Smithian (Early Triassic) ammonoids from Crittenden Springs, Elko County, Nevada: taxonomy, biostratigraphy and biogeography.
Abstract
We present a comprehensive monographic treatment of all currently known Smithian (Early Triassic) ammonoid
taxa from Crittenden Springs. Extensive collection efforts from numerous stratigraphically discontinuous, condensed
outcrops over a period spanning four decades has yielded a total of 60 taxa. This activity has also resulted in the recognition
of a new biostratigraphic succession unique to Crittenden Springs, consisting of 12 ammonoid intervals that normally
occur within a typical ~1 m thick condensed outcrop. Ammonoids of early Smithian age are reported for the first time
from this locality. Intraspecific variation of the more abundant taxa is documented and illustrated. Early and middle
Smithian ammonoid biostratigraphy is shown to correlate reasonably well with the latest early and nearly the entire middle
Smithian portion of the newly reported Utah and Nevada successions as well as most Tethyan and western Panthalassic
localities. Late Smithian biostratigraphy correlates well with both the Utah and Nevada successions as well as all major
worldwide localities. The latest late Smithian ammonoid fauna also contains well preserved, undoubted members of the
Glyptophiceras 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 common
to several Tethyan localities, have not yet been reported from Utah, Nevada or other western USA localities. Many of
the newly described taxa further confirm the paleoequatorial nature of ammonoid faunas from Crittenden Springs as
well as the low paleolatitude faunal exchange that occurred between opposite sides of the Panthalassic Ocean during
Smithian time. One new family, the Crittendentidae is erected, whose composition includes Crittendenites n. gen. and
Wyomingites Hyatt, 1900. Newly described taxa (three genera and six species) include a proptychitid, Gambleites eichhorni
n. gen., n. sp., a galfettitid, Montelloites stephensi n. gen., n. sp., a crittendenitid, Crittendenites jattioti n. gen., n. sp., an
arctoceratid, 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, the
xenoceltitid “Xenoceltites” youngi (Kummel and Steele) and family Incertae Sedis,“Dieneroceras” spathi (Kummel and
Steele), respectively. Also included are seven newly reported taxa, e.g., Proharpoceras carinatitabulatum, Meekoceras
millardense, Meekoceras cf. M. olivieri, Kashmirites cf. K. guangxiense and Glyptophiceras cf. G. sinuatum.
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