Data from: Early Paleocene tropical forest from the Ojo Alamo Sandstone, San Juan Basin, New Mexico, USA

Earliest Paleocene megafloras from North America are hypothesized to be
low diversity and dominated by long-lived cosmopolitan species following
the Cretaceous-Paleogene (K/Pg) mass extinction. However, megafloras used
to develop this hypothesis are from the Northern Great Plains of North
America, and relatively little is known about floras from southern basins.
Here, we present a quantitative analysis of an earliest Paleocene
megaflora (<350 kyr after K/Pg boundary) from the Ojo Alamo
Sandstone in the San Juan Basin (SJB), New Mexico. The megaflora,
comprised of 53 morphotypes, was dominated by angiosperms, with accessory
taxa composed of pteridophytes, lycophytes, and conifers. Diversity
analyses indicate a species rich, highly uneven, and laterally
heterogeneous flora. Paleoclimate estimates using multivariate and
univariate methods indicate warm temperatures and relatively high
precipitation consistent with a modern tropical seasonal forest. When
compared to contemporaneous floras from the Denver Basin (DB) of Colorado
and the Williston Basin (WB) of North Dakota, the SJB flora had
significantly higher species richness but lower evenness. Paleoclimate
estimates from the SJB were 7-14 °C warmer than the DB and WB, indicating
a shift from a temperate forest in the Northern Great Plains to a tropical
forest in the SJB. These results demonstrate the presence of a latitudinal
floral diversity and paleoclimatic gradient during the earliest Paleocene
in western North America. We hypothesize that the warm, wet conditions in
the earliest Paleocene SJB drove rapid rates of speciation following the
K/Pg boundary resulting in a diverse and heterogenous flora.