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RESEARCH PRODUCT

Smithian (Early Triassic) ammonoids from Crittenden Springs, Elko County, Nevada: taxonomy, biostratigraphy and biogeography.

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175 pages; International audience; We present a comprehensive monographic treatment of all currently known Smithian (Early Triassic) ammonoidtaxa from Crittenden Springs. Extensive collection efforts from numerous stratigraphically discontinuous, condensedoutcrops over a period spanning four decades has yielded a total of 60 taxa. This activity has also resulted in the recognitionof a new biostratigraphic succession unique to Crittenden Springs, consisting of 12 ammonoid intervals that normallyoccur within a typical ~1 m thick condensed outcrop. Ammonoids of early Smithian age are reported for the first timefrom this locality. Intraspecific variation of the more abundant taxa is documented and illustrated. Early and middleSmithian ammonoid biostratigraphy is shown to correlate reasonably well with the latest early and nearly the entire middleSmithian portion of the newly reported Utah and Nevada successions as well as most Tethyan and western Panthalassiclocalities. Late Smithian biostratigraphy correlates well with both the Utah and Nevada successions as well as all majorworldwide localities. The latest late Smithian ammonoid fauna also contains well preserved, undoubted members of theGlyptophiceras sinuatum fauna, originally reported from the Tethyan realm. At least nine taxa from Crittenden Springs(e.g., Preflorianites cf. P. radians, Mesohedenstroemia kwangsiana and Wasatchites cf. W. distractus), while commonto several Tethyan localities, have not yet been reported from Utah, Nevada or other western USA localities. Many ofthe newly described taxa further confirm the paleoequatorial nature of ammonoid faunas from Crittenden Springs aswell as the low paleolatitude faunal exchange that occurred between opposite sides of the Panthalassic Ocean duringSmithian time. One new family, the Crittendentidae is erected, whose composition includes Crittendenites n. gen. andWyomingites Hyatt, 1900. Newly described taxa (three genera and six species) include a proptychitid, Gambleites eichhornin. gen., n. sp., a galfettitid, Montelloites stephensi n. gen., n. sp., a crittendenitid, Crittendenites jattioti n. gen., n. sp., anarctoceratid, Arctoceras rubyae n. sp., a prionitid, Meekoceras bylundi n. sp. and an aspenitid, Aspenites weitschati n. sp.Additionally, two new genera (Condensoceras n. gen. and Elkoceras n. gen.) are erected for previously described taxa, thexenoceltitid “Xenoceltites” youngi (Kummel and Steele) and family Incertae Sedis,“Dieneroceras” spathi (Kummel andSteele), respectively. Also included are seven newly reported taxa, e.g., Proharpoceras carinatitabulatum, Meekocerasmillardense, Meekoceras cf. M. olivieri, Kashmirites cf. K. guangxiense and Glyptophiceras cf. G. sinuatum.