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The Global Boundary Stratotype Section and Point (GSSP) for the Katian Stage of the Upper OrdovicianSeries is defined as the 4.0 m-level above the base of the Bigfork Chert in the Black Knob Ridge section, southeastern Oklahoma. This point in this section is coincident with the first appearance of the graptolite Diplacanthograptus caudatus, which has proved to be a reliable datum for precise worldwide correlation. The FAD of D. caudatus occurs very near the first occurrences of the graptolites D. lanceolatus, Corynoides americanus, Orthograptus pageanus, O. quadrimucronatus, Dicranograptus hians, and Neurograptus margaritatus. This rapid succession of fossil species appearance events provides a secure basis for identification of the base of the Katian Stage of the Upper Ordovician Series and for its global chronostratigraphic correlation.In addition to graptolites, the Black Knob Ridge section also contains biostratigraphically important conodonts and chitinozoans. The conodonts and chitinozoans occur with graptolites on black shale bedding surfaces and allow for the precise correlation of the Katian Stage into regions where the succession is represented by carbonate facies. The base of the Katian Stage occurs high in the Amorphognathus tvaerensis North Atlantic Conodont Zone and just below the base of the Plectodina tenuis North American Midcontinent Conodont Zone. This stratigraphic level is also in close proximity to several important marker horizons -just above the Millbrig and Kinnekulle K-bentonite complexes in eastern North America and Scandinavia, respectively, and just below the beginning of the Upper Ordovician Guttenberg (GICE) ! 13 C excursion. These event and chemostratigraphic marker horizons provide an independent test of the global synchroneity of the base of the Katian Stage, and greatly increase the usefulness of that level for global chronostratigraphic correlation.

SUMMARY Normalograptids constitute a distinctive but not easily identified group of derived axonophorans. A new study of Normalograptus morphology indicates that many Late Ordovician taxa previously identified as Normalograptus are actually referable to Styracograptus and related climacograptoids. These re-identifications have led to the recognition of a complex biogeographic history among normalograptids and their descendants, including an interesting pattern that had previously been overlooked – a late Katian disappearance of Normalograptus from the palaeotropics. Normalograptid palaeogeographic distribution in the Ordovician appears to comprise 5 main phases: (1) evolutionary origin probably in relatively high palaeolatitudes in the early to mid Darriwilian; (2) spread to global distribution in later Darriwilian time; (3) retreat from most low palaeolatitude regions during the early Katian, with perhaps a slightly delayed retreat from Laurentia; (4) a complete extirpation from the low palaeolatitudes by the mid Katian (Ea4); (5) reinvasion of the low palaeolatitudes that accompanies the remarkable ecological and evolutionary replacement of the Diplograptina by species of Normalograptus and their descendants during the latest Katian–early Hirnantian. We propose two sets of hypotheses to explain Late Ordovician Normalograptus distribution. First, given the low species diversity of Normalograptus , we suggest as a null hypothesis that the disappearance of normalograptids from low palaeolatitudes during the late Sandbian and early Katian as simply a stochastic outcome – a small clade simply went extinct by chance alone. The alternative is that the loss of Normalograptus species reflects some form of extinction for cause, either: (1) competitive exclusion; or (2) an inability to adapt to changing environmental conditions. In the case of the competitive exclusion hypothesis, the most likely competitors are species of the Diplograptina.

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The Geobiodiversity Database (GBDB-www.geobiodiversity.com), an integrated system for the management and analysis of stratigraphic and paleontological information, was started in 2006 and became available online in 2007. Its goal is to facilitate regional and global scientific collaborations focused on regional and global correlation, quantitative stratigraphy, systematics, biodiversity dynamics, paleogeography and paleoecology. It is unique among global, public access databases in that it is a section-based online database system, incorporating data from a wide range of disciplines of stratigraphy and paleontology, with inherent interrelationship between different kinds of data sets. It provides the capability of completely digitizing raw data, as well as integrating of different interpretations to the same paleontological and stratigraphic content. Several Windows-based visualization and analysis applications, either fully integrated with the database or supported by subset-export functions, have been developed to make the database more useful as a scientific and educational tool. The GBDB became the formal database of the International Commission on Stratigraphy (ICS) in August 2012 at the 34 th International Geological Congress in Brisbane, and will produce comprehensive and authoritative web-based stratigraphic information service for global geoscientists, educators and the public.