Rudists arose in the Late Jurassic and survived for nearly 100 m.y. before becoming extinct at the end of the Cretaceous. Over this interval they diversified gradually during the Late Jurassic and Early Cretaceous, rapidly in the mid-Cretaceous, then more slowly in the Late Cretaceous. Total rates of origination and extinction during the Late Jurassic and Early Cretaceous were uniform and comparable to those reported for other groups. The Late Cretaceous, however, was characterized by high and widely fluctuating total origination and extinction rates. Per taxon rates reveal a similar pattern except for high and variable rates in the Jurassic. The number of genera increased from the Oxfordian to a peak in the Cenomanian, decreased in the Turonian and Coniacian coinciding with a minor mass extinction event, and rose to a zenith in the Maastrichtian. Unlike other groups investigated, the rudists were at their highest level of diversity immediately prior to their disappearance.

Rudist genera survived for a mean of 12 m.y., whereas families survived for a mean of 48 m.y. Survivorship curves for generic cohorts, based upon survival of all rudist genera that evolved during each stage, exhibit a concave shape when the effects of mass extinction and variance at low diversities are considered. Causal factors involved in the final disappearance of the rudists remain unclear; however, their tropical provinciality in the Late Cretaceous contributed to their vulnerability to mass extinction.

A low-diversity brachiopod assemblage from the upper member of the Zorritas Formation in the Sierra de Almeida, northern Chile, further confirms the presence of Lower Carboniferous (Tournaisian) strata in that region. Key taxa include Schuchertella? sp., Chilenochonetes anna new genus and species, Paurorhyncha chavelensis (Amos), and Septosyringothyris covacevichi new species. Other elements of the assemblage, including Paraconularia sp., Posidoniella sp., Bellerophon (Bellerophon) sp., Eocanites sernageominus, and Imitoceras? sp. support this Early Carboniferous age assignment. Local distribution of taxa suggests small-scale environmental control. Rhynchonelloid and syringothyroid shells, many articulated, occur in lenticular sandstone bodies that were deposited in deltaic distributary channels; chonetids, schuchertellids and mollusc-bearing, iron-rich concretions are found in siltstones and mudstones that reflect interdistributary quiet-water settings and possibly a delta-front setting. Certain elements of this fauna are also present in northwestern Argentina and Peru, indicating a regional nearshore clastic regime. The closest correlation elsewhere is with the Tournaisian faunas of southeastern Australia, although analogous big-shell assemblages are found in lower Mississippian clastic strata of the central Appalachians, Ohio, and Indiana.

Two new species of conchostracans, Cyclestherioides wyomingensis and Prolynceus laneyensis, belonging to the Cyclestheriidae and Lynceidae, respectively, are described from the Eocene Laney Member of the Green River Formation of Wyoming, USA. These are the first Cenozoic fossil conchostracans to be formally reported from North America. Cyclestherioides wyomingensis has a close affinity to the extant Cyclestheria hislopi. The latter is a pan-tropical species, found between approximately 30°N and 35°S. Thus, Cyclestherioides may indicate that the Laney Member was deposited in a subtropical setting. The conchostracans and associated fauna of the Laney Member suggest that this member was deposited nearshore in a shallow lake. The concept of Cyclestherioides is emended and some fossil species referred to this genus are revised.

The results of the first comprehensive paleobotanical survey of the northern portion of the late Miocene Ogallala Group are discussed. Several species of fossilized fruiting structures from vascular plants (Berriochloa, Celtis, Cryptantha, Biorbia, Lithospermum, Eleofimbris, Carex, and Cyperocarpus) in the mid- to late-Miocene are reported. Fewer taxa (12 genera) were found in the South Dakota-northern Nebraska area than have been reported previously (20 genera) from southern Nebraska-Kansas strata in the same formations and approximately the same area of exposures. Sites of Barstovian age near the Kilgore Flora site indicate that grasses were commonly found in the region. The results presented here support the hypothesis that grassland savanna vegetation was widely distributed in the northern Great Plains by the Clarendonian age.

An assemblage of Cambrian Series 2, Stages 3–4, conchiferan mollusks from the Shackleton Limestone, Transantarctic Mountains, East Antarctica, is formally described and illustrated. The fauna includes one bivalve, one macromollusk, and 10 micromollusks, including the first description of the species Xinjispira simplex Zhou and Xiao, 1984 outside North China. The new fauna shows some similarity to previously described micromollusks from lower Cambrian glacial erratics from the Antarctic Peninsula. The fauna, mainly composed of steinkerns, is relatively low diversity, but the presence of diagnostic taxa, including helcionelloid Davidonia rostrata (Zhou and Xiao, 1984), bivalve Pojetaia runnegari Jell, 1980, cambroclavid Cambroclavus absonus Conway Morris in Bengtson et al., 1990, and bradoriid Spinospitella coronata Skovsted et al., 2006, as well as the botsfordiid brachiopod Schizopholis yorkensis (Ushatinskaya and Holmer in Gravestock et al., 2001), in the overlying Holyoake Formation correlates the succession to the Dailyatia odyssei Zone (Cambrian Stages 3–4) in South Australia.

Based on range data and generic composition, four stages of evolution are recognized for late Paleozoic trilobites of the contiguous United States. Stage 1 occurs in the Lower Mississippian (Kinderhookian-Osagean) and is characterized by a generically diverse association of short-ranging, stenotopic species that are strongly provincial. Stage 2 species are present in the Upper Mississippian and consist of a single, eurytopic, pandemic genus, Paladin. Species of Stage 2 are much longer-ranging than those of Stage 1, and some species may have persisted for as long as 12 m.y. Stage 3 is present within Pennsylvanian and Lower Permian strata and consists initially of the eurytopic, endemic genera Sevillia and Ameura as well as the pandemic genus Ditomopyge. During the middle Pennsylvanian the very long-ranging species Ameura missouriensis and Ditomopyge scitula survived for more than 20 m.y. During the late Pennsylvanian and early Permian, a number of pandemic genera appear to have immigrated into what is now North America. Stage 4 is restricted to the Upper Permian (late Leonardian-Guadalupian) strata and is characterized by short-ranging, stenotopic, provincial genera.

The main causal factor controlling the four-stage evolution of late Paleozoic trilobites of the United States is interpreted to be eustacy. Whereas Stage 1 represents an adaptive radiation developed during the Lower Mississippian inundation of North America by the Kaskaskia Sequence, Stage 2 is present in strata deposited during the regression of the Kaskaskia sea. Stage 3 was formed during the transgression and stillstand of the Absaroka Sequence and, although initially endemic, Stage 3 faunas are strongly pandemic in the end when oceanic circulation patterns were at a maximum. A mid-Leonardian sea-level drop caused the extinction of Stage 3 fauna. Sea-level rise near the end of the Leonardian and into the Guadalupian created an adaptive radiation of stentopic species of Stage 4 that quickly became extinct with the latest Permian regression.

A revision of the Silurian paulinitid scolecodont taxa from the Power Glen Formation of the Medina Group at Niagara Gorge relies on multi-element taxonomy to place the five genera and ten species of Eller (1940) into just two species: Kettnerites invisibilis (Eller, 1940) and ?K. plenidens (Eller, 1940). The generic name Nereidavus should not be used for paulinitids; the type specimen of Nereidavus has been lost, and indications are that it was probably not a paulinitid.

Trilobites assigned to the Elvinia Zone (Lower Franconian, Upper Cambrian) have been recovered from the Collier Shale in the Ouachita Mountains of west-central Arkansas. The trilobites are preserved as disarticulated exuviae, and are found in both dark-colored limestone clasts and dark, thinly-bedded carbonate layers. Field observations and petrologic/petrographic evidence indicate that these trilobites were originally deposited in a deep-water, outer shelf setting, and that shortly after deposition they were transported by sediment gravity flows to the continental slope or basinal plain.

The faunal assemblage is very similar taxonomically and taphonomically to faunas of the Elvinia Zone previously reported from North American shelf environments. Two distinctive trilobite assemblages occur in the Collier Shale. Most common is a diverse fauna that is correlative with the middle to upper part of the Elvinia Zone in Missouri, Oklahoma, and Texas. One locality yielded numerous trilobites characteristic of the Irvingella major Subzone, which occurs at the top of the Elvinia Zone in these areas. These Elvinia Zone trilobites belong to the North American Faunal Province, a largely endemic group restricted to shelf environments around the perimeter of the North American craton. Their occurrence in the Collier Shale strongly indicates that the original site of Collier deposition was proximal to the Upper Cambrian shelf margin and that the Ouachita sedimentary section is not an exotic terrane.

More than 7,900 trilobites were identified during this study; they are assigned to 26 genera and 27 species. The family Cliffidae is proposed for a group of trilobites that includes species of Cliffia Wilson, Aphelotoxon Palmer (junior synonym Ponumia Hu), Drabia Wilson, and possibly Elyaspis Kurtz. Three new genera are erected (Kymagnostus, Pyttstrigis, and Jessievillia) and 10 new species are described and illustrated (Apachia genaitholix, Cliffia magnacilis, Dellea planafrons, Iddingsia hapsis, Jessievillia radiatus, Kymagnostus harti, Neoagnostus? dilatus, Aphelotoxon lumaleasa, Pulchricapitus fetosus, and Pyttstrigis dicilia).

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.

Remains of Halisaurus sternbergi (Wiman, 1920) from the latest Early Campanian (sensu germanico) of the Kristianstad Basin, southern Sweden, represent the first record of this species outside of the USA. The material comprises numerous marginal tooth-crowns, a premaxilla, an incomplete pterygoid, and vertebrae. The Kristianstad Basin population of H. sternbergi was probably derived from individuals that migrated from the Mississippi Embayment in North America sometime during the Early Campanian. Even though H. sternbergi thrived in great numbers in the coastal waters of the southern part of the Baltic Shield during the latest Early Campanian, the population appears to have been short-lived. Available data indicate that H. sternbergi, along with several other species of mosasaurs, vanished from the region following an intercontinental mosasaur extinction event, or a series of events, near the Early/Late Campanian boundary.

The Upper Cambrian sponge Wilbernicyathus donegani Wilson, 1950 was originally described as an archaeocyath. The original specimens were lost. Later, based on the original description and figures, this species was interpreted as an orchocladine lithistid, but family-level taxonomy has not been clear. A neotype is designated to help stabilize the taxonomy of this species. A redescription based on the neotype and other new material from the area of the type locality and elsewhere demonstrates that this species is an orchocladine lithistid sponge belonging to the family Anthaspidellidae. It has a regular skeleton consisting of dendroclones and trabs arranged in a ladderlike net, and radial canals are well organized. The species occurs within sponge-microbial and stromatolitic reefs in the Wilberns Formation of central Texas and possibly the Clinetop Bed of the Dotsero Formation of Colorado. Stratigraphically, it ranges from the Idahoia to the Saukia trilobite zones of the Upper Cambrian Ptychaspid Biomere. Ecologically, Wilbernicyathus Wilson, 1950 occupies a reefal niche and constitutes up to 30% of the reef volume. These Late Cambrian bioherms represent the initial Laurentian expansion in the sponge-microbial buildups that dominated reef environments worldwide during the Early Ordovician.

The radiodontans, including anomalocaridids and their allies, are enigmatic stem-group euarthropods and are the most ancient apex giant predators known from the fossil record. Most studies on their feeding behaviors have emphasized their diverse and abundant raptorial frontal appendages, while the oral cone surrounding the mouth opening in these animals has attracted less attention. At present, three oral cone morphotypes are known, from Anomalocaris Whiteaves, 1892, Peytoia Walcott, 1911, and Hurdia Walcott, 1912, respectively. In this paper, we report on a novel form of radiodontan oral cone from the Guanshan Lagerstätte (Cambrian Series 2, Stage 4) in the Wulongqing Formation, eastern Yunnan, South China. This oral cone is unique in combining features seen in Peytoia/Hurdia and Anomalocaris. It possesses a Peytoia/Hurdia-type ‘tetraradial’ configuration comprising a 32-plate outer ring that consists of four perpendicularly arranged large plates and 28 small plates, in addition to furrowed folds and scale-like nodes on plate surfaces otherwise seen only in Anomalocaris. As an intermediate morphotype, the Guanshan oral cone improves our understanding of the occurrence and morphological disparity of radiodontan oral cones, illuminates future investigations on potentially variable radiodontan feeding mechanisms, and reveals possible evolutionary transformations of these peculiar feeding structures. The resolution of current radiodontan phylogeny would be potentially improved by new knowledge on other body parts apart from frontal appendages in future studies.

Radiolarians have been recovered from lowermost Arenigian rocks of the Cow Head Group in Gros Morne National Park, Newfoundland. Two new faunal assemblages include eight families, 13 genera, and 25 species. Among these, the family Neoaspiculumidae, the genus Neoaspiculum, and 11 species, Beothuka aitchisoni, B. grosmornensis, B. stougei, B.? stellata, Neoaspiculum cancellium, N. headense, N. transformum, N. laxum, N.? amplum, Proventocitum cylindricum, and P. piriforme, are new.

This study elucidates the reason for the significant difference in species composition between pre-Arenigian and Arenigian radiolarian faunas. This difference does not appear to be due to mass extinction, but rather to phylogenetic evolution: most radiolarian families that flourished during pre-Arenig time were gradually but significantly reduced by the earliest Arenig. Characteristic features of the earliest Arenig assemblages that distinguish them from their Tremadocian predecessors are 1) the development of a distinctive skeletal constructional element referred to as “bandage” structure that evolved through modification of a mesh of thin bars and 2) the appearance of multiple concentric shells including a proloculus (or a microsphere), which developed from a primitive three-dimensionally interwoven meshwork or spongy shell wall. These forms, represented by beothukids, antygoporids, and inaniguttids, are rare but they appear to originate in the earliest Arenig. Transitional characteristics among those forms are developed in the Neoaspiculumidae, which flourished during the earliest Arenig.

The precise biostratigraphic age of one of the assemblages was determined with the recovery of the index condont Prioniodus adami Stouge and Bagnoli, 1988 from strata belonging to the Tetragraptus approximatus Graptolite Zone, which is at the base of the Arenigian.

The bizarre morphology of living Pycnogonida, known colloquially as sea spiders, has long fueled dissent over their status within the arthropods. Pycnogonids figure prominently in recent analyses of anterior limb homologies and ancestral crown-group euarthropod relationships, with support for the concept of Pycnogonida as sister taxon to Euchelicerata now contested by proponents of a more basal position between Radiodonta and all other arthropods. A challenge to further elucidation of their phylogenetic position is the exceptional rarity and disjunct distribution of pycnogonids in the fossil record, due largely to their fragile unmineralized exoskeletons. New fossil discoveries therefore have the potential to add significantly to knowledge of their evolution, paleoecology, and paleobiogeography. Here we report the first known occurrence of fossil pycnogonids from rocks of Ordovician age, bridging a 65 Myr gap between controversial late Cambrian larval forms and a single documented Silurian specimen. The new taxon, Palaeomarachne granulata n. gen. n. sp., from the Upper Ordovician (ca. 450 Ma) William Lake Konservat-Lagerstätte deposit in Manitoba, Canada, is also the first reported from Laurentia. It is the only record thus far of a fossil sea spider in rocks of demonstrably shallow marine origin. Four incomplete, partially disarticulated molts represent a relatively large, robust animal with a series of five segment-like elements in a ‘head’ region that does not incorporate the first of four preserved limb-bearing trunk segments. This unique pattern may reflect the plesiomorphic condition prior to complete fusion of anterior ‘head’ elements and first trunk segment to form a cephalosoma, as seen in all eupycnogonids. Palaeomarachne granulata is interpreted as occupying a basal stem-group position in the Pycnogonida.

A diverse crinoid fauna is described from the Upper Ordovician (Katian) Fombuena Formation from the eastern Iberian Chains of Spain. New crinoids include the diplobathrid camerates Fombuenacrinus nodulus n. gen. n. sp., Goyacrinus gutierrezi n. gen. n. sp., Dalicrinus hammanni n. gen. n. sp., and Ambonacrinus decorus n. gen. n. sp.; the monobathrid camerate Eopatelliocrinus hispaniensis n. sp.; and the cladid Picassocrinus villasi n. gen. n. sp. A new occurrence of Heviacrinus melendezi Gil Cid, Domínguez Alonso, and Silván Pobes, 1996 is also documented from the Castillejo Formation (Darriwilian, Middle Ordovician) from the eastern Iberian Chains of Spain. The Fombuena Formation comprises a Gondwanan crinoid assemblage from a high paleolatitude and has the highest crinoid diversity of any currently known Katian Gondwanan fauna. This assemblage is compared to other Katian age faunas around the globe, and its paleobiogeographic implications are discussed.

Silurian calcareous algae, cyanobacteria, and microproblematica are abundantly preserved in the Alexander terrane of southeastern Alaska. They represent a diverse population of calcified microbes that contributed to the formation of a variety of shallow- and deep-water carbonate deposits. Five associations are recognized on the basis of recurring groups of microbial taxa. These include a Girvanella-Tuxekanella association that formed oncoids and thick encrustations on skeletal grains in shelf environments. A Renalcis association predominated in a stromatoporoid-coral reef that developed at the incipient shelf margin on a crinoid-solenoporid shoal (“Solenopora” association). Other organic buildups are characterized by a Ludlovia association, which constructed skeletal stromatolite reefs, and by an Epiphyton-Sphaerina association that contributed to the formation of a stromatolitic mud mound. A mixed microbial assemblage reflects transport and mixing of shallow-water microbial biotas that were deposited by turbidity currents, debris flows, and slumps in a slope environment.

Reexamination of type and topotype material revealed the presence of well-developed ventral and dorsal interareas in two virgianid brachiopods from South China, Eoconchidium jiangshanensis Liang (in Liu et al., 1983) and Paraconchidium shiqianensis Rong, Xu, and Yang, 1974, of Late Ordovician and Early Silurian ages, respectively. A cladistic analysis of the common virgianid taxa, incorporating new data on the development of interareas, confirms Paraconchidium Rong, Xu, and Yang, 1974 as a valid genus (not a junior synonym of Pseudoconchidium Nikiforova and Sapelnikov, 1971) and warrants E. jiangshanensis as the type species of Deloprosopus new genus (not allied to either Eoconchidium or Tcherskidium as previously believed). Our preliminary survey on the suborder Pentameridina, based on available material or illustrations of well-preserved, disarticulated (typically silicified) valves, indicates that 1) the interareas are more commonly developed in the superfamily Pentameroidea than was reported previously, especially in the families Virgianidae and Subrianidae; 2) the ventral and dorsal interareas commonly do not occur as paired planar surfaces in the Pentameroidea, as they do in the superfamily Stricklandioidea; and 3) despite the common absence of a ventral interarea, the development of a sharply delimited dorsal interarea appears to be ubiquitous in the Pentameroidea and possibly in the suborder Pentameridina. In the currently adopted classification, the presence of matching ventral and dorsal interareas is treated as one of the diagnostic characters that separate Stricklandioidea from other superfamilies of the Pentameridina. The new data presented herein on the development of interareas imply the need to reevaluate the taxonomic and evolutionary significance of the ventral and dorsal interareas, pending a thorough survey on their distribution in the suborder Pentameridina.

A moderately diverse assemblage of anthaspidellid demosponges has been recovered from reef-bearing carbonate platform deposits of Early Ordovician, Tremadoc to early Arenig age, in Hubei Province. The sponges occur, in part, in the Tremadoc Fenxiang Formation and, in part, in the lower Arenig Honghuayuan Formation at several localities near Yichang, Xintan, and Liujiachang. Archaeoscyphia nana Beresi and Rigby, 1993, Archaeoscyphia pulchra (Bassler, 1927), and Archaeoscyphia minganensis (Billings, 1859) occur with the new genera and species, Jianghania yichangensis and Velellospongia adnata, and the new species Rhopalocoelia sanxiaensis and Anthaspidella lamellata. This is the first reported occurrence of Anthaspidella in Ordovician rocks of China. Great numbers of these species of fossil sponges have been found in Lower Ordovician outcrops, particularly in the eastern Yangtze Gorge area of Hubei Province.

The polycotylidae is a family of short-necked (pliosauromorph) plesiosaurs, with examples known from epicontinental marine deposits of every major landmass except Antarctica. Our knowledge of its diversity and distribution has increased tremendously in the last decade, with new material described from North America (Sato, 2005; Albright et al., 2007; Schumacher, 2007; Schmeisser, 2008), South America (Gasparini and de la Fuente, 2000; Salgado et al., 2007), Africa (Bardet et al., 2003; Buchy et al., 2005), and Asia (Sato and Storrs, 2000; Arkhangel'skii et al., 2007). Polycotylid diversity is greatest in the Late Cretaceous, and particularly so in the Turonian; however, knowledge of the group's initial history in the Early Cretaceous is limited to a handful of specimens from North America (Storrs, 1981; Druckenmiller, 2002) and Australia (Kear 2003, 2005).

Abundant and well-preserved assemblages of disarticulated sponge spicules occur in Middle and Late Cambrian platform carbonates of western Hunan, China. Assemblages recovered from 11 stratigraphic horizons include calcisponges, demosponges, and hexactinellids. Hexactinellida, in particular, are both abundant and diverse in Upper Cambrian carbonates. Comparison with spicule assemblages from Australia indicates that many of these taxa have long stratigraphic ranges, limiting their use in correlation. The morphological diversity of these spicules exceeds that known for living siliceous sponges, supporting the observation that during the Cambrian radiation, sponges, like other metazoans, evolved a variety of architectural forms not observed in later periods. Like conodonts, individual sponges can produce more than one spicule form; thus, an “apparatus genus” concept based on multiple cooccurring elements may eventually prove useful in the biostratigraphic and paleobiological interpretation of disarticulated sponge spicules. Four distinctive forms are recognized as new taxa: Australispongia sinensis new genus and species, Flosculus gracilis new genus and species, Pinnatispongia bengtsoni new genus and species, and Nabaviella paibiensis new species.