Systematics and biostratigraphy of non-mammalian vertebrates across the K/Pg transition, southern Wyoming, USA

Non-mammalian vertebrate fossils from the Ferris Formation in southern
Wyoming span the Cretaceous/Paleogene boundary and add to the growing
paleontological data set for testing models of biostratigraphic and
paleobiogeographic change in Laramidia during this interval. The
collection comprises over 6500 skeletal, dental, and epidermal elements
from 56 fossil sites and has not previously been described. New
stratigraphic and paleontological data suggest that the local K/Pg
boundary is 50 m stratigraphically above its previously proposed location,
but its precise location remains uncertain because an iridium layer has
not yet been located. Prior claims that dinosaurian diversity remained
high and non-mammalian vertebrate diversity was unchanged through the
Maastrichtian part of the formation are not supported by the fossil data.
Euselachian numerical abundance and taxonomic richness increase through
the Maastrichtian section, are at their highest ca. 94-26 ky before the
K/Pg event and then decline towards the boundary. Dinosaurian taxonomic
richness decreases through the Maastrichtian section, but low numerical
abundance of fossils makes the cause of this decrease uncertain. The
decrease in dinosaur fossils towards the K/Pg boundary corresponds to a
change in lithology of the formation and may not signal a true ecological
trend.