Paper clams or "flat clams" were widespread in the Triassic. They often dominate the rocks in which they are found, as in these specimens from the "Daonella dubia' zone. This designation was coined by J. P. Smith in the early 1900's for specific localities in the Humboldt Mountain Range.
Because of their widespread distribution and very high species turnover rates, they make for excellent biochronological macrofossils, helping us to correlate biological events through time.
We see the "cousins" of these Nevada specimens up in Pine Pass near Chetwynd, British Columbia.
Pine Pass is part of the Pardonet Formation. Just a short hike from the road we were able to easily find the abundant outcroppings of the paper clam Monotis subcircularis, perfectly preserved and cemented in this strata from the Late Triassic.