Article

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

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Abstract

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

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... Flynn and Peppe (2019) recognized a latitudinal difference in the composition of plant communities recovering from the K/Pg mass extinction event. According to their study, Anemia-like ferns were the dominant ferns in the San Juan Basin following the K/Pg mass extinction event (Flynn and Peppe 2019). Although the K/Pg boundary is not preserved at the location of their study because of an unconformity, this result appears to agree with the findings of other researchers in the neighboring Raton and Denver Basins (Berry 2019c;Lyson et al. 2019). ...
... Accordingly, this study is the first to recognize that the northernmost and southernmost lowest Danian plant assemblages appear to have contained different Cyathidites-producing ferns ( fig. 1). Consequently, my findings agree with those of Flynn and Peppe (2019). ...
... In turn, Flynn and Peppe (2019) argued that fundamental climatic differences between the northern Great Plains and the southern Western Interior of North America were primarily responsible for disparity among plant communities in these regions following the K/Pg mass extinction event-an argument that parallels earlier observations by Johnson and Ellis (2002), Ellis et al. (2003), Wilf and Johnson (2004), and Peppe (2010). However, the depauperate nature of some earliest Danian plant assemblages, coupled with a lack of high-frequency sampling, taxonomic bias, and other factors, has made it difficult to use leaf physiognomic methods to reliably estimate mean annual temperature or precipitation at many of these low-diversity sites (Nichols and Johnson 2008;Flynn and Peppe 2019;Lyson et al. 2019;Berry 2020b). ...
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Premise of research. A two-phase fern spike occurred immediately after the Cretaceous-Paleogene (K/Pg) mass extinction event. Solely on the basis of palynological evidence, researchers have traditionally attributed the first phase of this spike to the proliferation of a single species of a Cyathea-like fern in the earliest Danian. This traditional perspective is challenged by recent investigations linking Anemia-like fern foliage with Cyathidites spores at K/Pg boundary localities in the Raton Basin, where the fern spore spike was first discovered by R. H. Tschudy. Although evidence emerging from neighboring basins appears to corroborate this new perspective, it remains to be seen whether this generalization applies to the northern Great Plains. Methodology. A comprehensive list of the most common fern megafossils collected from earliest Danian plant localities across western North America was compiled to determine the number and potential identity of Cyathiditesproducing ferns. Pivotal results. Three K/Pg survivors commonly collected from basal Paleocene strata in western North America conceivably produced psilate, trilete (Cyathidites) fern spores essentially identical to those observed at the K/Pg boundary fern spore spike: Anemia elongata (Newberry) Knowlton, Dennastra sorimarginata McIver et Basinger, and the Coniopteris-like fern “Dennstaedtia” americana Knowlton. Conclusions. Arborescent ferns were not among the first plants in western North America to thrive in the immediate wake of ecological collapse at the K/Pg boundary. Basal polypod ferns can be linked to Cyathidites spores in the northern Great Plains, perhaps because of a latitudinal climatic gradient. These results could explain taxonomic inversion in the dual-phase fern spore spike between western North America and New Zealand.
... Flynn and Peppe (2019) recognized a latitudinal difference in the composition of plant communities recovering from the K/Pg mass extinction event. According to their study, Anemia-like ferns were the dominant ferns in the San Juan Basin following the K/Pg mass extinction event (Flynn and Peppe 2019). Although the K/Pg boundary is not preserved at the location of their study because of an unconformity, this result appears to agree with the findings of other researchers in the neighboring Raton and Denver Basins (Berry 2019c;Lyson et al. 2019). ...
... Accordingly, this study is the first to recognize that the northernmost and southernmost lowest Danian plant assemblages appear to have contained different Cyathidites-producing ferns ( fig. 1). Consequently, my findings agree with those of Flynn and Peppe (2019). ...
... In turn, Flynn and Peppe (2019) argued that fundamental climatic differences between the northern Great Plains and the southern Western Interior of North America were primarily responsible for disparity among plant communities in these regions following the K/Pg mass extinction event-an argument that parallels earlier observations by Johnson and Ellis (2002), Ellis et al. (2003), Wilf and Johnson (2004), and Peppe (2010). However, the depauperate nature of some earliest Danian plant assemblages, coupled with a lack of high-frequency sampling, taxonomic bias, and other factors, has made it difficult to use leaf physiognomic methods to reliably estimate mean annual temperature or precipitation at many of these low-diversity sites (Nichols and Johnson 2008;Flynn and Peppe 2019;Lyson et al. 2019;Berry 2020b). ...
Article
Premise of research. A two-phase fern spike occurred immediately after the Cretaceous-Paleogene (K/Pg) mass extinction event. Solely on the basis of palynological evidence, researchers have traditionally attributed the first phase of this spike to the proliferation of a single species of a Cyathea-like fern in the earliest Danian. This traditional perspective is challenged by recent investigations linking Anemia-like fern foliage with Cyathidites spores at K/Pg boundary localities in the Raton Basin, where the fern spore spike was first discovered by R. H. Tschudy. Although evidence emerging from neighboring basins appears to corroborate this new perspective, it remains to be seen whether this generalization applies to the northern Great Plains. Methodology. A comprehensive list of the most common fern megafossils collected from earliest Danian plant localities across western North America was compiled to determine the number and potential identity of Cyathidites-producing ferns. Pivotal results. Three K/Pg survivors commonly collected from basal Paleocene strata in western North America conceivably produced psilate, trilete (Cyathidites) fern spores essentially identical to those observed at the K/Pg boundary fern spore spike: Anemia elongata (Newberry) Knowlton, Dennastra sorimarginata McIver et Basinger, and the Coniopteris-like fern “Dennstaedtia” americana Knowlton. Conclusions. Arborescent ferns were not among the first plants in western North America to thrive in the immediate wake of ecological collapse at the K/Pg boundary. Basal polypod ferns can be linked to Cyathidites spores in the northern Great Plains, perhaps because of a latitudinal climatic gradient. These results could explain taxonomic inversion in the dual-phase fern spore spike between western North America and New Zealand. https://www.journals.uchicago.edu/doi/abs/10.1086/711847
... Spores , from their lowest Danian plant assemblage, 2.75 m above the K/Pg boundary (~10 000 years after the K/Pg impact). Both of these ferns also crossed the K/Pg boundary in the neighboring Raton Basin (Barclay et al., 2003;Berry, 2019aBerry, ,b,c, 2020, and Anemia-like ferns were the most abundant pteridophyte in the lowest Paleocene section of the neighboring San Juan Basin (Flynn and Peppe, 2019). Therefore these are good candidates for Cyathidites-producing ferns and Laevigatosporites-producing ferns, respectively. ...
... In the area of this study, Anemia-like fern megafossils (Fig. 3) were among the first to recover from the K/Pg impact (Berry, 2019a;Flynn and Peppe, 2019;Lyson et al., 2019). This is consistent with their production of psilate, trilete spores like those observed in the first (Cyathidites) phase of the fern-spore spike (Chandler, 1955(Chandler, , 1963Berry, 2019a) and their presence in lowest Danian plant assemblages concomitant with the Cyathidites fernspore spike (Berry, 2019a;Lyson et al., 2019). ...
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The presence of the amino acid α-aminoisobutyric acid (Aib) within Cretaceous/Paleogene (K/Pg) boundary clay in the Raton and Powder River basins in Colorado and Wyoming, respectively, has been described as compelling evidence that extraterrestrial Aib survived the high-energy Chicxulub impact. Based on contemporary experiments and simulations, however, it is highly unlikely that extraterrestrial Aib survived the impact, which had peak impact pressures and temperatures in excess of 600 GPa and 10,000 K, respectively. In other words, the amino acid signature of the carbonaceous chondritic asteroid that impacted Chicxulub was undoubtedly destroyed upon impact during formation of the vapor plume or so-called “fireball.” The only organisms known to produce Aib are the suite (more than 30 genera) of cosmopolitan saprotrophic filamentous fungi that include Trichoderma Pers., which has recently been hypothesized to have thrived during the K/Pg mass-extinction event. Therefore it is proposed that the Aib horizon in the K/Pg boundary clay in the Raton and Powder River basins correlates with the K/Pg boundary fungal spike, which thus far has only been observed in New Zealand (Southern Hemisphere). This proposition is based upon superimposing the Aib horizon on the well-known iridium and fern-spore spikes, as its stratigraphic position precisely matches that predicted by the fungal spike. If correct, this hypothesis alters the conventional perspective on the tempo and mode of terrestrial ecosystem recovery in western North America, as the heavily sampled K/Pg boundary section in the Raton Basin was instrumental in shaping the traditional narrative of the rapid recolonization of a denuded landscape by ferns via wind-blown spores in the immediate wake of regional deforestation caused by the K/Pg impact event. Perhaps more importantly, it could present an alternative to traditional palynological approaches for locating the fungal spike in other terrestrial K/Pg boundary sections and could provide additional support for the generalization that global mass-extinction events are frequently accompanied by fungal spikes.
... The +38 m horizon is constrained to chron C29n (Hicks et al. 2002;Johnson 2002), serving as a temporal analog to the PL1 locality in Patagonia ( Fig. 1D) (Clyde et al. 2014). While acknowledging work on diverse Paleocene floras from the more southerly Denver and San Juan basins (Johnson and Ellis 2002;Flynn and fig. 3), contain both Cretaceous and Paleocene floras that are well sampled in a single area, and remain the best-sampled and described boundary-spanning K/Pg macrofloras of NAM. ...
... Our results suggest that the rich Cenozoic macrofloras of Patagonia also carry a legacy of rich Cretaceous floras, as well as significantly earlier recovery of Paleocene species richness resulting from the persistence of most higher taxonomic levels ( Supplementary Tables 1, 2). Nonetheless, an emerging body of research shows that floral diversity in the early Paleocene of the Denver and San Juan Basins can be higher relative to the more northerly WB (Johnson and Ellis 2002;Flynn and Peppe 2019;Lyson et al. 2019). These studies show heterogeneity in NAM floral richness during the early Paleocene, a pattern warranting further intensive study. ...
Article
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The Cretaceous-Paleogene (K/Pg) extinction appears to have been geographically heterogeneous for some organismal groups. Southern Hemisphere K/Pg palynological records have shown lower extinction and faster recovery than in the Northern Hemisphere, but no comparable, well-constrained Southern Hemisphere macrofloras spanning this interval had been available. Here, macrofloral turnover patterns are addressed for the first time in the Southern Hemisphere, using more than 3500 dicot leaves from the latest Cretaceous (Maastrichtian) and the earliest Paleocene (Danian) of Argentine Patagonia. A maximum ca. 90% macrofloral extinction and ca. 45% drop in rarefied species richness is estimated across the K/Pg, consistent with substantial species-level extinction and previously observed extir-pation of host-specialized leaf mines. However, prior palynological and taxonomic studies indicate low turnover of higher taxa and persistence of general floral composition in the same sections. High species extinction, decreased species richness, and homogeneous Danian macrofloras across time and facies resemble patterns often observed in North America, but there are several notable differences. When compared with boundary-spanning macrofloras at similar absolute paleolatitudes (ca. 50°S or 50°N) from the Williston Basin (WB) in the Dakotas, both Maastrichtian and Danian Patagonian species richnesses are higher, extending a history of elevated South American diversity into the Maastrichtian. Despite high species turnover, our analyses also reveal continuity and expansion of leaf morphospace, including an increase in lobed and toothed species unlike the Danian WB. Thus, both Patagonian and WB K/Pg macro-floras support a significant extinction event, but they may also reflect geographically heterogeneous diversity, extinction, and recovery patterns warranting future study.
... There are still few studies that provide quantitative paleoclimate reconstructions for the early Paleocene (e.g., Davies-Vollum, 1997;Kennedy et al., 2002;Wilf et al., 2003;Hinojosa, 2005;Domingo Martínez et al., 2006;Uhl et al., 2007;Upchurch et al., 2007;Hao et al., 2010;Greenwood and West, 2017;Flynn and Peppe, 2019;Lyson et al., 2019), or paleoecological reconstructions based on leaf morphology (e.g. Blonder et al., 2014;Flynn and Peppe, 2019;Lyson et al., 2019). ...
... There are still few studies that provide quantitative paleoclimate reconstructions for the early Paleocene (e.g., Davies-Vollum, 1997;Kennedy et al., 2002;Wilf et al., 2003;Hinojosa, 2005;Domingo Martínez et al., 2006;Uhl et al., 2007;Upchurch et al., 2007;Hao et al., 2010;Greenwood and West, 2017;Flynn and Peppe, 2019;Lyson et al., 2019), or paleoecological reconstructions based on leaf morphology (e.g. Blonder et al., 2014;Flynn and Peppe, 2019;Lyson et al., 2019). Therefore, there is a need for additional paleoclimate and paleoecological data from this important interval of the Paleocene. ...
Article
The Ravenscrag Butte flora in southwestern Saskatchewan, Canada, provides a record of an early Paleocene (Danian) forest ecosystem that followed the K-Pg boundary event. Plant macrofossil collections were investigated to assess the paleoclimate and paleoecology of the forest. An ensemble approach to climate analysis using leaf physiognomic and nearest living relative methods indicates that the forest grew under warm and wet temperate conditions, with mild frost-free winters, and did not experience a significant drying season—although some precipitation seasonality is indicated. Reconstructed leaf mass per area suggests that the woody broadleaf dicot flora had an entirely deciduous habit, despite temperature and precipitation conditions that were suitable for evergreen taxa. The reconstructed climate of the Ravenscrag Butte flora is similar to modern coastal climates with proximity to an inland sea (e.g., Croatia and Slovenia on the Adriatic Sea and Georgia on the Black Sea), suggesting that the Ravenscrag Butte flora was influenced by its proximity to the western margin of the early Paleocene Cannonball Seaway. The leaf physiognomy of the Ravenscrag Butte flora is most similar to contemporaneous fossil macrofloras from throughout western and northern North America, which suggests physiognomic homogeneity over broad latitudes during the early Paleocene, a potential consequence of vegetation reorganization after the K-Pg event.
... 50⁰N) in North America (i.e., North Dakota, Montana; e.g., Johnson, 2002;Iglesias et al., 2007;Donovan et al., 2014). However, there is increasing evidence of higher floral richness in some North American early Paleocene floras at lower paleolatitudes (e.g., Colorado, New Mexico; Johnson and Ellis, 2002;Flynn and Peppe, 2019;Lyson et al., 2019). ...
... Our results suggest that compositionally homogeneous regional floras, potentially dominated by generalist taxa, may have occupied extensive areas of the Earth for long stretches of time after the end-Cretaceous extinction. However, several paleobotanical sites from North America, as well as the Rancho Grande flora in the Salamanca Formation, show that much remains to be learned about how latitudinal, topographic, and environmental variation fostered heterogeneous patterns of early Paleocene floral recovery and diversity (Johnson and Ellis,78 2002; Ellis et al., 2003;Flynn and Peppe, 2019;Lyson et al., 2019). ...
Article
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Early Paleocene macrofloras from the Southern Hemisphere are little known, despite their significance for understanding plant evolution, biogeography, and global variation in recovery after the end-Cretaceous extinction. As a foundation for systematic and paleoecological work, we describe 51 angiosperm leaf morphotypes from three distinct, precisely dated early to late Danian time intervals, using collections from the Salamanca and Peñas Coloradas formations in the San Jorge Basin, Chubut Province, Patagonia, Argentina. These rich floras were previously analyzed but with minimal descriptions. The assemblages comprise the first stratigraphically controlled and quantitatively collected floras for the early Paleocene of the Southern Hemisphere. Botanical affinities of the angiosperm morphotypes are not formally assigned here, but we informally associate some of them with families including Arecaceae, Fabaceae, Cunoniaceae, Lauraceae, Nothofagaceae, Rhamnaceae, and Rosaceae; in addition, leaves of Menispermaceae and other Rhamnaceae were formally described in previous work. Other families potentially present in these assemblages include Akaniaceae, Anacardiaceae, Apiaceae, Araceae, Bixaceae, Juglandaceae, Malvaceae, Sapindaceae, and Urticaceae. Remarkably, there is little floral turnover or change in dominance through the Danian floral sequence spanned by the studied localities, even among estuarine vs. continental depositional environments. This finding indicates a homogeneous, generalist, long-lived floral association following the K-Pg extinction, similar in these respects to many North American Danian floras. However, the richness of the Danian Patagonian floras, from paleolatitudes >50 degrees South, along with other lines of evidence from the region, suggests differences in the response of terrestrial ecosystems in southern South America to the terminal Cretaceous event from those of the Northern Hemisphere. The flora appears to be largely paleo-endemic in nature and shows several compositional links to the Eocene floras of Patagonia, emphasizing the importance of diversification within Patagonia after the end-Cretaceous event as a factor leading to the hyperdiverse Eocene regional floras. Plain language and multilingual abstracts at: https://palaeo-electronica.org/content/2021/663-1124/3258-patagonia-danian-forests-abstracts
... In contrast, composite studies of megafloral records from New Mexico to Alberta show consistent extinction on the order of 50e75% of morphospecies across the KPB (Wolfe and Upchurch, 1986;Johnson et al., 2003;Barclay et al., 2003). However, these studies typically focus on individual megafloral localities (e.g., Wing et al., 1995;Johnson and Ellis, 2002;Dunn, 2003;Peppe, 2010) and are frequently biased towards Paleogene megafloras (e.g., Davies-Vollum, 1997;Dunn, 2003;Barclay and Johnson, 2004;Peppe, 2010;Flynn and Peppe, 2019). Therefore, they do not allow evaluation of the lead-up to the mass extinction or the role of biogeography in shaping patterns of floral change (i.e., local extirpation versus extinction). ...
... Three gymnosperms (MT002, MT003, and MT005), three angiosperms (MT013, MT017, and MT027), and one pteridophyte (MT033) described from Seafood Salad can be attributed to taxa reported from elsewhere in the Williston Basin (Hickey, 1977;Peppe et al., 2007) and the Hanna Basin (Dorf, 1942;Dunn, 2003) (see Table A1 for list of synonymous taxa). In contrast, the Denver Basin Lyson et al., 2019), Raton Basin (Wolfe and Upchurch, 1987), and San Juan Basin (Flynn and Peppe, 2019) only yield Paleocene-age megaflora and have few taxa in common with the Seafood Salad flora. Although most of the paleofloras from these Western Interior basins are taxonomically dominated by angiosperm taxa (as noted by others, e.g., Wing and Boucher, 1998), the taxa shared across these basins are most frequently gymnosperms (e.g., Metasequoia, Glyptostrobus, Taxodium, and Ginkgo). ...
Article
The Cretaceous-Paleogene (K/Pg) boundary marks a mass extinction resulting in global biotic turnover. Exposures of the Hell Creek Formation in northeastern Montana contain some of the most well-studied vertebrate localities recording this mass extinction; however, very little is known of the floral record in this area. As part of an effort to reconstruct floral changes across the K/Pg in northeastern Montana, this study presents a taxonomically diverse flora from the Seafood Salad locality, located ∼ 65 m below the K/Pg boundary in the Hell Creek Formation, Garfield County, Montana. Leaves, stems, and reproductive structures (e.g., cones and seeds) are preserved as compression and impression fossils in massive, bedded siltstones and very fine sandstones. Seafood Salad is significant in that it is represents a “pre-disaster” community approximately 1.3 m.y. before the K/Pg mass extinction. We interpret the plants in these deposits as reflecting a local riparian community. The vegetation was taxonomically diverse and dominated by angiosperm trees; it also included abundant conifer specimens of a few taxa and relatively few ginkgoes and ferns. We describe 34 morphotypes and propose taxonomic affinities to modern groups and to fossil taxa from contemporaneous-age deposits in Montana and North Dakota. The Seafood Salad flora shares several taxa with other Late Cretaceous floras of the Western Interior, but substantial differences in taxonomic composition and relative abundances among these assemblages indicate that regional plant communities in the latest Cretaceous were spatially heterogeneous, rapidly changing, or both.
... Paleoclimatic estimates using additional paleobotanical proxies, such as digital leaf physiognomy (DiLP), may help clarify ancient climate amidst such widely varying results. Though currently, studies using DiLP are few (e.g., Flynn and Peppe, 2019;Lowe et al., 2018), and further applications of the proxy on fossil floras are required to assess its applicability. ...
Article
The uppermost Eocene lacustrine Florissant Formation in central Colorado preserves a diverse flora and fauna at a key time in Earth history immediately preceding the Eocene-Oligocene boundary. Laminated shales in the Florissant Formation record impression fossils of woody non-monocot angiosperm leaves that were used to estimate paleoecological and paleoclimatic parameters using leaf physiognomic methods (leaf mass per area (MA), digital leaf physiognomy (DiLP), leaf margin analysis (LMA), and leaf area analysis (LAA)). The majority (58%) of the morphotypes analyzed for MA suggested a semi-evergreen leaf lifespan, whereas another 27% indicated a deciduous habit and just 15% an evergreen habit. There was no significant relationship between MA and insect damage based on a small subset of Florissant's leaves. Higher MA values (~73% of leaves ≥ one-year lifespan), coupled with a tendency toward long and narrow leaf shapes and small leaf areas, support the presence of sclerophyllous vegetation at Florissant. Using the global regression for mean annual temperature (MAT), the DiLP estimate of MAT was anomalously cold: 5.5 ± 4 °C. However, using a ‘Northern Hemisphere’ regression the DiLP MAT estimate of 11.6 ± 3.3 °C was more plausible. Using DiLP, mean annual precipitation (MAP) for Florissant was estimated at 740 + 608/−334 mm∙yr⁻¹, which supports dry conditions. Estimates for MAT and MAP using the univariate LMA and LAA methods overlapped within uncertainty of the DiLP results. In addition, Florissant taxa classified as growing in wet areas (riparian) had significantly more teeth than non-riparian taxa. These paleoclimatic and paleoecological results suggest that outside the riparian forest, the Florissant flora sampled a seasonally dry temperate sclerophyllous shrubland to woodland, perhaps similar to modern chaparral forests, in the Western Interior of the USA just before the transition into the cooler Oligocene.
... This floral work in Montana is ongoing, but preliminary trends can be compared with prior work in North America. Early Paleocene floras from elsewhere in the Williston Basin (e.g., North Dakota; Wilf and Johnson 2004;Peppe 2010) and farther south in the Western Interior (e.g., Hanna Basin, San Juan Basin, Denver Basin; Dunn 2003, Flynn and Peppe 2019 present differing patterns of plant recovery during this interval. These works broadly present two alternative hypotheses for the pattern of plant recovery: that floras regained pre-extinction diversity within the earliest~300 ka of the Paleocene or that floras remained homogeneous and depauperate for at least 1 Ma (Wilf and Johnson 2004). ...
... Paleoclimatic estimates using additional paleobotanical proxies, such as digital leaf physiognomy (DiLP), may help clarify ancient climate amidst such widely varying results. Though currently, studies using DiLP are few (e.g., Flynn and Peppe, 2019;Lowe et al., 2018), and further applications of the proxy on fossil floras are required to assess its applicability. ...
... This floral work in Montana is ongoing, but preliminary trends can be compared with prior work in North America. Early Paleocene floras from elsewhere in the Williston Basin (e.g., North Dakota; Wilf and Johnson 2004;Peppe 2010) and farther south in the Western Interior (e.g., Hanna Basin, San Juan Basin, Denver Basin; Dunn 2003, Flynn and Peppe 2019 present differing patterns of plant recovery during this interval. These works broadly present two alternative hypotheses for the pattern of plant recovery: that floras regained pre-extinction diversity within the earliest~300 ka of the Paleocene or that floras remained homogeneous and depauperate for at least 1 Ma (Wilf and Johnson 2004). ...
Article
The Hell Creek region of northeastern Montana is an excellent study system to explore the rise to dominance of mammalian faunas after the Cretaceous-Paleogene (K-Pg) mass extinction. The Tullock Member of the Fort Union Formation exposed in that region was deposited during the first 1.2 Ma after the Chicxulub bolide impact. Some aspects of post-K-Pg mammalian succession remain obscure, however, due to a lack of finer stratigraphic resolution between vertebrate fossil localities. Here, we present a new stratigraphic model for the lower and middle Tullock and identify a stratigraphic succession of five mammal-bearing sedimentary units that span the first~900 ka of the Paleocene. Most notably, we find that middle Tullock fossil localities, which were previously thought to be deposited by a single, large fluvial channel complex, are derived from two temporally and lithologically distinct sedimentary units: the Biscuit Springs unit (BS) and the Garbani channel (GC). The top of the GC is stratigraphically above the top of the BS, but in some places cuts through the entirety of the BS, a relationship that previously complicated interpretations of their relative age. This cross-cutting relationship reveals that the BS is older than the GC. Thus, the BS local fauna represents a potential intermediate between the older local faunas from the post-K-Pg 'disaster' interval and the younger, more taxonomically/ecologically diverse GC local fauna. This new stratigraphic framework sets the stage for future studies focused on the pattern and timing of biotic recovery in the aftermath of the K-Pg mass extinction.
... Fossils were assigned to the genus Platanites based on foliar architecture and leaf venation (e.g. Flynn and Peppe, 2019;Flynn, 2020). In addition, stomata have a raised ledge over the guard cell which is characteristic of modern Platanaceae (Carpenter et al., 2005) (Fig. 2C). ...
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Premise: Reconstructing plant canopy light environment and architecture from the fossil record includes proxies derived from cell wall undulation, cell size, and carbon isotopes. All approaches assume that plant taxa will respond predictably to changes in light environments. However, most species-level studies looking at cell wall undulation only consider "sun" or "shade" leaves, therefore we lack a fully quantitative taxon-specific method. Methods: We quantify the response of cell wall undulation, cell size, and carbon isotopes of Platanus occidentalis using two different experimental setups: (1) two growth chambers at low and high light and (2) a series of outdoor growth experiments using green and black shade cloth at different densities. We then developed and applied a proxy for daily light integral (DLI) to fossil Platanites leaves from two early Paleocene floras from the San Juan Basin in New Mexico. Results: All traits responded to light environment. Cell wall undulation was the most useful trait for reconstructing DLI in the geological record. Median reconstructed DLI from early Paleocene leaves was ~44 mol m-2 d-1, with values ranging from 28 - 54 mol m-2 d-1. Conclusions: Cell wall undulation of P. occidentalis is a robust, quantifiable measurement of light environment that can be used to reconstruct paleo-light environment from fossil leaves. The distribution of high DLI values from fossil leaves may provide information on canopy architecture; indicating that either (1) most of the canopy mass is within the upper portion of the crown or (2) leaves exposed to more sunlight are preferentially preserved. This article is protected by copyright. All rights reserved.
... This floral work in Montana is ongoing, but preliminary trends can be compared with prior work in North America. Early Paleocene floras from elsewhere in the Williston Basin (e.g., North Dakota; Wilf and Johnson 2004;Peppe 2010) and farther south in the Western Interior (e.g., Hanna Basin, San Juan Basin, Denver Basin; Dunn 2003, Flynn and Peppe 2019 present differing patterns of plant recovery during this interval. These works broadly present two alternative hypotheses for the pattern of plant recovery: that floras regained pre-extinction diversity within the earliest~300 ka of the Paleocene or that floras remained homogeneous and depauperate for at least 1 Ma (Wilf and Johnson 2004). ...
... Lastly, site DP1311 fossils were collected from a carbonaceous shale interpreted to have been a ponded crevasse splay or overbank deposit. Fossils were assigned to the genus Platanites based on foliar architecture and leaf venation (e.g., Flynn, 2020;Flynn & Peppe, 2019). In addition, stomata have a raised ledge over the guard cell, which is characteristic of modern Platanaceae (Carpenter et al., 2005). ...
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Plain Language Summary Throughout Earth history, temperature and atmospheric CO2 usually track each other. During the Late Cretaceous to early Paleocene (∼70–60 Ma), global mean surface temperature was ∼8–12.5°C higher than today. However, CO2 estimates are variable, with some estimates equal to or less than present‐day CO2 (∼415 ppm) and at odds with the estimated global temperatures. Here we use a proxy based on leaf gas‐exchange principles (i.e., photosynthesis) to estimate early Paleocene CO2 from fossil Platanites leaves (family Platanaceae) of four early Paleocene localities from the San Juan Basin, New Mexico (65.66–64.59 Ma). We first test and calibrate the proxy on two modern Platanus species, Platanus occidentalis and P. × acerifolia. We find the leaf gas‐exchange model accurately predicts present‐day CO2. Applying the leaf gas‐exchange model to the early Paleocene, we find CO2 varies between ∼660 and 1,140 ppm. Our results are consistent with other proxies, such as boron, paleosol, leaf gas‐exchange, and liverwort proxies, that all suggest moderate to elevated levels of CO2 during the Late Cretaceous and early Paleocene. These levels of atmospheric CO2 are more in line with elevated temperature during this period, consistent with most observations of CO2 and temperature throughout the Phanerozoic.
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The lower Paleocene Ojo Alamo Sandstone and Nacimiento Formation from the San Juan Basin (SJB) in northwestern New Mexico preserve arguably the best early Paleocene mammalian record in North America and is the type location for the Puercan (Pu) and Torrejonian (To) North American land mammal ages (NALMA). However, the lack of precise depositional age constraints for the Ojo Alamo Sandstone and lower Nacimiento Formation has hindered our understanding of the timing and pacing of mammalian community change in the SJB following the Cretaceous−Paleogene mass extinction. Here we produced a high-resolution age model for the Ojo Alamo Sandstone and lower Nacimiento Formation combining magnetostratigraphy and 40Ar/39Ar geochronology spanning the first ∼3.5 m.y. of the Paleocene. Mean sediment accumulation rates during C29n were relatively low (<50 m/m.y.) and equalized from basin center to basin margin indicating an accommodation minimum; sediment accumulation rates approximately double (>90 m/m.y.) during C28r and are highest in the basin center and lowest on basin margin, which indicates high accommodation and an increase in basin subsidence near the C29n/C28r boundary (ca. 64.96 Ma). Puercan fossil localities were restricted to C29n, Torrejonian 1 localities to C28n, and lower Torrejonian 2 localities to C27r. Our revised age model for the SJB suggests that the first appearance of To1 mammals may have been diachronous across North America, with the Torrejonian 1 mammals first appearing in the north (Montana and North Dakota) during C29n, then in middle latitudes (Utah) in C28r, and lastly in southern North America (New Mexico) in C28n.
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Mammals are the most encephalized vertebrates, with the largest brains relative to body size. Placental mammals have particularly enlarged brains, with expanded neocortices for sensory integration, the origins of which are unclear. We used computed tomography scans of newly discovered Paleocene fossils to show that contrary to the convention that mammal brains have steadily enlarged over time, early placentals initially decreased their relative brain sizes because body mass increased at a faster rate. Later in the Eocene, multiple crown lineages independently acquired highly encephalized brains through marked growth in sensory regions. We argue that the placental radiation initially emphasized increases in body size as extinction survivors filled vacant niches. Brains eventually became larger as ecosystems saturated and competition intensified.
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Leaf carbon isotope fractionation (Δleaf) is sensitive to environmental conditions and can provide insights into the state and evolution of leaf gas-exchange in response to climate and environment factors. In modern plants, water availability is the strongest environmental predictor of Δleaf across sites that experience relatively uniform and low concentrations of CO2 in the atmosphere (pCO2). Growth chamber experiments show Δleaf of modern plants can also be sensitive to changing pCO2. However, over geologic time, it is uncertain how Δleaf has responded to shifts in pCO2 and precipitation. To address this problem, we collected sediment (rock) samples from fossil leaf sites that represent a range of pCO2 values from ∼200 to 900 ppmV, over 40 degrees of latitude from New Mexico to the High Arctic, and 40 million years spanning the Late Cretaceous to the Oligocene. For each site, the carbon isotope composition of atmospheric CO2 (δ13Catm), pCO2, mean annual precipitation, and mean annual temperature were constrained from independent proxies. From sediment samples, we extracted long-chain n-alkanes (biomarkers derived from plant wax). We then measured the carbon isotope ratios of sediment-derived n-C29 and n-C31 alkanes to calculate Δleaf. Results show a negative correlation between Δleaf and pCO2 even after controlling for mean annual precipitation. The Δleaf response to pCO2 is small (−0.3 ± 0.09‰/100 ppmV), suggesting plants are adjusting internal leaf CO2 concentrations to atmospheric pCO2 concentrations, likely by optimizing leaf gas-exchange to maximize carbon intake and minimize water loss in response to environmental conditions. Similar to previous studies of geologic sediments and living plants, Δleaf was also positively correlated with water availability and, to a lesser extent, sensitive to plant type and possibly altitude. As a result, the Δleaf – pCO2 relationship in the geologic past may be more complex than observed in modern studies and therefore, precludes its use as a pCO2 proxy.
Article
The Cretaceous/Paleogene (K/Pg) boundary Classopollis pollen “spike” in Patagonia, Argentina, is viewed as a singular event with no coeval analog anywhere else in the world. Review of global palynological records, however, reveals that similar K/Pg boundary Classopollis spikes involving monotaxial C. classoides (Pflug) Pocock and Jansonius assemblages have previously been reported from the Colorado Basin, Argentina, as well as the Tarim Basin, China, suggesting that this was a global phenomenon. The presence of this morphotaxon in the Danian strata of western North America has previously been interpreted as evidence of reworking from older, pre-Turonian (i.e., Triassic through Early Cretaceous) sediments during the Laramide orogeny. This hypothesis appears supported by the results of contemporary detrital zircon studies coupled with the physical degradation of pollen. However, the interpretation that all Danian examples of this pollen, particularly those from coal deposits, have been reworked from much older sediments is questioned on the basis of this review. Within this context, assorted hypotheses regarding the enigmatic coup de grâce of Classopollis-producing Cheirolepidiaceae are also considered, particularly the hypotheses that the ecologic distribution of Cheirolepidiaceae retracted to include xeric, upland habitats (e.g., the Rocky Mountains) or brackish-water, physiologically dry habitats (e.g., the margin of the Cannonball Sea) during the Late Cretaceous and Danian.
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Plants are strongly influenced by their surrounding environment, which makes them reliable indicators of climate and ecology. The relationship between climate, ecology, plant traits and the geographic distribution of plants based on their climatic tolerances have been used to develop plant-based proxies for reconstructing paleoclimate and paleoecology. These proxies are some of the most accurate and precise methods for reconstructing the climate and ecology of ancient terrestrial ecosystems and have been applied from the Cretaceous to the Quaternary. Despite their utility, the relationships between plant traits and climate that underlie these methods are confounded by other factors such as leaf life-span and phylogenetic history. Work focused on better understanding these confounding factors, incorporating the influence of phylogeny and leaf economic spectrum traits into proxies, expanding modern leaf trait-climate and ecology calibration datasets to additional biogeographic areas and climate regimes, and developing automated computer algorithms for measuring leaf traits are important growing research areas that will help considerably improve plant-based paleoclimate and paleoecological proxies.
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The Southern Hemisphere may have provided biodiversity refugia after the Cretaceous/Palaeogene (K/Pg) mass extinction. However, few extinction and recovery studies have been conducted in the terrestrial realm using well-dated macrofossil sites that span the latest Cretaceous (late Maastrichtian) and early Palaeocene (Danian) outside western interior North America (WINA). Here, we analyse insect-feeding damage on 3,646 fossil leaves from the latest Maastrichtian and three time slices of the Danian in Chubut, Patagonia, Argentina (palaeolatitude approximately 50° S). We test the southern refugial hypothesis and the broader hypothesis that the extinction and recovery of insect herbivores, a central component of terrestrial food webs, differed substantially from WINA at locations far south of the Chicxulub impact structure in Mexico. We find greater insect-damage diversity in Patagonia than in WINA during both the Maastrichtian and Danian, indicating a previously unknown insect richness. As in WINA, the total diversity of Patagonian insect damage decreased from the Cretaceous to the Palaeocene, but recovery to pre-extinction levels occurred within approximately 4 Myr compared with approximately 9 Myr in WINA. As for WINA, there is no convincing evidence for survival of any of the diverse Cretaceous leaf miners in Patagonia, indicating a severe K/Pg extinction of host-specialized insects and no refugium. However, a striking difference from WINA is that diverse, novel leaf mines are present at all Danian sites, demonstrating a considerably more rapid recovery of specialized herbivores and terrestrial food webs. Our results support the emerging idea of large-scale geographic heterogeneity in extinction and recovery from the end-Cretaceous catastrophe.
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Dopamine signaling occurs on a subsecond timescale, and its dysregulation is implicated in pathologies ranging from drug addiction to Parkinson's disease. Anatomic evidence suggests that some dopamine neurons have cross-hemispheric projections, but the significance of these projections is unknown. Here we report unprecedented interhemispheric communication in the midbrain dopamine system of awake and anesthetized rats. In the anesthetized rats, optogenetic and electrical stimulation of dopamine cells elicited physiologically relevant dopamine release in the contralateral striatum. Contralateral release differed between the dorsal and ventral striatum owing to differential regulation by D2-like receptors. In the freely moving animals, simultaneous bilateral measurements revealed that dopamine release synchronizes between hemispheres and intact, contralateral projections can release dopamine in the midbrain of 6-hydroxydopamine-lesioned rats. These experiments are the first, to our knowledge, to show cross-hemispheric synchronicity in dopamine signaling and support a functional role for contralateral projections. In addition, our data reveal that psychostimulants, such as amphetamine, promote the coupling of dopamine transients between hemispheres.
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Leaf mass per area (LMA) is a morphological trait widely used as a good indicator of plant functioning (i.e. photosynthetic and respiratory rates, chemical composition, resistance to herbivory, etc.). The LMA can be broken down into the leaf density (LD) and leaf volume to area ratio (LVA or thickness), which in turn are determined by anatomical tissues and chemical composition. The aim of this study is to understand the anatomical and chemical characteristics related to LMA variation in species growing in the field along a water availability gradient. We determined LMA and its components (LD, LVA and anatomical tissues) for 34 Mediterranean (20 evergreen and 14 deciduous) woody species. Variation in LMA was due to variation in both LD and LVA. For both deciduous and evergreen species LVA variation was strongly and positively related with mesophyll volume per area (VA or thickness), but for evergreen species positive relationships of LVA with the VA of epidermis, vascular plus sclerenchyma tissues and air spaces were found as well. The leaf carbon concentration was positively related with mesophyll VA in deciduous species, and with VA of vascular plus sclerenchymatic tissues in evergreens. Species occurring at the sites with lower water availability were generally characterised by a high LMA and LD.
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Dinosaur fossils are present in the Paleocene Ojo Alamo Sandstone and Animas Formation in the San Juan Basin, New Mexico, and Colorado. Evidence for the Paleo-cene age of the Ojo Alamo Sandstone includes palynologic and paleomagnetic data. Palynologic data indicate that the entire Ojo Alamo Sandstone, including the lower dinosaur-bearing part, is Paleocene in age. All of the palynomorph-productive rock samples collected from the Ojo Alamo Sandstone at multiple localities lacked Creta-ceous index palynomorphs (except for rare, reworked specimens) and produced Paleocene index palynomorphs. Paleocene palynomorphs have been identified strati-graphically below dinosaur fossils at two separate localities in the Ojo Alamo Sand-stone in the central and southern parts of the basin. The Animas Formation in the Colorado part of the basin also contains dinosaur fossils, and its Paleocene age has been established based on fossil leaves and palynology. Magnetostratigraphy provides independent evidence for the Paleocene age of the Ojo Alamo Sandstone and its dinosaur-bearing beds. Normal-polarity magnetochron C29n (early Paleocene) has been identified in the Ojo Alamo Sandstone at six localities in the southern part of the San Juan Basin. An assemblage of 34 skeletal elements from a single hadrosaur, found in the Ojo Alamo Sandstone in the southern San Juan Basin, provided conclusive evidence that this assemblage could not have been reworked from underlying Cretaceous strata. In addition, geochemical studies of 15 vertebrate bones from the Paleocene Ojo Alamo Sandstone and 15 bone samples from the underlying Kirtland Formation of Late Creta-ceous (Campanian) age show that each sample suite contained distinctly different abundances of uranium and rare-earth elements, indicating that the bones were miner-alized in place soon after burial, and that none of the Paleocene dinosaur bones ana-lyzed had been reworked.
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We here investigate the sedimentology of the early Danian (ca. 66–64 Ma) Salamanca Formation in the north-central San Jorge Basin, southern Chubut Province, Patagonia, Argentina, in order to place the outstandingly diverse and well-preserved fossil floras it contains into specific environmental settings. These assemblages are among very few of Danian age from the entire Southern Hemisphere and thus provide critical data about geographic variation in recovery from the end-Cretaceous extinction. Understanding the depositional context of the Salamanca floras is necessary for comparison with other assemblages and for interpreting their exceptional preservation. The Salamanca Formation was deposited above a widespread erosional sequence boundary (SB-1) resulting from a relative base level rise and widespread marine transgression during the early Danian (Chron C29n). In response to this increase in accommodation space, a broad, shallow estuary formed that most likely extended westward at least as far as the San Bernardo belt. A transgressive systems tract was deposited in this estuary, consisting of bioturbated sand fining upwards to silt. The maximum marine flooding surface at the beginning of the highstand systems tract is defined by well laminated, unburrowed, clay deposits of a low energy, deep shelf. The Salamanca highstand systems tract (HST) consists of sandy and silty facies capped by accreting subtidal bars and sandy shoals containing an abundance of tidal indicators, suggesting deposition proximal to the San Jorge paleo-estuary head. A second sequence boundary (SB-2), formed during Chron C28r and early C28n, separates the older highstand deposits from younger lowstand and transgressive deposits. These consist of estuarine sand shoals, trough cross-bedded sands deposited in aggrading, fluvially influenced tidal channels, tidal flat muds, and bayhead deltas. The best preservation of compression floras and petrified trees occurred near the tops of subtidal bars below SB-2; at the end of the shallowing-upward cycle that caps the second HST; and in fluvially-influenced tidal channels, tidal flat mudstones, and bayhead deltas of the lowstand and transgressive systems tracts that lie above SB-2. These settings were proximal to the source forests and had rapid rates of burial. We interpret the dark muds of the Banco Negro Inferior, which cap the Salamanca Formation, as a late transgressive and highstand systems tract deposited during a time of rising groundwater table and declining river slopes in a widespread, lowland coastal forest.
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Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico. Free Downloads NMGS has decided to make peer-reviewed papers from our Fall Field Conference guidebooks available for free download. Non-members will have access to guidebook papers two years after publication. Members have access to all papers. This is in keeping with our mission of promoting interest, research, and cooperation regarding geology in New Mexico. However, guidebook sales represent a significant proportion of our operating budget. Therefore, only research papers are available for download. Road logs, mini-papers, maps, stratigraphic charts, and other selected content are available only in the printed guidebooks.
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To assess the degree to which forest litter reflects the source forest, three 1-ha plots of temperate deciduous forest were mapped and litter accumulating in these forests was sampled. Identity, position, and diameter of all stems 2 cm or larger diameter at breast height are known for each forest. Composition of the leaf litter is governed by two key factors: (1) abscised leaves are deposited primarily on the forest floor directly underneath the canopy that produced them, and (2) the leaf mass of a species is highly correlated with its stem cross-sectional area. These factors produce autochthonous litter samples that correspond closely in composition to the forest within a circle of canopy-height radius or less. Even relatively small litter samples (350 leaves) consistently contained all the common species in the local area. However, the rarer tree species were seldom recovered in the litter samples. Correlation coefficients for litter mass and basal area by species are typically over .80. These observations have three important implications for interpreting autochthonous compression-fossil assemblages. First, approximate relative abundances of locally dominant and subdominant forest taxa can be obtained from relatively small samples of autochthonous compression-fossil assemblages. Second, representation of rare forest species, even in large fossil samples, will be fortuitous. For this reason, complete species lists and consistent estimates of richness cannot be derived directly from most existing samples of autochthonous compression-fossil assemblages. Third, the strong tendency for leaves to fall beneath the canopy of the tree that sheds them suggests that properly sampled autochthonous fossil leaf assemblages may yield information on crown size of individual trees and the spatial distribution of individuals and species, aspects of vegetational structure that have been thought accessible only in well-preserved “fossil forests” with standing trunks.
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Fossil wood is common in the Late Cretaceous and Early Paleocene of the San Juan Basin, New Mexico. Six types of dicotyledonous wood are recognized: Paraphyllanthoxylon arizonense Bailey, Paraphyllanthoxylon anasazi sp. nov., Plataninium piercei sp. nov., Metcalfeoxylon kirtlandense gen. et sp. nov., Chalkoxylon cretaceum gen. et sp. nov., Carlquistoxylon nacimientense gen. et sp. nov. Woods with the characteristics of Paraphyllanthoxylon arizonense Bailey are the most common and occur in the Cretaceous Kirtland Shale and the Paleocene Ojo Alamo Sandstone and Nacimiento Formation. This wood type's characteristics are stable from the Cretaceous to the Paleocene. There were no significant differences in the vessel diameters, vessel densities, ray sizes, or estimated specific gravities of the P. arizonense woods from the Late Cretaceous (Kirtland Shale) and Early Paleocene (Nacimiento Formation and Ojo Alamo Sandstone). Based on the samples examined for this study, dicotyledonous woods were more diverse in the Cretaceous (five types) than in the Paleocene (two types) of the San Juan Basin. Diameters of the Cretaceous woods examined ranged from 14-40cm indicating they were trees rather than shrubs; diameters of the Paleocene woods examined ranged from 10-80cm. All the woods have generalized structure with combinations of features seen in more than one extant family, order, or subclass. Information from databases for fossil and extant woods indicates that some combinations of features (e. g., solitary narrow vessels, low vessel density and scalariform perforation plates, as seen in Metcalfeoxylon kirtlandense and Chalkoxylon cretaceum), while relatively common in the Cretaceous, represent strategies of the hydraulic system that are extremely rare in the Tertiary and at present. None of the dicotyledonous woods have distinct growth rings, although some samples of Paraphyllanthoxylon arizonense from the Paleocene show variations in vessel density and vessel diameter that may correspond to seasonal variations in water availability.
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Extraordinarily well preserved fern macrofossils of Ruffordia goeppertii (Dunker) Seward (Schizaeales, Anemiaceae) are described from the Lower Cretaceous (late Aptian) Nova Olinda Member of the Crato Formation, northeast Brazil. The identification is based on the morphology of macrofossils and in situ spores, taken from organically preserved material. This extinct, relatively small fern exhibits dimorphic fronds with sterile and fertile pinnules and schizaeoid sporangia, including cicatricose spores. The growth form with clearly differentiated sterile and fertile pinnae may be interpreted as an ancestral state in the phylogeny of the extant genus Anemia. The abundance of this fern reflects its role as ground cover in at least partly (dry) sunny areas, possibly in fern savannah-like habitats, with adaptations to survive drought stress. Finds of Ruffordia in northern Gondwana extend the wide palaeogeographic range of this taxon.
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Three new wood types from the Late Cretaceous and one from the Paleocene of Big Bend National Park, Texas, U.S.A. add to our knowledge of North Ameri-can Late Cretaceous and Paleocene plants. Sabinoxylon wicki sp. nov. provides further evidence of similarities in late Campanian-early Maastrichtian vegetation of Texas, New Mexico, and northern Mexico. This species is characterized by mostly solitary vessels, scalariform perforation plates, vessel-ray parenchyma pits similar to intervessel pits, vasicentric tracheids, and two size classes of rays. Storage tissue accounts for close to 50% of its wood volume. Another of the new Cretaceous wood types, referred to as Big Bend Ericalean Wood Type I, has more than 40 % ray parenchyma. Both Big Bend Ericalean Wood Type I and Sabinoxylon have a combination of characters that occurs in the order Ericales (sensu APGII). The third new Cretaceous wood type is from a small axis (less than 3 cm diameter), and has a combination of features that is the most common pattern in extant eudicots (vessels solitary and in radial multiples randomly arranged, simple perforation plates and alternate intervessel pits, and heterocellular rays). The Paleocene wood (cf. Cunonioxylon sensu Gottwald) differs from all other North American Paleocene woods and has characteristics found in the predominantly Southern Hemisphere family Cunoniaceae. The characteristics of these new Big Bend woods contribute to a database for fossil angiosperm woods, and allow for comparison of incidences of selected wood anatomical features in Northern Hemisphere Cretaceous woods from Albian to Maastrichtian time as well as comparison with extant woods. Cretaceous woods as a whole differ from Recent woods in having higher incidences of exclusively solitary vessels, scalariform perforation plates, and wide rays (>10-seriate), and lower incidences of ring porosity, wide vessels (> 200 µm), vessels in groups, non-random arrangements of vessels, and marginal parenchyma. The occur-rence of relatively high percentages of storage cells (> 40%) in some Cretaceous trees is noteworthy; the ability to produce wood with varying amounts and arrangements of parenchyma is likely to be a contributing factor to the success of angiosperm trees in a wide variety of environments.
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In the San Juan Basin, New Mexico, the Ojo Alamo Formation includes two members, the upper Kimbeto Member and the lower Naashoibito Member (previously assigned to the underlying Kirtland Formation). The Naashoibito Member produces dinosaur fossils, as does the De-na-zin Member of the Kirtland Formation, which lies unconformably beneath it. A lignite bed in the upper part of the De-na-zin Member has been identified as the horizon of a major unconformity and the source of some Paleocene palynomorphs. The overlying dinosaur remains in the Naashoibito Member thus have been assigned a Paleocene age, but new pollen data refute this interpretation. The dinosaurs from the Naashoibito Member are not well-known, but late Maastrichtian (Lancian) dinosaur taxa (Torosaurus latus and Tyrannosaurus rex), as well as the early Maastrichtian Torosaurus utahensis, are not demonstrably present in this unit, despite previous claims. Vertebrate biostratigraphy suggests an early Maastrichtian age for the Naashoibito Member of the Ojo Alamo Formation, and palynological analyses of this unit does not support a Paleocene age; thus there are no Paleocene (non-avian) dinosaurs in the San Juan Basin.
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Author Summary Sixty-six million years ago the Chicxulub bolide impacted the Earth, marking the Cretaceous–Paleogene boundary (KPB). This event caused the planet's most recent mass extinction, but the selectivity and functional consequences of the extinction on terrestrial plants has been largely unknown. A key untested hypothesis has been that a subsequent impact winter would have selected against slow-growing evergreen species, a possible cause of the modern dominance of high-productivity deciduous angiosperm forests. We tested this hypothesis using fossil leaf assemblages across a 2-million-year interval spanning the KPB. We assess two key ecological strategy axes—carbon assimilation rate and carbon investment—using leaf minor vein density and leaf mass per area as proxies, respectively. We show that species that survive the KPB have fast-growth ecological strategies corresponding to high assimilation rates and low carbon investment. This finding is consistent with impact winter leading to the nonrandom loss of slow-growing evergreen species. Our study reveals a dramatic example of the effect of rapid catastrophic environmental change on biodiversity.
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Changes in pollen and spore assemblages across the Cretaceous–Paleogene (K–Pg) boundary elucidate the vegetation response to a global environmental crisis triggered by an asteroid impact in Mexico 66 Ma. The Cretaceous–Paleogene boundary clay, associated with the Chicxulub asteroid impact event, constitutes a unique, global marker bed enabling comparison of the world-wide palynological signal spanning the mass extinction event. The data from both hemispheres are consistent, revealing diverse latest Cretaceous assemblages of pollen and spores that were affected by a major diversity loss as a consequence of the K–Pg event. Here we combine new results with past studies to provide an integrated global perspective of the terrestrial vegetation record across the K–Pg boundary. We further apply the K–Pg event as a template to asses the causal mechanism behind other major events in Earths history. The end-Permian, end-Triassic, and the K–Pg mass-extinctions were responses to different causal processes that resulted in essentially similar succession of decline and recovery phases, although expressed at different temporal scales. The events share a characteristic pattern of a bloom of opportunistic “crisis” tax followed by a pulse in pioneer communities, and finally a recovery in diversity including evolution of new taxa. Based on their similar extinction and recovery patterns and the fact that the Last and First Appearance Datums associated with the extinctions are separated in time, we recommend using the K–Pg event as a model and to use relative abundance data for the stratigraphic definition of mass-extinction events and the placement of associated chronostratigraphic boundaries.
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A comprehensive, but simple-to-use software package for executing a range of standard numerical analysis and operations used in quantitative paleontology has been developed. The program, called PAST (PAleontological STatistics), runs on standard Windows computers and is available free of charge. PAST integrates spreadsheettype data entry with univariate and multivariate statistics, curve fitting, time-series analysis, data plotting, and simple phylogenetic analysis. Many of the functions are specific to paleontology and ecology, and these functions are not found in standard, more extensive, statistical packages. PAST also includes fourteen case studies (data files and exercises) illustrating use of the program for paleontological problems, making it a complete educational package for courses in quantitative methods.
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Known for centuries, the geographical pattern of increasing biodiversity from the poles to the equator is one of the most pervasive features of life on Earth. A longstanding goal of biogeographers has been to understand the primary factors that generate and maintain high diversity in the tropics. Many ‘historical’ and ‘ecological’ hypotheses have been proposed and debated, but there is still little consensus. Recent discussions have centred around two main phenomena: phylogenetic niche conservatism and ecological productivity. These two factors play important roles, but accumulating theoretical and empirical studies suggest that the single most important factor is kinetics: the temperature dependence of ecological and evolutionary rates. The relatively high temperatures in the tropics generate and maintain high diversity because ‘the Red Queen runs faster when she is hot’.
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Precise estimates of past temperatures are critical for understanding the evolution of organisms and the physical biosphere, and data from continental areas are an indispensable complement to the marine record of stable isotopes. Climate is considered to be a primary selective force on leaf morphology, and two widely used methods exist for estimating past mean annual temperatures from assemblages of fossil leaves. The first approach, Leaf Margin Analysis, is univariate, based on the positive correlation in modern forests between mean annual temperature and the proportion of species in a flora with untoothed leaf margins. The second approach, known as the Climate-Leaf Analysis Multivariate Program, is based on a modern data set that is multivariate. I argue here that the simpler, univariate approach will give paleotemperature estimates at least as precise as the multivariate method because (1) the temperature signal in the multivariate data set is dominated by the leaf-margin character; (2) the additional characters add minimal statistical precision and in practical use do not appear to improve the quality of the estimate; (3) the predictor samples in the univariate data set contain at least twice as many species as those in the multivariate data set; and (4) the presence of numerous sites in the multivariate data set that are both dry and extremely cold depresses temperature estimates for moist and nonfrigid paleofloras by about 2°C, unless the dry and cold sites are excluded from the predictor set. New data from Western Hemisphere forests are used to test the univariate and multivariate methods and to compare observed vs. predicted error distributions for temperature estimates as a function of species richness. Leaf Margin Analysis provides excellent estimates of mean annual temperature for nine floral samples. Estimated temperatures given by 16 floral subsamples are very close both to actual temperatures and to the estimates from the samples. Temperature estimates based on the multivariate data set for four of the subsamples were generally less accurate than the estimates from Leaf Margin Analysis. Leaf-margin data from 45 transect collections demonstrate that sampling of low-diversity floras at extremely local scales can result in biased leaf-margin percentages because species abundance patterns are uneven. For climate analysis, both modern and fossil floras should be sampled over an area sufficient to minimize this bias and to maximize recovered species richness within a given climate.
Book
In Plants and the K-T Boundary, two of the world's leading experts in palynology and paleobotany provide a comprehensive account of the fate of land plants during the ‘great extinction’ about 65 million years ago. They describe how the time boundary between the Cretaceous and Paleogene Periods (the K-T boundary) is recognized in the geological record, and how fossil plants can be used to understand global events of that time. There are case studies from over 100 localities around the world, including North America, China, Russia and New Zealand. The book concludes with an evaluation of possible causes of the K-T boundary event and its effects on floras of the past and present. This book is written for researchers and students in paleontology, botany, geology and Earth history, and everyone who has been following the course of the extinction debate and the K-T boundary paradigm shift.
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The decline of species richness from equator to pole, or latitudinal diversity gradient (LDG), is nearly universal among clades of living organisms, yet whether it was such a pervasive pattern in the geologic past remains uncertain. Here, we calculate the strength of the LDG for terrestrial mammals in North America over the past 65 My, using 27,903 fossil occurrences of Cenozoic terrestrial mammals from western North America downloaded from the Paleobiology Database. Accounting for temporal and spatial variation in sampling, the LDG was substantially weaker than it is today for most of the Cenozoic and the robust modern LDG of North American mammals evolved only over the last 4 My. The strength of the LDG correlates negatively with global temperature, suggesting a role of global climate patterns in the establishment and maintenance of the LDG for North American mammals.
Chapter
Lithofacies analysis of the Tertiary Ojo Alamo Sandstone and related strata in the San Juan Basin indicates that Laramide (Late Cretaceous-early Tertiary) volcanism and uplift north of the present-day San Juan Basin controlled sedimentation patterns of Upper Cretaceous and lower Tertiary rocks. Eight major lithofacies reflect changes in sedimentation that occurred during this time. The Ojo Alamo Sandstone is characterized in most areas of the San Juan Basin by a pebbly, trough-crossbedded lithofacies. A related channel-form sandstone and shale facies makes up the Ojo Alamo at Mesa Portales. Both lithofacies include both sediment derived from north of the present-day San Juan Basin and sediment eroded and reworked from (1) a carbonaceous shale and channel-form sandstone facies, (2) a shale and volcaniclastic sandstone facies, and (3) a volcaniclastic conglomerate and sandstone facies. The pebbly, trough-crossbedded lithofacies, which was deposited by streams on alluvial plains, differs in grain size, pebble composition, and transport direction on the east and west sides of the present-day basin. At least two distinct source areas for the streams are suggested by these differences. One source is in the area of the present-day Needle Mountains and western San Juan Mountains. A second source is located in the area of the central to eastern San Juan Mountains of southwest Colorado. Sediments deposited by alluvial streams in the western San Juan basin include sand- and pebblesize material. Initially, Ojo Alamo streams carried up to 25 percent volcanic pebbles reworked from the Animas Formation or from Upper Cretaceous andesitic flows in the source area. Later streams, however, carried an increasing percentage of quartz pebbles over volcanic pebbles. Lithofacies of the Ojo Alamo in the eastern San Juan Basin include channel sandstone and conglomerates and a channel-form sandstone and shale facies. Compared to sediments of the western alluvial complex, the eastern sediments (mapped as Ojo Alamo Sandstone, upper part of the Animas Formation, and Nacimiento Formation) are finer grained, contain few pebbles, contain less than 1 percent volcanic pebbles, and show different transport directions. Mudstone interbeds are thicker and more abundant, especially at Mesa Portales where an accompanying down-dip change in the alluvial system contributes to formation of the channel-form sandstone and shale lithofacies.
Chapter
The Hell Creek and Fort Union Formations in southwestern North Dakota and northwestern South Dakota have yielded a diverse megaflora of 380 species from 158 quarry sites. These sites are situated in a stratigraphic framework, delimited by palynology, magnetostratigraphy, and vertebrate paleontology, that contains both the Cretaceous-Tertiary (K-T) boundary event horizon and stratigraphic evidence for rapid base-level increase. The late Maastrichtian Hell Creek flora is dominated by angiosperms; ferns, fern allies, cycads, ginkgo, and conifers represent <10% of total taxa and specimens. Megafloral extinction at the K-T boundary is extensive, effectively eliminating all dominant plant taxa of the upper Hell Creek Formation. K-T survivorship appears to be greatest in plants that occupied Cretaceous mire facies. The Hell Creek megaflora is heterogeneous with respect to stratigraphic position and sedimentary facies, allowing the recognition of three superposed megafloral zones and two facies-controlled megafloras. Hell Creek vegetation represents an angiospermdominated woodland composed of small-to medium-sized trees, often with lobed leaves. One exception is a diverse angiosperm-dominated herbaceous vegetation associated with large paleochannels in the middle of the formation. The uppermost Hell Creek megaflora zone (HCIII) first occurs near the base of magnetic polarity subchron C29R. The HCIII megaflora is significantly more diverse than earlier Hell Creek floras, and foliar physiognomy suggests a significant climate warming during the final 300-500 k.y. of the Cretaceous. The Paleocene megaflora is depauperate, less heterogeneous than the Cretaceous megaflora, and dominated, in all facies, by taxa that were most common in Cretaceous mire facies.
Article
Rarefaction predicts the morphological diversity that would probably be observed in a sample of reduced size, thereby allowing both compensation for differences in sample size that may be strictly preservational, and analysis of diversity structure, that is, the relationship between morphological and taxonomic diversity. Middle and Late Cambrian trilobites exhibit a diversity structure characterized by many variations on a few morphological themes. In contrast, Middle and Late Ordovician trilobites occupy a larger range of morphospace per unit of species richness. Diversity structure in the Devonian is similar to that in the Middle and Late Ordovician, but the magnitude of morphological diversity is lower in the Devonian, as many fewer species are observed. For blastoids, different aspects of morphological diversity exhibit different relationships to taxonomic richness. In all cases Permian blastoids are characterized by a diversity structure in which morphological diversity per unit of taxonomic richness is greater than for Devonian blastoids. Rarefaction curves are also presented for idealized increases and decreases in diversity, and these are compared to some of the obesrved changes in trilobites, blastoids, and ammonoids. -from Author
Article
The latest Cretaceous (Santonian to Maastrichitan) Normapolles and Aquilapollenites floristic provinces are well known in N America. The contiental margin floristic province of this paper differs from the other 2 provinces because of its largely endemic pollen species, its abundance of Proteacidites group pollen, and its generally low abundance or lack of pollen of the Aquilapollenites, Callistropollenites, Normapolles, wind-pollinated? triporate, and angiosperm monosulcate groups. Characteristic features and geographic distribution of the continental margin province are based on previously described assemblages from British Columbia and newly examined assemblages from California. Latest Cretaceous sediments of this province rest on rocks of the Wrangellia terrane, which with others have been translated N at least 2000km since the Campanian according to paleomagnetic data. Thus, latest Cretaceous floras of the continental margin province were isolated from floras to the E partly because of oceanic and mountain barriers but probably also because they formed in more tropical climates than most floras of the other 2 provinces.-from Author
Article
Phenology of 108 species (1094 trees) was monitored for 42 months in a tropical deciduous forest in the Pacific lowlands of Mexico. Leaf expansion was highly concentrated in June-July; the forest canopy was at least 75 percent full in only 30 percent of the study period. With few exceptions, the species were leafless for several months each year. Gradual leaf loss in most species suggested there were large inter- and intraspecific differences in length of the growing season. Peak flowering was in June-July. Flowering lasted less than two months in most cases. Closely related species typically flowered concurrently. The delay from flowering to dispersal showed no prominent mode. Peaks of seed dispersal showed no community mean, but endozoochores differed from other species in seasonality. Reproduction was annual for most populations, and sub-annual intervals were related to rainfall anomalies. The response of many species to rains in December or January indicated their phenology was driven by water availability, but other species were probably limited by photoperiod. Intensive use of stored resources was indicated by simultaneous flushing and flowering in many species.
Article
We characterize forest floor leaf litter and transported leaf samples from several depositional environments in both a temperate and a tropical forest to provide well-characterized modern analogs for the evaluation of fossil leaf localities. We compare the low-diversity, deciduous, temperate Wharton Brook forest (Connecticut, United States) with the high-diversity, evergreen, tropical Noah Creek Rainforest (Queensland, Australia) by mapping one half-hectare of each forest, collecting 25-29 leaf litter samples from four to five depositional settings in each forest and analyzing the relative abundance of species based on >31,750 leaves. In both studies, we analyze the samples as if they were fossil sites, evaluating floral composition, numerical diversity measures, rarefied richness, and climate estimates based on leaf physiognomy. We compare this analysis with data from the standing mapped forest to evaluate the biases inherent in the data derived from fossil assemblages from different depositional settings. In both forests, sample sites that were revisited over multiple years produced different species on subsequent visits, suggesting that fossil sites with close stratigraphic spacing and different composition may actually represent the same source forest. In both forests, species diversity in laterally transported samples appears to increase as the distance of transport increases. Because the species richness of a leaf sample is impacted by the diversity of the original forest, the amount of time the leaf sample spent accumulating, and the effect of transport distance, it is not possible to interpret the diversity of ancient forests without also evaluating the sedimentary facies of the fossil collections.
Book
Ferns are an integral part of the world's flora, appreciated for their beauty as ornamentals, problematic as invaders and endangered by human interference. They often dominate forest understories, but also colonize open areas, invade waterways, and survive nutrient-poor wastelands and eroded pastures. This is the first comprehensive summary of fern ecology, with worldwide examples from Siberia to Hawaii. Topics include a brief history of the ecological study of ferns, their biogeography and population dynamics, their role in ecosystem nutrient cycles and adaptations to xeric environments, and their responses to disturbance and interactions with other organisms. Fully illustrated concepts provide a framework for students and professionals in ecology, conservation, and land management, and a wealth of information for anyone interested in ferns.
Article
A floral gradient for the early Mesozoic has been reconstructed from localities ranging from the subtropics to the polar region of the Northern Hemisphere, encompassing climates interpreted as having ranged from the warm dry subtropical to the cool wet temperate regime. Our previous ordination studies on the floras had demonstrated a gradual replacement of morphological types: from coniferophytes and cycadophytes with thick cuticles and small leaves in low latitudes, through broader-leaved forms of cycadophytes with filicopsids, to broad-leaved deciduous ginkgophytes and coniferophytes in near-polar positions. Parallels with the Recent tropical and subtropical distributions of the cycads and with the late Cenozoic temperate distribution of Ginkgo can be drawn. Floral lists were assembled from eight exceptionally well sampled regions in Northern Eurasia ranging in age from late Triassic through late Jurassic, and were used to determine the correlation of the floral gradient with paleo-latitude. Floral lists were also assembled from basins associated with the Chinese microcontinents of South China, North China and Tarim, which were converging with Northern Eurasia at the time. Their positions are therefore less well known, and our purpose is to show that the floral gradient is sensitive enough to be used as a check on the tectonic-and paleomagnetic-based reconstructions currently available. South China and North China were in the warm temperate zone in the late Triassic and early Jurassic, and collision with the southward-moving Eurasia was complete by the late Jurassic. During the Jurassic, the complex was moving equatorward into the dry subtropical zone. These conclusions accord with current tectonic interpretations, but the available paleomagnetic data seem to underestimate significantly the paleo-latitude of these blocks during some time intervals.
Conference Paper
Upper Cretaceous and lower Paleocene rocks in the San Juan Basin, New Mexico, contain a robust record of dinosaur and mammal evolution, diversification, and extinction. Despite this rich fossil record, the ages and durations of the Upper Cretaceous Naashoibito Member of the Kirtland Formation and the lower Paleocene Ojo Alamo Sandstone and Nacimiento Formation have been relatively poorly constrained. These poor age constraints have limited the ability to accurately correlate these vertebrate records to others across North America and to assess rates of speciation and extinction of dinosaurs in the Cretaceous and mammals before and after the Cretaceous-Paleogene (K-Pg) mass extinction. Further, the ages of the Naashoibito and the Ojo Alamo are contentious and have been interpreted to range from Campanian to early Paleocene. Here we present new geochronologic results that combine magnetostratigraphy and 40Ar/39Ar dating of detrital sanidine from sedimentary units and sanidine phenocrysts from a volcanic ash to constrain the ages of the Naashoibito Member, the Ojo Alamo Sandstone, and the lower Nacimiento Formation. Coupled detrital sanidine dates and magnetostratigraphy indicate that the Naashoibito correlates to chrons C31n – C29r, suggesting a protracted depositional history with multiple disconformities. Further, our results indicate that the youngest Cretaceous sedimentary rocks in the San Juan Basin were likely deposited within the last 300 kyr of the Cretaceous. A 40Ar/39Ar sanidine date of 65.59±0.01 Ma (1S, analytical error only) from an ash within the Nacimiento demonstrates that biozone Pu2 (2nd biozone of the Puercan Land Mammal “age”) began within ~440 kyr of the K-Pg boundary. A probable volcanic ash coincident with the first occurrence of Pu3 mammals yielded an age of 65.43±0.04 Ma, tentatively suggesting that Pu2 was only ~150 kyr long. These dates and our magnetostratigraphy indicate that the Ojo Alamo was deposited in chron C29r and the lower Nacimiento in chrons C29r – C28r. This new geochronology helps to constrain the ages of the first occurrence of the Pu2 and Pu3 faunas in the San Juan Basin and indicates that deposition of basal Paleocene strata in the basin began <300 kyr after the K-Pg boundary. All argon dates are relative to FC-2 sanidine at 28.201 Ma and 40K decay constant of 5.463e-10 /a.
Article
Non-avian dinosaurs went extinct 66 million years ago, geologically coincident with the impact of a large bolide (comet or asteroid) during an interval of massive volcanic eruptions and changes in temperature and sea level. There has long been fervent debate about how these events affected dinosaurs. We review a wealth of new data accumulated over the past two decades, provide updated and novel analyses of long-term dinosaur diversity trends during the latest Cretaceous, and discuss an emerging consensus on the extinction’s tempo and causes. Little support exists for a global, long-term decline across non-avian dinosaur diversity prior to their extinction at the end of the Cretaceous. However, restructuring of latest Cretaceous dinosaur faunas in North America led to reduced diversity of large-bodied herbivores, perhaps making communities more susceptible to cascading extinctions. The abruptness of the dinosaur extinction suggests a key role for the bolide impact, although the coarseness of the fossil record makes testing the effects of Deccan volcanism difficult.
Article
1 The number of woody species in tropical forests tends to increase with precipitation, forest stature, soil fertility, rate of canopy turnover and time since catastrophic disturbance, and decrease with seasonality, latitude, altitude, and diameter at breast height (d.b.h.).2 A model is presented to account for these trends. Novel hypotheses include how increased rainfall and substrate fertility, and decreased seasonality, might (i) increase attacks by natural enemies, and thus the overall level of density-dependent plant mortality; (ii) increase shade tolerance, canopy turnover, and stem density of the species-rich understorey; and (iii) increase reliance on relatively sedentary forest-interior birds for seed dispersal, fostering high rates of speciation in understorey genera.3 High rainfall and low seasonality in the tropics favour two key groups of natural plant enemies – insects and fungi – that are directly responsible for promoting high rates of density-dependent plant mortality. Lower rainfall, greater seasonality, soil infertility, or unfavourable rooting conditions favour greater allocation to anti-herbivore defences, and thus lead to lower rates of such mortality and thence to lower tree diversity. The increased number of individuals on rainier sites is a minor contributor to increased tree diversity, accounting for only about 17% of the 8.3-fold increase with rainfall in the lowland Neotropics.4 Predictions of the model are consistent with many ecological patterns of variation in tropical tree diversity within regions, and may help explain the decrease in tree diversity with elevation and the accompanying decrease in horizontal patchiness (within-habitat  diversity).5 Random drift over evolutionary time in the relative effectiveness of density-dependent control of individual tree species by specialized natural enemies may better account for the observed distribution of tropical tree abundance than a random walk of species abundance through ecological time.
Article
THEORIES that explain the extinctions characterizing the Cretaceous/Tertiary (K/T) boundary1-3 need to be tested by analyses of thoroughly sampled biotas. Palynological studies are the primary means for stratigraphic placement of the terrestrial boundary and for estimates of plant extinction4-12, but have not been combined with quantitative analyses of fossil leaves (megaflora). Megafloral studies complement palynology by representing local floras with assemblages capable of high taxonomic resolution13, but have previously lacked the sample size and stratigraphic spacing needed to resolve latest Cretaceous floral history5,14-18. We have now combined megafloral data from a 100-m-thick composite K/T boundary section in North Dakota with detailed palynological analysis. Here the boundary is marked by a 30% palynofloral extinction coincident with iridium and shocked-mineral anomalies and lies ~2 m above the highest dinosaur remains. The megaflora undergoes a 79% turnover across the boundary, and smaller changes 17- and 25-m below it. This pattern is consistent with latest Cretaceous climatic warming preceding a bolide impact.
Book
"Measuring Biological Diversity assumes no specialist mathematical knowledge and includes worked examples and links to web-based software. It will be essential reading for all students, researchers, and managers who need to measure biological diversity."--BOOK JACKET.