Most biostratigraphic schemes for conodonts (and other fossils) are based on a combination of geographically separated stratigraphic sequences that contain abundant fossils. In developing biostratigraphy, generally little attention is given to identification of lithofacies that yield the fossils. Many sections in western North America include a mixture of sediments that represent a variety of marine environments. Such a stratigraphic mix of environment types yields a vertical sequence of fossils that represent a range of environments. Geographically separated but chronologically similar sections containing different environmental sequences may produce different sequences of fossils within a similar stratigraphic framework. Because of this, biostratigraphic schemes for similar age sequences may differ. Lower Triassic biostratigraphy in western North America is based on study of rock sequences that represent a variety of transgressional and progradational sediments. The “standard” Lower Triassic conodont zonation that has emerged is real, even usable, but includes conodont species representing a range of environments from shallow inner shelf to deeper basinal. This ecologic mix has utility simply because most comparable Triassic rock sequences are also a mix of lithofacies, and at least some of the conodont species in the “standard” can be found in any other section. Because certain conodont species probably were more sensitive to a narrow set of environmental parameters than has been realized, application of the ecostratigraphy concept may develop actual conodont biofacies biostratigraphy, a different biostratigraphy for each definable position along an environmental gradient.

Five marine biofacies based on conodont distributions are recognized for the Permian Phosphoria Formation and related rocks. They are: (1) facies with no conodonts, (2) facies with Hindeodus only, (3) facies with Hindeodus and (or) Neostreptognathodus and (or) Stepanovites and (or) Merrillina, (4) a transitional facies containing any of the components of biofacies 3 with either Neogondolella or Xaniognathus, (5) facies dominated by Neogondolella and Xaniognathus. These biofacies (1–5) represent progressive shore or nearshore to offshore differentiation of the conodont faunas. Intervals of phosphate deposition within the Phosphoria Formation correspond to shoreward encroachment of offshore biofacies during trasgressive events. Elements of these conodont faunas, including the new species Neostreptognathodus newelli , are described.

The Lower Triassic (Smithian) Thaynes Formation represents a broad spectrum of paleoenvironments. Samples collected along a depth-related gradient from tidal flats to a relatively deep, commonly dysaerobic, basin yielded an abundant conodont fauna. Simple chi-square tests and multivariate analyses using six conodont entities indicate the presence of three distinctive biofacies related to the general environmental gradient. The restricted inner shelf is characterized by Parachirognathus . The outer shelf is distinguished by a diverse conodont fauna including Furnishius . Basinward, the low diversity conodont fauna is dominated by species of Neogondolella. Some Early Triassic conodonts such as Neospathodus are ubiquitous and provide the best foundation for inter-basinal conodont zonation. Correlation of assemblages with corresponding position along an environmental gradient defined on lithologic criteria indicates that quantitative measures of conodont faunas are potentially useful in the analysis of paleogeography and changes in relative position of sea level.