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Considerable numbers of exceptionally preserved conodont apparatuses with hyaline elements are present in the middle-upper Darriwilian (Middle Ordovician, Whiterockian) Winneshiek Konservat-Lagerstätte in northeastern Iowa. These fossils, which are associated with a restricted biota including other conodonts, occur in fine-grained clastic sediments deposited in a meteorite impact crater. Among these conodont apparatuses, the common ones are identified as Archeognathus primus Cullison, 1938 and Iowagnathus grandis new genus new species. The 6-element apparatus of A. primus comprises two pairs of archeognathiform (P) and one pair of coleodiform (S) elements. The 15-element apparatus of I. grandis n. gen. n. sp. is somewhat reminiscent of the prioniodinid type and contains ramiform elements of alate (one element) and digyrate, bipennate, or tertiopedate types (7 pairs). Both conodont taxa are characterized by giant elements and the preservation of both crowns and basal bodies, the latter not previously reported in Ordovician conodont apparatuses. Comparison of the apparatus size in the Winneshiek specimens with that of the Scottish Carboniferous soft-part-preserved conodont animals suggests that the Iowa animals were significantly larger than the latter. The apparatus of A. primus differs conspicuously from the apparatuses of the prioniodontid Promissum from the Upper Ordovician Soom Shale of South Africa although the apparatus architecture of I. grandis n. gen. n. sp. shows some similarity to it. Based on the Winneshiek collections, a new family Iowagnathidae in Conodonta is proposed.

The outcrop at Whiterock Canyon Narrows, Nevada, is the stratotype for the Middle Ordovician Whiterockian Series in Laurentia. Contrasts in the distribution of trilobites and conodonts between two parallel sections at the stratotype demonstrate the presence of an unconformity separating Ibexian faunas (the historic trilobite Zone J, the more recent restricted “Pseudocybele nasuta” trilobite Zone, the Reutterodus andinus conodont Zone) from overlying Whiterockian faunas (Zone L, the Psephosthenaspis pseudobathyurus trilobite Zone, the Orthidiella brachiopod Zone, the Tripodus combsi conodont Zone). The unconformity represents the erosional loss of a minimum of 10 m of shale and bedded limestone within the upper Ninemile Formation. In comparison to more continuous section in the Ibex region, Utah, the equivalent to the thin Psephosthenaspis microspinosa trilobite Zone and, possibly, the uppermost interval of the underlying “P. nasuta” Zone are missing. Illaenus welchi new species is described from the Whiterockian faunas of the upper Ninemile and Antelope Valley formations.

The Romaine Formation of the Mingan Islands, Québec, contains a limited trilobite fauna of five genera (Bolbocephalus, Peltabellia, Petigurus, Strigigenalis, Strotactinus) with Lower Ordovician Ibexian (Floian) affinity, succeeded by two genera (Acidiphorus, Pseudomera) of early Middle Ordovician Whiterockian (Dapingian) affinity. Trilobites of later Whiterockian (Darriwillian) affinity are more abundant in the overlying Mingan Formation, with 29 genera (Amphilichas, Bathyurus, Calyptaulax, Ceraurinella, Cybeloides, Dolichoharpes, Encrinuroides, Eobronteus, Eorobergia, Failleana, Glaphurina, Glaphurus, Hibbertia, Hyboaspis, Illaenus, Isotelus, Kawina, Nieskowskia, Phorocephala, Pandaspinapyga, Pliomerops, Remopleurides, Sphaerexochus [including S. valcourensis n. sp.], Sphaerocoryphe, Stenopareia, Thaleops, Thulincola, Uromystrum, and Vogdesia). Lectotypes are selected for Mingan species of Illaenus, Peltabellia, Petigurus, Sphaerexochus, Stenopareia, and Thaleops. A number of genera form biofacies which can be related to lithofacies. Taken together with Chazy Group and Northwest Territories trilobite faunas, Mingan trilobites provide critical information on late Whiterockian trilobite distributions in Laurentia in far more detail than seen in the stratotype area of Nevada.

Storm-generated event beds are an important source of paleoecological information, especially in Paleozoic strata. Storm deposition and subsequent physical and biological modification can potentially alter the diversity structure of death assemblages significantly. To examine the effects of storm deposition on fossil assemblage composition, storm beds are compared with co-occurring beds representing background sedimentation in 67 samples from six Ordovician mixed carbonate-clastic units deposited above the maximum storm wave base. In the great majority of pairwise comparisons, evenness and sampled richness are higher in storm beds than in background beds. This effect is not explained by differences in lithification, skeletal fragmentation, or in the proportions of aragonitic or multielement skeletons. The elevated diversity of storm beds can result from homogenization of fine-scale faunal patchiness preserved in background beds or may be due to taphonomic feedback. The relative importance of these two end-member scenarios can be evaluated with detrended correspondence analysis. In shallow, carbonate-dominated environments, the former appears to predominate, while the latter is more important in a deeper setting dominated by fine-grained clastics. The disparity between background beds and storm beds suggests that, at least in the Lower Paleozoic, background beds may record a higher-resolution paleoecological signal while storm beds record a more complete census of alpha diversity. Because post–Middle Ordovician increases in the depth and intensity of bioturbation may have diminished the temporal resolution and increase the faunal completeness of background beds, this disparity is not necessarily expected in younger strata.

Relative abundance data are of primary importance in paleoecology, but it is not always obvious how they should be interpreted. Because relative abundance is expressed as a proportion of the total sample, change in the abundance of one group necessarily changes the relative abundance of all groups in the sample. There are two possible interpretations for a trend in the relative abundance of a taxon: an “active” scenario in which the trend reflects change in the population density of the group itself, or a “passive” scenario in which the change is driven by population changes in other taxa. To discriminate between these scenarios it is necessary to collect absolute abundance data (abundance expressed as a function of sample area or volume). We examine both absolute and relative abundance trends through a major paleoecological transition: the shift from trilobite-dominated to brachiopod-dominated paleocommunities in shallow marine carbonates spanning the Lower/Middle Ordovician boundary in western Utah and eastern Nevada. We sampled 61 carbonate mudstone and wackestone beds from the upper Ibex Series (Lower Ordovician) and lower Whiterock Series (Middle Ordovician) at three sections that span the boundary. All samples come from the shallow subtidal Bathyurid trilobite biofacies. Samples were broken into small pieces, and all skeletal fragments >2 mm were identified to the finest possible taxonomic level. Consistent with previous work on this interval, the relative abundance of trilobites declines sharply across the boundary, while the relative abundance of brachiopods increases. Absolute abundance data indicate that the decline in trilobite abundance is genuine and not an artifact of normalization. The trend is not easily explained by sampling bias, facies distribution, taphonomic regime, or sedimentation style. The dramatic shift in abundance contrasts with relatively minor changes in relative genus richness across the boundary. This is partly ascribable to differences in the relative abundance structure of trilobite faunas. Though comparable numbers of trilobite and brachiopod genera occur above and below the boundary, the trilobite fauna from the upper Ibex Series has lower evenness then the lower Whiterock Series fauna. Hence sampled trilobite richness is high in the lower Whiterock despite the small number of specimens. This highlights the importance of collecting abundance data. Although these data suggest that in at least some cases richness and abundance patterns are not closely coupled, more robust richness data are necessary to confirm this conclusion.

The Kanosh Formation of the Great Basin of western North America contains the oldest abundant and moderately diverse bryozoan fauna known from North America. Six species are here described from this formation at Ibex in the Confusion Range, Utah. They comprise three species of esthonioporine stenolaemates and three trepostomes. Two new genera (Ibexella and Kanoshopora) and three new species (I. multidiaphragmata, K. droserae, and Eridotrypa hindsi) are introduced. The endozone of Kanoshopora n. gen. is very unusual among bryozoans in being filled with vesicles that are divided by beaded walls into longitudinal files close to the boundary with the exozone.

Middle and Upper Ordovician Triarthrinae from the Precordillera of San Juan, Argentina, include the Whiterock/Llanvirn Porterfieldia turneri (Baldis and Pöthe, 1995) and P. acava new species, and the early Caradoc Triarthrus jachalensis (Harrington and Leanza, 1957). Each of these species is described based on silicified material, including ontogenies, from the Las Aguaditas Formation. Porterfieldia maanssonae new species from the lower member of the Gualcamayo Formation (late Arenig) at Río Gualcamayo, San Juan Province, and Río Guandacol, La Rioja Province, is closely allied to P. turneri. Two protaspid stages are present in Porterfieldia, whereas mineralized protaspid stages are apparently lacking in Triarthrus jachalensis. Triarthrus jachalensis was capable of sphaeroidal enrollment by meraspid degree 2. Precordilleran species bear closest comparison to others from Spitsbergen (Porterfieldia acava n. sp. and P. parapunctata) and Sweden/Norway (Triarthrus jachalensis and T. linnarssoni).

Gastropods that occur in the Anomalorthis brachiopod zone in the Spring Inlet Member of the Table Point Formation and in the Orthidiella brachiopod zone of the Shallow Bay Formation of the Cow Head Group are documented. Gastropods from western Newfoundland comprise part of the Toquima-Table Head fauna, and six of the seven genera described here are also found in Whiterockian strata of Nevada. Four species assigned to Monitorella Rohr, 1994, Maclurites Le Sueur, 1818, and Malayaspira Kobayashi, 1958, originally described by E. Billings in 1865 from Middle Ordovician (Whiterockian) strata of Newfoundland are revised. Five species of Helicotoma Salter, 1859, Malayaspira Kobayashi, 1958; Lytospira Koken, 1896; Rossospira Rohr, 1994; and Pachystrophia Perner, 1903, not previously reported from Newfoundland are also described. The probable opercula of Monitorella crenulata (Billings, 1865), and Maclurites emmonsi (Billings, 1865), are also illustrated for the first time.

Here we reaffirm and document fossil ranges at the strato-type section for the base of the Whiterock Series in Whiterock Canyon, northern Monitor Range, Nevada, and designate a reference section at Meiklejohn Peak, Bare Mountain quadrangle, Nevada. In both sections, stratigraphic ranges of conodonts indicate that the boundary between the Whiterock and the underlying Ibex Series lies between Oepikodus evae below and Tripodus laevis above. This level is correlated with the inception of the Isograptus victoriae graptolite lineage. Coeval brachiopod and trilobite faunas are summarized and their ranges graphically illustrated. The base of the Whiterock Series seems to be coincident with the start of the Taconic Orogeny. During the Whiterock other tectonically controlled events preceded the Tippecanoe Sequence in North America.