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.
Supplementary Tables 1-8
Supplementary Tables 1-8 which includes (1) systematic list of megafloral morphotypes from the San Juan Basin, (2) stratigraphic position, depositional facies, location, and morphotype tallies for all floral sites, (3) megafloral census data, (4) megafloral presence-absence data, (5) total Ojo Alamo Sandstone and facies mean physiognomic variables using the DiLP paleoclimate calculation, (6) measured leaf physiognomy values for all measureable specimens/morphotypes, (7) regional diversity comparison, and (8) - calculated p-values for Margalef Index, Pielou's Evenness, and Berger-Parker Index for all San Juan Basin, Denver Basin, and Williston Basin diversity indice comparison.
Appendix 1 - Morphotype Catalog
Ojo Alamo Sandstone Morphotype Catalog Morphological descriptions, botanical affinities, photographs, and line drawings of all identified Ojo Alamo Sandstone megafloral morphotypes. All dicotyledonous angiosperm leaf morphotypes were described using the Manual of Leaf Architecture (Ellis et al. 2009). Each dicotyledonous angiosperm leaf morphotype description contains leaf architecture description, margin classification, and Raunkiaer-Webb (Webb 1959) size classification. All other groups (i.e. dicotyledonous angiosperm reproductive structures, pteridophytes, monocotyledonous angiosperms, and conifers) were described based on their gross morphology. Botanical affinities of morphotypes were determined after comparison with previously published taxonomy. Each morphotype also has a specimen number which corresponds with the morphotype exemplar. See Supplementary Table 1 for detailed systematic morphotype list and Supplementary Table 2 for morphotype abundance by fossil locality.
Morphotype Catalog.pdf
Supplementary Figure 1 - Facies and Formation Photos Small
Generalized latest Cretaceous and earliest Paleocene stratigraphic units and Ojo Alamo Sandstone lithofacies. A: contact between the Maastrichtian Naashoibito Member of the Kirtland/Fruitland Formation and the overlying earliest Paleocene Ojo Alamo Sandstone. B: the contact between the earliest Paleocene Ojo Alamo Sandstone and overlying early Paleocene Nacimiento Formation. C: representative overbank leaf Locality AF1409D in the Ojo Alamo Sandstone. D: closeup of the overbank flora deposits which are interbedded siltstone and medium to coarse grained sandstone and have been interpreted to represent downstream accretionary bars. E: is a coarse grained cross-bedded sandstone with occasional gravel lag deposits which account for the majority of the Ojo Alamo Sandstone. F: representative pond/swamp floral locality AF1407 and the contact between earliest Paleocene Ojo Alamo Sandstone and early Paleocene Nacimiento Formation. G: close up of pond/swamp leaf locality AF1407 showing fine grained carbonaceous shales typical of pond/swamp floral facies.
Supplementary Figure 2 - Digital Leaf Physiognomy Examples
Examples of the 4 different types of leaves prepared for digital leaf physiognomy (DiLP) following the protocol of Peppe et al. 2011. All digital preparation was done using Adobe Photoshop.
Supplementary Figure 2 with Caption.pdf