded the new brachiopod species Mcewanella vulcanica and Hesperinia asturica. The new species of Mcewanella, close to the Irish Rawtheyan Mcewanella dorsisulcata, is characterized by a great delay of the insertion of costellae, which gives many adults a strikingly costate ornament for this genus. Hesperinia was, up to now, poorly known from a small number of specimens from the Llanvirnian Tank Hill Formation in Nevada; thus, the new record, besides allowing a better understanding of the genus and its relationship with other oepikinids, extends its known time span to the Late Ordovician. These two species were dwellers on a low-energy bottom formed of loose sand and gravel supplied by nearby volcanic eruptions. The ash-flow depositional pattern of these sediments would have had lethal effects on the brachiopod communities, periodically causing their destruction. These species of the genera Mcewanella and Hesperinia are new representatives of the immigration of North American and Northern European warm-water faunas into the circumpolar Mediterranean Province during the Late Ordovician.

Watsonella crosbyi Grabau, 1900, a senior synonym of Heraultipegma varensalense (Cobbold, 1935) and H. yannense He and Yang, 1982, is the oldest known rostroconch. The species ranges through most of the Early Cambrian and has been recovered from temperate siliciclastic (Avalon Platform) and tropical carbonate (south China, Mongolia?, southern France) environments. Watsonella crosbyi occurs through approximately 880 meters of the sub-trilobitic Lower Cambrian of southeastern Newfoundland. Its lowest occurrence corresponds to the first appearance of relatively diverse small shelly faunas of the pre-Tommotian Watsonella crosbyi Zone (new).

The general form of Watsonella crosbyi conchs (laterally compressed, prosogyrate, elongate posterior, subdued comarginal growth lines, very thin shell with anterior and posterior gapes) is similar to that in a number of larger burrowing pelecypods, but this does not rule out other benthic habits. However, recovery of locally common in situ conchs (plane of commissure vertical, long axis subhorizontal) in the lower and upper parts of its stratigraphic range in southeastern Newfoundland corroborates an infaunal life habit for the species. The animal is a prominent element in faunas from offshore, cohesive, siliciclastic mudstones but also occurs in calcareous nodule-rich mudstones, shell hash limestones, and, infrequently, in peritidal algalaminate limestones. A phylogenetic sequence from laterally compressed monoplacophorans to early ribeiroid rostroconchs and leading to the oldest pelecypods was completed by the middle Early Cambrian and involved infaunal mollusks.

A paleoecological study of the Point Loma Formation (Upper Cretaceous, southern California) resulted in the discovery of a new genus assigned to the gastropod family Aporrhaidae. The individuals recovered provide the basis for the designation of Teneposita n. gen. based upon T. laeva n. sp. Teneposita is characterized by two delicate labral digitations, a short opposing digitation, and elongate anterior and posterior canals. Teneposita laeva is one of the smallest aporrhaids yet described.

A single limestone slab is described from the Mississippian Bear Gulch Limestone of central Montana containing more than 100 bivalves, including Caneyella sp. and ?Ptychopteria (Actinopteria) sp., attached in original life positions along an 80-cm-long ?brown alga. The assemblage provides clear evidence of life position and choice of substrate for these pterioids. The bivalves increase in size, and appear to be radially disposed in their attachment sites, along the loosely coiled “kelp-like” alga, indicating little postmortem transport and current activity. The bivalve population is interpreted as living on an algal thallus that was either planktonic or attached to the substrate. Observations and comparisons with modern bivalve—seaweed associations support either view. Evidence for local anoxic conditions and stagnant water help explain the superb preservation and confirm past interpretations of the Bear Gulch Limestone.

The Chesterian Imo Formation in north-central Arkansas contains an abundant and diverse bivalve fauna which is dominated in numbers by nuculoids. The pterioids, pholadomyoids, and nuculoids show the greatest, and nearly equal, species diversity. Ecologically, on a generic level, the fauna is dominated by infaunal, burrowing, suspension feeders with attached suspension feeders a close second.

Among the 40 taxa identified, the following new taxa are proposed: Economolopsis gordoni n. gen. and sp.; Spathelopsis browni n. gen. and sp.; Paleyoldia angustia n. sp.; P. bruta n. sp.; Phestia corrugata n. sp.; P. wortheni n. sp.; P. obtusa n. sp.; Imoella obscura n. gen. and sp.; Prothyris (Lophoprothyris) crista n. subgen. and sp.; Ectogrammysia crassatis n. gen. and sp.; Asketomorpha grandis n. gen. and sp.; and Sphenotus pisinnus n. sp.

On the basis of ammonoids, the upper portion of the Imo Formation falls within the Elvirian Stage, E2b–c undifferentiated. Foraminifera place the formation in Mamet zone 19. The bivalve fauna discussed herein was collected from the E2b–c portion of the Imo.

A diverse, well-preserved assemblage of nautiloid cephalopods was collected from the Treptoceras duseri shale, a 1.5-m-thick claystone within the Waynesville Formation (Late Ordovician, early Richmondian) exposed in southwest Ohio. The strata, the enclosed fauna, and its taphonomy indicate deposition in a low-energy, mud-bottom marine environment, in water depths of 20–25 m, below wave base but within the zone of storm-current reworking.

Nautiloid specimens consist of complete conchs that have been replaced by calcite. Twelve species of nautiloids, belonging to eight genera, representative of four orders, have been collected from the shale in southwest Ohio. Longiconic orthocones are clearly the dominant nautiloid morphotype present, with the assemblage dominated by three species of the longiconic orthocerid Treptoceras and with fewer numbers of the endocerid Cameroceras and the slender orthocerid Isorthoceras?, the cyrtoconic oncocerids Oncoceras and Manitoulinoceras, and rare specimens of the orthocerid Gorbyoceras, the oncocerid Zittelloceras, and the ascocerid Schuchertoceras.

Nautiloid taphonomy, the diversity of nautiloid taxa present, the lack of postmortem buoyancy in the shells of the more common taxa, the recurrent nature of this assemblage, and the restricted distribution of this Treptoceras–Cameroceras fauna to portions of eastern North America in the Late Ordovician suggest that this nautiloid assemblage represents an in-situ accumulation of nautiloids representative of a living assemblage. These nautiloids were important elements associated with benthic communities in these epeiric sea mud-bottom environments and not simply assemblages of drifted, necroplanktonic shells.

Modern Nautilus, in natural and laboratory settings, scavenges both dead and molted decapod crustaceans. Ingestion of palinurid lobster exuviae by Nautilus follows a specific pattern in which the cephalopod consumes the exoskeleton beginning at the posteriormost part of the abdomen and continuing anteriorly. During the ingestion process, the cephalothorax is least likely to be consumed, either because the Nautilus may abandon the remains, or the cephalothorax may become separated from the abdomen at its weakest point, the articulation of the cephalothorax with the abdomen. Examination of 767 fossil lobster specimens from 50 formations, 41 of Cretaceous age, demonstrates that the fossil record of lobsters, the preponderance of which appear to be exuviae, is strongly biased in favor of cephalothoraxes. Observations on Nautilus suggest that anatomically selective scavenging by ancient cephalopods, both nautiloids and ammonoids, may explain, in part, the selective preservation of lobster cephalothoraxes over abdomens. Despite the range of variation in jaw morphologies among ammonoids, probably most could have fragmented and ingested decapod remains. Evidence for selective scavenging in the geologic past is purely circumstantial; no cephalopod bitemarks have been identified on fossil lobster exuviae. Pre-burial decomposition of connective tissues and subsequent disarticulation of the abdomen in the absence of scavenging may also have contributed significantly to the observed anatomical taphonomic bias.

Two species of the heteromorph ammonite genus Diplomoceras Hyatt are described from the Upper Cretaceous of the James Ross–Seymour Islands area, Antarctica. The late Campanian–early Maastrichtian D. lambi Spath has a relatively high rib density, whereas D. maximum n. sp. has a lower rib density and is known only from the uppermost Maastrichtian of the Lopez de Bertodano Formation on Seymour Island. Both species attain an exceptionally large size with the body chamber of D. maximum n. sp. attaining a length in excess of one meter. The structure of the shell wall in Diplomoceras is characterized by the thickening of the nacreous layer below the ribs. The shell thickening results in an inner flat surface and a smooth phragmocone. Reconstruction of the shell suggests at least four parallel shafts and three U-connectives. Estimates of the total density, center of buoyancy, and center of mass in this reconstructed shell indicate a slightly positive buoyant shell with a relatively unstable floating position.

New specimens of Beckwithia typa, from the upper Middle Cambrian of Utah, show that, contrary to previous descriptions, the animal had at least 10 tergites (possibly 12) and probably a tail-spine. There is no evidence for a fused tail-plate, the one character that made Beckwithia appear anomalous with respect to other aglaspidid arthropods. It did, however, differ from most other aglaspidids in having a single series of axial spines along the trunk, but this cannot be regarded as a basis for continued separation of Beckwithia into a monogeneric family. A possible relationship with Kodymirus vagans is suggested by the presence of axial spines, although there may have been significant differences in the nature of the ventral sclerites. Beckwithia? major from the Upper Cambrian of Wisconsin is known only from fragmentary specimens and no evidence of a fused tail-plate has been found. Beckwithia? daubikhensis from the Khanka Massif, Soviet Union, is unlikely to be a member of this genus; the single specimen on which the taxon was based may be a poorly preserved Khankaspis bazhanovi.

Standards have been empirically developed to describe various morphological characters of eurypterids. The standards pertain to the following characters: 1) shape of the prosoma; 2) shape of the metastoma; 3) shape of the eyes; 4) position of the eyes; 5) types of prosomal appendages; 6) types of swimming leg paddles; 7) structure of the doublure; 8) differentiation of the opisthosoma; 9) structure of the genital appendages; 10) shape of the telson; and 11) types of ornamentation.

For the first time, a uniform, standardized taxonomy is proposed for classification and identification of most genera. The taxonomy is based on the observation that most higher taxonomic levels for arthropods are based on the structure and arrangement of the appendages. Details of the taxonomy rely on the morphological standards proposed here.

The order Eurypterida Burmeister, 1843, is here defined by the presence of only six pairs of prosomal appendages, the first pair being the chelicera, the next five pairs being the gnathobasic, uniramus legs. Suborders are characterized by the gross morphology of the chelicera. Superfamilies and families are characterized by the use of a single character complex, specifically the structure and arrangement of the second through sixth pairs of prosomal appendages. Genera are recognized by more specific standards.

A new classification of the order Eurypterida is proposed. Three new superfamilies, Kokomopteroidea, Megalograptoidea, and Brachyopterelloidea, and five new families, Brachyopterellidae, Adelophthalmidae, Lanarkopteridae, Erieopteridae, and Hardieopteridae, are proposed.

Two alternative hypotheses for proximal column growth are tested in Taxocrinus cf. T. whitfieldi, a late Mississippian flexible crinoid. The first hypothesis states that new columnals are added at the base of the proximal column (immediately above the generating columnal), whereas the second hypothesis has columnals of the proximal column inserted beneath the aboral cup. In both hypotheses, middle column columnals are inserted beneath the generating columnal and are independent from the proximal column.

External features used to determine points of columnal insertion include wedge-shaped columnals and sharp changes in columnar morphology. Sagittal sections reveal the presence of small columnals, some of which can be interpreted as the last columnals inserted prior to death. Data collected on Taxocrinus cf. T. whitfieldi confirm the first hypothesis. This hypothesis may be applicable to other crinoids with xenomorphic columns.

Illusioluidia teneryi is a new genus and species of asteroid echinoderm described from the Missourian (Upper Pennsylvanian) Wolf Mountain Shale of Texas. Illusioluidia is important because it is strongly homeomorphic with modern Luidia; Luidia has been considered primitive among living asteroids by some authors. Illusioluidia, however, is not ancestral to Luidia or any other modern genus; similarities are convergent. Luidia is a predator, largely on active invertebrates (other echinoderms, mollusks), whereas Illusioluidia is inferred to have been a small-particle feeder. Homeomorphy reflects neither descent nor feeding habits; environmental controls are suggested.

The first occurrence of a pterosaur fossil from the Early Cretaceous of Peru is reported. The specimen consists of a nearly complete right humerus of a pteranodontid pterosaur preserved in three dimensions, presumably in a concretion. The Pteranodontidae is rediagnosed, and included genera and materials are listed. The Nyctosauridae and Dsungaripteridae are also diagnosed on the basis of postcranial characters, and the relationships of those three taxa plus the Azhdarchidae are discussed. The species Santanadactylus spixi Wellnhofer (1985) is reassigned to the Dsungaripteridae.

The tarsus and distal end of the tibia are described in Herrerasauridae, a family that includes the oldest known dinosaurs. This tarsal configuration is compared to those of more advanced dinosaurs and to other archosaurs. Through phylogenetic analysis of the morphological characters, a picture emerges of the evolutionary changes in the ankles of early dinosaurs.

The tibia of the herrerasaurids has a quadrangular distal articular surface, with a shallow ventrolateral notch. This morphology is strikingly similar to that of the lagosuchid thecodonts Pseudolagosuchus and Lagosuchus and represents the most primitive tibial condition known for Dinosauria.

Aside from the derived states possessed by Theropoda, Sauropodomorpha, and Ornithischia, respectively, it was impossible to recognize synapomorphies in tibiotarsal anatomy shared by these groups exclusive of Herrerasauridae. The transverse broadening of the distal end of the tibia seems to have been attained independently by ornithischians, theropods, and sauropodomorphs.

The tarsus of herrerasaurids is characterized by an astragalus with a small but conspicuous lateroventral depression, by a pyramidal calcaneum with a ventromedial projection that articulates into the cavity of the astragalus just mentioned, and by a posterolaterally directed calcaneal tuber. These characters are also seen in Lagosuchus (a close relative of dinosaurs), in the prosauropod Riojasaurus and, insofar as the astragalus is concerned, in the primitive dinosaur Walkeria, which suggests that dinosaurs of different lineages shared the same tarsal condition.

By definition, this type of articulation between the astragalus and calcaneum follows the “crocodile-reversed” tarsal condition, suggesting that the tarsus in lagosuchids and dinosaurs could be derived from the “crocodile-reversed” pattern present in Ornithosuchidae and Euparkeria. In contrast, the mesotarsal ankle of lagosuchids and dinosaurs lacks the synapomorphies of the “crocodile-normal” ankle present in Crocodylia, Rauisuchidae, Aetosauria, and other archosaurs.

It is concluded that Herrerasauridae retained the primitive tibiotarsal condition for Dinosauria, from which those of the Ornithischia, Sauropodomorpha, and Theropoda were derived. Furthermore, tibiotarsal anatomy supports monophyly of Dinosauria.

Notoschizaea was described by Graham in 1934 but has not been generally used since then and has been a problem for evaluation of coenopterid fern diversity. The monotypic genus Notoschizaea is placed in synonymy with Corynepteris Baily, and N. robusta Graham is redescribed as C. robusta (Graham) Mickle comb. nov. The original specimens are reillustrated and reinterpreted in light of more recent discoveries of permineralized Corynepteris species. Spores within sporangia are identified as being of the Apiculatisporis Potonie and Kremp type.

The nomenclatorial history of the ichnogenera Lockeia and Pelecypodichnus has been confused by duality during the past 20 years. Many authors presume Pelecypodichnus is correct because Lockeia is a nomen oblitum. This presumption is rejected on both objective and subjective grounds. First, Lockeia is not a nomen oblitum. Two major gaps in the citational history of Lockeia exist, the first one of 35 years duration and the second of 43 years duration. Thus, no 50-year gap exists in the valid use of the name Lockeia. Second, the Committee on Zoological Nomenclature was not petitioned to declare Lockeia a nomen oblitum during the period of time that the nomen oblitum concept was in effect. Third, the name Pelecypodichnus implies a specific trace-maker for the trace—a practice we, and others, judge should be avoided. Fourth, topotype specimens and the lectotype of Lockeia are available for study. Fifth, even many of those authors who use Pelecypodichnus instead of Lockeia commonly note the existence of Lockeia as a synonymous generic name. Thus, use of Lockeia by numerous authors in the past 20 years results in no confusion or destabilization of the generic-level taxonomy. Lockeia, the senior synonym of Pelecypodichnus, has been used by numerous authors, is well understood, and therefore should be used instead of Pelecypodichnus.