Pollen Evidence of Floristic Turnover Forced by Cool Aridity During the Oligocene in Colorado GEOSPHERE; V

Research Paper

GEOSPHERE Pollen evidence of floristic turnover forced by cool aridity during the Oligocene in Colorado GEOSPHERE; v. 15, no. 1 Estella B. Leopold and Stephanie Zaborac-Reed University of Washington, Department of Biology, Box 351800, Seattle, Washington 98195, USA https://doi.org/10.1130/GES01689.1

7 figures; 6 plates; 11 tables; ABSTRACT Manchester, 1997). In Colorado, the EOT is associated with a period of cooling 1 set of supplemental files and severe aridity lasting most of the Oligocene. One of our strongest contri- New pollen data from four Oligocene floras in volcanic landscapes of Colo butions is the addition of the pollen record from four Oligocene floras, which CORRESPONDENCE: eleopold@uw.edu rado record important climatic shifts that reshaped the local flora and promoted had not been reported previously. This pollen record is an important aspect the development of sub-arid vegetation types. We combined new pollen data of this paper for assessing the total flora. The emphasis of this study is on the CITATION: Leopold, E.B., and Zaborac-Reed, S., 2019, Pollen evidence of floristic turnover forced by with previous megafossil evidence to assess vegetation changes during the evolutionary and climatic significance of the floristic changes during the EOT. cool aridity during the Oligocene in Colorado: Geo- Eocene–Oligocene Transition (EOT). Pollen data are the basis for updating Five Colorado floras of late Eocene through Oligocene age lie within the sphere, v. 15, no. 1, p. 254–294, https://doi.org/10 the list of flora identified at Creede. Local extinctions in response to lower sum geographic mix of caldera and volcanic settings in the central Colorado vol .1130/GES01689.1. mer rainfall abruptly removed many of the exotic woody taxa of eastern North canic area and in the San Juan volcanic field in southwestern Colorado (Fig. 1). American and Asian affinity. This loss was followed by the appearance of xeric The floras are, in ascending order: the Florissant (34.1 Ma), Antero (33.8 Ma), Science Editor: Shanaka de Silva Associate Editor: Rhawn Denniston shrubland taxa of the Ponderosa pine-fir woodland and sagebrush flora that Pitch-Pinnacle (between 32.9 and 29 Ma), Platoro (28.0 Ma), and Creede characterize the Colorado area today. Tell-tale genera appear and suggest an (26.9 Ma) assemblages (Fig. 2; Table 1). The purpose of this report is to sup- Received 6 March 2018 understory of shrubs such as Artemisia, Elaeagnus, Ribes, Ephedra, Jamesia, plement previous work on plant megafossils of the Oligocene in Colorado with Revision received 22 August 2018 and Shepherdia. Poaceae are also present. Significantly, herbaceous taxa of our new work on fossil pollen. We characterize the pollen and megafossil floras Accepted 9 November 2018 the Asteraceae, Rosaceae, Cucurbitaceae, Euphorbiaceae, and Caryophyllaceae from just before and after the EOT and interpret the climatic and floristic shifts Published online 10 January 2019 make their first appearances in the fossil record of Colorado here. that they demonstrate with emphasis on the following questions: The new Oligocene pollen data record a significant drop in summer rainfall and a climatic cooling at 33.8 Ma of several degrees that relates to the Oi-1 (1) What was the scale of the climatic shift based on the floras, and how glaciation in Antarctica. The particular taxa that continued after the EOT were does it relate to possible uplift of the region? a basis for estimating changes in soil moisture during this time. The condi (2) What was the evolutionary significance of the floristic changes during tions in Colorado are reminiscent of Wolfe’s “terminal Eocene event.” This re the Colorado EOT? markable shift precipitated the development of a local pollen and megafossil (3) What estimates of paleoelevation may be based on these floras and the flora more “modern” in aspect (e.g., a larger proportion of extant local genera local geology of the sites? are present). The impressive floristic turnover was probably a response to the (4) How do climate tools such as coexistence approach, detrended corre- increasingly continental climate that embraced the area during the Oligocene. spondence analysis, the Sørensen index, and nearest living relatives analysis assist the interpretation of the floras in terms of inferred mean OLD G 1. INTRODUCTION annual temperature (MAT) and precipitation (PPT)? (5) How do the inferred climate shifts compare to conditions in other parts The global climate change at the Eocene–Oligocene transition (EOT) of the world during the EOT? (33.4 Ma; Prothero and Berggren, 1992) is the largest abrupt cooling of the OPEN ACCESS Cenozoic (Zachos et al., 2001). During the EOT, changes in circulation result- 2. BACKGROUND ing from the development of deep-water passages separating Antarctica from South America (beginning ca. 33 Ma) (Graham, 2011; Lawver et al., 2011) may Our fossil records span the latest Eocene Florissant flora (34.1 Ma) and have contributed to the major worldwide cooling and associated aridity re- four progressively younger Oligocene floras (33.8 Ma–26.9 Ma; Table 1). This lated to Antarctic glaciation Oi-1 (Cather et al., 2008). This post-Eocene cool- interval is closely synchronous with large-scale explosive volcanism in the ing and aridity resulted in local and regional extinctions of plant, vertebrate, southern Rocky Mountains (mainly 37–27 Ma), the development of the Oi-1 This paper is published under the terms of the and invertebrate taxa (Prothero, 1985a, 1985b; Hutchison, 1992; Legendre and glaciation and the “Ice House,” and the period of great aeolian activity along CC‑BY-NC license. Hartenberger, 1992; Prothero and Berggren, 1992; Wolfe, 1992; Meyer and the Arizona–New Mexico border (Zachos et al., 2001; Cather et al., 2008).

2.1. Regional Geological Setting of the Five Paleogene Floras in Colorado

The Florissant fossil beds formed after a comparatively small volcanic event that dammed a lake at the end of the Eocene. In contrast, the Oligocene floras that immediately followed in southwestern Colorado developed in local volcanic sediments. The San Juan volcanic field produced 28 large-volume ignimbrite eruptions between 36.9 Ma and 26.9 Ma (Lipman and McIntosh, 2008; Lipman et al., 2015). Ponding of distal ash from these and the formation of lakes within source calderas are the main sites for the floras discussed here. The Florissant Formation formed when a lahar blocked the Florissant Valley in the Thirtynine Mile volcanic area (36.9 Ma to 34.3 Ma), leading to the development of Lake Florissant (McIntosh and Chapin, 2004; Fig. 1). Distal ash asso ciated with Mount Aetna nearby accumulated in another intermontane lake to form the Oligocene Antero Formation (33.8 Ma). In addition, lake deposits of the Pitch-Pinnacle flora accumulated within and near the Marshall caldera at ca. 33.8 Ma (Lipman et al., 2013, 2015). Shortly after this, a dune field of aeolian dust and sand in the Chuska Mountains of northwestern New Mexico

Figure 1. Reference map of the Colorado and New Mexico Oligocene calderas, with the five and Arizona (Fig. 1) formed at ca. 33.5 Ma and lasted until 28–26 Ma (Cather flora sites indicated (after Chapin, 2012). The floras studied are: (1) Florissant;( 2) Antero; et al., 2008, 2012). Called the Chuska erg, or sand sea, these deposits (as thick (3) Pitch-Pinnacle; (4) Platoro, and (5) Creede. The La Garita caldera is represented by the as 535 m) resulted from large accumulations of airborne and fluvial material in outline surrounding the group of San Juan volcanic field calderas clustered around Creede. the central and southern Colorado Plateau (McIntosh et al., 1992).

Figure 2. Map of Creede area, including lo cations of pollen collections (D numbers) and megafossil collections (circles). Based on The National Map (http://nationalmap .gov) shaded relief map and the 7.5 min series Creede quadrangle map, U.S. Geo logical Survey, 2013.

TABLE 1. IE ROCY MONTAIN PALEOGENE LORAS O COLORADO IN STRATIGRAPHIC ORDER lora Present elevation lora source and No. of taa for Ages of associated formations or volcaniclastics kmegetation type stratigraphic source this report Oligocene Creede 2.7–3.3 Open coniferous forest, mid-montane and Aelrod 1987 49 26.87 0.03 Ma 40Ar/39Ar using l-rich dacite youngest montane olfe and Schorn 1989, 1990 from Snowshoe Mountain Tuff; Lipman, 2007 eposures Ecotone between mied conifer forest upland Lanphere 2000 and pinyon uniper woodlands and scrub Leopold and Zaborac-Reed 2014 Aelrod This report Platoro 3.1 Open coniferous forest, montaneChase et al. 1998 36 27.98 0.11 Ma 40Ar/39Ar using biotite from Meyer 1986 Chiuito Peak Tuff; Lipman and Bachmann, Lipman 2000 2015 Lipman and McIntosh 2008 This report pollen Pitch Pinnacle 3 Conifer mied forest Gregory and McIntosh 1996 28 Between 32.9 oldest and 29 youngest Ma Lipman et al. 2015 40Ar/39Ar using sanidines from Pitch-Pinnacle This report pollen ormation; unit is epiclastic; so date cannot be pinned down; Gregory and McIntosh, 1996 Antero 2.9 Conifer mied forest Durden 1966 45 33.76 0.10 Ma 40Ar/39Ar using sanidine from Cool coniferous olfe Meyer et al. 2012 Antero ormation ignimbrites; Meyer et al., arm-temperate similar to mountains olfe 1992 2012 of modern northern Meico, with mesic streamside, eric upland, and perhaps montane elements Durden, 1966 Eocene lorissant 2.5 Hardwood and conifer valley forest MacGinitie 1953 108 34.07 0.10 Ma 40Ar/39Ar using sanidine from Rich mesic Sequoia forest along streams, scrub Zaborac-Reed and Leopold 2016 lorissant ormation; Evanoff et al., 2001 forest on higher ground MacGinitie Manchester 2001 Leopold and Clay-Poole 2001 ingate and Nichols 2001 heeler 2001 Meyer 2003 Leopold et al. 2008 Bouchal et al. 2016 Bouchal 2013 Boyle et al. 2008 This report Average level of Oligocene ash-flow plateau lake elevation 1.2 km Note: lcrystal.

The most intense volcanic activity was focused in the San Juan volcanic Hay, 2000; Larsen and Lipman, 2016) provides data on paleolimnology based field from 34 to ca. 26 Ma (Lipman, 2007; Lipman et al., 2015). Multiple ig- in part on two drill cores penetrating >700 m through the caldera lake deposits nimbrites of the Treasure Mountain Group erupted between 31 and 28.6 Ma, (Larsen and Nelson, 2000). The depth of the lake fluctuated at times by tens of creating the Platoro caldera complex (Lipman et al., 2013). Lake deposits in the meters, with waters variously saturated with carbonates and saline mixtures caldera contain the Platoro flora. Among the San Juan eruptions was one of (Larsen and Lipman, 2016). the largest single volcanic events in Earth history: the 5000 km3 Fish Canyon Aerosols from these multiple and sizeable volcanic events probably had Tuff erupted from La Garita caldera in the central San Juan volcanic field at a cooling effect on the mean annual temperature of the region, similar to the 28.02 Ma (Mason et al., 2004; Lipman, 2007). The Creede flora was deposited aerosols from recent eruptive events (such as Krakatau, Tambora, and Pina- within the Creede caldera, the youngest of seven calderas nested within La tubo) that have influenced climate by blocking solar energy (Williams, 2012). Garita (Lipman, 2000). The history of the Oligocene Lake Creede (Bethke and Given their magnitude, such large-scale eruptive events in the San Juan vol

canic field could potentially have influenced not just regional but global climate. Cather et al. (2009) postulated that enormous amounts of volcanogenic silicic dust generated episodically in this region may have contributed locally to Oligocene global cooling by intercepting solar radiation and enhancing oxy gen production via iron fertilization of the oceans. Because of the close tem- poral relationship between the Oi-1 event of Zachos et al. (2001) and the onset of aeolian deposition and increasing aridity of the region, Cather et al. (2008) suggested that the Oi-1 event helped to drive the Oligocene aridification of the Colorado Plateau.

2.1.1. Paleoelevation

An important question in the geologic literature deals with the elevational history of the Southern Rocky Mountain region relative to the high elevations of the fossil plant localities today. A wide range of methods and results have been presented, predicting extremely high (>3000 m) or extremely low (<500 m) paleoelevations for certain floras at their time of deposition (Fig. 3; Tables 1 and 2); e.g., multiple methods examined by Gregory and McIntosh (1996), the enthalpy-based method of Wolfe et al. (1998), the lapse rate method based on Axelrod and Bailey (1976), and Wolfe’s (1994) paleobotanical method, which combined lapse rates with MAT of a flora and MAT of an isochronous flora at sea level to calculate paleoelevation. As a result, two constraints in particular must be recognized in order to come up with a reasonable estimate TABLE S1. SLIDES USED IN THIS STUDYAND THEIR COLLECTION LOCATIONS FloraSlide #Catalog Location#/ Locality data of paleoelevation for the five floras: the initial Paleogene elevation, plus any Number Collection CreedeR-2912-3/OTC UCM36936, Location #84001 Creede (General), R-2912-4/OTC UCM39959 Caplan, ca. 1935, Mineral Co., CO potential subsequent tectonic activity in the Colorado Plateau and southern Univ.Colo. D1181-1 to - 19 samples, USGS, E. Leopold Near Hubbard’s Rocky Mountains. 19 laminae coll. 5/10/56. Cabins. Creede, spanning a Section 3 Finely Mineral Co., CO. 50-mm laminated ashy Corner Sec 9, 10 section orange-tan layers 2- or 16 T41N 4 mm each; with R1W.This is a 2.2. Previous Paleobotanical Descriptions gypsum land-slide section. D1138-5 G.E. Lewis and Tom West of loc. D1138- Steven July-Aug. 3; 1.5 mi. S. of 1955. Creede., 1/2 mi W. of Willow Creek at In-depth analyses of the pollen data from the Oligocene floras have not 8700 ft. D1138-1 – G.E. Lewis & Tom 3 mi. SW of Creede. been previously published. The report on the Antero megafossil flora was by D1138-4 Steven, July, 1955 S of Shallow brook and N. of road, Figure 3. Graph showing the previously published estimated elevation data for the five Paleo 9000 ft. elev., Durden (1966). Gregory and McIntosh (1996) described the Pitch-Pinnacle flora. Mineral Co., CO. gene floras of Colorado at the time of deposition (Table 2). Error bars are shown where available. D4293-E, 10 samples E. Leopold & Tom 30’, below 5’ thick; Lipman (1975) and Meyer (1986) each published details on the Platoro flora. D4293-G, taken every Steven coll.; EL white tuff; 30 ft. The blue circles show the present elevation of the floras. The green rectangles represent esti D4293-J 10 feet down Section 1, USGS, below ridge top. section. June 9, 1956. N. of Creede, Mineral After the early work on the Creede flora by Knowlton (1923), Axelrod (1987) mated paleoelevations just prior to late Miocene uplift (Cather et al., 2012; Karlstrom et al., 2012). 7- mile bridge. Co., CO. See Tom NW1/4 Sec. 16, Stevens’ No. C- completed a detailed revision and geologic description of the flora. Steven T41N R1W. 1077. Needles & leaf fragments. and Ratté (1965) mapped and described the physical stratigraphy of the Creede D4294A, E. Leopold Section Creede, Mineral Co., D4295A 2, USGS; Five-Mile CO. Center Sec. area and included a few identifications of pollen and megafossils. Howard 3. METHODS Bridge Loc.; rich 10, R1W, T41N leaf locality Schorn undertook a taxonomic revision of the Creede megafossil flora (Schorn PlatoroRME-72-1D, Lipman, P W (2000) Red Mt 7.5 min. 71L-91-A GSA spec. paper quad Sec. 1, T.35 and Wolfe, 1989), part of which was then published by Wolfe and Schorn (1989) In this paper, the isotopic dates are rounded to the nearest first decimal 346, p9-69; N, R4.5 E Lipman,PW & McIntosh (2008) on the evolutionary significance of the flora. Wolfe and Schorn (1990) followed (tenth). Dates of the fossil-bearing sediments are given in Table 1. A list of GSA Bull. 120 USGS loc. D4772 with a major taxonomic revision of the Creede flora, which included a critical collections consulted and slides made from pollen and/or spore samples col- samples A thru E review of the study by Axelrod (1987). The earlier reports show that the Creede lected at the Eocene and Oligocene sites used in this study are listed in Table 1 1Supplemental Items. Table S1: Slides used in flora was warmer and more arid in aspect than the present local vegetation, S1 of the Supplemental Items. Pollen and/or spore slides bearing paleobotany this study and their collection locations. Table S2: indicating that a post-Eocene climate cooling and/or uplift had occurred (Axel- “D” and “W-1” locality numbers are reposited at the U.S. Geological Survey warm-adapted versus cool-adapted taxa (support rod, 1987; Wolfe and Shorn, 1989). These Eocene and Oligocene floras are a (USGS) Core Research Center at the Denver Federal Center. Slides from the for Figure 7B). Please visit https://doi.org/10.1130 /GES01689.S1 or access the full-text article on www window into the history of the Cordilleran (Axelrod and Raven, 1985; Benedict, Antero and Pitch-Pinnacle pollen floras were kindly made available by Dena .gsapubs.org to view the Supplemental Items. 1991) flora of the southern Rocky Mountains. Smith at the University of Colorado Museum and Herb Meyer of the National

TABLE 2. PALEOELEATION ESTIMATES, AT THE TIME O DEPOSITION, OR THE IE PALEOGENE COLORADO LORAS lora Paleoelevation Modern elevation kmSourceMethod Oligocene Creede 1.1 and 1.5–1.8 Aelrod, 1987 NLR Elevation: 1.2–1.5 Aelrod and Bailey, 1976 NLR and lapse rate 2.7–3.3 km 1.1 lake Steven and Ratt,1965 2.0–2.4 plateau 1.8 Meyer, 1986 NLR and lapse rate 6.6 C/km 2.2–2.5 olfe and Schorn, 1989 rim Lapse rate, CLAMP 1.5–1.75 olfe and Schorn, 1989 plateau Lapse rate, CLAMP 2.6 and 2.8 olfe et al., 1998 Lapse rate, CLAMP Platoro 1.8 Meyer, 1986 Lapse rate Elevation: 3.1 km Pitch-Pinnacle 0.8 0.4 or 0.8 0.7Gregory and McIntosh, 1996; using Meyer, 1992 Lapse rate 5.9 C/km, CLAMP Elevation: 3.0 km postdeterioration, 68 or 95 confidence Lipman et al., 2015 1.0 0.7 or 1.0 1.4Gregory and McIntosh, 1996; using olfe, 1992 Lapse rate 3.0 C/km, CLAMP postdeterioration, 68 or 95 confidence 2.0 0.7 Gregory and McIntosh, 1996; using orest et al., 1995 Enthalpy Antero No data for depositional elevation Elevation: 2.9 km Eocene lorissant 0.455 Aelrod, 1998 p. 31 NLR, global lapse rate 5.5 C/km Elevation: 2.5 km 0.3–0.9 MacGinitie, 1953 NLR Low elevationBarton and ricke, 2006; consistent with 1 km Clumped isotopes Low elevation Hyland and Huntington, 2015 Clumped isotopes of lacustrine sediments 1.0–1.5 Zaborac-Reed and Leopold, 2016 NLR 1.4 Cather et al., 2012 Erosional history reconstruction geologic and thermochronomatic 1.6 to 2.8 Boyle et al., 2008 eighted average partial least-suares regression APLS and genus-derived MAT 1.9 0.5, 1.9 1.0 Gregory and McIntosh, 1996; using Meyer 1986, 1992 Lapse rate 5.9 C/km, CLAMP 2.4–2.7 Gregory and Chase, 1992 Lapse rate 2.45 Meyer 1986, 1992 Lapse rate 6.7 C/km 2.0–2.9 olfe, 1992 Lapse rate 2.9 0.7 Gregory and McIntosh, 1996; using orest et al., 1995 Enthalpy 2.3 and 4.1 olfe, 1994 Lapse rate 5.5 C/km and 3.0 C/km 3.1 0.8 Gregory and McIntosh, 1996; using olfe, 1992 Lapse rate 3.0 C/km, CLAMP 3.8 0.8 olfe et al., 1998Moist static energy and enthalpy, CLAMP Abbreviations: CLAMPClimate Leaf Analysis Multivariate Program; MATmean average temperature; NLRnearest living relative.

Park Service, and collections from the Platoro caldera (D4772) were provided (1987) along the north rim of the Creede crater. Sediments from locality D1811 by Peter Lipman. Plant megafossils and pollen samples were collected by were sampled as paper shale laminae containing pollen but no megafossils. Leopold and Steven at several localities in the Creede caldera: at Five-Mile Among our pollen and spore collections from seven Creede Formation local- Bridge, about five miles southwest of Creede, Colorado, and near Birdseye ities, four samples yielded preservation adequate for confident identification Gulch, one mile directly south of Creede (Fig. 2). Both areas are also collection of the grains. Pollen of Ephedra, which is a shrub, is counted with the non- sites of Axelrod (1987) and Knowlton (1923). Leopold’s other Creede collec- arboreal (non-tree) pollen (NAP). tions are from a site north of Seven Mile Bridge (D4293) and another lakeside Pollen preparation of USGS samples followed Doher (1980) and involved site (D1811) in the caldera (Fig. 2). These Creede collections were closely asso treatment with KOH, HF, and acetolysis. Residues were mounted in glycerin ciated with a prominent 5-m-thick white volcanic ash described by Axelrod jelly and cured and sealed with clear plastic (Doher, 1980; Traverse, 2007).

Some preparations from the University of Colorado Museum collections sets, and it is therefore helpful for evaluating differences between ecolog- (some of which were collected by Herb Meyer) were done at Global Geo- ical communities (Looman and Campbell, 1960). The formula used for the lab Limited in Medicine Hat, Alberta, Canada, where the Creede pollen was Sørensen index is: mounted in clear plastic (polyvinyl alcohol). Photomicroscopy was performed using a Leica DFC295 camera running the Leica Application Suite version 4.0 S = (2A/2A + B + C), software package. Pollen counts were conducted using 13 samples from the five Paleogene sites; these are recorded in Table 3 and are listed in chronolog- where “A” is the number of taxa found in both data sets, “B” is the number of ical order. Megafossil and pollen compositions of the five Paleogene floras, taxa unique to data set 1, and “C” is the number of taxa unique to data set 2. along with their sources, are compiled in Table 4. Family-level ids, conifers, monocots, and dicots identified in Table 4 were used Using PAST version 3.0.4 (Hammer et al., 2001), a detrended correspon- for these statistical analyses. Fern allies, extinct taxa, and the IDs “small pine” dence analysis (DCA) was performed in 2016 by Cindy Looy of University of and “legume” were not evaluated. The results appear as percentage values for California Berkeley to evaluate ecological trends among the five floral commu- ease of discussion (% = S*100). nities (Fig. 4). The pollen counts in Table 3 were used for this purpose, omit- ting those group taxa described as “undetermined” or not assigned to a living 4. RESULTS plant group. The information for a taxon’s abundance, presence, or absence in each sample can determine whether the taxa have a similar distribution on The floral lists for the five floras include megafossil, pollen, and spore iden- the DCA plot. tifications obtained from various samples (Tables 1 and 4). Because a number Moisture availability in the soil is a critical factor controlling the success of of the taxa in these floras are wind pollinated, it is important to note when plant life in semi-arid environments. Soil moisture indexes of particular taxa pollen identifications were also confirmed by megafossil evidence. Relative provide one way to estimate the balance between actual evaporation (AE) abundance of pollen types in sequential samples is portrayed in the histogram versus potential evaporation (PE) and represent an important environmental (Fig. 5), which serves to provide a snapshot of the overall vegetation change feature. The annual rainfall and evaporation conditions expressed by this ratio during the EOT. (AE/PE) demonstrate a relationship critical to plant survival in many western (continental) environments (Thompson et al., 2012) and can be used to reveal 4.1. Floral Composition local and regional patterns of influx and loss of floral taxa. Our interpretation of paleoclimate and environments here used nearest 4.1.1. Late Eocene (Florissant) living relatives (NLR; Mosbrugger and Utescher, 1997) as well as the coexistence approach (CA) method (Utescher et al., 2014; Zaborac-Reed and Leopold, The Florissant megafossil and pollen flora is extremely diverse and 2016), by which generic identification of the nearest living relatives are a basis warm-temperate in character, including more than 100 taxa (MacGinitie, 1953 for estimating temperature tolerances for the entire flora. These represent as modified by Manchester, 2001; Leopold and Clay-Poole, 2001; Bouchal, rough approximations of temperature conditions for the floras and are not 2013; Bouchal et al., 2016; Zaborac-Reed and Leopold, 2016; Table 4). Rosaceae adjusted according to the estimated elevations of the sites. We used the CA is the main family (eight genera). method to apply the ranges of MAT tolerances on the pollen and megafossil The pollen flora demonstrates a great diversity of arboreal dicots, including genera of the various floras based on values from Thompson et al. (2015), a few East Asian genera. Pollen counts record a flora rich in arboreal pollen Fang et al. (2011; see Zaborac-Reed and Leopold, 2016), and others (Table 5). (AP) types, especially woody broad-leaved dicots (10%–55% in abundance); Taxa previously identified as outliers by Utescher et al. (2014), monotypic taxa, some 63 taxa include 22 summer-moist tree taxa (Tables 3 and 4). An earlier uncertain identifications, and taxa identified by singleton pollen grains were pollen assignment identified asPteroceltis (Leopold et al., 2008) is incorrect excluded from CA analysis. Mean annual temperature (MAT) and cold-month and is now rejected. mean temperature (CMMT) values were examined (Table 5). The pollen histogram (Fig. 5; Table 3) shows a relatively important role for Table 6 includes estimates of MAT and annual rainfall (PPT) by Axelrod Pinaceae (12%–30%) and other conifers, as well as Taxaceae/Cupressaceae/ (1987), MacGinitie (1953), Gregory and McIntosh (1996; Climate Leaf Analysis Taxodium-type (TCT) pollen (8%–65%), presumably representing pollen of Multivariate Program [CLAMP] data), and Wolfe and Schorn (1989). Evaluating Sequoia affinis, Juniperus, or Chamaecyparis. At Florissant, cool indicators precipitation using the CA method has not proven feasible here (Zaborac-Reed such as Picea and Abietineae are rare (~5%). The non-tree pollen (NAP) such and Leopold, 2016). as Ephedra and other dryland shrubs are a minor group (2%–12%). The Sørensen index of similarity was used to evaluate similarities between A considerable number of families and genera found at Florissant are the five floras (in particular, the Eocene Florissant versus the Oligocene floras). known for their tropical or subtropical distribution today (Table 7). Some, such The Sørensen index is weighted to recognize similarity between binary data as Platycarya and Eucommia, have East Asian affinities.

TABLE 3. POLLEN COUNTS Pitch- Florissant Antero Pinnacle Platoro Creede R2063-3 / R2910-1 / D4294A (2) D1083 D3496 D1496 Fish Beds OTC(1) OTC “101” R2912-2/ D4772 D4772 D4772C(2) D1181-18 Five Mile Bridge D4293G(2) R2912-3 3/15/12 3/15/12 recount 10/01/12 3/15/12 8/24/12 OTC(1) B(2) C(1) (2 counts) recount 8/15/12 10/15/12 8/20/12 “1” 7/11/12 (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) Taxa (FLO-a) (FLO-b) (FLO-c) (ANT-a) (ANT-b) (PIT-PIN) (PLA-a) (PLA-b) (PLA-c) (CRE-a) (CRE-b) (CRE-c) (CRE-d) Gymnosperms Small pine 0.0 0.0 0.0 2.5 6.1 16.18.9 21.10.6 13.13.8 1.36.4 Contorted pine 0.0 0.0 0.0 0.0 0.0 10.96.3 12.1 18.30.0 0.00.0 0.0 Pinus 2.7 11.8 22.9 31.0 24.8 47.4 56.0 40.0 55.4 28.4 54.4 30.1 30.1 Picea 5.7 3.2 4.2 34.7 7.5 5.30.2 0.30.7 9.23.2 8.67.9 Abies 0.6 4.2 1.4 3.1 2.3 3.91.0 1.82.2 7.34.1 5.3 24.3 A. concolor type 0.0 0.0 0.0 0.0 0.0 0.00.0 0.00.0 2.40.0 0.00.0 A. cf. bracteata 0.9 1.0 0.3 0.3 0.6 0.00.0 0.00.0 0.31.8 1.50.6 Keteleeria type 0.0 0.0 0.0 5.2 8.1 1.00.0 0.00.0 20.53.5 6.64.6 Larix 0.3 0.0 0.3 0.9 2.9 0.00.0 0.00.0 0.30.0 0.00.3 Tsuga 0.0 0.0 0.0 2.1 0.3 0.00.0 0.30.0 0.00.0 0.00.3 undet Pinaceae 0.0 0.3 0.2 0.3 4.3 0.00.0 0.00.0 4.6 11.54.0 0.3 TCT 65.0 40.9 7.0 0.0 3.7 1.63.4 2.42.2 2.10.3 2.43.0 Podocarpus type 0.0 2.2 0.5 0.9 0.3 0.00.2 0.30.0 0.60.6 0.71.5 Total Gymnosperms 75.2 63.6 36.8 81.0 60.8 86.2 76.1 78.2 79.3 89.0 83.2 60.4 79.3 AP Dicots Acer 0.0 0.0 0.3 0.0 0.6 0.00.2 0.00.1 0.00.0 0.00.0 Alnus sp. 0.0 0.0 0.0 0.3 0.0 0.00.0 0.00.0 0.00.0 0.00.3 Betula/ Betulaceae 0.3 0.0 0.7 3.1 0.0 0.30.0 0.00.1 0.00.0 0.00.3 Carya 1.5 0.6 5.6 0.0 3.2 0.00.0 0.00.2 0.00.0 0.00.0 Castanea type 0.0 0.0 0.0 0.0 0.0 0.00.2 0.00.0 0.00.0 0.20.0 Celtis 0.0 0.0 0.2 0.0 0.6 0.00.0 0.00.0 0.00.0 0.00.0 Eucommia 0.0 0.3 0.2 0.6 0.0 0.00.0 0.00.0 0.00.0 0.00.0 Fremontia 0.0 0.0 0.0 0.0 0.0 0.00.2 0.00.0 0.00.0 0.00.0 Other AP dicots 0.0 0.3 39.4 0.0 0.0 0.00.0 0.00.0 0.00.6 0.20.0 Englehardtiae 0.0 0.3 0.0 0.0 0.0 0.00.0 0.00.0 0.00.0 0.00.0 Cf. Fagus 0.0 0.0 0.0 0.0 0.0 0.00.0 0.00.0 0.00.0 0.00.3 Fraxinus 0.0 0.0 0.0 0.0 0.0 0.00.0 0.00.0 0.00.0 0.00.3 Ilex 0.0 0.0 0.0 0.0 0.0 0.00.2 0.00.0 0.00.0 0.00.0 Itea 0.0 0.3 0.0 0.0 0.0 0.00.0 0.00.0 0.00.0 0.00.0 Juglandaceae? 0.0 13.1 0.0 0.0 6.1 0.00.2 0.00.0 0.30.0 0.00.0 Juglans 3.3 0.0 2.8 1.8 0.6 0.70.2 0.30.7 0.00.6 0.20.0 Ostrya/Carpinus 0.3 0.0 0.0 0.3 1.2 0.00.0 0.00.0 0.00.0 0.20.0 Populus 0.0 0.0 0.0 0.0 0.0 0.00.2 0.00.2 0.00.0 0.00.3 Pterocarya 0.6 0.0 1.4 0.3 0.9 0.30.2 0.30.0 0.00.3 0.00.0 Quercus type 0.6 0.0 0.5 0.0 0.0 0.00.2 0.00.0 0.60.0 0.70.0 Salix 0.0 0.0 0.0 0.0 0.0 0.00.2 0.00.0 0.00.0 0.00.3 Ulmus/Ulmaceae 1.2 4.8 1.2 4.6 5.2 0.70.5 1.10.5 0.00.0 0.00.3 Total AP Dicots 7.9 19.8 52.4 11.0 18.2 2.02.9 1.61.9 0.91.5 1.52.1 (continued)

TABLE 3. POLLEN CONTS continued Pitch- lorissant Antero Pinnacle PlatoroCreede R2063-3 / R2910-1 / D4294A 2 D1083 D3496 D1496 ish Beds OTC1 OTC 101 R2912-2/ D4772 D4772 D4772C2 D1181-18 ive Mile Bridge D4293G2 R2912-3 3/15/12 3/15/12 recount 10/01/12 3/15/12 8/24/12 OTC1 B2 C1 2 counts recount 8/15/12 10/15/12 8/20/12 1 7/11/12 Taa LO-a LO-b LO-c ANT-a ANT-b PIT-PIN PLA-a PLA-b PLA-c CRE-a CRE-b CRE-c CRE-d

NAP Ephedra Artemisia type 0.0 0.0 0.0 0.0 0.0 1.00.0 0.00.0 0.00.3 0.70.3 Asteraceae 0.0 0.0 0.0 0.0 0.0 0.00.0 0.00.0 0.00.0 0.00.0 Chenopodiaceae 0.0 0.0 1.2 0.0 0.0 0.00.0 0.00.0 0.00.0 0.00.3 Cf. Caryophyllaceae 0.0 0.0 0.0 0.3 0.0 0.00.0 0.00.0 0.00.0 0.00.0 Elaeagnaceae 0.0 0.0 0.0 0.0 0.0 0.00.5 0.50.2 0.30.0 0.00.0 Mistletoe/ Arceuthobium 0.0 0.0 0.0 0.3 0.0 0.00.0 0.00.1 0.00.0 0.00.0 Other NAP dicots 5.4 0.3 5.6 4.0 12.1 3.60.2 7.13.7 2.85.9 10.3 2.1 Potentilla 0.0 0.0 0.0 0.0 0.0 0.00.0 0.00.0 0.00.0 0.00.3 Rosaceae 0.0 0.0 0.0 0.0 0.0 0.00.0 0.00.0 0.00.0 0.00.9 Ribes 0.3 0.0 0.0 0.0 0.0 0.00.0 0.00.0 0.00.0 0.00.9 Sarcobatus 0.6 0.0 2.3 0.3 5.2 0.31.7 2.42.8 4.37.1 20.2 9.4 Total NAP Dicots 6.3 0.3 9.1 4.9 17.3 4.92.4 10.0 6.87.3 13.2 31.2 14.3 Ephedra 0.0 1.3 0.5 0.9 2.6 1.06.8 3.73.7 2.41.8 6.22.1 Total NAP + Ephedra 6.3 1.6 9.6 5.8 19.9 5.9 9.213.710.5 9.815.0 37.4 16.4 Other Colpate 4.8 8.6 0.0 0.0 0.0 0.00.0 0.01.1 0.00.0 0.00.9 Porate 2.7 5.1 0.0 0.0 0.0 1.60.0 0.03.3 0.00.0 0.00.3 Monolete 0.0 0.0 0.0 0.0 0.0 0.00.0 0.00.1 0.00.0 0.00.0 Tr ilete 1.2 1.3 0.5 1.2 0.3 0.30.0 0.80.6 0.00.3 0.20.3 Tr ilete: Selaginella 0.3 0.0 0.0 0.0 0.0 0.00.0 2.10.6 0.30.0 0.20.3 Total Other 9.1 15.0 0.5 1.2 0.3 2.00.0 2.95.7 0.30.3 0.41.8 Total Monocots including Poaceae 1.5 0.0 0.7 0.9 0.9 3.911.83.7 2.5 0.00.0 0.20.3 TOTAL COUNT (grains) 331 313 573 326 347 304414 380836 327340 455 329 AParboreal pollen; NAPnon-tree pollen; TCTTaaceae/Cupressaceae/Ta xodium-type pollen.

4.1.2. Oligocene (Antero, Pitch-Pinnacle, Platoro, and Creede) are present, as well as non-tree types such as Cnidoscolus, Rhus, Ribes, Rosa, and streamside types (Salix and Ulmus) (Table 4). 4.1.2.1. Antero. The pollen and spores of the Antero flora are figured in 4.1.2.3. Platoro. The pollen and spores of the Platoro flora are figured in Plate I. Importantly, the Antero flora contains cool indicators, such as mega- Plates II, III, and IV. Some Platoro samples contain only burnt and charred plant fossils and abundant pollen of Picea (up to 30%) and Abietineae (Fig. 5; Tables tissue, pollen, and spore specimens (Plate IV) (Lipman, 1975). Megafossils and 3 and 4). Other taxa include Pinus pollen (~25%), along with megafossils and pollen of Pinus, Picea, Abies cf. bracteata, and Juniperus are present. NAP pollen of Juniperus, Sequoia, and some broad-leaved trees common in nearby types are diverse and include pollen of Artemisia, Ephedra, Mahonia, Elaeag- Florissant (e.g., Juglandaceae, Ostrya-Carpinus, and Eucommia). Other woody nus, Shepherdia, Ribes, and Poaceae. Megafossils of Berberis, Cercocarpus, taxa include Betula, Crataegus, and mesic streamside types such as Ulmus Mahonia, and Ribes are also present (Table 4). Streamside taxa included Pop- and Salix (Table 4). ulus and Salix. 4.1.2.2. Pitch-Pinnacle. The pollen and spores of the Pitch-Pinnacle flora are 4.1.2.4. Revised list of Creede. We present a revised complete flora of figured in Plate I. Megafossils and pollen ofPinus , Abies, Picea, and Juniperus the Creede Formation (Table 8), which includes megafossil identifications by

GEOSPHERE | Volume 15 | Number 1 Leopold and Zaborac-Reed | Pollen evidence of floristic turnover during the Colorado Oligocene Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/254/4619230/254.pdf 261 by guest on 03 October 2021 on 03 October 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/254/4619230/254.pdf Research Paper Cedrus- Larix Pinus cf Abie s Gymnospe rm Tsug Picea Chamaec Ke Sequoia af Juniperus To Gink Ephedr P Art Ar Arbutus Amaranthaceae Amelanchie r Araceae Monocots Small pine (uncer Alnus Acer Dicots Liliales/Liliata e– Betula Berberis Ast Alangium Ailanthu s T Po Stipa Smila x Scir Spa P Dioscor Caesalpinia -t Bombax C Car Cast Ca Ca rya Cr Cedr Cat Cnidoscolu s Celtis-t Cr Cer Cer ypha oaceae odoc apr . br rr ceuthobium at ot t t ry emisia eraceae (Ast amoge to eleeria- alpa diosper coc cis ey pus rg anium aegus on go anea -Pseudotsug oph if a ela/T act a oliaceae ar ype ar a Sub to ea eat t - t yllaceae pus- t ype pus oona yparis ype –t t f a mum inis –t ype ype pollen n ype tal (e s ype er ype pollen a tain id) oideae-t x Ta cluding small pine) xa ype) Sub to ta l1 W/H W– W– W– W– W– W– W– W– W– W– W– W– W– W– W– W– W– W– W– W– W– W– WS WS W– WS WS WS W– WS W– WS W– W– WS WS H– H– H– HS H– H– –– –– –– –– –– –– –– –– –– –– T ABLE 4. SM/SD/Scl –– M Mt M Mt Mh Mt Mt M Ds D COMPOSI Gr (t sh v h) o sh, v t, sh, h wth habit sh, h sh, h t, sh t, sh t, sh t, sh t, sh t, sh sh sh – – – h –P – –M – – –P –M –P TION OF P tP t t tP t t tP tM tP t t tM t t t t tP t tP t tM tP h , h Flor ALEOGENE FL M - P M - P M - P M - P M - P M - P M - P M - P M - P M - P M - P M - P M - P M - P M - P 13 issan tA M MM M PPPPP PPPPP PPPPP P PP PPPPP P PM P P P 0 ORA M - P M - P M - P M - P M - P M - P M - P M - P M - P nt 12 M M P P P PMP PPP P P P P M 2123 er S o Pinnacle Pitch - M - P M - P M - P M - P MMM M P PP P 77 M Plat M - P M - P M - P M- P PP P PP P P P P M or oC ( continued M - P M - P M - P M - P M - P M - P M - P M - P M - P re 10 M M P P P ed e )

GEOSPHERE | Volume 15 | Number 1 Leopold and Zaborac-Reed | Pollen evidence of floristic turnover during the Colorado Oligocene 262 Research Paper Lonice Pt Zel X Vitis Cf V Ulmus/Ulmaceae T T T Sorbus Shepher Sar Sambucus Salix Rubus R Cf Ribes Rhus Rhoipt Re P Po P Plat Plat P Pa Ost Cf Mahonia Legume K Juglans J Ile Hy Humulus Ho Holodiscus Het Cf Fr Eucommia Elaeagnus Dipt Diosp C Cucurbitaceae Dicots ( Semeiandr Quer V R Philadelphus- It Halesia Engelhar aber etr amesia auquelinia aleriana ylonagr ilia ea arthenocissus runus opulus oelr osa osaceae ycloc axinus er . . . . x ch t dr Malus e venia kov entilla Vibur R Fr cobatus er ry acentr anus yc oc vesia er angea obinia cus y eut emontia a/Car omeles naemont yr onia sandr a a a elea- ra a rya rya continued os rya eria num dia a dioideae on pinus a t a/Sar ype lik ana eW cococc ) Ta xa a Subt otal W/H T WS WS W– W– W– W– WS W– W– W WS WS WS WS W– W– W– W– W– WS WS W– W– WS W– W– W– W– W– W– W– WS W– W– WS WS W– WS WS W– WS WS W– WS W– WS WS W– W– WS W– H– H– H– H– H– HS ABLE 4. –– SM/SD/Scl COMPOSI SCL –s Mt Mt Mt Mt Mt Mt Mt Mt Mt Mt Mt Mt Mt Mh Mt Ms Ds Ds Ds Dh Ds Ds TION OF P Gr (t sh v h) ow t, sh, h t, sh, h t, sh, v sh, h sh, h sh, v t, sh t, sh t, sh t, sh t, sh t, sh , sh sh sh sh sh sh sh sh sh th habit hP hM hM h vP t t t t t t t t t t t hP hM h hP h h hP ALEOGENE FL Flor M - P M - P M - P M - P M - P M - P M - P M - P M - P M - P 66 issant M M M M M M M M M MMM M MM M M P P P P P PPPP P P P PP PPPPP PPPPP P PP P P P ORA S ( continued ) Ant M - P M - P 29 M MM P P P P P P M M er o Pinnacle Pitch - M - P 20 M M M M MM M P Plat M - P M - P 25 M PP PP P P P PP P P P or oC ( continued M - P M - P M - P M - P M - P M - P re 31 M M M M P P ed e )

GEOSPHERE | Volume 15 | Number 1 Leopold and Zaborac-Reed | Pollen evidence of floristic turnover during the Colorado Oligocene 263 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/254/4619230/254.pdf by guest on 03 October 2021 on 03 October 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/254/4619230/254.pdf Research Paper Ly To To Extinct Lo Other angiosper Dicots: Dicots: To To Fa To Po Cedr To To To To Dicots: Br Grand t A A Extinct T Selaginella A Lo Linder Other Fe Florissantia Monocot Gymnosper C Chane Pe Nuphar (aquatic St Pa Leguminosit Eleopoldia Eleiosina Diplodipelt De W—woody; the f Leopold et al., 2008 (Flor 1986 (Plat (Flor Gr z st poc yper Not Sour oc godium eakdo tal summer tal summer tal e tal nativ tal e tal Scleroph tal dicots (including F tal nativ tal wer plant egor gopsis wer Plant olla r l ra r viacer ypodiaceae er n t sea lora. keya ca issant); elosper oc ynosper es: ypes acit Angiosper a -lik xo xo ya ces other herbaceous woody -lik y and McInt r otal ar pinus wns ax Gr s tic tax tic dicots pinus es e (magnoliid) e dicot e tax : A or e (magnoliid) a a H—herbaceous een f s ms cf this r s o); es mum x -dr -moist dicot s2 mum . elr yllous dicot s1 densa a4 W a4 , basal angiosper y dicot s5 ms od, 1987 (Cr ms ill—tax s3 epor heeler osh, 1996 (Pitch-Pinnacle); Ta xa t . a nativ amil , 2001 (Flor issant); y ids) . Gr eede); e t Subt Subt Subt ow o the r Lipman, 1975 (Plat m) th Habits: otal otal otal Bouchal et al., 2016 (Flor issant); egion t W t—tr ing oda Leopold and Cla W/H T WS W– H– ABLE 4. –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– –– at ee; y; e and Nichols pink f sh—shr or o); SM/SD/Scl COMPOSI MacGinitie ill—tax Mt ub; issant); y- v—vine; , 2001 (Flor a non-nativ P oole TION OF P Gr , 1953 (Flor Bouchal, 2013 (Flor (t sh v h) ow , 2001 (Flor t, sh h—herb; th habit –M –M –M –M –M –P –M –M – –M –M –P –M – – e (e issant); ALEOGENE FL xo issant); tic) t M—me ga issant); W Flor Flor ol fe o the r Manchest M - S M - P 107 107 11 11 35 61 66 10 13 issant issant M M M and Schor SS SS 41032 30000 issant); Leopold and Zaborac-R 4735 4 4103 2 3000 0 0010 1 5512 3 71 11 52 fo egion; ssil; ORA Bo P—pollen; er SM—summer S ( continued ) , 2001 (Flor yle et al., 2008 (Flor n, 1989, 1990 (Cr Ant Ant 44 24 29 12 44 SS 0103 59 61 31 1011 6266 9776 0103 2123 er er o o S—spor issant); -moist; eed, 2014 (Flor Pinnacle Pinnacle e. eede); Pitch - Pitch - M ey M – P indicat SD—summe r- 29 18 20 29 issant ) 21 72 77 er Zabo et al., 2012 (Ant ; Du iss rac-R rd ant, en, 1966 (Antero) ; es both a Plat Plat dr 37 23 25 37 eed and Leopold, 2016 y; Ant 91 62 33 or or S cl—Scler oC oC er er o re , and Cr o) ; f ound in Me oph ye r r eede eede 49 27 31 49 10 eede) ; M M M S S 2 0 0 r, yllous ;

GEOSPHERE | Volume 15 | Number 1 Leopold and Zaborac-Reed | Pollen evidence of floristic turnover during the Colorado Oligocene 264 Research Paper

Figure 4. Detrended correspondence analy sis plot for the five Paleogene Colorado floras. Data points on the right side of the x-axis (Florissant flora) may represent summer-moist regimes, while data points on the left side of the x-axis (Oligocene floras) probably represent summer-dry regimes. Note that Florissant-c (FLO-c), Antero-a (ANT-a), and Antero-b (ANT-b) rep resent transitional or intermediate regimes.

Axelrod (1987), with revisions and additions by Howard Schorn (Schorn and locality and reported that Crataegus creedensis was a widespread rosaceous Wolfe, 1989), later published as Wolfe and Schorn (1989, 1990). Our pollen tree or shrub, because its leaves were found at several Oligocene sites (e.g., in identifications (Table 8) expand the Creede flora and indicate that Ulmaceae Montana, Oregon, and Colorado). Wolfe and Schorn (1989) and Axelrod (1987) and the following genera rejected by Wolfe and Schorn (1989, 1990) were in- identified the following Rosaceous megafossil genera at Creede:Crataegus , deed present in the flora:Shepherdia , Fraxinus, Acer, Larix/Pseudotsuga-type, Prunus creedensis, and Potentilla (2 spp.), Sorbus (mountain ash), and Holo- Tsuga, Alnus, and Quercus. Streamside shrubs (e.g., Acer, Betula, and Ulmus- discus stevenii Schorn and Wolfe. type) are also present. The pollen and spore flora of the Creede Formation are Extinct taxa of the Rosaceae include Eleopoldia (identified at Pitch-Pinnacle shown in Plates V and VI. The fossil pollen and spores in some samples are and Creede by Wolfe and Schorn, 1990), an herb with highly lobed leaves re- very well preserved. lated to Geum. Another extinct (megafossil) taxon of Rosaceae identified at The pollen histogram (Fig. 5; Table 3) shows that at Creede, cool indicators Creede was Eleiosina praeconciana (Cockr.) Schorn and Wolfe, an herb with include Picea pollen, which was consistently present (~8% in three samples), alternate leaves. Stockeya creedensis (R.W. Br.) Wolfe and Schorn (1990, and Abietineae pollen, which was significant in two samples (~28%; Fig 5). p. 23), another Rosaceae element, was suggested to be ancestral to the genus Pinus is an important element. Low biomass types lumped as NAP expanded Chamaebatiaria . One megafossil specimen from Creede currently assigned to at Creede; these include Ephedra, Artemisia, Ambrosia-type, Sarcobatus, and the genus Eleopoldia (Wolfe and Schorn, 1990, their plate 13 and their figure 3) Amaranthaceae. has been examined by Adams and is being reassigned to Juniperus cf. califor- Remarkable megafossil specimens of Abies cf. bracteata have been figured nica (Robert Adams, 2013, written commun.). (Axelrod, 1987). Leopold and Zaborac-Reed (2014) also identified its distinctive 4.1.2.5. Comparison of the four Oligocene floras. The Oligocene floras of Colo- pollen. Axelrod (1987) found abundant leaves of Cercocarpus at each Creede rado were less diverse than at Florissant (Table 4) and had a great deal in common.

TABLE 5. CLIMATE REQUIREMENTS OF THE TAXA USED IN COEXISTENCE APPROACH ANALYSIS Taxon name Florissant Antero Pitch-Pinnacle PlatoroCreede MAT LowMAT HighMAT Source CMMT Low CMMT High CMMT Source Abies M - PM - PM - PPP –8.0 18.21–29.1 12.51 Abies cf. bracteata PM - PM - PM - P7.8 18.22;3 No dataNo dataNo data Picea M - PM - PM - PM - PM - P –12.4 22.84–33.48.6 1 Pinus M - PM - PM - PM - PM - P –8.3 24.21–30.8 19.51 Larix/Pseudotsuga PP M - P –10.1 20.11–30.89.9 1 Tsuga M - PP M - P –1.8 24.14–16.2 18.91 (low); 4 (high) Chamaecyparis MM –0.2 20.81 –8.8 13.01 Juniperus M - PM - PM- PM - P –14.6 22.91–33.4 16.81 To rreya M7.3 18.24 –2.59.0 4 Ephedra P PPPP3.2 23.31 –9.2 13.51 Acer (West) M - P PMPM - P –2.4 22.41–14.3 10.71 Ailanthus M0.4 22.14–15.9 15.14 Alangium P –0.7 24.84–12.5 20.14 Alnus PP P –10.8 21.11–31.4 13.31 Amelanchier M –9.0 18.21–30.6 10.31 Arbutus M4.5 20.11 –3.3 12.71 Arceuthobium PPP –4.1 19.34–17.3 13.14 Artemisia PPPM - P –2.4 20.01–13.1 11.21 Berberis MMM1.6 23.11 –8.9 14.31 Betula PM - PP PM - P –16.9 20.61–33.4 12.41 Caesalpinia cf.M - P3.8 24.84 –4.3 24.84 Carya M - PP P3.5 23.31–14.5 17.61 Castanea P5.1 22.21–10.0 15.31 Catalpa M2.2 22.74–17.2 14.24 Cedrela/Toona M - P0.2 24.84–12.4 20.14 Celtis PP 2.4 24.21–18.3 19.51 Cercis MM6.6 23.71 –7.8 15.21 Cercocarpus MM - PMM0.1 21.01–10.9 12.71 Crataegus M - PM M –3.2 20.51–17.7 10.21 Croton P3.8 24.84 –4.3 20.14 Cyclocarya P7.4 21.04 –6.5 12.24 Diospyros P8.5 24.21 –5.4 19.51 Dipteronia M1.6 21.14 –8.0 14.24 Elaeagnus/Shepherdia PP PM - P –4.3 24.14–20.9 18.94 Engelhardioideae P5.4 24.84 –1.7 20.14 Eucommia M - PP 3.4 22.04 –6.0 13.54 Fraxinus PP P –1.4 23.71–22.9 17.91 Fremontia PP5.6 18.21 –1.99.3 1 Halesia M8.8 20.61 –2.0 12.01 Heteromeles M8.5 18.21 0.9 13.71 Holodiscus MMM2.0 21.05;6 No dataNo dataNo data Hovenia M3.2 24.84–13.7 20.04 Hydrangea M –1.8 21.74–10.2 18.94 Ilex P0.7 24.21–16.1 19.51 Itea P2.2 21.04 –6.3 18.34 Jamesia M –2.0 22.07No dataNo dataNo data Juglans P PPP 1.2 21.41–14.7 12.71 Koelreuteria M2.0 21.44–15.9 15.14 Lonicera P –5.8 24.84–29.8 20.14 Mahonia MM MM - PM 1.8 24.24 –7.0 18.94 (continued)

TABLE 5. CLIMATE REQUIREMENTS OF THE TAXA USED IN COEXISTENCE APPROACH ANALYSIS (continued) Taxon nameFlorissant Antero Pitch-PinnaclePlatoroCreedeMAT Low MAT High MAT Source CMMT Low CMMT High CMMT Source Ostrya / Carpinus PP P1.0 21.6 1–19.3 14.5 1 Parthenocissus PP–1.8 22.2 4–14.3 18.1 4 Platanus M5.4 22.1 1–9.613.31 Platycarya P3.3 23.4 4–13.7 16.1 4 Populus M - P MPM - P –15.023.31–32.813.31 Potentilla M - P –5.9 18.9 4–29.8 12.5 4 Prunus M? M–6.322.61–28.816.61 Pterocarya P PPPP2.6 22.4 4–13.7 16.1 4 Quercus (West) M - P M - P PM - P–0.320.71–12.412.71 Reevesia P2.0 24.8 4–7.220.14 Rhus MM –0.4 24.2 1–22.2 19.5 1 Ribes M - P MMM - P –5.7 19.2 4–25.5 9.34 Robinia M–2.819.04–20.910.14 Rosa MM –5.8 24.8 4–29.8 16.7 4 Rubus M–1.824.84–12.715.34 Salix M - P MMPM - P–16.2 24.2 1–33.4 19.5 1 Sambucus M–3.924.21–19.219.51 Sarcobatus P PPPP–6.737.08; 9No data No dataNo data Sorbus M–5.824.84–29.820.14 Tabernaemontana P8.6 24.8 41.3 20.1 4 Tetracentron P–0.721.04 –9.6 14.9 4 Tilia M - P 0.722.51–18.915.81 Ulmus/Ulmaceae M - P M - P M - P PP–1.2 23.7 1–29.8 18.9 4 Vauquelinia M14.322.61 6.013.21 Vitis M - P –1.1 24.1 4–23.8 20.1 4 Zelkova M - P MM - P2.6 21.7 4–10.1 15.3 4 Notes: Not used (uncertain or controversial ID): Keteleeria, Cedrus, Podocarpus, Malus, Pachysandra/Sarcococa, Philadelphus, Prunus (Florissant only), and Pteroceltis. Not used (outlier or monotypic): Cathaya, Sequoia, and Ginkgo Phoiptelea. Not used (single grain): Bombax cf. Viburnum. Not used (Family-level id): Asteraceae, Caryophyllaceae, Cucurbitaceae, Legume, and Rosaceae. Not used (aquatic, basal angiosperm or magnoliid): Lindera, Nuphar, and Persea. Not used (cannot find data): Cardiospermum, Cnidoscolus, Humulus, Semeiandra, Valeriana, and Xylonagra. Used for MAT data only (no CMMT data): Abies cf. bracteata, Holodiscus, Jamesia, and Sarcobatus. Sources of climatic data: 1—Thompson et al., 2015; 2—Las Pilitas Nursery, 2012; 3—Griffin and Critchfield, 1976; 4—Fang et al., 2011; 5—Pond, 2003; 6—U.S. Department of Agriculture, 2011; 7—Burns and Honkala, 1990; 8—Anderson, 2004; 9—U.S. Department of Agriculture Plants Database, 2016. Abbreviations: CMMT—cold month mean temperature; MAT—mean annual temperature; M—megafossil; and P—pollen. M - P—megafossil and pollen.

The gymnosperms in particular were very similar in composition and included (which is morphologically unique) were represented at Creede (Leopold many genera of Pinaceae. Pinus megafossils and pollen were found in each and Zaborac-Reed, 2014, Plate 1, G), Antero, and Platoro. Keteleeria-type of the floras studied (Table 4).Pinus was consistently the most abundant pol- pollen, which is similar to Abies pollen (Zanni and Ravazzi, 2007; Leopold len in the Oligocene (yellow bars, Fig. 5; Table 3). Pinus aristata-type pollen and Zaborac-Reed, 2014), was seen in Antero, Pitch-Pinnacle, and Creede. (which bears a distinctive lacy frill around the equator of the central cell, a fea- Keteleeria megafossils have been reported from the Pacific NW in the Latah ture shared with Pinus contorta) was present and may have been related to flora near Spokane, Washington (Brown, in LaMotte, 1952), the Bridge Creek the megafossil Pinus crossii (of Axelrod, 1987; Plate V, 10). Picea pollen and flora of Oregon (Meyer and Manchester, 1997), and the Quilchena locality megafossils were also present in all the Paleogene floras; its pollen (see blue of British Columbia (Mathewes et al., 2016). We found pollen unmistakably bars in Fig. 5; Plate V, 9) was common in all but the Platoro samples. Abietineae of Tsuga, though rare and poorly preserved, at Antero, Platoro, and Creede pollen (Abies plus Keteleeria-type) (green bars, Fig. 5; Table 3), was abundant (Plate V, 12), which may substantiate Axelrod’s Tsuga petranensis at Creede. in the Creede flora, reaching 25%.Abies pollen was found in all floras, while Both the pollen and megafossil records of the Creede specimens suggest the megafossils were confirmed in Antero, Pitch-Pinnacle, and Creede. Tsuga cf. caroliniana type. In particular, megafossils identified asAbies rigida (which have diagnostic Taxaceae/Cupressaceae/Taxodium-type (TCT) pollen was rare at the four cone scales and foliage) and pollen of the Eocene species A. cf. bracteata Oligocene floras (Fig. 5), with its typical form resemblingTaxodioipollenites

TABLE 6. INFERRED MEAN ANNUAL TEMPERATURE (MAT) AND PRECIPITATION (PPT) FOR PALEOGENE FLORAS OF COLORADO Flora MAT now °C Inferred paleoMAT °C Method Inferred PPT Source Oligocene Creede 1.9° 0 to 2.5° Inferred from flora >635 mm annual, summer dryWolfe and Schorn, 1989 4.2° From Wolfe (1981) Gregory and McIntosh, 1996 11.5° NLR 460–520 mm (18″–20″) in lowlands Axelrod, 1987 Between 8° and 18° CA Summer dry: <100 mm (July) This report ~9° ± 2° Clumped isotopes Hyland and Huntington, 2015 9° NLR Summer dry: <100 mm (July) Leopold and Zaborac-Reed, 2014

Platoro ~3° 5–7.5° Enthalpy? Summer dryMeyer, 1986 Lipman, 1975 Between 8° and 18° CA <100 mm (July)This report

Pitch-Pinnacle ~4° 12.7° ± 1.7° CLAMP >1000 mm (total growing season)Gregory and McIntosh, 1996 (CLAMP) Between 9° and 18° CA This report

Antero ~4° 12.7° ± 1.7° NLR Summer dryLeopold and Zaborac-Reed, 2014 Between 8° and 18° CA This report Eocene Florissant 4.1° 15–18°; frost free NLR Summer moistLeopold and Clay-Poole, 2001 11–18° NLR Summer moistLeopold et al., 2008 ~18.3°; frost free NLR ~520 mm; summer moist MacGinitie, 1953 Likely summer moist; sclerophyllus vegetation adapted to seasonal drought Bouchal et al., 2014 Between 14.3° and 18.2° CA Summer moistZaborac-Reed and Leopold, 2016 Between 10° and 13° CA Emphasis on megafossil recordsBaumgartner and Meyer, 2014 ~18°± 2° Clumped isotopes Hyland and Huntington, 2015 12.8° ± 1.5°; Mean monthly Growth rings 720 ± 310 mm annual MAP; 570 ±160 mm during growing season. Climate Gregory-Wodziki, 2001 temps >10 °C more favorable for Sequoia growth than today due to higher growing season

rainfall, higher levels of CO2, and/or higher MAT range 14°, 15° Boyle et al., 2008 Notes: Bold inferred paleoMAT values are accepted by this report. Abbreviations: CA—coexistence approach; CLAMP—Climate Leaf Analysis Multivariate Program; NLR—nearest living relatives.

hiatus of Potoniè (1951), which may have represented Juniperus (Plate V, 17– rickson or to Ephedripites lusaticus Krutzsch, which are similar in appearance 19). However, leafy Juniperus remains were found at the four Oligocene floras and found in Eocene floras (Fredrickson, 1981; Garcia et al., 2016). This form of and were also abundant at two of Axelrod’s (1987) Creede sites. Ephedra pollen was found at Florissant (Wingate and Nichols, 2001, their plate Ephedra pollen was present in all four Oligocene floras (Table 4).Ephedra 3 and their figure 9) as well as the Oligocene floras. On the histogram, pollen of pollen was represented by three species, following characters documented by Ephedra was grouped among the NAP types (purple bars, Fig. 5) because of its Steeves and Barghoorn (1959; Plate I, 1; Plate II, 20–27; Plate V, 20–22). The shrubby growth habit. Ephedra pollen is a minor element at Florissant, Antero, two medium-sized forms we clearly identified were the first- and second-order and Pitch-Pinnacle (up to 2.6%) but becomes more common (up to 7%) in the branch-furrowed pollen of E. nevadensis and the smooth-furrowed pollen of Platoro and Creede floras (Table 3). E. torreyana (Davis, 2001; Bolinder et al., 2016; Bouchal et al., 2016). These In the Oligocene floras (as well as at Florissant), we have recorded a tiny were accompanied by a third species differentiated from above-mentioned by form of bisaccate Pinaceae pollen that we call “small pine” hereafter. While its small size and distinctive sculpture, short axis, and first- and second-order some of these grains may have been aberrant and/or shrunken forms of the branched furrows (Plate I, 1; Plate II, 24; Plate V, 22). This pollen morphology is genus Pinus, they were somewhat degraded specimens, as seen in Plate II visually distinct from other Ephedra pollen, because it is more breviaxial, hav- (33–36) and Plate V (15 and 16). Some could represent Cathaya (see Saito ing a relatively high polar/equator (P/E) ratio (~0.63) and small size (~35µm). et al., 2000), a member of the Pinaceae, whose pollen resembles that of Pinus The high P/E ratio, small size, and secondary branching furrows combine to but is slightly smaller (Ying et al., 1993; T. Saito, 2013, personal commun.). indicate that this pollen form may be related to either Ephedra exiguua Fred- However, many specimens of “small pine” were quite weathered and very

Figure 5. Pollen percentages diagram/histo gram showing relative abundance of key el ements in the Paleogene floras of Colorado (Table 3). TCT—Taxaceae/Cupressaceae/ Taxodium-type pollen. Abietineae—Abies and cf. Keteleeria. AP Dicots—arboreal dicot pollen. NAP+Ephedra—other non- arboreal (shrub, herb) pollen.

small (less than half the size of Pinus) and did not have characteristics to as- the subtropical lower montane wet climate of Tamaulipas, Mexico (Boyle et al., sign them to Cathaya. 2008; Reinink-Smith et al., 2017). Larger bisaccate grains strongly resembling Podocarpus (Erdtmann, 1957) Although pollen of broad-leaved arboreal dicots and Sequoia-type (TCT) (Plate II, 17; Plate V, 13 and 14) were found as occasional in all five floras and pollen dominated in the Eocene Florissant flora (~50%) (Fig. 5), the composi- designated as such in Table 3. While there is some disagreement among tion of the dicot taxa changed greatly in the Oligocene; their numbers became others as to this identification, these specimens had the characteristically much reduced (~20% in Antero and 1%–2% by the late Oligocene) (Fig. 5). By robust, thick-walled, rugulate cells with over-sized sacci typically seen in Podo- the end of the Oligocene, summer-moist hardwood trees, particularly those carpus (Sivak, 1975; Liu and Basinger, 2000). Well-preserved wood found in with an East Asian affinity, had largely disappeared from the megafossil record Brown’s Canyon (Oligocene) in Colorado was identified by R.A. Scott (in Van (Table 4). Alstine, 1969) as probable wood of Podocarpoxylon. These grains appeared The angiosperm records in the four Oligocene floras included only a few as trace elements in most of the study samples (Table 3). Previous records families (Table 4). Rosaceae was the main dicot family of the Paleogene Colo demonstrate clearly that Podocarpus pollen was frequent in the late Creta- rado floras and included several tree, shrub, and herb genera represented in ceous of Alabama (Leopold and Pakiser, 1964, their plates 4 and 7). Dilcher both the megafossil and pollen floras. Because pollen of rosaceous taxa was (1969) described Podocarpus megafossils from an Eocene flora in Tennessee, typically difficult to identify to genus, we have placed a number of simple tri- and Jarzen and Dilcher (2006) identified Podocarpaceae pollen in an Eocene colpate pollen of rosaceous structure in a group as Rosaceae undet. (Plate I, deposit in Florida. Reinink-Smith and Leopold (2005) and Morley (2011) report 30 and 31; Plate VI, 14–16). The Oligocene Rosaceae included the megafossil Podocarpaceae pollen as consistent minor elements in the Neogene of Alaska. record of Cercocarpus (mountain mahogany) at Antero, Platoro, and Creede. Other Alaskan trace occurrences include White and Ager (1994, plate 2, p. 68) Mahonia (Oregon grape and Berberidaceae) megafossils tended to be abun- and Reinink-Smith et al. (2017). Modern species of Podocarpus grow today in dant at all Axelrod’s (1987) Oligocene sites as well as at Florissant.

TABLE 7. TROPICAL AND SUBTROPICAL TAXA IDENTIFIED AT FLORISSANT FamilyGenus SourceNative rangePollination vector Taxaceae To rreya type (M) 1,3 Florida Wind Alangiaceae or Cornaceae Alangium (P)6 Tropical Insect Apocynaceae Tabernaemontana (P) 2,4,5Tropical, pantropical; S. AmericaUncertain; cross-pollinating, insect Arecaceae Undetermined (M) 3,5,7Subtropical Insect Dioscoreaceae Dioscorea (M) 1,3Tropical, Warm temperate; SE United States, Africa, Asia Insect Eucommiaceae Eucommia (M, P) 2,4,6Central to E. ChinaWind Euphorbiaceae Croton (P) 3,4Tropical, Pantropical, some temperate; SE Asia Insect Juglandaceae Engelhardtia (P) 2,4,6Pan tropical, E. Asia, New Guinea, Borneo, ChinaWind Malvaceae Bombacacidites aff. 2,4Central Mexico, S. Florida, SE Asia Bats, birds, insects Bombacoideae (P) Meliaceae Cedrela/Toona (M) 1,2,4Tropical, subtropical; SE Asia, C. AmericaInsect Sapindaceae Athyana (M)2 Tropical; S. AmericaUncertain Cardiospermum (M) 1,2,4Tropical AfricaInsect Dipteronia (M) 1,3Central and South China Koelreuteria (M)1,5 SW ChinaInsect, bird or wind Sterculiaceae Reevesia (P) 2,4Pantropical animal Tetracentraceae or Trochodendraceae Tetracentron (P)6 Warm temperate Mixed wind and insect Notes: Sources for data: 1—MacGinitie, 1953; 2—Leopold and Clay-Poole, 2001; 3—Manchester, 2001, Table 1; 4—Wingate and Nichols, 2001; 5—Manchester, 2001; 6—Bouchal et al., 2014; 7—Carrington et al., 2003. Abbreviations: M—megafossils; P—pollen.

The tree dicots found in the Oligocene floras included mainly streamside Eucommia, Carya, and Juglans pollen, so obvious in Florissant, were types such as Salix (Plate III, 4; Plate VI, 7), Populus (Plate I, 13; Plate VI, 5 and 6), sparse minor elements (1%–6%) in the early to mid-Oligocene (Table 4). These and Betula (Plate I, 12; Plate VI, 21). Minor elements of the Oligocene floras pollen are wind-blown types that dropped out before the Creede flora and did included pollen and megafossils, such as Acer-type tricolpate pollen (Plate I, not appear in the Oligocene megafossil records. These pollen records might 8–10, 27; Plate VI, 8), Alnus (Antero and Creede, Table 3; Plate VI, 21), Quercus therefore be a product of long-distance wind transport or redeposition. (Plate I, 7; Plate III, 5; Plate VI, 11 and 12), and Fraxinus (Plate VI, 19). Acer-type The role of NAP increased significantly from 15% to 40% in the younger pollen found at Creede (Plate VI, 8) supports the identification of the megafossil samples, especially at Creede (Fig. 5). Ribes pollen (identifiable to genus) Acer riogrande of Axelrod (1987), which was dismissed by Wolfe and Schorn is present at Pitch-Pinnacle, Platoro, and Creede, affirming the leafy mega- (1989, 1990) as Ribes lacustroides. Mahonia megafossils were found at all four fossil remains of seven Ribes species at Creede (Plate VI, 22–24; Table 8). Oligocene floras as well as at Florissant. Many of the woody dicots found in The pollen is distinctive, with few large, simple pores (from seven to nine the Oligocene were microphyllous and have relatives living in southwestern in number). United States and Mexico today. However, a very large cordate-shaped entire Sarcobatus (Family Sarcobataceae) pollen was a common (2%–20%) and leaf was identified at Creede asCatalpa by Wolfe and Schorn (1990), who said it consistent shrub element in most Oligocene pollen samples in all four Oligo might be related to an Asian species, C. ovata. Alternatively, this may be a leaf cene floras (Table 4; Plate I, 17; Plate III, 32–34; Plate IV, 15 and 16; Plate VI, of Nuphar, which was identified at Creede by Axelrod at several field localities 27–29). The pollen count indicates that it played a significant role at Creede (1987, p. 27). This is especially likely in a flora chiefly of microphyllous leaves. (Table 3). This periporate form was unmistakable: its 12–20 pores have thick- Pollen of Nuphar has not yet been found. ened annulae that help to distinguish them from similar grains of Ama Ulmaceae pollen, which was important in the late Eocene, comprised a ranthaceae/Chenopodiaceae. The pollen is almost identical to that of the ex- trace element (1%–4%; Table 3) of the four Oligocene floras (Plate I, 15, 16, 24, tant salt-tolerant shrub Sarcobatus vermiculatus (greasewood) of the Great 25; Plate III, 23–27; Plate VI, 31 and 32). This pollen reaffirms the presence of the Basin—a plant found in all desert communities of the western United States. Ulmus type leaves in megafossils at Creede as suggested by Knowlton (1923) Various diverse examples of Elaeagnaceae pollen (Plate I, 14; Plate III, 10– and Brown (in Steven and Ratté, 1965). Ulmaceae taxa may, like Ulmus, thrive 17; Plate VI, 33), and Shepherdia cf. argentea (buffalo berry) (Table 3) pollen along lake-shore environments. Both Knowlton (1923) and Brown (in Steven were seen in Platoro and Creede samples. Megafossils of Shepherdia are also and Ratté, 1965) identifiedPlanera leaves at Creede. However, Wolfe and recorded at Creede by Axelrod (1987). This hardy shrub has thrived in desert Schorn (1990) re-identified somePlanera specimens as Cercocarpus (1990). environments of the western United States.

GEOSPHERE | Volume 15 | Number 1 Leopold and Zaborac-Reed | Pollen evidence of floristic turnover during the Colorado Oligocene 271 on 03 October 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/254/4619230/254.pdf Research Paper (28, 29, 31, 32, and 33) D4772 C; (30, 34, 35, and 36) D4772 B(1). D4772 B(1); (25) Ephedra , shrunkennevadensis - type, nevadensis D4772 B(1);, (26) Ephedranevadensis cf. D4772 C;, (27) Ephedra D4772 B(1). cf. Malformed small conifer bisaccates: Cupressaceae - type, D4772 C; (19) TCT Cupressaceae - type, torreyana D4772 B(1); (20–23) Ephedra cf. , 20 and 21, D4772 B(1), 22 and 23 D4772 C; (24) Ephedra , Chadron - type, B(1); (12) spore, D4772 B(1); (5) Trilete spore, D4772 C; (6) Selaginella - type, D4772 densa , D4772 A; (7 and 8) Selaginella cf. A; (9) Tsuga , D4772 C; (10) Abies , D4772 C; (11) Picea , D4772 Plate II. Platoro (500×), pollen and spore taxa. Note that many small fungal spores are present. (1) Monolete spore, D4772 C; (2) Trilete spore, D4772 B(1); (3 and 4) Trilete Picea , D4772 C; (13) Pinus , D4772 C; (14, 15) Pinus , D4772 B(1); (16) Pinus , D4772 E; (17) Podocarpus - type, D4772 C; (18) Taxaceae/Cupressaceae/ Taxodium - type (TCT)

GEOSPHERE | Volume 15 | Number 1 Leopold and Zaborac-Reed | Pollen evidence of floristic turnover during the Colorado Oligocene 272 on 03 October 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/254/4619230/254.pdf Research Paper (38) Undet. periporate reticulate, D4772 C; (39, 41, 42, and 44) Undet. angiosperms, D4772 B(1); (40 and 43) Undet. angiosperms, D4772 C. D4772 B(1); (32) Sarcobatus , D4772 C; (33 and 34) Sarcobatus , D4772 B(1); (35) Amaranthaceae, D4772 A; (36) Undet. reticulate, D4772 C; (37) Undet. reticulate, D4772 B(1); type D4772 C; (24–26) Ulmaceae, D4772 B(1); (27) Ulmaceae, D4772 C; (28) Pterocarya - type, D4772 B(1); (29) Pterocarya - type, D4772 C; (30) Porate D4772 B(1); (31) Juglandaceae, 17) Elaeagnaceae, D4772 C; (18) Castanea - type, D4772 E; (19) Castanea - type, D4772 B(1); (20 and 21) Asteraceae, D4772 A; (22) Asteraceae, D4772 B(1); (23) Ulmaceae, Zelkova - dicot, D4772 B(1); (7) Ilex or - type, D4772 B(1); (8) Fremontia - type, D4772 B(1); (9) C4, D4772 B(1); (10–12) Elaeagnaceae, D4772 A; (13–15) Elaeagnaceae, D4772 B(1); (16 and Plate III. Platoro pollen types (750×): (1) Monosulcate, D4772 B(1); (2) Poaceae?, D4772 B(1); (3) Dicot, D4772 B(1); (4) Salix - type, D4772 B(1); (5) Quercus, D4772 B(1); (6) C3P3

GEOSPHERE | Volume 15 | Number 1 Leopold and Zaborac-Reed | Pollen evidence of floristic turnover during the Colorado Oligocene 273 on 03 October 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/254/4619230/254.pdf Research Paper (14) Undet.; (15 and 16) Sarcobatus - type; (17–28) Undet. Angiosperms. Plate IV. Platoro (750×), burnt tissues and pollen spores (D4807): (1 and 2) Plant tissue; (3) TCT - type; (4–6) Ephedra- type; (7–10) Ferns and fungal spores; (11–13) Bisaccates?;

GEOSPHERE | Volume 15 | Number 1 Leopold and Zaborac-Reed | Pollen evidence of floristic turnover during the Colorado Oligocene 274 Research Paper

TABLE 8. LIST OF THE REVISED CREEDE FLORA INCLUDING MACROFOSSIL AND POLLEN IDENTIFICATIONS

GYMNOSPERMS DICOTS Oleaceae Fraxinus (pollen)2; F. creedensis Axel. Pinaceae Amaranthaceae (pollen)1 Abies rigida Knowlton1,4 (pollen) Exotic 1 Abies sp. (pollen)1 Asteraceae Rosaceae 1 1 Picea sp. (pollen)1,3; seeds Artemisia (pollen) Rosaceae (pollen) 1 3 Pinus riogrande Axel.4 Bidens-type (pollen Asteroideae) Cercocarpus hendricksonii Schorn & Wolfe Cercocarpus nanophyllus Schorn & Wolfe3 Pinus sanjuanensis Axel4 Betulaceae Prunus creedensis Axel.4 Pinus crossii2 Knowlton4 Alnus (pollen)1 Potentilla cf. palustris (pollen)1,3; P. creedensis (Axel.) Schorn & Wolfe Pinus sp. (pollen)1,3 Betula (pollen)2; B. smithiana (Axel.) Axel. Sorbus potentilloides (Knowlt.) Axel.4 Exotic Larix/Pseudotsuga (pollen)2 1 Ostrya/Carpinus (pollen) Exotic 3 Keteleeria-type (pollen)1 Exotic Holodiscus stevenii Schorn & Wolfe 4 Tsuga cf. caroliniana (pollen)2; T. petranensis Axel. Berberidaceae Crataegus creedensis Axel. Mahonia aceroides (Knowlt.) Schorn & Wolfe4 Podocarpaceae Berberis coloradoensis Axel.4 Salicaceae 1 Podocarpus (pollen)1 Exotic Populus sp. (pollen) Bignoniaceae P. larsenii (Knowlt.) Schorn & Wolfe3 3 Catalpa coloradoensis (Axel) Schorn & Wolfe Exotic 1,3 Ephedraceae2 Salix sp. (pollen) Ephedra cf. nevadensis (pollen)1 Elaeagnaceae E. cf. torreyana (pollen)1 Elaeagnus sp.; Shepherdia argentea (pollen)1 Santalaceae 1 E. chattian-type (pollen)1 Shepherdia creedensis Axel.2 Arceuthobium (pollen) Fabaceae Cupressaceae Sapindaceae 3 2 4 Cercis sp. Exotic Acer (pollen) ; A. riogrande Axel. Juniperus creedensis Axel. (including Taxaceae/Cupressaceae/ 3 Taxodium-type [TCT] pollen1); J. cf. californica Legume (undetermined) Sarcobataceae Fagaceae Sarcobatus (pollen)1 MONOCOTS Quercus (pollen)2; Q. creedensis Axel. Poaceae (pollen)1 Grossulariaceae Ulmaceae (pollen)1 Exotic Liliatae-type (pollen)1 Ribes (pollen)1 1 Potamogeton (pollen) Ribes lacustroides Axel.4 LOWER PLANTS R. robbinsoni3 Selaginella cf. densa1 R. obovatum (Schorn & Wolfe)3 Fern spores undetermined1 Hydrangeaceae Jamesia caplanii4

Note: Bold marks genera exotic to Colorado today. The following taxa reported by Wolfe and Schorn (1990) are extinct genera: Eleiosina praeconcinna (Cocker.) Schorn and Wolfe; Eleopoldia lipmanii (Axelr.) Schorn & Wolfe, of which one specimen (plate 13, Fig. 3) is probably Juniperus cf. californica (R.Adams, written commun., 2013) and two specimens may be Artemisia (this report); Stockeya creedensis (R. W. Br.) Wolfe and Wehr. Carya, Juglans, Pterocarya, and Podocarpus pollen are considered to be wind blown from a distance, as there are no megafossil records of them in this Oligocene flora. 1Our identifications from pollen. 2Taxa that we corroborate (with pollen evidence) from Axelrod’s (1987) megafossil taxa discarded by Wolfe and Schorn. 3Wolfe and Schorn (1990) taxa that we are accepting. 4Axelrod’s identifications accepted by Wolfe and Schorn (1990).

Asteraceae types were represented in the four Oligocene floras by mega- Axelrod assigned to Fallugia (Axelrod, 1987, his plate 29 and figures 2 and 3) are fossils and pollen. These represent early Rocky Mountain records of the fam- extremely similar to the living species Artemisia rigida and/or A. scopulorum, ily Asteraceae (Leopold and MacGinitie, 1972; Graham, 1996). R.W. Brown (in which might match with our finding ofArtemisia pollen there. R.W. Brown (in Durden, 1966) reported Artemisia? megafossil remains at Antero. We found Durden, 1966) reported Artemisia leaves and an Asteraceae fruit identified as Artemisia pollen at Antero, Pitch-Pinnacle, and Creede (Plate I, 3 and 23; Plate Bidens sp. (beggar’s tick) at Antero. Along with this, spiny tricolpate pollen of VI, 17 and 18). Axelrod (1987) described specimens in plate 29 as Fallugia, Asteraceae (Asteroideae-type) occurred at Platoro and Creede (Plate III, 20–22; which Wolfe and Schorn (1989, 1990) later described as Eleopoldia. Upon fur- Plate VI, 30). Finally, Cockerell (1933) reported a Solidago praecoccinea mega- ther examination, we concluded that at least some of these leaf specimens that fossil herb at Creede, although this was rejected by Axelrod (1987).

GEOSPHERE | Volume 15 | Number 1 Leopold and Zaborac-Reed | Pollen evidence of floristic turnover during the Colorado Oligocene 276 on 03 October 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/254/4619230/254.pdf Research Paper –20 –20 1 (1) UCM 36936 –20 Ambrosia - type, D1183_3 Creede; (31 and 32) Ulmaceae, R2912 - 3/OTC Creede 1 (1) UCM 36936 –20 µ µ Plate VI. Creede (750×), monocot and dicot pollen types. Monocots: (1) Liliales?, R2912–3 (1) Creede 1 UCM 36936 +20 (3, 4): Poaceae, R2912 - 3 (1) Creede 1 UCM 36936 ±20 Creede 1 (1) UCM 36936 –20 m; (12) Quercus, R2912 - 4/OTC Creede (2) UCM 39959 +10 m; (8) Acer , R2912–4/OTC Creede (2) UCM 39959 +10 µ µ m; (15) Rosaceae, R2912 - 3 (1) Creede 1 UCM 36936 ±20 m; (18) C3, D4293 - J Sec. I EL µ m; (26) Chenopodium - type, R2912 - 3/OTC Creede 1 (1) UCM 36936 –20 µ m; (22, 23) - 56; (19) Fraxinus , R2912–3 (1) Creede 1 UCM 36936 ±20 Ribes , R2912 - 3/OTC Creede 1 (1) UCM 36936 –20 µ m. Dicots: (5 and 6) Populus ,- 3/OTC R2912 Creede 1 (1) UCM 36936 –20 µ m; (9 and10) Potentilla ,- 3/OTC R2912 Creede 1 (1) UCM 36936 –20 µ m; (13) Undet.— Fagaceae ,- 3 (1) Creede R2912 1 UCM 36936 ±20 µ m; (16) Rosaceae?, R2912 - 3/OTC Creede 1 (1) UCM 36936 –20 µ µ m; (24) Ribes , R2912 - 4/OTC Creede (2) UCM 39959 +10 m; (20) Betula, R2912 - 3/OTC Creede 1 (1) UCM 36936 –20 µ m; (27–29) Sarcobatus , R2912 - 3/OTC Creede 1 (1) UCM 36936 –20 µ m; (33) Elaeagnaceae, R2912 - 4/OTC Creede (2) UCM 39959 +10 µ m; (2) Liliales, R2912 - 4/OTC Creede (2) UCM 39959 +10 µ m; (11) Quercus? ,- 4/OTC R2912 Creede (2) UCM 39959 +10 µ µ m; (17) Artemisia , R2912 - 3/OTC Creede 1 (1) UCM 36936 µ m; (14) Rosaceae, R2912 - 3/OTC Creede 1 (1) UCM 36936 m; (7) Salix , R2912–3/OTC Creede 1 (1) UCM 36936 –20 µ m; (25) C3, R2912 - 3/OTC Creede µ m; (21) Alnus ,- 3/OTC R2912 µ ; (30) Aster m; µ m. aceae aceae µ m; m;

GEOSPHERE | Volume 15 | Number 1 Leopold and Zaborac-Reed | Pollen evidence of floristic turnover during the Colorado Oligocene 277 Research Paper

These are tantalizing records of some importance because unequivocal 4.2.3. Continuing (Western Shrubs and Streamside Types) pollen of this highly derived family (Asteraceae) was present as rare elements at Florissant (Wingate and Nichols, 2001; Bouchal et al., 2016) as well as at Another group represented taxa that were minor elements in the Floris- all four of these Oligocene sites but are not characteristic of earlier Cenozoic sant and continued on through the Oligocene floras. These include “western” floras of the United States. shrubs such as Shepherdia, Sarcobatus, Cercocarpus, and Ephedra. Immedi- ately after the Florissant samples, the Antero flora contained a number of the Florissant genera (Table 4). However, some of these did not persist beyond 4.2. Pattern of Floristic Turnover: Change in Composition Antero. Instead, streamside taxa that frequent moist habitats persisted in the of the Eocene and Oligocene Floras Oligocene, including Alnus, Salix, Populus, and Ulmus. These taxa are adapted to broad, variable soil-moisture conditions (AE/PE = 0.3–0.9) and thrive in 4.2.1. Sørensen Index of Similarity streamside environments during severe drought conditions (Fig. 6B).

The Sørensen index was used to evaluate the similarity of the five Paleo- gene floras. As shown in Table 9, the Florissant and the four floras evaluated 4.2.4. Newcomers (Incoming Types) together as a single unit (done in order to increase the likelihood of similarity) only yield a 57.3% similarity—a moderate but not strong result. The high- This group includes newly evolved taxa of dryland environments. Most est similarity value observed was when the older Oligocene floras (Antero are members of highly evolved and herbaceous or shrub groups not typical and Pitch-Pinnacle) were evaluated against the younger floras (Platoro and before the Oligocene in Colorado; examples are Asteraceae, Caryophyllaceae, Creede), yielding a value of 73.6%—an indication of moderately strong simi- Cucurbitaceae, and Potentilla (Table 4). Some new shrubs included Artemisia, larity among these floras. One striking result was the similarity index of 50.4% Jamesia, Berberis, Arceuthobium, Halesia?, and Heteromeles. This group of between the Florissant flora with the nearby Antero flora (which followed only incoming taxa was of particular interest because they are members of to- 0.3 m.y. later). day’s regional sub-arid cool flora of the southern Rocky Mountains. Benedict (1991) has listed these genera as current natives of the Ponderosa pine shrub land community of southern Colorado: Artemisia, Sarcobatus, Jamesia, and 4.2.2. Dropouts (Outgoing Types) others. They tolerate low soil-moisture conditions with AE/PE values generally between 0.2 and 0.6 (Fig. 6C). Hence their appearance here is ecologically A moderate number of tree dicots were prominent at Florissant, including significant. hardwoods such as Carya, Carpinus, Juglans, Ostrya, Platanus, Tilia, and a number of Quercus species, essentially “dropped out” of the Colorado megafossil record immediately after the Eocene (Table 4). In contrast, the number of 4.3. Results of the Coexistence Approach (CA) taxa represented by a shrub growth habit increased (Table 4). In the histogram, the overall abundance of arboreal dicot pollen dropped from ~45% in some Climate tolerances for the taxa used in CA analyses of the four Oligocene Florissant samples and 11% –18% in Antero, to a trace 2% in the Pitch-Pinnacle, floras studied herein are found in Table 5. Using CA, Baumgartner and Meyer Platoro, and Creede samples (Fig. 5). A number of the broad-leaved dicot drop- (2014) evaluated the macrofossil-only assemblage of Florissant to initially con- outs seemed to have no further record in the Colorado Oligocene, although clude a MAT of between 10 °C and 18 °C for the local climate. Further analysis some mesic types did reappear in the Miocene Troublesome Formation farther using the Palaeoflora database (http://www.palaeoflora.de/) and supplemental north near Grand Lake in central Colorado (Leopold, 1969, p. 409). Many of sources narrowed the range to between ~10 °C and 13 °C. Zaborac-Reed and these outgoing taxa prefer summer-moist soil conditions that typify hardwood Leopold (2016) evaluated the megafossil and pollen data together and con- forests of eastern United States and East Asia. cluded that the MAT range was between 14.3 °C and 18.2 °C. Baumgartner and The modern soil-moisture index values of AE/PE for the outgoing hard- Meyer (2014) pointed out that the climate signal based only on megafossils wood taxa found at Florissant, such as Carya, Juglans, and Tilia, are high and probably gives a better reading of the local climate, while pollen might give narrow, between 0.8 and 1.0 (Fig. 6A). The disappearance of these taxa may a more regional climate signal since some grains could potentially be blown mark local extinctions or extirpations through aridity in the Oligocene floras in from a distance. Differences in site elevation may also play a part in the of southern Colorado. As Wolfe (1987) reported, many of these taxa dispersed interpretations of MAT; Zaborac-Reed and Leopold (2016) suggested a lower and appeared in other western floras (see also Wing, 1987). paleoelevation for Florissant, along with a slightly higher MAT.

1 ounger Oligocene Flor Ant S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) Plat Pitch-Pinnacle Plat Cr Older Oligocene (Ant Taxa & Pitch-Pinnacle) Y (Plat Union of Oligocene (Ant ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC Abies 1 1111 11110050.4% 100 30.5% 100 39.7% 100 47.4% 10057.3% 10046.4% 10068.4% 10069.8% 10060.0% 10055.1% 10067.5% 10073.6% A. cf. bracteata 1 1011 111100 010 100 100 100 010 100 100 001 001 100100 Keteleeria-type 0 1101 111001 001 000 001 001 100 010 100 010 100 001100 Picea 1 1111 111100 100 100 100 100 100 100 100 100 100 100100 Pinus 1 1111 111100 100 100 100 100 100 100 100 100 100 100100 Cedrus-type 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Larix-Pseudotsuga 1 1001 111100 010 010 100 100 010 010 100 000 001 001100 Tsuga 1 1001 111100 010 010 100 100 010 010 100 000 001 001100 Chamaecyparis 1 1000 101100 010 010 010 100 010 010 010 000 000 000010 Sequoia affinis 1 1000 101100 010 010 010 100 010 010 010 000 000 000010 Juniperus 0 1111 111001 001 001 001 001 100 100 100 100 100 100100 To rreya 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Ginkgo 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Ephedra 1 1111 111100 100 100 100 100 100 100 100 100 100 100100 Podocarpus-type 1 1111 111100 100 100 100 100 100 100 100 100 100 100100 Araceae 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Liliales/Liliatae10001 011010 010 010 100 100 000 000 001 000 001 001001 Smilax 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Dioscorea 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Poaceae 1 1011 111100 010 100 100 100 010 100 100 001 001 100100 Stipa 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Potamogeton 1 1001 111100 010 010 100 100 010 010 100 000 001 001100 Sparganium 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Scirpus 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Typha 1 0010 011010 010 100 010 100 000 001 000 001 000 010001 Acer (West) 1 1111 111100 100 100 100 100 100 100 100 100 100 100100 Ailanthus 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Alangium 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Alnus 1 1001 111100 010 010 100 100 010 010 100 000 001 001100 Amelanchier 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Amaranthaceae 0 0001 011000 000 000 001 001 000 000 001 000 001 001001 Arbutus 0 0100 101000 001 000 000 001 001 000 000 010 010 000010 Arceuthobium 0 1011 111001 000 001 001 001 010 100 100 001 001 100100 Artemisia 0 1111 111001 001 001 001 001 100 100 100 100 100 100100 Asteraceae 0 1011 111001 000 001 001 001 010 100 100 001 001 100100 Berberis 0 0111 111000 001 001 001 001 001 001 001 100 100 100100 Betula 1 1111 111100 100 100 100 100 100 100 100 100 100 100100 Bombax-type 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Caesalpinia-type 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Caprifoliaceae 0 1000 101001 000 000 000 001 010 010 010 000 000 000010 Cardiospermum 1 1000 101100 010 010 010 100 010 010 010 000 000 000010 Carya 1 1010 111100 010 100 010 100 010 100 010 001 000 010100 Caryophyllaceae 0 1010 111001 000 001 000 001 010 100 010 001 000 010100 Castanea 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 (continued)

1 ounger Oligocene Pitch-Pinnacle Plat Cr Older Oligocene (Ant Flor Ant S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) S = (2A)/(2A+B+C) Taxa & Pitch-Pinnacle) Y (Plat Union of Oligocene (Ant Plat ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC Catalpa 0 0001 011000 000 000 001 001 000 000 001 000 001 001001 Cedrela/Toona 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Celtis-type 1 1000 101100 010 010 010 100 010 010 010 000 000 000010 Cercis 1 0001 011010 010 010 100 100 000 000 001 000 001 001001 Cercocarpus 1 1011 111100 010 100 100 100 010 100 100 001 001 100100 Cnidoscolus 0 0100 101000 001 000 000 001 001 000 000 010 010 000010 Crataegus 1 1001 111100 010 010 100 100 010 010 100 000 001 001100 Croton 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Cucurbitaceae 0 1000 101001 000 000 000 001 010 010 010 000 000 000010 Cyclocarya 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Diospyros 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Dipteronia 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Elaeagnus 1 1011 111100 010 100 100 100 010 100 100 001 001 100100 Engelhardioideae 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Eucommia 1 1000 101100 010 010 010 100 010 010 010 000 000 000010 Fraxinus 1 1001 111100 010 010 100 100 010 010 100 000 001 001100 cf. Fremontia 0 1010 111001 000 001 000 001 010 111 010 001 000 010111 Halesia 0 0100 101000 001 000 000 001 001 000 000 010 010 000010 Heteromeles 0 0100 101000 001 000 000 001 001 000 000 010 010 000010 Holodiscus 1 0101 111010 100 010 100 100 001 000 001 010 100 001100 Hovenia 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Humulus 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Hydrangea/Jamesia 1 0001 011010 010 010 100 100 000 000 001 000 001 001001 Ilex 0 0010 011000 000 001 000 001 000 001 000 001 000 010001 Itea 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Juglans 1 1110 111100 100 100 010 100 100 100 010 100 010 010100 Koelreuteria 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Lindera-like10000 000010 010 010 010 010 000 000 000 000 000 000000 Lonicera 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Mahonia 1 1111 111100 100 100 100 100 100 100 100 100 100 100100 Cf. Malus 1 1000 101100 010 010 010 100 010 010 010 000 000 000010 Nuphar (aquatic) 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Ostrya/Carpinus 1 1001 111100 010 010 100 100 010 010 100 000 001 001100 Pachysandra/ 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Sarcococca Parthenocissus 1 0010 011010 010 100 010 100 000 001 000 001 000 010001 Persea-like10000 000010 010 010 010 010 000 000 000 000 000 000000 Philadelphus-like10000 000010 010 010 010 010 000 000 000 000 000 000000 Platanus 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Platycarya 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Populus 1 0111 111010 100 100 100 100 001 001 001 100 100 100100 Potentilla 0 0001 011000 000 000 001 001 000 000 001 000 001 001001 Prunus 1 0001 011010 010 010 100 100 000 000 001 000 001 001001 Pterocarya 1 1111 111100 100 100 100 100 100 100 100 100 100 100100 (continued)

TABLE 9. SIMILARITY PERCENTAGE BETWEEN FLORAS: SØRENSEN INDEX [(2A/2A + B + C)] (continued) Flora Presence/Absence Counts Florissant to Florissant to Florissant to Florissant to Florissant to Union Antero to Pitch- Antero to Platoro Antero to Creede Pitch-Pinnacle Pitch-Pinnacle Platoro to Creede Older Oligocene to Antero Pitch-Pinnacle Platoro Creede of Oligocene Pinnacle to Platoro to Creede Yo unger Oligocene o , er eede) eede) , Pitch-Pinnacle o & Cr o o o & Cr o or er issant or or er eed e

1 ounger Oligocene Pitch-Pinnacle Plat Cr Older Oligocene (Ant Plat Taxa Flor Ant & Pitch-Pinnacle) Y (Plat Union of Oligocene (Ant ABC S = (2A)/(2A+B+C) ABC S = (2A)/(2A+B+C) ABC S = (2A)/(2A+B+C) ABC S = (2A)/(2A+B+C) ABC S = (2A)/(2A+B+C) ABC S = (2A)/(2A+B+C) ABC S = (2A)/(2A+B+C) ABC S = (2A)/(2A+B+C) ABC S = (2A)/(2A+B+C) ABC S = (2A)/(2A+B+C) ABC S = (2A)/(2A+B+C) ABC S = (2A)/(2A+B+C) Quercus (West) 1 1011 111100 010 100 100 100 010 100 100 001 001 100100 Reevesia 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Rhoiptelea-type 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Rhus 1 0100 101010 100 010 010 100 001 000 000 010 010 000010 Ribes 1 0111 111010 100 100 100 100 001 001 001 100 100 100100 Cf. Robinia 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Rosaceae 0 0011 011000 000 001 001 001 000 001 001 001 001 100001 Rosa 1 0100 101010 100 010 010 100 001 000 000 010 010 000010 Rubus 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Salix 1 1111 111100 100 100 100 100 100 100 100 100 100 100100 Sambucus 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Sarcobatus 1 1111 111100 100 100 100 100 100 100 100 100 100 100100 Semeiandra 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Shepherdia 1 1011 111100 010 100 100 100 010 100 100 001 001 100100 Sorbus 0 0001 011000 000 000 001 001 000 000 001 000 001 001001 Tabernaemontana 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Tetracentron 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Tilia 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Ulmus/Ulmaceae-type 1 1111 111100 100 100 100 100 100 100 100 100 100 100100 Valerniana 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Vauquelinia 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 cf. Viburnum 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Vitis 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Xylonagra 1 0000 000010 010 010 010 010 000 000 000 000 000 000000 Zelkova 1 1010 111100 010 100 010 100 010 100 010 001 000 010100 Totals 92 43 26 34 43 53 51 65 34 58 9 18 74 8 25 67 9 32 60 11 454720 16 27 10 27178 301313 18 816 19 724 26 817 39 15 13 1 a (%) (%) ro ro issant (%) of tax . unger eede (%) Flor An te Pitch-Pinnacle (%) Pla to Sørensen Index Totals Cr Older Oligocene (%) Yo Oligocene (%) No Florissant 50.4 30.5 39.7 47.4 92 Antero 50.4 46.4 68.4 69.8 43 Pitch-Pinnacle 30.5 46.4 60.0 55.1 26 Platoro 39.7 68.4 60.0 67.5 34 Creede 47.4 69.8 55.1 67.5 43 Older Oligocene 73.6 53 Younger Oligocene 73.6 51 Union of Oligocene 57.3 65 Notes: A is the number of taxa found in both datasets; B is the number of taxa unique to the first dataset; and C is the number of taxa unique to the second dataset. 1Family-level ids, gymnosperms, and angiosperms identified in Table 4 were used for these statistical analyses. Fern allies, extinct taxa, and the IDs “small pine” and “Legume” were not evaluated.

Figure 6. Patterns of moisture indices (actual evaporation/potential evaporation—AE/PE) in various groups of taxa. (A) The outgoing (summer-moist) taxa. (B) The streamside taxa. (C) The incoming (summer-dry) taxa. After Thompson et al. (2015).

The ranges of MAT estimated for the four Oligocene floras were not as moisture-loving hardwoods such as Carya, Juglans, Engelhardia, and others well constrained as those of Florissant. The Genus Abies set the upper limit fall on the right along the X axis. This suggests the taxa became arranged here for all four floras at 18.2 °C, but the lower constraints resulted in broad ranges according to their adaptations to mesic growing season conditions on the right for MAT (Table 10). Even so, the results for the Creede flora are supported by side, and arid-tolerant taxa fell on the left side of the plot. Axis 1 accounted for results from clumped isotope Δ47 thermography based on original lacustrine 60% of the variance in the data, while Axis 2 accounted for another 10% of the carbonates, which suggest a MAT of 9 °C ± 2 °C (Hyland and Huntington, 2015). variance in the data (Fig. 4) (C. Looy, 2016, personal commun.). The total cooling between the late Eocene Florissant flora and the Oligocene Creede flora is estimated at between 5 °C and 9 °C. 4.5. Other

4.4. Detrended Correspondence Analysis (DCA) We provide estimated PPT values suggested by Axelrod (1987), MacGinitie (1953), and Wolfe and Schorn (1989) (Table 6). The relatively small average leaf One presentation that highlights the contrast between the late Eocene size (microphylls) and the prevalence of teeth on leaf margins suggested that and the Oligocene floras is the detrended correspondence analysis (DCA) plot the precipitation for the four Oligocene floras was somewhat limited (Mac (Fig. 4). Eocene samples fell to the right of the plot, while Oligocene samples Ginitie, 1953; Axelrod, 1987; see Wright et al., 2017). Additionally, the propor- primarily fell to the left. Samples from the Antero Formation fell in the middle tion of summer-moist dicots to total dicots dropped from 36% at Florissant to between Florissant samples and the Oligocene samples. Xeric type of genera 13% by Creede (Table 4). The loss of dicots requiring summer-moist conditions such as Juniperus, Sarcobatus, Artemisia, and Ephedra fell on the left, while (Fig. 7A) clearly suggests a decline in summer rainfall.

TABLE 10. CA CANDIDATES AND RESLTS OR RANGES O MEAN ANNAL TEMPERATRE MAT AND COLD MONTH MEAN TEMPERATRE CMMT OR THE ARIOS PALEOGENE LORAS Low High ossil type Low High ossil type MAT CMMT Creede Creede A. bracteata 7.8 M–P Mahonia –7 M Cercis 6.6 M Cercis –7.8 M Ephedra 3.2 P Berberis –8.9 M Catalpa 2.2 M Picea 8.6M–P A. bracteata 18.2M–P Ribes 9.3M–P Abies 18.2P Larix/Pseudotsuga 9.9M–P Potentilla 18.9M–P Crataegus 10.2 M Platoro Platoro A. bracteata 7.8 M–P Mahonia –7 M–P Carya 3.5 P Berberis –8.9 M Ephedra 3.2 P Picea 8.6M–P Pterocarya 2.6 P Ribes 9.3M Zelkova 2.6 M–P Pitch-Pinnacle A. bracteata 18.2M–P Abies 18.2P Heteromeles 0.9M Arceuthobium 19.3P Halesia –2 M Artemisia 20 P Arbutus –3.3 M Betula 20.6P Picea 8.6M–P Quercus est 20.7P Ribes 9.3M Cercocarpus 21 M Antero Pitch-Pinnacle Eucommia –6 P Halesia 8.8 M Mahonia –7 M Heteromeles 8.5 M Chamaecyparis –8.8 M Abies 18.2M–P Picea 8.6M–P Heteromeles 18.2M Larix/Pseudotsuga 9.9P Artemisia 20 P Crataegus 10.2 M Arbutus 20.1Mlorissant Halesia 20.6M Vauquelinia 6M Betula 20.6P Ta bernaemontana 1.3P Antero Engelhardioideae –1.7 P A. bracteata 7.8 M–P To rreya –2.5 M Fremontia 5.6 P Picea 8.6M–P Abies 18.2M–P To rreya 9M A. bracteata 18.2M–P Ribes 9.3M–P Fremontia 18.2P Larix/Pseudotsuga 9.9P Arceuthobium 19.3P lorissant Vauquelinia 14.3 M Tabernaemontana/ Diospyros 8.6 / 8.5 P A. bracteata 18.2P Torreya/Amelanchier 18.2M Abies 18.2M–P

Notes: CAcoeistence approach; Mmegafossil; Ppollen. Taa selected to set the upper and lower constraints are in bold.Taa, MAT and CMMT values used for CA analyses found in Tables 4 and 5.

Figure 7. (A) Diminishing role of summer- moist dicots of the hardwood forest in the Paleogene floras of Colorado (Table 4). (B) Percent role of “warm-adapted” taxa (MAT >0 °C) versus “cool-adapted” taxa (MAT ≤0 °C) in Paleogene floras of Colo rado (Table S2 [text footnote 1]).

While reviewing the results of the CA analyses, we observed an apparent The CA method was used to analyze cold-month mean temperature trend after Florissant in the decreasing role of “warm-adapted” taxa; these (CMMT) values as well to see if trends in winter temperatures could be de- are taxa requiring MAT ranges above 0 °C (e.g., Carya) (MAT Low column on termined (Table 5). The CMMT values at Florissant were well constrained to Table 5). In comparison, Juniperus and Artemisia are more “cool adapted” between 6.0 °C to 8.6 °C based on the presence of Vauquelinia and Picea (Table because they grow in areas where MAT values are at or below 0 °C (MAT Low 10). However, the ranges of CMMT for three of the Oligocene floras were in column on Table 5). About 53% of the taxa at Florissant are warm adapted excess of 10 °C. Picea set the upper end of the range of CMMT at 8.6 °C for all and require MAT ranges above freezing (Fig. 7B), but Antero records an ap- the Oligocene floras (Table 10). The lower value for Antero was set by either parent shift to majority of cool-adapted taxa (~60%). The diminishing role of Eucommia (a pollen ID) at –6.0 °C or by Mahonia (a megafossil ID) at –7.0 °C warm-adapted taxa continues through the Oligocene so that by the time of (a difference of at least 14.6 °C). The lower value for Pitch-Pinnacle was set the Creede flora (27 Ma), the warm-adapted taxa represented only ~32% of by Heteromeles at 0.9 °C, which is better constrained than Antero. At –7.0 °C, the floral list. This trend exemplifies the onset of cooler conditions during Mahonia set the lower threshold for Platoro and Creede. These very broad the Oligocene. ranges made interpreting the role of CMMT difficult.

5. DISCUSSION of eastern North American and East Asian affinity. These were warm-temperate, broad-leaved hardwood trees from the late Eocene flora (Wing, 1987). Be- 5.1. Vegetation at Creede cause most genera of that group require summer-moist conditions, this loss of mesophytic hardwoods has distinct climatic overtones. The change suggests At Creede, the generic composition of our pollen data suggests the de- that a major drop of summer rainfall occurred. The graph in Figure 7A shows velopment of a mixed pine woodland with understory shrubs such as Arte- the severity of this abrupt loss at 33.8 Ma in the Antero flora. Many arboreal misia, Elaeagnus, Shepherdia, and Ribes (gooseberry), along with Juniperus dicots were lost at the EOT; these include exotic taxa such as Platycarya, Carya, and Poaceae (Benedict, 1991). These taxa are common in the understory of Eucommia, and Bombacoideae, all of which prefer fully humid summer-moist the Ponderosa pine and juniper woodland today. With the megafossil evi- habitats. This trend in increasing aridity continued through the Oligocene so dence provided by the reports of Wolfe and Schorn (1989) and Axelrod (1987), that by 27 Ma, all megafossil records of the summer-moist, broad-leaved taxa, the vegetation represented by the Creede flora clearly establishes a type of including East Asian genera (e.g., Platycarya and Eucommia) were missing Pinus ponderosa and Juniperus woodland. Axelrod reported that the mega- (Fig. 7A; Table 4). The number of woody dicots rebounded slightly, but taxa fossil species of shrubs at Creede are slightly different but closely related to with a tree growth habit did not dominate the flora the way they did at Floris- the modern species of the area. The common plants of that woodland include sant (Table 4). Axelrod (1987) observed that the Creede climate was too cool to the monotypic genus Jamesia, along with Ribes, Juniperus, and Cercocarpus. include the rich diversity of oaks found in Florissant. We record Quercus pollen, which supports the record of Quercus at Creede Because the Creede flora had many generic similarities to the present local in Axelrod’s (1987) report. The Oligocene Creede flora seemed to be at the flora, botanists H.D. MacGinitie (1953) and D.I. Axelrod (1987) both declared ecotone between forest and woodland: it resembled the mixed Pinus ponder- that the Creede flora looked so “modern” (young) in aspect that it was prob- osa and Juniperus woodland but also included megafossil elements of the ably late Miocene or Pliocene in age. However, the isotopic age of 26.9 Ma present-day mixed conifer forest zone with Abies, Picea, and Pinus cf. aristata is well established (Lipman, 2007). The increasing similarity with the modern (Axelrod, 1987). Pollen from the cooler spruce and fir forest zone appears at local flora has been used as a rough index of geologic age as expressed by Antero, Pitch-Pinnacle, and Creede (Fig. 5). Barghoorn (1951) and Wolfe and Barghoorn (1960) (see also Leopold, 1967, p. 226) for this feature in Rocky Mountain floras. 5.2. Vegetation Changes: Three Trends during the EOT 5.2.2. Incoming New Taxa MacGinitie (1953) spoke of the Florissant flora as having been very like the semi-deciduous vegetation type of San Luis Potosi Province of Mexico A second feature, along with the loss of broad-leaved trees, was the re- (Rzedowski, 1966; Rzedowski, 1978). Boyle et al. (2008) called the Florissant placement by new incoming taxa. These included low-biomass, arid-adapted vegetation subtropical to warm temperate in terms of modern counterparts. shrubs such as Artemisia, Shepherdia, Chamaebatiaria, Ribes, and Berberis. MacGinitie (1953) further described the terminal Eocene floristic trend as indi- They represent some of the first appearances of understory plants that now cating increased seasonality of precipitation. characterize the native Ponderosa pine woodland and juniper shrublands of During the Oligocene, three important changes in the Paleogene floras oc- the southern Rockies (Benedict, 1991) not previously present in these Colo- curred, and they demonstrate an increasingly continental climate: the loss of rado floras. the warm-adapted, summer-moist arboreal dicots that typify the Eocene; the influx of new taxa, including sub-arid shrubs such asArtemisia ; and the shift 5.2.3. Herbaceous Habit to the low-biomass shrubs and herbs, such as Bidens, Potentilla, Caryophylla- ceae, Cucurbitaceae, and Sarcobatus, which typify the Oligocene of Colorado. The third development we see among the Oligocene samples is the ap- It should be noted that grasses played a regular but minor role in the Eocene pearance of low biomass plants with an herbaceous habit. Previous to the and Oligocene pollen floras of Colorado. Later, pollen data at some Miocene Oligocene, records of herbaceous Poaceae go back to the Cretaceous (Ström- sites in Idaho record open grassland conditions (Leopold and Wright, 1985; berg, 2011), but the typical herbs of the early Tertiary are aquatics such as Pota- Leopold and Denton, 1987). mogeton or Nymphaea (Leopold and MacGinitie, 1972). In the Oligocene sedi ments, as an example, we see a record of perennial herbs such as the unique 5.2.1. Loss of Arboreal Dicots Potentilla, the pollen of which corroborates the herbaceous megafossil of that genus at Creede (Wolfe and Schorn, 1989). Potentilla is a widespread perennial While the gymnosperm taxa were similar in the late Eocene and Oligo- herb or shrub of the Rosaceae. Poaceae are present in the Oligocene floras, as cene floras here, the composition of the angiosperms changed greatly during evidenced by regular minor appearances of grass pollen. Pollen and mega the EOT. The first shift was the loss by local extinction of many exotic taxa fossils of Artemisia and other Asteraceae, including a megafossil of Bidens, are

on record in the Oligocene floras; these are significant because pollen of the sant and the Oligocene communities. The similarity of Florissant to Creede highly evolved family Asteraceae becomes more common in the Oligocene was only 47%, which supports the notion that the differences in these commu- of Colorado. These are evolutionary jumps in the plant world (Axelrod, 1987; nities were becoming increasingly pronounced over time. These results are Graham, 1996), leading to the singular development in the Neogene of her- consistent with shifts in the ecological communities, beginning at the EOT, as baceous groups such as Caryophyllaceae, Violaceae, Cucurbitaceae, Euphor shown by the disappearance of many warm-adapted taxa after Florissant and biaceae, Chenopodiineae, Amaranthaceae, and others, especially in the Aster- the influx of new, derived families that appear in the Oligocene floras (Table 4). aceae. Similar pollen records of new herbaceous and shrub taxa occur in the The similarity between the older versus younger Oligocene data sets is mod- Neogene of Alaska (Leopold and Liu, 1994; Reinink-Smith et al., 2017) and con- erate at 74%. This, along with the similarity between Antero and Creede (70%), currently in northwest China (Liu, 1988). All these features mark the Oligocene underscores the influence of the new families and low biomass taxa in defin- of Colorado as a special opening door for plants of a modern low-biomass ing the Oligocene communities; the shift emphasizes the climatic changes that landscape. these new families and taxa were able to exploit.

5.3. Evaluation of Climate Change 5.3.1. Climatic Cooling

The Oligocene floras demonstrate an increase in taxa that are frost adapted A trend across the Eocene–Oligocene floral transition is marked by striking and tolerate a cool climate. This is first seen at Antero (33.8 Ma), with a decline climatic changes. These include (1) an apparent cooling seen as a decline in in MAT of ~3.3 °C. This condition continued through Creede time (Table 6). MAT first seen in the Antero flora; (2) evidence of clear differences between the The main cooling took place abruptly prior to ca. 33.8 Ma. More than half of Oligocene floras and the late Eocene Florissant flora; and (3) a growing aridity, the taxa at Florissant require MAT values above freezing, while the number as demonstrated by the DCA graph (Fig. 4). Though the Oligocene floras are of taxa at the four Oligocene floras were increasingly cool adapted, tolerating less diverse, they contain an increasing number of taxa that tolerate cool to MATs at or below freezing (Fig. 7B; Table 5). Antero records a shift to majority cold conditions. We infer that the MAT probably declined to ~9 °C by Creede of cool-adapted taxa (58%), and over two-thirds of the taxa at Creede were cool time (26.9 Ma), a total cooling of ~6 °C, over ~7 m.y. (Table 6). adapted (66%) (Fig. 7B; Table S2 [footnote 1]). Axelrod (1987) determined the paleoMAT by the modern range of several 5.3.2. Evidence of Drying: DCA and Growing Aridity species that are related to Creede taxa. These include Pinus chihuahuana (Pinus coloradensis fossil), Pinus montezumae (Pinus riogrande fossil), and The DCA pattern reinforces the ecological pattern (moist-loving taxa of Pinus engelmanii (Pinus engelmannoides fossil). These taxa now occur at ele- Florissant versus many sub-arid Oligocene types) that we recorded among vations from 2.0 to 2.3 km and have a MAT of 11 °C to 12 °C. Axelrod reported the fossil taxa. When the DCA method was applied to these floras, a change that a wide number (about a third) of the taxa at Creede are clearly related to was obvious immediately at Antero. The results of DCA demonstrate clearly a living species at the forest-woodland ecotone. Axelrod suggested therefore fundamental shift from the summer-moist elements of the Florissant flora on that the MAT at Creede was ~11.5 °C (Axelrod, 1987, p. 57) as compared to the the right (e.g., FLO-a and FLO-b, Fig. 4) to the transitioning Antero and FLO-c 1.9 °C MAT at Creede today (Axelrod, 1987; Wolfe and Schorn, 1989) and that samples in the middle, and the semi-arid Pitch-Pinnacle, Platoro, and Creede the CMMT was 3.5 °C. In contrast, Wolfe and Schorn (1989) suggest a very low floral data together on the left. The component genera of each flora cluster paleoMAT of <2.1 °C. closely together (Fig. 4; Table 6); the taxa themselves suggest that the data The trends across the EOT record a definite decline in winter tempera- along the horizontal axis represent a sharply declining precipitation regime tures, corresponding to the “terminal Eocene event,” a cold period described during the early Oligocene. for other western U.S. floras by Wolfe (1978, 1981, 1995). The EOT is marked by major environmental change, namely the development of a cooler climate 5.3.3. Moisture Index Values: AE/PE—Interpreting Aridity overall and in the trend toward colder winters (CMMT; noted by Wolfe and Leo- pold, 1967; Axelrod, 1987; Wolfe and Schorn, 1989, p. 192) (Fig. 7B; Table 10), Water stress is one of the most important physiological challenges for as well as a definite drop of estimated PPT. The increase in aridity is suggested tropical tree species (Brenes-Arguedas et al., 2011). In addition, seasonal rain- by several authors, the DCA findings, and by our moisture-index data (Fig. 6; fall clearly determines the geographical distribution of warm-temperate forest Wolfe, 1981; Axelrod, 1987, p. 57; Wolfe and Schorn, 1989; Wolfe, 1992). ecotypes in eastern United States (Thompson et al., 2012; Fig. 1). Precipitation The Sørensen index results indicate that the Florissant similarity to the gradients correlate with patterns of species richness at macroecological scales Oligocene floras is only 57% (when all the Oligocene floras were combined (Clinebell et al., 1995). Because of this relationship, we would expect that a pro- into a single unit; Table 9). Even allowing for taphonomic bias (Pitch-Pinnacle gressive turnover of species identities would occur due to changes in precipi- and Platoro being small floras), there is no strong similarity between the Floris tation. The transition in composition of the floras during the EOT demonstrates

turnover of species relating to moisture availability, as indicated by inferred (e.g., Carya, Betula, and Quercus) at a time when the evaporation rates were soil-moisture indices. low enough in relation to summer rainfall to permit the broad-leaved hard- Figure 6 shows a plot of the values for actual evaporation (AE) rate di- woods to exist (typically >100 mm July average precipitation). In contrast, vided by the potential evaporation (PE), on the horizontal axis. These are some the smaller Oligocene assemblages that followed shifted in aspect from sum- examples of soil-moisture data (in different taxa) that represent three groups mer-moist to summer-dry conditions. Clearly the factor that was critical in the of taxa considered as “outgoing,” “continuing,” or “incoming” types during loss of the broad-leaved trees was the impact of increased evaporation rate the EOT. The data were based on biogeographic range of taxa presented by (relative to precipitation; AE/PE <0.8), resulting in the lower diversity observed Thompson et al. (2012), e.g., from summer-moist hardwood forest and xeric in the late Oligocene floras. Significantly the streamside and lakeside taxa (Fig. southwestern regions that exemplify the changing phases of the EOT with re- 6B) were able to persist during the EOT on the margins of wetland areas in spect to soil-moisture availability (Fig. 6). spite of this change. The incoming new families and taxa of which we have 5.3.3.1. Group One (Fig. 6A: Outgoing taxa). The broad-leaved hardwood record had the advantage of tolerating high evaporation rates (AE/PE <0.8; Fig. taxa (e.g., megafossils of Carya, Juglans, Tilia, Ostrya, Carpinus, Castanea, and 6C). Their influx demonstrates that they succeeded in the increasingly conti- Diospyros) require high moisture-index values between 0.8 and 1.0. These are nental climate. Finally, the loss of summer-moist dicots, seen in the drop from the outgoing arboreal genera that have distributions in summer-moist areas of ~36% at Florissant to almost 13% by Creede (Fig. 7A; Table 4), supports our eastern United States or East Asia, with a preference for moist growing-season conclusion of a decline in summer PPT. conditions in July (Thompson et al., 2012). These elements were present in the Florissant flora but are absent in the Oligocene floras. Summer-moisture 5.4. Local Environments of the EOT in Colorado availability in the area undoubtedly dropped below AE/PE = 0.8 after the EOT. Axelrod came to a similar conclusion (1987, p. 62), as did Wolfe and Schorn The plants record the temperature trends and demonstrate that the climate (1989, p. 191). at Florissant and the Oligocene floras were warmer than they are today. For ex- 5.3.3.2. Group Two (Fig. 6B: Continuing or streamside taxa). The continuing ample, many species identified by Axelrod (1987) and Wolfe and Schorn (1989) taxa are streamside forms (e.g., species of Betula, Alnus, Populus, and Salix) now grow in regions farther south, in New Mexico and Mexico. that have AE/PE moisture-index values that run the gamut from low to high be- The final record of the latest Eocene local environment is well recorded at tween 0.2 and 1.0 on the horizontal axis. Their tolerance of moisture conditions Florissant. The lakeside slopes were characterized by a mesic forest dominated is wide ranging. These taxa can succeed by occupying streamside positions in by Sequoia affinis. Broad-leaved deciduous hardwood trees with diverse spite of drought. Ulmus may be one of these taxa because it thrives on stream members of Juglandaceae, Tilia, and such flourished, along withSequoia in margins. Most of these continue in time through the Creede flora. the Florissant lowland forest. A rich mixture of Ulmaceae, Salix, and Fagopsis 5.3.3.3. Group Three (Fig. 6C: Incoming taxa). Within the incoming taxa covered the shorelines. Herbs were a minor element. The climate was warm group are the now-native western shrubs and trees well adapted to high (MAT between ~14 and 18 °C; Zaborac-Reed and Leopold, 2016; Table 6) with evaporation values in the environment. They grow in arid areas of interior semi-arid conditions marked by gypsum accumulations occurring on certain United States (see Barnosky, 1984). We have called these “newcomers,” be- highland pond areas (MacGinitie, 1953, p. 56). Occasional light frosts may have cause many of these first appear in the Oligocene records in Colorado. They occurred (MacGinitie, 1953). are highly adaptable, with low AE/PE values of soil moisture ranging from 0.2 In contrast, the younger floras that followed Florissant record simpler flora to <0.8. These moisture-index values do not overlap with those of the decid- with smaller leaves, an increasingly drier environment (evaporation increased uous hardwood taxa, Group A (Fig. 7A). The incoming new taxa (e.g., Arte- relative to rainfall), a lower average mean annual temperature of 12.7 °C misia, Quercus cf. grisea, and Shepherdia cf. argentea) have smaller leaves (Antero and Pitch-Pinnacle), and later ~9 °C at Creede (Table 6), and a growing and can compete in a high-stress (high-evaporation rate) environment. Along role of cool-adapted taxa. The samples from Antero showed a smaller flora with these were the herbs that, in the United States, appear as new derived in transition, suggesting that vegetation changes were likely due to one large families mainly known from Miocene and younger floras (e.g., Cucurbitaceae climatic shift immediately after Florissant. The region was increasingly raked and Caryophyllaceae). by fire and ash fall from nearby volcanoes (as indicated by the burnt plant tissue and pollen grains at Platoro). Extremes in aridity occurred under a cool 5.3.4. Evaluation of Growing Aridity and Floristic Consequences climate driven at least in part by the global cooling associated with Antarctic glaciation (Oi-1; Cather et al., 2008). By Creede time, the vegetation became For many plant taxa, data are available that suggest soil-moisture condi- open woodland with an assortment of rosaceous shrubs, Artemisia (sage- tions (Thompson et al., 2012). Soil moisture represents a limiting factor that brush), Elaeagnaceae, and grass (Table 4). Pine and fir forests were dominant relates strongly to the groups of taxa that responded to climate change at the at higher levels on the Creede crater walls, while at lower woodland sites, the EOT (Fig. 6). The Florissant flora embraced a few genera in these three groups dominant conifer was Juniperus with largely drought-tolerant shrub genera

native to Colorado today (Wolfe and Schorn, 1989). The dry, cool conditions Karlstrom et al. (2012) concluded that the region experienced 0.5–1.0 km with frosts apparently continued to the end of the Oligocene at Creede. of surface uplift in the Neogene. The uplift in elevation since Creede deposi- Our data suggest three broad changes in temperature may have occurred tion inferred by Steven and Ratté (1965), using structural evidence, provides a in Colorado during the Oligocene (Table 6). The first change was the abrupt presumed uplift of ~1.5 km. These results constrain the paleoelevation of the difference in MAT (from Florissant to Antero) from an average of ~16 °C to floras of this study to low to mid elevations at the time of deposition, allowing 12.7 °C in 0.3 m.y. The second and more moderate drop (from Pitch-Pinnacle for Neogene uplift of between 0.5 and 1.5 km to their subsequent modern ele to Platoro) was ~6.5 °C (over 5.3 m.y.), which is significantly slower. The third vations (Fig. 3; Table 2). This gives a rough estimate for paleoelevation prior change suggests a difference in MAT of ~2.8 °C (between Platoro and the Lake to the Neogene (Fig. 3). It should be noted, however, that elevation estimates Creede), which may be due in part to elevational differences between the two can vary due to many factors. Differences in elevation between sites give the sites (Table 2). Overall the botanical data support a regional cooling during the potential for a great deal of complexity in how temperature differences might EOT that probably began very rapidly. A trend of continuing and increasing be calculated and interpreted. aridity is displayed by the vegetation and flora. Wolfe (1992) stated that the paleoelevation of a floral site may also be estimated appropriately by using paleotemperature—especially MAT. There are various techniques for calculating MAT: e.g., CA, NLR, and plant physi- 5.5. How Do the Following Tools Assist in Interpretation? ognomic methods such as CLAMP (Wolfe, 1993). However, CLAMP was considered problematic because the inferred temperature results tended to be The coexistence approach serves to quantify estimates of the main tem- consistently cooler than expected (e.g., by 2 °C; Peppe et al., 2010), producing perature features. The detrended correspondence analysis documents the paleoelevations near modern levels and with large margins for error (Fig. 3). basic shift toward arid-adapted taxa after Florissant. As a statistical tool, Furthermore, Cather et al. (2012) stipulated that high paleoelevational results the Sørensen index of similarity quantifies similarities between floras. The use predicted by the use of leaf physiognomic techniques (such as CLAMP) are of NLR analysis gives a very direct way to quantify the significance of floral very unlikely, given the results of their mapping study. changes, e.g., of temperature and/or aridity of the environment. Soil-moisture Finding paleoelevation using methods that depend on modern lapse rates indexes provide a link between the identified taxa and their requirements. of a region can be problematic. Axelrod and Bailey (1976) suggested many reasons why lapse rates may have been different in past climatic regimes. Lo- cal lapse rates reflect local topography; however, lapse rate patterns from one 5.6. Development of the Cordilleran Flora and Creede side of a range can be completely different from the other side, especially in complex terrain (Minder et al., 2010). For instance, applying a normal lapse The combined loss of exotic taxa, along with the replacement of these by rate of 183m/°C to the projected uplift of between 500 and 1500 m, a cooling newer plant groups important in the modern vegetation at Creede, are evi- of ~2°–8 °C might have resulted from the Neogene uplift. When topography dence that the Cordilleran flora of southern Colorado became more modern in is unknown, assumptions about a site invariably lead to such widely varying aspect at this time. Axelrod and Raven (1985) wrote very clearly that the pres- results (e.g., Gregory and McIntosh, 1996; Cather et al., 2012; Table 2; Fig. 3). ent-day Cordilleran flora probably originated back in 27 Ma with the Creede The paleoelevations derived from using botanical assemblage-based meth- flora; they suggested that this was the time for the origin and development of ods such as NLR and CA fit well with additional support from studies using the present southern Rocky Mountain flora. vesicle paleoaltimetry, oxygen-isotope geochemistry, and carbonate-clumped isotope thermometry. These are all generally compatible with episodes of uplift and erosion observed in Cather et al.’s (2012) and Karlstrom et al.’s (2012) 5.7. What Estimates of Paleoelevation Can Be Made summaries. Based on These Floras?

Evidence of erosional events brought forth by Cather et al. (2012) and Karl- 5.8. Regional and Global Correlation strom et al. (2012) supports low to moderate paleoelevations for the five floras examined in this study but not the high (or in some cases extremely high) In northern Europe during the EOT, a sharp cooling lowered the MAT by paleoelevations reported by some authors (Fig. 3; Tables 1 and 2). Cather et al. ~5°–8 °C (Mosbrugger et al., 2005). Sea-surface temperature dropped 9°–10 °C (2012) concluded that the average elevation of the Rocky Mountains at ca. around the globe (Zachos et al., 2001) causing “icehouse conditions.” An ex- 45 Ma was ~350 m above sea level and that the Florissant area paleoelevation tinction of ~60% of woody plant taxa occurred in Oregon, where the MAT may have been ~1.5 km at the time of deposition. MacGinitie (1953, p. 53) indi- dropped ~10 °C (Retallack et al., 2004; Dunn, 2007; Table 11). However, the EOT cated the paleoelevation of Florissant may have been between 0.3 and 0.9 km. resulted not so much in the extinction of plant taxa as in a local extirpation and

TABLE 11. GLOBAL ENVIRONMENTAL CHANGES DURING THE EOCENE–OLIGOCENE TRANSITION IN DIFFERENT LOCALITIES Location Eocene–Oligocene change Source Florissant, Colorado, 34.1 Ma This paper Badlands, NebraskaDrop of ~8° C mean annual temperature Zanni and Ravazzi, 2007 White River Formation, Western Plains Overall drying Evanoff, 2013 Badlands, NebraskaDrying during early through middle Oligocene Clark et al., 1967 NW Europe MAT drop Mosbrugger et al., 2005 Winter temperature decline 5° C Gulf of AlaskaLoss of dicot taxaRidgway et al., 1995 Sea surface temperature, globalDrops ~9°–10° C Zachos et al., 2001 Pacific NW Mean annual temperature decline of ~10° C Dunn, 2007 Eugene, Oregon Extinction of 60% of plant taxa Retallack et al., 2004 China, Weihe Basin Loss of evergreen forest and influx of conifers Sun et al., 1980 Eastern China, Oligocene Low biomass and dry shrub vegetation denoting extensive dry periodLeopold et al., 1992 Tanzania Extinctions and environmental changes Pearson et al., 2008 Cooling 9°–10° C Northern Rocky Mountains, SW Montana Loss of diversity Lielke et al., 2012 Increased xeric component Argentina Dusty environment, dry, cool Selkin et al., 2015

dispersal to lower elevations and latitudes (Wolfe, 1987). A decline in aquatic recorded by Zachos et al. (2001). We interpret that the subsequent slower cool- amphibians and some reptiles in North America occurred, related to an in- ing (between 32.9–29 Ma and 28 Ma) may also be related to global cooling. crease in aridity as well as a decrease in the number of rivers, streams, and At the end, the increase of almost 3 °C per m.y. (between 28 Ma and 27 Ma) other water sources (Hutchison, 1992, in Prothero and Berggren, 1992). In Ne- might reflect the combination of elevational differences between Platoro and braska, the physical differences in soil type between the Brule and the Chadron the Lake Creede as well as a slight warming near the end of the Oligocene formations demonstrate a clear trend toward aridity at the Eocene–Oligocene (see Zachos et al., 2001). The total MAT decline in the region of between 5 °C boundary (Terry, 2001). and 9 °C during the Oligocene may have involved a complex interaction be- In the early Oligocene of northeastern China, the southward spread and tween global cooling, minor surface uplift at local volcanoes, and some local increasing importance of shrubs such as Ephedra and cf. Nitraria is evident. cooling due to volcanic aerosols. During the Miocene, the flora at the Trouble- The setting in China is interpreted as a low-biomass, woody savannah with some Formation of Central Colorado records a number of mesic hardwoods arid-adapted shrubs or open deciduous forest with temperate hardwoods by that indicate their continuance and a return to somewhat more summer-moist the end of the Oligocene (Liu, 1988; Leopold et al., 1992). A sharp cooling in Ar- growing conditions (Leopold, in Tschudy and Scott, 1969, p. 409). Indepen- gentina accompanied by evidence of fire and burnt phytoliths portray environ- dent evidence demonstrates that major surface uplift in the southern Rocky ments of severe conditions (Selkin et al., 2015) that mirror volcanic conditions Mountains occurred during the past 10 m.y. (Cater, 1966; Cather et al., 2012; at the Platoro site (Plate V), where some foliage, pollen, and spores appear Karlstrom et al., 2012). badly burnt. A wave of extinctions off the coast of Tanzania occurred at this time (Pearson et al., 2008). In Colorado and New Mexico, the EOT was a turbulent period. Violent 6. CONCLUSIONS eruptions in the Southern Rocky Mountain volcanic field of Colorado and the Mogollon-Datil volcanic field of New Mexico were accompanied by large cal- The Eocene–Oligocene transition (EOT) was marked globally by one of dera collapses. Enormous ash falls created dunes covering an area the size of the most abrupt and severe environmental changes in the Cenozoic record Wisconsin (Cather et al., 2012). Called the aeolian Chuska erg (Fig. 1), these (see Zachos et al., 2001). The present report emphasizes the significance of deposits had a thickness of as much as ~535 m in the Chuska Mountains. Their floristic change during the Oligocene in Colorado. We document a major flo- aerosols may have been a local factor in cooling the climate by blocking solar ristic turnover based on five local floras that span the late Eocene through radiation. most of the Oligocene. The late Eocene Florissant and the Oligocene Antero, The initial drop in temperature of ~3.3 °C in 0.3 m.y. (34.1 Ma to 33.8 Ma) Pitch-Pinnacle, Platoro, and Creede floras are a basis for estimating mean an- was so fast that it seems unlikely to have resulted solely from uplift. It was nual temperature (MAT) changes and developing aridity through the EOT and probably related to the global cooling and Antarctic glaciation Oi-1 event as the Oligocene interval. In addition, we combined the new Oligocene pollen

data (not previously published) with the megafossil identifications at Creede in flora (e.g.,Jamesia and Chamaebatiaria). Additional Oligocene taxa include order to access the whole flora. Based on these data, we prepared a corrected the appearance of several highly evolved “new” plant groups (e.g., Astera- list of the Creede flora. ceae, Caryophyllaceae, and Elaeagnaceae) not typical of the early Cenozoic in Based on recent studies, the southern Rocky Mountains probably lay the Rocky Mountains. Such taxa expanded regionally during the Oligocene. at ~1.5 km in elevation, though growth of volcanoes may have raised local Our data lend support to the theme of Axelrod and Raven (1985), who de- areas to as high as ~1.8 km during the Oligocene (Meyer, 1986; Axelrod, 1987; scribed the Oligocene interval in Colorado as being the time when the Cor Cather et al., 2012; Table 2). Major uplift of the Colorado Plateau began in the dilleran flora of the southern Rocky Mountains first appeared. late Miocene and may have continued until the Holocene, raising these sites The developing cooling and aridity caused a loss of broad-leaved dicots by ~0.5 km to 1.5 km in elevation after the Oligocene floras were deposited that were replaced by drought-resistant and cold-tolerant conifers, shrubs, and (Steven and Ratté, 1965; Karlstrom et al., 2012). new herbs during the Oligocene in Colorado. The environmental changes fa- vored understory plants of low biomass resistant to drought. In summary, the reshaping of the montane flora in southern Colorado Climate and Floristic Change during the Eocene–Oligocene transition was a product of interactions between several environmental factors: active volcanism; global cooling; the Antarctic The four Oligocene floras of south-central Colorado formed during a pe- glaciation of Oi-1; and losses in warm season precipitation. The developing riod of super-active volcanism and heavy ash fall. The Oligocene cooling and aridity and cooling caused a loss of broad-leaved dicots that were replaced by increased aridity in Colorado correlate with the Oi-1 glaciation in Antarctica. drought- and cool-tolerant conifers, shrubs, and herbs during the Oligocene The EOT data reveal a severe drop in floral diversity at 33.8 Ma immediately in Colorado. This floristic shift may illustrate a cause and effect, namely that after the summer-moist, warm Florissant flora. This change records an abrupt cooling and aridity were the main stimulus that forced evolutionary changes shift to a cool, semi-arid climate that lasted through most of the Oligocene in the regional vegetation. interval (to 27 Ma). The Oligocene floras appear to represent a cool period that Jack Wolfe called the “terminal Eocene event” (1978). Because the Florissant and Antero floras are close in terms of age, location, and elevation, the floristic ACKNOWLEDGMENTS differences between the two floras observed at the EOT are likely related to The authors wish to express their gratitude for the editorial comments and support of Herb Meyer, global cooling and increasing aridity rather than surface uplift. Karl Karlstrom, Peter Lipman, Cindy Looy, Jeff Benca, Caroline Strömberg, Robyn Burnham, Steve Manchester, David W. Love, and Peter Wilf. The authors also wish to thank the University of Wash- The estimated decline in mean annual temperature of between 5° and ington Biology Department and the Expo ’90 Foundation and International Cosmos Prize for their 9 °C during the Colorado Oligocene involved a complex interaction between support. We thank Shanaka de Silva, Rhawn Denniston, and the anonymous reviewers at Geo- global cooling and volcanic aerosols. This cooling compares with the global sphere for their thoughtful comments. EOT cooling of ~5 °C. Indications from Europe, Africa, northern China, Argen- tina, and other sites, including global marine records (Table 11), record remark- REFERENCES CITED able changes in world climate starting at the end of the Eocene or earliest Oligocene. Anderson, M.D., 2004, Sarcobatus vermiculatus: Fire Effects Information System (online): U.S. Department of Agriculture Forest Service, Rocky Mountain Research Station, Fire Sciences In Colorado, many exotic plant genera of eastern North American and East Laboratory (producer): http://www.fs.fed.us/database/feis/plants/shrub/sarver/all.html (Jan- Asian affinity that depend on July rainfall became locally extinct, and were uary 2014). replaced by taxa tolerant of semi-arid conditions. The lost genera are a basis Axelrod, D.I., 1987, The Late Oligocene Creede Flora, Colorado: University of California Publica- tions in Geological Sciences, v. 130, p. 1–235. for estimating the decline of summer precipitation leading to growing aridity Axelrod, D.I., 1998, The Oligocene Haynes Flora of Eastern Idaho: University of California Publi- during the Oligocene. Physical changes in soil profiles are noted in the EOT cations in Geological Sciences, v. 143, p. 1–235. Chadron and Brule formations. Axelrod, D.I., and Bailey, H.P., 1976, Tertiary Vegetation, Climate, and Altitude of the Rio Grande Depression, New Mexico–Colorado: Paleobiology, v. 2, no. 3, p. 235–254, https://doi .org/10 .1017/S0094837300004814. Axelrod, D.I., and Raven, P.H., 1985, Origins of the Cordilleran Flora: Journal of Biogeography, Evolutionary Significance v. 12, no. 1, p. 21–47, https://doi.org/10.2307/2845027. Barghoorn, E.S., 1951, Age and Environment: A survey of North American Tertiary floras in relation to paleoecology: Journal of Paleontology, v. 25, no. 6, p. 736–744. This important fossil record demonstrates an abrupt floral shift during the Barnosky, C.W., 1984, Late Miocene vegetational and climatic variations inferred from a pollen EOT from a hardwood forest flora rich in exotic mesic hardwoods to a modern, record in northwest Wyoming: Science, v. 223, no. 4631, p. 49–51, https://doi .org/10.1126 pine-fir woodland, with an understory of arid-adapted shrubs such asArte - /science.223.4631.49. Barton, M.A., and Fricke, H.C., 2006, Mapping topographic relief and elevation of the Central misia, Cercocarpus, and low biomass herbs. This shift features the appearance Rocky Mountain Region during the latest Eocene using stable isotope data from mammalian of several endemic and small genera that now characterize the Cordilleran tooth enamel: Geological Society of America Abstracts with Programs, v. 38, no. 7, p. 1–202.

Baumgartner, K.A., and Meyer, H.M., 2014, Coexistence Climate Analysis of the Late Eocene Flo- Davis, O.K., 2001, Palynology: Ephedra: University of Arizona: http://www.geo.arizona.edu rissant Flora, Colorado: Vancouver, British Columbia, Geological Society of America Annual /palynology/pid00008.html#ko (October 2016). Meeting, paper no. 199-5, https://gsa.confex.com/gsa/2014AM/webprogram/Paper244071 Dilcher, D.L., 1969, Podocarpus from the Eocene of North America: Science, v. 164, no. 3877, .html. p. 299–301, https://doi.org/10.1126/science.164.3877.299. Benedict, A.D., 1991, A Sierra Club Naturalist’s Guide: The Southern Rockies: San Francisco, Doher, L.I., 1980, Palynomorph preparation procedures currently used in the paleontology and Sierra Club Books, 578 p. stratigraphy laboratories: U.S. Geological Survey Circular 830, p. 1–38. Bethke, P.M., and Hay, R.L., 2000, Ancient Lake Creede: Its Volcano-Tectonic Setting, History Dunn, R., 2007, Climatically induced floral change across the Eocene-Oligocene transition in the of Sedimentation, and Relation to Mineralization in the Creede Mining District: Geological John Day and Clarno Formations of eastern Oregon: Geological Society of America Ab- Society of America Special Paper 346, 332 p., https://doi.org/10.1130/SPE346. stracts with Programs, v. 39, no. 6, p. 567. Bolinder, K., Norbäck Ivarsson, L., Humphreys, A.M., Ickert-Bond, S.M., Han, F., Hoorn, C., and Durden, C.J., 1966, Oligocene Lake Deposits in Central Colorado and a New Fossil Insect Locality: Rydein, C., 2016, Pollen morphology of Ephedra (Gnetales) and its evolutionary implications: Journal of Paleontology, v. 40, no. 1, p. 215–219. Grana, v. 55, no. 1, p. 24–51, https://doi.org/10.1080/00173134.2015.1066424. Erdtmann, G., 1957, Pollen and spore morphology/plant taxonomy: Gymnospermae, Pterido- Bouchal, J., 2013, The Microflora of the Uppermost Eocene (Priabonian) Florissant Formation, a phyta, Bryophyta (An introduction to palynology. II): Stockholm, Almqvist and Wiksell, 151 p. combined method approach [Ph.D. thesis]: Vienna, Austria, Universität Wien, 120 p. Evanoff, E., 2013, Late Eocene and Early Oligocene Topography of the Western Great Plains: Bouchal, J., Zetter, R., Grímsson, F., and Denk, T., 2014, Evolutionary trends and ecological differ- Geological Society of America Abstracts with Programs, v. 45, no. 7, p. 191. entiation in early Cenozoic Fagaceae of western North America: American Journal of Botany, Evanoff, E., McIntosh, W.C., and Murphey, P.C., 2001, Stratigraphic summary and 40Ar/39Ar geo- v. 101, no. 8, p. 1332–1349, https://doi.org/10.3732/ajb.1400118. chronology of the Florissant Formation, Colorado: Proceedings of the Denver Museum of Bouchal, J.M., Zetter, R., and Denk, T., 2016, Pollen and spores of the uppermost Eocene Flo- Nature and Science Series, v. 1350 4, no. 1, p. 1–16. rissant Formation, Colorado: A combined light and scanning electron microscopy study: Fang, J., Wang, Z., and Tang, Z., 2011, Atlas of Woody Plants In China: Distribution and Climate Grana, v. 55, no. 3, p. 179–245, https://doi.org/10.1080/00173134.2015.1108362. (Vol. 1): Berlin, Springer-Verlag, 2000 p. Boyle, B., Meyer, H.W., Enquist, B., and Salas, S., 2008, Higher taxa as paleoecological and paleo Fredrickson, N.O., 1981, Sporomorphs from the Jackson Group (Upper Eocene) and Adjacent climatic indicators: A search for the modern analog of the Florissant fossil flora,in Meyer, H.W., Strata of Mississippi and Western Alabama: U.S. Geological Survey Professional Paper 1084, and Smith, D.M., eds., Paleontology of the Upper Eocene Florissant Formation, Colorado: Geo- 118 p. logical Society of America Special Paper 435, p. 33–51, https://doi.org/10.1130/2008.2435(03). Garcia, M.J., Premaor, E., De Oliveira, P.E., Bernardes-De-Oliveira, M.E.C., Dino, R., Antonioli, Brenes-Arguedas, T., Roddy, A.B., Coley, P.D., and Kursar, T.A., 2011, Do differences in understory L., and De Menezes, J.B., 2016, Cenozoic distribution of Ephedripites Bolkhovitina (1953) ex light contribute to species distributions along a tropical rainfall gradient?: Oecologia, v. 166, Potonié (1958) emend. Krutzsch (1961) in Brazil: Grana, v. 55, no. 1, p. 52–70, https://doi .org no. 2, p. 443–456, https://doi.org/10.1007/s00442-010-1832-9. /10.1080/00173134.2015.1119882. Burns, R.M., and Honkala, B.H., 1990, Silvics of North America: Vol. 1. Conifers; 2. Hardwoods. Graham, A., 1996, A Contribution to the Geologic History of the Compositae, in Hind, D.J.N., and Agriculture Handbook 654: Washington, D.C., U.S. Department of Agriculture, Forest Beentje, H.J., eds., Compositae: Systematics: Kew, Australia, Proceedings of the Interna- Service, v. 2, 877 p., https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_1/silvics_vol1 tional Compositae Conference, 1994, v. 1, Royal Botanic Gardens, p. 123–140. .pdf (May 2018). Graham, A., 2011, The age and diversification of terrestrial New World ecosystems through Cre- Carrington, M.E., Gottfried, T.D., and Mullahey, J.J., 2003, Pollination Biology of Saw Palmetto taceous and Cenozoic time: American Journal of Botany: Special Issue on Biodiversity, v. 98, (Serenoa repens) in Southwestern Florida: http://www .palms .org /palmsjournal /2003 /serenoafl p. 336–351. .htm (June 2014). Gregory, K.M., and Chase, C.G., 1992, Tectonic significance of paleobotanically estimated cli- Cater, F.W., 1966, Age of the Uncompahgre Uplift and Unaweep Canyon, West-Central Colorado: mate and altitude of the late Eocene erosion surface, Colorado: Geology, v. 20, p. 581–585, U.S. Geological Survey Professional Paper 550-C, p. C86–C92. https://doi.org/10.1130/0091-7613(1992)020<0581:TSOPEC>2.3.CO;2. Cather, S.M., Connell, S.D., Chamberlin, R.M., McIntosh, W.C., Jones, G.E., Potochnik, A.R., Gregory, K.M., and McIntosh, W.C., 1996, Paleoclimate and paleoelevation of the Oligocene Lucas, S.G., and Johnson, P.S., 2008, The Chuska erg: Paleogeomorphic and paleoclimatic Pitch-Pinnacle flora, Sawatch Range, Colorado: Geological Society of America Bulletin, implications of an Oligocene sand sea on the Colorado Plateau: Geological Society of Amer- v. 108, no. 5, p. 545–561, https://doi.org/10.1130/0016-7606(1996)108<0545:PAPOTO>2.3.CO;2. ica Bulletin, v. 120, no. 1–2, p. 13–33, https://doi.org/10.1130/B26081.1. Gregory-Wodziki, K.M., 2001, Paleoclimatic implications of tree-ring growth characteristics of Cather, S.M., Dunbar, N.W., McDowell, F.W., McIntosh, W.C., and Scholle, P.A., 2009, Climate 34.1 Ma Sequoioxylon pearsallii from Florissant, Colorado, in Evanoff, E., Gregory-Wodziski, forcing by iron fertilization from repeated ignimbrite eruptions: The icehouse-silicic large K.M., and Johnson, K.R., eds., Fossil Flora and Stratigraphy of the Florissant Formation, Colo- igneous province (SLIP) hypothesis: Geosphere, v. 5, no. 3, p. 315–324, https://doi .org/10 rado: Proceedings of the Denver Museum of Nature and Science Series, v. 4, no. 1, p. 163–186. .1130/GES00188.1. Griffin, J.R., and Critchfield, W.B., 1976, The Distribution of Forest Trees in California: U.S. De- Cather, S.M., Chapin, C.E., and Kelley, S.A., 2012, Diachronous episodes of Cenozoic erosion in partment of Agriculture Forest Service Research Paper PSW-82 with supplement: California, southwestern North America and their relationship to surface uplift, paleoclimate, paleo Berkeley Pacific Southwest Forest and Range Station: Washington, D.C., U.S. Government drainage, and paleoaltimetry: Geosphere, v. 8, no. 6, p. 1177–1206, https://doi.org/10.1130 Printing Office, 118 p. /GES00801.1. Hammer, Ø., Harper, D.A.T., and Ryan, P.D., 2001, PAST: Paleontological statistics software pack- Chapin, C.E., 2012, The origin of the Colorado Mineral Belt: Geosphere, v. 8, no. 1, p. 28–43, age for education and data analysis: Palaeontological Association, v. 4, no. 1, p. 1–9, http:// https://doi.org/10.1130/GES00694.1. palaeo-electronica.org/2001_1/past/issue1_01.htm (October 2016). Chase, C.G., Gregory-Wodzicki, K.M., Parrish, J.T., and Decelles, P.G., 1998, Topographic History Hutchison, J.H., 1992, Western North American reptile and amphibian record across the Eocene/ of the Western Cordillera of North America and Controls on Climate, in Crowley, T.J., and Oligocene boundary and its climatic implications, in Prothero, D.R., and Berggren, W.A., Burke, K.C., eds., Tectonic Boundary Conditions for Climate Reconstructions: Oxford, UK, eds., Eocene–Oligocene Climatic and Biotic Evolution: Princeton, New Jersey, Princeton Uni- Oxford University Press, p. 73–99. versity Press, p. 451–463, https://doi.org/10.1515/9781400862924.451. Clark, J., Beerbower, J.R., and Kietze, K.K., 1967, Oligocene sedimentation, stratigraphy, paleo- Hyland, E., and Huntington, K., 2015, Resolving paleo-floral temperatures using the clumped ecology, and paleoclimatology in the Big Badlands of South Dakota: Fieldiana. Geology isotope thermometer: Implications for Florissant and the uplift of the Colorado Plateau: San Memoirs, v. 5, p. 1–158. Francisco, American Geophysical Union Meeting, 2015, abstract PP21A-2210, http://adsabs Clinebell, R.R., Phillips, O.L., Gentry, A.H., Stark, N., and Zuuring, H., 1995, Prediction of neotropi .harvard.edu/abs/2015AGUFMPP21A2210H (April 2016). cal tree and liana species richness from soil and climatic data: Biodiversity and Conserva- Jarzen, D.M., and Dilcher, D.L., 2006, Middle Eocene terrestrial palynomorphs from the Dolime tion, v. 4, no. 1, p. 56–90, https://doi.org/10.1007/BF00115314. Minerals and Gulf Hammock Quarries, Florida, U.S.A: Palynology, v. 30, p. 89–110, https://doi Cockerell, T.D.A., 1933, A fossil golden rod: Torreya, v. 33, p. 1–72. .org/10.2113/gspalynol.30.1.89.

Karlstrom, K.E., Coblentz, D., Dueker, K., Ouimet, W., Kirby, E., Van Wijk, J., Schmandt, B., Kelley, Leopold, E.B., Liu, GengWu, and Clay-Poole, S., 1992, Low Biomass Vegetation in the Oligocene?, S., Lazear, G., Crossey, L.J., Crow, R., Aslan, A., Darling, A., Aster, R., Maccarthy, J., Hansen, in Prothero, D.R., and Berggren, W.A., eds., Eocene–Oligocene Climatic and Biotic Evolution: S.M., Stachnik, J., Stockli, D.F., Garcia, R.V., Hoffman, M., Mckeon, R., Feldman, J., Heizler, Princeton, New Jersey, Princeton University Press, p. 399–420. M., and Donahue, M.S., and The Crest Working Group, 2012, Mantle-driven dynamic uplift Leopold, E.B., Manchester, S., and Meyer, H.W., 2008, Phytogeography of the Late Eocene Flo- of the Rocky Mountains and Colorado Plateau and its surface response: Toward a unified rissant flora reconsidered,in Meyer, H.W., and Smith, D.M., eds., Paleontology of the Upper hypothesis: Lithosphere, v. 4, no. 1, p. 3–22, https://doi.org/10.1130/L150.1. Eocene Florissant Formation, Colorado: Geological Society of America Special Paper 435, Knowlton, F.H., 1923, Fossil plants from the Tertiary lake beds of south-central Colorado: U.S. p. 53–70, https://doi.org/10.1130/2008.2435(04). Geological Survey Professional Paper 131-G, p. 183–197. Lielke, K., Manchester, S., and Meyer, H., 2012, Reconstructing the environment of the north- LaMotte, R.S., 1952, Catalogue of the Cenozoic plants of North America through 1950: Geological ern Rocky Mountains during the Eocene/Oligocene transition: Constraints from the palaeo Society of America Memoir 51, p. 1–378, https://doi.org/10.1130/MEM51-p1. botany and geology of southwestern Montana, USA: Acta Palaeobotanica, v. 52, no. 2, Lanphere, M.A., 2000, Duration of sedimentation of Creede Formation from 40Ar/39Ar ages, in p. 317–358. Bethke, P.M., and Hay, R.L., eds., Ancient Lake Creede: Its Volcano-Tectonic Setting, History Lipman, P.W., 1975, Evolution of the Platoro Caldera Complex and Related Volcanic Rocks, of Sedimentation, and Relation to Mineralization in the Creede Mining District: Geological Southeastern San Juan Mountains, Colorado: U.S. Geological Survey Professional Paper Society of America Special Paper 346, p. 71–76, https://doi.org/10.1130/0-8137-2346-9.71. 852, p. 1–128. Larsen, D., and Lipman, P., 2016, Exploring the ancient volcanic and lacustrine environments of Lipman, P.W., 2000, The central San Juan caldera cluster: Regional volcanic framework, in the Oligocene Creede caldera and environs, San Juan Mountains, Colorado, in Keller, S.M., Bethke, P.M., and Hay, R.L., eds., Ancient Lake Creede: Its Volcano-Tectonic Setting, History and Morgan, M.L., eds., Unfolding the Geology of the West: Geological Society of America of Sedimentation, and Relation of Mineralization in the Creede Mining District: Geological Field Guide 44, p. 1–40, https://doi.org/10.1130/2016.0044(01). Society of America Special Paper 346, p. 9–69, https://doi.org/10.1130/0-8137-2346-9.9. Larsen, D., and Nelson, P.H., 2000, Stratigraphy, correlation, depositional setting and geophysi- Lipman, P.W., 2007, Incremental assembly and prolonged consolidation of Cordilleran magma cal characteristics of the Oligocene Snowshoe Mountain Tuff and Creede Formation in two chambers: Evidence from the Southern Rocky Mountain volcanic field: Geosphere, v. 3, cored boreholes, in Bethke, P.M., and Hay, R.L., eds., Ancient Lake Creede: Its Volcano-Tec- no. 1, p. 42–70, https://doi.org/10.1130/GES00061.1. tonic Setting, History of Sedimentation, and Relation to Mineralization in the Creede Mining Lipman, P.W., and Bachmann, O., 2015, Ignimbrites to batholiths: Integrating perspectives from District: Geological Society of America Special Paper 346, p. 159–178, https://doi.org/10.1130 geological, geophysical, and geochronological data: Geosphere, v. 11, p. 705–743, https://doi /0-8137-2346-9.159. .org/10.1130/GES01091.1. Las Pilitas Nursery, 2012, Abies bracteata: http://www.laspilitas.com/nature-of-california/plants Lipman, P.W., and McIntosh, W.C., 2008, Eruptive and noneruptive calderas, northeastern San /1–abies-bracteata (September 2013). Juan Mountains, Colorado: Where did the ignimbrites come from?: Geological Society of Lawver, L.A., Gahagan, L.M., and Dalziel, I.W.D., 2011, A Different Look at Gateways: Drake Pas- America Bulletin, v. 120, no. 7–8, p. 771–795, https://doi.org/10.1130/B26330.1. sage and Australia/Antarctica, in Anderson, J.B., and Wellner, J.S., eds., Tectonic, Climatic, Lipman, P.W., McIntosh, W.C., and Zimmerer, M.J., 2013, From ignimbrite to batholith, northeast- and Cryospheric Evolution of the Antarctic Peninsula: Washington, D.C., American Geophys- ern San Juan Mountains, Colorado: Bonanza, Cochatopa Park, and North Pass calderas, in ical Union, p. 5–33, https://doi.org/10.1029/2010SP001017. Abbott, L.D., and Hancock, G.S., eds., Classic Concepts and New Directions: Exploring 125 Legendre, S., and Hartenberger, J.-L., 1992, Evolution of Mammalian Faunas in Europe during Years of GSA Discoveries in the Rocky Mountain Region: Geological Society of America the Eocene and Oligocene, in Prothero, D.R., and Berggren, W.A., eds., Eocene–Oligocene Field Guide 33, p. 357–388. Climatic and Biotic Evolution: Princeton, New Jersey, Princeton University Press, p. 516–528, Lipman, P.W., Zimmerer, M.J., and McIntosh, W.C., 2015, An ignimbrite caldera from the bot- https://doi.org/10.1515/9781400862924.516. tom up: Exhumed floor and fill of the resurgent Bonanza caldera, Southern Rocky Moun- Leopold, E.B., 1967, Late-Cenozoic Patterns of Plant Extinctions, in Martin, P.S., and Wright, Jr., tain volcanic field, Colorado: Geosphere, v. 11, no. 6, p. 1902–1947, https://doi.org/10.1130 H.E., eds., Pleistocene Extinctions, the Search for a Cause: New Haven, Connecticut, Yale /GES01184.1. Press, p. 203–246. Liu, GengWu, 1988, Neogene palynological sequence of northern China: Acta Palaeontologica Leopold, E.B., 1969, Late Cenozoic Palynology, in Tschudy, R.H., and Scott, R.A., eds., Aspects of Sinica, v. 27, no. 1, p. 86–90. Palynology: New York, John Wiley and Sons, p. 377–438 and Plate 17.2, p. 409. Liu, Yu-Sheng, and Basinger, J.F., 2000, Fossil Cathaya (Pinaceae) Pollen from the Canadian High Leopold, E.B., and Clay-Poole, S., 2001, Florissant leaf and pollen floras of Colorado compared: Arctic: International Journal of Plant Sciences, v. 161, no. 5, p. 829–847, https://doi.org/10 climatic implications, in Evanoff, E., Gregory-Wodziski, K.M., and Johnson K.R., eds., Fossil .1086/314296. Flora and Stratigraphy of the Florissant Formation, Colorado: Proceedings of the Denver Looman, J., and Campbell, J.B., 1960, Adaptation of Sorensen’s K (1948) for estimating unit Museum of Nature and Science Series, v. 4, no. 1, p. 17–55. affinities in prairie vegetation: Ecology, v. 41, no. 3, p. 409–416, https://doi .org/10.2307 Leopold, E.B., and Denton, M.F., 1987, Comparative Age of Grassland and Steppe East and West /1933315. of the Northern Rocky Mountains: Annals of the Missouri Botanical Garden, v. 74, p. 841–867, MacGinitie, H.D., 1953, Fossil Plants of the Florissant Beds, Colorado: Publications of the Carne- https://doi.org/10.2307/2399452. gie Institute of Washington, v. 599, p. 1–82. Leopold, E.B., and Liu, GengWu, 1994, A long pollen sequence of Neogene Age, Alaska Range: Manchester, S.R., 2001, Update on the Megafossil Flora of Florissant, Colorado, in Evanoff, E., Quaternary International, v. 22–23, p. 103–140, https://doi.org/10.1016/1040-6182(94)90009-4. Gregory-Wodziski, K.M., and Johnson K.R., eds., Fossil Flora and Stratigraphy of the Flo- Leopold, E.B., and MacGinitie, H.D., 1972, Development and Affinities of Tertiary Floras in the rissant Formation: Colorado: Proceedings of the Denver Museum of Nature and Science Rocky Mountains, in Graham, A., ed., Floristics and Paleofloristics of Asia and Eastern North Series, v. 4, no. 1, p. 137–161. America: Amsterdam, The Netherlands, Elsevier Publishing Company, p. 147– 200. Mason, B.G., Pyle, D.M., and Oppenheimer, C., 2004, The size and frequency of the largest ex- Leopold, E.B., and Pakiser, H.M., 1964, Preliminary report on the pollen and spores of the pre- plosive eruptions on Earth: Bulletin of Volcanology, v. 66, p. 735–748, https://doi .org/10.1007 Selma Upper Cretaceous strata of western Alabama, in Studies of Pre-Selma Cretaceous /s00445-004-0355-9. Core Samples from the Outcrop Area in Western Alabama: U.S. Geological Survey Bulletin Mathewes, R.W., Greenwood, D.R., and Archibald, B., 2016, Paleoenvironment of the Quilchena 1160-E, p. 71–95. flora, British Columbia, during the Early Eocene Climatic Optimum: Canadian Journal of Leopold, E.B., and Wright, V.C., 1985, Pollen profiles of the Plio-Pleistocene transition in the Earth Sciences, v. 53, no. 6, p. 574–590, https://doi.org/10.1139/cjes-2015-0163. Snake River Plain, Idaho, in Smiley, C.J., ed., Late Cenozoic History of the Pacific Northwest: McIntosh, W.C., and Chapin, C.E., 2004, Geochronology of the central Colorado volcanic field: Pacific Division, American Academy of Sciences, p. 323–348. New Mexico Bureau of Geology and Mineral Resources Bulletin, v. 160, p. 205–237. Leopold, E.B., and Zaborac-Reed, S.J., 2014, Biogeographic history of Abies bracteata (D. Don) McIntosh, W.C., Chapin, C.E., Ratté, J.C., and Sutter, J.F., 1992, Time-stratigraphic framework A. Poit. in the Western United States, in Stevens, W.D., Montiel, O.M., and Raven, P.H., for the Eocene–Oligocene Mogollon-Datil volcanic field, southwest New Mexico: Geological eds., Paleobotany and Biogeography: St. Louis, Missouri, Missouri Botanical Garden Press, Society of America Bulletin, v. 104, p. 851–871, https://doi.org/10.1130/0016-7606(1992)104 p. 252–286. <0851:TSFFTE>2.3.CO;2.

Meyer, H.W., 1986, An Evaluation of the Methods for Estimating Paleoaltitudes Using Tertiary Saito, T., Wang, W.-M., and Nakagawa, T., 2000, Cathaya (Pinaceae) pollen from Mio-Pliocene Floras from the Rio Grande Rift Vicinity, New Mexico and Colorado [Ph.D. thesis]: University sediments in the Himi area, central Japan: Grana, v. 39, no. 6, p. 288–293, https://doi.org/10 of California Berkeley, 217 p. .1080/00173130052504324. Meyer, H.W., 1992, Lapse rates and other variables applied to estimating paleoaltitudes from Schorn, H., and Wolfe, J.A., 1989, Taxonomic Revision of the Spermopsida of the Oligocene fossil floras: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 99, p. 71–99, https://doi Creede Flora, Southern Colorado: U.S. Geological Survey Open-File Report 89-433, 95 p. .org/10.1016/0031-0182(92)90008-S. Selkin, P.A., Strömberg, C.E.A., Dunn, R., Kohn, M.J., Carlini, A.A., Davies-Vollum, K.S., and Mad- Meyer, H.W., 2003, The Fossils of Florissant: Washington D.C., Smithsonian Institution Press, den, R.H., 2015, Climate, dust, and fire across the Eocene–Oligocene transition, Patagonia: 258 p. Geology, v. 43, no. 7, p. 567–570, https://doi.org/10.1130/G36664.1. Meyer, H.W., and Manchester, S.R., 1997, The Oligocene Bridge Creek flora of the John Day For- Sivak, J., 1975, Les caractères de diagnose des Grains de Pollen a Ballonnets (Diagnostic charac- mation, Oregon: University of California Publications in Geological Sciences, v. 141, p. 1–195. teristics of saccate pollen grains): Pollen et Spores, v. 17, no. 3, p. 349–421. Meyer, H.W., Leopold, E.B., Smith, D.M., and Barton, M.A., 2012, Paleobotanical and pollen Steeves, M., and Barghoorn, E.S., 1959, The Pollen of Ephedra: Journal of the Arnold Arboretum, evidence from the Antero Formation (Colorado, USA) for climate and vegetation change v. 40, p. 221–259. during the Eocene–Oligocene transition, in Abstracts, 13th International Palynological Con- Steven, T.A., and Ratté, J.C., 1965, Geology and Structural Control of Ore Deposition in the gress and 9th International Organization of Palaeobotany Conference: Japanese Journal of Creede District, San Juan Mountains, Colorado: U.S. Geological Survey Professional Paper Palynology, v. 58, p. 150–151. 487, p. 1–95. Minder, J.R., Mote, P.W., and Lundquist, J.D., 2010, Surface temperature lapse rates over com- Strömberg, C.A.E., 2011, Evolution of Grasses and Grassland Ecosystems: Annual Review of plex terrain: Lessons from the Cascade Mountains: Journal of Geophysical Research, v. 115, Earth and Planetary Sciences, v. 39, p. 517–544, https://doi.org/10.1146/annurev-earth-040809 D14122, https://doi.org/10.1029/2009JD013493. -152402. Morley, R.J., 2011, Ch. 2: Dispersal and Palaeoecology of Tropical Podocarps, in Turner, B.L., and Sun, X.Y., Fan, Y., Denb, C., and Yu, Z., 1980, Cenozoic Sporo-Pollen Assemblage of the Weihe Cernusak, L.A., eds., Ecology of the Podocarpaceae in Tropical Forests: Washington, D.C., Basin, Shaanxi Province: Bulletin of the Chinese Academy of Geological Sciences Series II, Smithsonian Contributions to Botany, v. 95, Smithsonian Institution Scholarly Press, p. 21–41. v. 1, no. 1, p. 106–107. Mosbrugger, V., and Utescher, T., 1997, The coexistence approach—A method for quantitative Terry, D., 2001, Paleopedology of the Chadron Formation of northwestern Nebraska: Implications reconstruction of Tertiary terrestrial paleoclimate data using plant fossils: Palaeogeogra- for paleoclimatic change in the North American midcontinent across the Eocene–Oligocene phy, Palaeoclimatology, Palaeoecology, v. 134, p. 61–86, https://doi.org/10.1016/S0031-0182 boundary: PALAEO, v. 168, p. 1–38, https://doi.org/10.1016/S0031-0182(00)00248-0. (96)00154-X. Thompson, R.S., Anderson, K.H., Pelltier, R.T., Strickland, L.E., Bartlein, P.J., and Shafer, S.L., Mosbrugger, V., Utescher, T., and Dilcher, D.L., 2005, Cenozoic continental climatic evolution of 2012, Quantitative estimation of climatic parameters from vegetation data in North America Central Europe: Proceedings of the National Academy of Sciences of the United States by the mutual climatic range technique: Quaternary Science Reviews, v. 51, p. 18–39, https:// of America, v. 102, p. 14,964–14,969, https://doi.org/10.1073/pnas.0505267102. doi.org/10.1016/j.quascirev.2012.07.003. Pearson, P.N., Wade, B.S., Jones, T.D., Coxall, H.K., Brown, P.R., and Lear, C.H., 2008, Extinction Thompson, R.S., Anderson, K.H., Pelltier, R.T., Strickland, L.E., Shafer, S.L., Bartlein, P.J., and and environmental change across the Eocene–Oligocene boundary in Tanzania: Geology, McFadden, A.K., 2015, Atlas of relations between climatic parameters and distributions of v. 36, no. 2, p. 179–182, https://doi.org/10.1130/G24308A.1. important trees and shrubs in North America—Revisions for all taxa from the United States Peppe, D.J., Royer, D.L., Wilf, P., and Kowalksi, E.A., 2010, Quantification of large uncertain- and Canada and new taxa from the western United States: U.S. Geological Survey Profes- ties in fossil leaf paleoaltimetry: Tectonics, v. 29, TC3015, p. 1–14, https://doi .org/10.1029 sional Paper 1650-G, https://pubs.usgs.gov/pp/p1650-g/ (May 2016). /2009TC002549. Traverse, A., 2007, Paleopalynology (second edition): Dordrecht, The Netherlands, Springer Pond, R., 2003, Plant Propagation Protocol for Holodiscus discolor, ESRM 412–Native Plant Pro- Netherlands, 813 p. duction, http://courses.washington.edu/esrm412/protocols/HODI.pdf (October 2016). U.S. Department of Agriculture, 2011, PSME 52: DOUGLAS-FIR/CREAMBUSH OCEAN-SPRAY/ Potoniè, R., 1951, Revision Stratigraphisch Wichtiger Sporomorphen des Mittleleuropaischen WHIPPLEVINE-SWO: http://www .fs .usda .gov /Internet /FSE _DOCUMENTS /stelprdb5319422 .pdf Tertiars: Palaeontographica, Abteilung B, v. 91, p. 129–151. (October 2016). Prothero, D.R., 1985a, Mid-Oligocene extinction event in North American land mammals: Sci- U.S. Department of Agriculture Plants Database, 2016, Conservation Plant Characteristics for Sarco ence, v. 229, no. 4713, p. 550–551, https://doi.org/10.1126/science.229.4713.550. batus vermiculatus: http://plants .usda .gov /java /charProfile ?symbol =SAVE4 (October 2016). Prothero, D.R., 1985b, North American mammalian diversity and Eocene–Oligocene extinctions: U.S. Geological Survey, 2013, 20130806, USGS US Topo 7.5-minute map for Creede, CO: USGS– Paleobiology, v. 11, no. 4, p. 389–405, https://doi.org/10.1017/S0094837300011696. National Geospatial Technical Operations Center (NGTOC), https://www .sciencebase.gov Prothero, D.R., and Berggren, W.A., 1992, Eocene–Oligocene Climatic and Biotic Evolution: Prince /catalog/item/5825ac1fe4b01fad86dcc631 (last accessed May 2017). ton, New Jersey, Princeton University Press, 588 p., https://doi.org/10.1515/9781400862924. Utescher, T., Bruch, A.A., Erdei, B., Francois, L., Ivanov, D., Jacques, F.M.B., Kern, A.K., Liu, Reinink-Smith, L.M., and Leopold, E.B., 2005, Warm Climate in the Late Miocene of the South Y.S.(C.), Mosbrugger, V., and Spicer, R.A., 2014, The Coexistence Approach—Theoretical Coast of Alaska and the Occurrence of Podocarpaceae Pollen: Palynology, v. 29, p. 205–262, background and practical considerations of using plan fossils for climate quantification: https://doi.org/10.1080/01916122.2005.9989607. Palaeogeography, Palaeoclimatology, Palaeoecology, v. 410, p. 58–73, https://doi.org/10.1016 Reinink-Smith, L.M., Zaborac-Reed, S.J., and Leopold, E.B., 2017, Clamgulchian (Miocene–Plio- /j.palaeo.2014.05.031. cene) pollen assemblages of the Kenai Lowland, Alaska and the persistence of the family Van Alstine, R.E., 1969, Geology and mineral deposits of the Poncha Springs NE quadrangle, Podocarpaceae: Palynology, https://doi.org/10.1080/01916122.2017.1310767. Chaffee County, Colorado: U.S. Geological Survey Professional Paper 626, p. 1–52. Retallack, G.J., Prothero, D.R., Duncan, R.A., Kester, P.R., and Ambers, C.P., 2004, Eocene–Oligo Wheeler, E.A., 2001, Fossil dicotyledonous woods from the Florissant Fossil Beds National Mon- cene extinction and paleoclimatic change near Eugene, Oregon: Geological Society of ument, Colorado, in Evanoff, E., Gregory-Wodziski, K.M., and Johnson K.R., eds., Fossil Flora America Bulletin, v. 116, no. 7–8, p. 817–839, https://doi.org/10.1130/B25281.1. and Stratigraphy of the Florissant Formation, Colorado: Proceedings of the Denver Museum Ridgway, K.D., Sweet, A.R., and Cameron, A.R., 1995, Climatically induced floristic changes of Nature and Science Series, v. 4, no. 1, p. 197–214. across the Eocene–Oligocene transition in the northern high latitudes, Yukon Territory, Can- White, J.M., and Ager, T.A., 1994, Palynology, paleoclimatology and correlation of middle Mio- ada: Geological Society of America Bulletin, v. 107, no. 6, p. 676–696, https://doi.org/10.1130 cene beds from Porcupine River (Locality 90-1), Alaska: Quaternary International, v. 22–23, /0016-7606(1995)107<0676:CIFCAT>2.3.CO;2. p. 43–77, https://doi.org/10.1016/1040-6182(94)90006-X. Rzedowski, J., 1966, Nombres regionales de algunas plantas de la Huesteca potosina: Acta Cien- Williams, M., 2012, The ~73 Ka Toba super-eruption and its impact: History of a debate: Quater- tifica Potosina, v. 6, no. 1, p. 7–58. nary International, v. 258, p. 19–29, https://doi.org/10.1016/j.quaint.2011.08.025. Rzedowski, J., 1978, Vegetación de México: Limusa, México, Comisión Nacional para el Conoci Wing, S.L., 1987, Eocene and Oligocene Floras and Vegetation of the Rocky Mountains: Annals miento y Uso de la Biodiversidad, 432 p. of the Missouri Botanical Garden, v. 74, no. 4, p. 748–784, https://doi.org/10.2307/2399449 .

Wingate, F.H., and Nichols, D.J., 2001, Palynology of the Uppermost Eocene Lacustrine Deposits Wolfe, J.A., and Leopold, E.B., 1967, Neogene and Early Quaternary Vegetation of Northwestern at Florissant Fossil Beds National Monument, Colorado, in Evanoff, E., Gregory-Wodziski, North America and Northeastern Asia, in Hopkins, D.M., ed., The Bering Land Bridge: Stan- K.M., and Johnson, K.R., eds., Fossil Flora and Stratigraphy of the Florissant Formation, ford, California, Stanford University Press, p. 193–206. Colorado: Proceedings of the Denver Museum of Nature and Science Series, v. 4, no. 1, Wolfe, J.A., and Schorn, H.E., 1989, Paleoecologic, Paleoclimatic, and Evolutionary Significance p. 71–135. of the Oligocene Creede Flora, Colorado: Paleobiology, v. 15, no. 2, p. 180–198, https://doi Wolfe, J.A., 1978, A paleobotanical interpretation of Tertiary climates in the Northern Hemi- .org/10.1017/S0094837300009350. sphere: American Scientist, v. 66, p. 694–703. Wolfe, J.A., and Schorn, H.E., 1990, Taxonomic revision of the Spermatopsida of the Oligocene Wolfe, J.A., 1981, A chronologic framework for Cenozoic megafossil floras of northwestern North Creede flora, southern Colorado: U.S. Geological Survey Bulletin 1923, p. 1–40. America and its relation to marine geochronology, in Armentrout, J.M., ed., Pacific North- Wolfe, J.A., Forest, C.E., and Molnar, P., 1998, Paleobotanical evidence of Eocene and Oligocene west Cenozoic Biostratigraphy: Geological Society of America Special Paper 184, p. 39–48, paleoaltitudes in midlatitude western North America: Geological Society of America Bulletin, https://doi.org/10.1130/SPE184-p39. v. 110, no. 5, p. 664–678, https://doi .org /10 .1130 /0016 -7606 (1998)110 <0664: PEOEAO>2 .3 .CO;2 . Wolfe, J.A., 1987, An Overview of the Origins of the Modern Vegetation and Flora of the Northern Wright, I.J., Dong, N., Maire, V., Prentice, I.C., Westoby, M., Díaz, S., Gallagher, R.V., Jacobs, B.F., Rocky Mountains: Annals of the Missouri Botanical Garden, v. 74, p. 785–803, https://doi.org Kooyman, R., Law, E.W., Leishman, M.R., Niinemets, Ü., Reich, P.B., Sack, L., Villar, R., Wang, /10.2307/2399450. H., and Wilf, P., 2017, Global climatic drivers of leaf size: Science, v. 357, p. 917–921, https:// Wolfe, J.A., 1992, Climatic, floristic, and vegetational changes near the Eocene/Oligocene bound- doi.org/10.1126/science.aal4760. ary in North America, in Prothero, D.R., and Berggren, W.A., eds., Eocene–Oligocene Cli- Ying, T., Zhang, Y., and Boufford, D.E., 1993, The Endemic Genera of Seed Plants of China: Bei- matic and Biotic Evolution: Princeton, New Jersey, Princeton University Press, p. 421–436, jing, China, Science Press, 824 p. https://doi.org/10.1515/9781400862924.421. Zaborac-Reed, S.J., and Leopold, E.B., 2016, Determining the paleoclimate and elevation of the Wolfe, J.A., 1993, A method of obtaining climatic parameters from leaf assemblages: U.S. Geo- late Eocene Florissant flora: Support from the coexistence approach: Canadian Journal of logical Survey Bulletin 2040, p. 1–73. Earth Sciences, v. 53, p. 565–573, https://doi.org/10.1139/cjes-2015-0165. Wolfe, J.A., 1994, Tertiary climatic changes at middle latitudes of western North America: Palaeo Zachos, J., Pagani, M., Sloan, L., Thomas, E., and Billups, K., 2001, Trends, Rhythms and aberra- geography, Palaeoclimatology, Palaeoecology, v. 108, p. 195–205, https://doi .org /10 .1016 tions in global climate 65 Ma to present: Science, v. 292, p. 686–693, https://doi .org/10.1126 /0031-0182(94)90233-X. /science.1059412. Wolfe, J.A., 1995, Paleoclimatic Estimates from Tertiary Leaf Assemblages: Annual Review of Earth Zanni, M., and Ravazzi, C., 2007, Description and differentiation of Pseudolarix amabilis pollen: and Planetary Sciences, v. 23, p. 119–142, https://doi .org /10 .1146 /annurev .ea .23 .050195 .001003 . Palaeoecological implications and new identification key to fresh bisaccate pollen: Review Wolfe, J.A., and Barghoorn, E.S., 1960, Generic change in Tertiary floras in relation to age: Amer- of Palaeobotany and Palynology, v. 145, p. 35–75, https://doi.org/10.1016/j.revpalbo.2006.08 ican Journal of Science: Bradley, v. 258A, p. 388–399. .004.