Papers by Garland Upchurch
Palaeogeography, Palaeoclimatology, Palaeoecology, Dec 1, 2000
It has been hypothesized that major global fires occurred following a bolide impact at the Cretac... more It has been hypothesized that major global fires occurred following a bolide impact at the Cretaceous-Tertiary boundary. Evidence for this has been mainly from 'soot' or black carbon at a number of marine boundary sites as well as the occurrence of inertinites (fusinite) in coals above the boundary. In addition, the occurrence of fossil charcoal (inertinites) in potential Tsunami deposits has been used to strengthen this idea. However, fire is known to have been widespread throughout the Cretaceous based on the distribution of fossil charcoal, and it is necessary to evaluate the claims for a global fire at the K-T boundary within the context of this more extensive record of ancient fires. The occurrence of the K-T boundary within the Sugarite coal sequence in the Raton Basin, New Mexico, offers the opportunity to assess the incidence of fire in local peat-forming vegetation, in the latest Cretaceous, across the Cretaceous-Tertiary boundary interval and in the earliest Tertiary. The distribution of fire products, i.e. fossil charcoal, is assessed using a combination of inertinite group macerals in polished blocks of coal and plant particles released by chemical maceration of coal. Inertinite group macerals (fusinite, semifusinite, inertodetrinite), which represent fossil charcoal, and particles of charcoal in maceration residues are abundant throughout the Sugarite coal sequence, both before, during and after the K-T boundary event. Samples from below the boundary yield inertinites that constitute more than 20% of the coal; three horizons are inertinite rich (>50%). Fire was obviously an important element of the terrestrial environment during the latest Cretaceous. High inertinite values and abundant charcoal particles characterize the latest Cretaceous part of the coal, the carbonaceous shale just below the boundary, the boundary interval itself and Tertiary coals and carbonaceous shales above the boundary. Charcoal in mineral-rich units of the latest Cretaceous, immediately below the boundary, in the boundary interval and in the Tertiary, is dominated by small inertodetrinite particles. These might have been wind blown from regional fires or they may reflect reworking during erosion, which led to sediment input into the mire. In either case the charcoal signature in these units is the same, irrespective of their position in the sequence. Our data, combined with that from two other sites in terrestrial sequences in North America, show that fires were an integral part of mire ecosystems through the latest Cretaceous and into the early Tertiary. Therefore, evidence for distinctive global wildfires at the Cretaceous-Tertiary boundary would have to be sought from careful consideration of other aspects of charcoal deposition, including flux rates for charcoal and soot.
Geophysical Research Letters, Jul 15, 2000
Investigations of long-term (103-105 yr) environmental change across the Cretaceous-Tertiary (K/T... more Investigations of long-term (103-105 yr) environmental change across the Cretaceous-Tertiary (K/T) boundary resulting from the impact of a large bolide indicate increases in temperature and precipitation due to the impact-related release of CO2. We evaluate the effects of these long-term changes in the global environment on terrestrial ecosystems using a vegetation-biogeochemistry model forced with a 'best guess' modified latest Cretaceous climate simulation by the GENESIS atmospheric general circulation model. The imposition of long-term global environmental changes after the K/T impact resulted in spatially heterogeneous increases in canopy leaf area index, net primary productivity, and soil carbon concentrations, relative to the latest Cretaceous preimpact situation. Terrestrial carbon storage increased by circa 2000 Gt.
Philosophical Transactions of the Royal Society B, Jan 29, 1998
Forest vegetation has the ability to warm Recent climate by its effects on albedo and atmospheric... more Forest vegetation has the ability to warm Recent climate by its effects on albedo and atmospheric water vapour, but the role of vegetation in warming climates of the geologic past is poorly understood. This study evaluates the role of forest vegetation in maintaining warm climates of the Late Cretaceous by (1) reconstructing global palaeovegetation for the latest Cretaceous (Maastrichtian); (2) modelling latest Cretaceous climate under unvegetated conditions and different distributions of palaeovegetation; and (3) comparing model output with a global data base of palaeoclimatic indicators. Simulation of Maastrichtian climate with the land surface coded as bare soil produces high-latitude temperatures that are too cold to explain the documented palaeogeographic distribution of forest and woodland vegetation. In contrast, simulations that include forest vegetation at high latitudes show significantly warmer temperatures that are sufficient to explain the widespread geographic distribution of high-latitude deciduous forests. These warmer temperatures result from decreased albedo and feedbacks between the land surface and adjacent oceans. Prescribing a realistic distribution of palaeovegetation in model simulations produces the best agreement between simulated climate and the geologic record of palaeoclimatic indicators. Positive feedbacks between high-latitude forests, the atmosphere, and ocean contributed significantly to highlatitude warming during the latest Cretaceous and imply that high-latitude forest vegetation was an important source of polar warmth during other warm periods of geologic history.
ABSTRACT A b s t r a c t In 1981 orth et al. (orth et al. 1981) provided the first micropaleontol... more ABSTRACT A b s t r a c t In 1981 orth et al. (orth et al. 1981) provided the first micropaleontological evidence for terrestrial mass-mortality at the Cretaceous-Tertiary (or K-T) boundary associated with the impact of a large bolide on Earth. Five years later WoLfe and UpchUrch (WoLfe & UpchUrch 1986; WoLfe & UpchUrch, 1987a) published corroborative evidence from leaf fossils and proposed that long-term increases in precipitation, and possibly temperature, were also associated with the K-T boundary impact event. Over the subsequent two decades numerous palynological and paleobotanical studies have corroborated early evidence for mass mortality at the K-T boundary in North America and other regions of the world, refined interpretations, and suggested additional long-term environmental changes associated with the terminal Cretaceous event. In this paper we review what we consider to be some of the more important paleobotanical and palynological literature for the K-T boundary of North America and evaluate hypothesized climatic changes. Patterns of change in species diversity and patterns of life form dominance in the pollen and leaf records are consis-tent with a reduction in solar radiation over a period of one year to more than a century by a global cloud of dust and/or sulfate aerosols resulting from an impact at the K-T boundary. However, limited evidence exists for associated freezing temperatures or global wildfires. Changes in the physiognomy of leaf fos-sils, plant communities, sedimentary facies, and paleosols provide evidence for up to a four-fold increase in mean annual precipitation after the K-T boundary that may have lasted for >1 million years. Evidence from leaf margin analysis for an early Paleocene cooling of ~5 °C is restricted to the northern Western Interior and is contradicted by evidence for no temperature change or a temperature increase. Multivariate analysis of foliar physiognomy (CLAMP) suggests a temperature increase of as much as 9 °C. Preliminary evidence for a four-fold or greater increase in atmospheric pCO 2 across the K-T boundary (to >2300 ppm) is consistent with a proposed warming of 9 °C during the early Paleocene, based on the range of sensitivity of Earth-system models to increased pCO 2 . Biogeochemical modeling indicates that a one-year period of darkness, with the lower temperatures and partial biomass burning proposed by some authors, would be sufficient to shut down photosynthesis and significantly reduce terrestrial biomass. Long lasting (10 2 to 10 6 yr) increases in precipitation, temperature, and pCO 2 created favorable environmental conditions for the recovery of net primary productivity and terrestrial biomass. This may help explain why plants at the K-T boundary, while experiencing high extinction at the level of species regionally, experienced relatively little extinction at the level of genus and family, and why the K-T mass extinction event is more pronounced in the marine realm.
Proceedings of The Royal Society B: Biological Sciences, Mar 22, 2015
Despite more than a century of research, some key aspects of habitat preference and ecology of th... more Despite more than a century of research, some key aspects of habitat preference and ecology of the earliest angiosperms remain poorly constrained. Proposed growth ecology has varied from opportunistic weedy species growing in full sun to slow-growing species limited to the shaded understorey of gymnosperm forests. Evidence suggests that the earliest angiosperms possessed low transpiration rates: gas exchange rates for extant basal angiosperms are low, as are the reconstructed gas exchange rates for the oldest known angiosperm leaf fossils. Leaves with low transpirational capacity are vulnerable to overheating in full sun, favouring the hypothesis that early angiosperms were limited to the shaded understorey. Here, modelled leaf temperatures are used to examine the thermal tolerance of some of the earliest angiosperms. Our results indicate that small leaf size could have mitigated the low transpirational cooling capacity of many early angiosperms, enabling many species to survive in full sun. We propose that during the earliest phases of the angiosperm leaf record, angiosperms may not have been limited to the understorey, and that some species were able to compete with ferns and gymnosperms in both shaded and sunny habitats, especially in the absence of competition from more rapidly growing and transpiring advanced lineages of angiosperms.
AGU Fall Meeting Abstracts, Dec 1, 2011
International Journal of Plant Sciences, 2018
Premise of research. Over the past 3 decades, angiosperm woods have been reported from the Campan... more Premise of research. Over the past 3 decades, angiosperm woods have been reported from the Campanian to the Maastrichtian of southern Laramidia, including Coahuila and Chihuahua, Mexico; Big Bend National Park, Texas; and the San Juan Basin, New Mexico. Recent investigations of the upper Campanian (76.5 to >72.5 Ma) Jose Creek Member of the McRae Formation, south-central New Mexico, indicate an abundance of well-preserved silicified woods, representing one of the most diverse Cretaceous wood floras in the world. In this report, we describe four new angiosperm wood types. Methodology. The fossil woods described here were collected from the upper Campanian of south-central New Mexico, along the northeastern flank of the Caballo Mountains and in the adjacent Cutter Sag, and were studied using thin sections. The potential affinities of these McRae woods were determined by comparison with fossil and extant woods. Pivotal results. The woods reported here comprise one magnoliid and three eudicots with varying levels of comparability to extant taxa. Laurinoxylon rennerae sp. nov. belongs to Lauraceae and has a combination of features found in multiple extant genera variously referred to as Cinnamomeae Nees, Laureae Maout & Decaisne, or Lauroideae Burnett/core Lauraceae. Turneroxylon newmexicoense gen. et sp. nov. is a eudicot with many similarities to Dilleniaceae but differs in having narrower rays. Mcraeoxylon waddellii gen. et sp. nov. has a suite of features seen in several families of Malpighiales, Myrtales, and Oxalidales. McRae angiosperm wood type 1 has a suite of features found in genera of Dilleniales, Ericales, and Malpighiales. Conclusions. All wood types, with the exception of M. waddellii, have minimum axis diameters of >10 cm (12–50 cm), indicating that they represent trees. This reinforces previous evidence for the presence of small to large angiosperm trees in the Jose Creek Member and underscores the importance of woody angiosperms in vegetation of the southern Western Interior during the Campanian-Maastrichtian.
Geological Society of America Bulletin, 2017
The Laramide orogeny is a classic yet controversial mountain-building event that resulted, in the... more The Laramide orogeny is a classic yet controversial mountain-building event that resulted, in the southwest United States, in uplifts, sedimentation, and magmatism that can be used to constrain the onset of this event in the region and expand our knowledge of Late Cretaceous to Paleogene tectonism. The McRae Formation marks the onset of deposition in the Laramide Love Ranch Basin, which was located to the northeast of the west-northwest-trending coeval Rio Grande uplift in south-central New Mexico, but its age is not well constrained. A previously published late Maastrichtian age for the McRae Formation was based on the presence of dinosaur bones in the upper of two members of the formation. We obtained new U-Pb dates from one dacite clast and three ash-fall tuffs from the lower Jose Creek Member and from one ash-fall tuff from the lower part of the overlying Hall Lake Member of the McRae Formation. The clast yielded a date of 75.0 ± 1.1 Ma, whereas the ages of the tuffs, in ascending stratigraphic order, are 74.
Systematic Botany, 2011
Vie describe in detail the foliar architecture of extant Nelumbo and propose a new genus, Exnclum... more Vie describe in detail the foliar architecture of extant Nelumbo and propose a new genus, Exnclumbites Estrada-Ruiz, Upchurch, Wolfe & Cevallos-Ferriz, for recently discovered leaf macrofossils from the Upper Cretaceous (Campanian-Maastrichtian) Olmos Formation of Coahuila, Mexico and Jose Creek Member of the McRae Formation of south-central New Mexico, U. S. A. The fossils described here consist of centrally peltate leaves with 12-13 actinodromous primary veins that terminate in broad glandular teeth of the chloranthoid type. No secondary veins are present on the midvein, and tertiary veins are organized in an alternate percurrent to reticulate pattern. Areolation is of variable shape with four to six sides. The fossil leaves are placed within Nelumbonaceae on the basis of their orbicular shape and centrally peltate organization, the presence of a funnel-form lamina, and especially the absence of secondary venation along the midvein, but are interpreted to be more primitive than extant Neiumbo In having no central disk, a smaller number of primary veins, less highly organized tertiary venation, and predominantly non-hexagonal areolation. The presence of chloranthoid teeth in the fossils is consistent with suggestions that the chloranthoid tooth type is basal to both Proteales and eudicots as a whole. The newly described leaves add to a growing diversity of plant macrofossils from the Cretaceous that are more closely related to Nelumbo than any other extant genus, but are more primitive in their vegetative and reproductive morphology.
American Journal of Botany, Feb 1, 1984
Angiosperm leaf cuticles from the oldest part of the Potomac Group reinforce previous paleobotani... more Angiosperm leaf cuticles from the oldest part of the Potomac Group reinforce previous paleobotanical evidence for a Cretaceous flowering plant diversification. Dated palynologically as Zone I of Brenner (Aptian?), these remains show a low structural diversity compared to later Potomac Group and modern angiosperms. All cuticle types conform to a single plan of stomatal construction that is unusual in its extraordinary plasticity: both the number of subsidiary cells and their arrangement vary greatly on a single epidermis, such that the stomata might be classified as paracytic, anomocytic, laterocytic, and intermediate. Such stomatal diversity is uncommon in extant angiosperms but is known from a few Magnoliidae. Many species possess secretory cells comparable to the oil cells of modern Magnoliidae, and a few show the bases of probable uniseriate hairs. None of the cuticle types can be assigned to a single modern family, but several show similarities with Chloranthaceae and Illiciales. These results support the concept that subclass Magnoliidae includes some of the most primitive living angiosperms.
Palaeogeography, Palaeoclimatology, Palaeoecology, 1987
Analyses of physiognomy of Late Cretaceous leaf assemblages and of structural adaptations of Late... more Analyses of physiognomy of Late Cretaceous leaf assemblages and of structural adaptations of Late Cretaceous dicotyledonous woods indicate that megathermal vegetation was an open-canopy, broad-leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year, with a moderate increase at about 40-45CN. Many dicotyledons were probably large, massive trees, but the tallest trees were evergreen conifers. Megathermal climate extended up to paleolatitude 45-50°N. Mesothermal vegetation was at least partially an open, broad-leaved evergreen woodland (perhaps a mosaic of woodland and forest), but the evapotranspirational stress was less than in megathermal climate. Some dicotyledons were large trees, but most were shrubs or small trees; evergreen conifers were the major tree element. Some mild seasonality is evidenced in mesothermal woods; precipitational levels probably varied markedly from year to year. Northward of approximately paleolatitude 65°N, evergreen vegetation was replaced by predominantly deciduous vegetation. This replacement is presumably related primarily to seasonality of light. The southern part of the deciduous vegetation probably existed under mesothermal climate. Comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational-climatic patterns suggested from North American data. Limited data from equatorial regions suggest low rainfall. Late Cretaceous climates, except probably those of the Cenomanian, had only moderate change through time. Temperatures generally appear to have warmed into the Santonian, cooled slightly into the Campanian and more markedly into the Maastrichtian, and then returned to Santonian values by the late Maastrichtian. The early Eocene was probably warmer than any period of the Late Cretaceous. Latitudinal temperature gradients were lower than at present. For the Campanian and Maastrichtian, a gradient of about 0.3' C/1 ° latitude is inferred. Equability was high: a mean annual range of temperature of about 8°C is inferred for paleolatitude 51-56°N during the Campanian. Most Late Cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation. A brief, low-temperature excursion and a major, long-lasting increase in precipitation occurred at the Cretaceous Tertiary boundary. In megathermal climates, these events selected for plants that could exist in rainforest environments. In mesothermal climates, deciduousness and concomitant structural adaptations were selected. The events at the Cretaceous-Tertiary boundary had a major and long-lasting impact on the evolution of land plants and their ecosystems. Low precipitation at low to middle Late Cretaceous latitudes is suggested to be the result of high levels of atmospheric CO2, which, in turn, are probably related to inability of warm, saline oceans to store large amounts of carbon. Conditions appear to have rapidly changed at the Cretaceous Tertiary boundary, when oceanic circulation and stratification may have been fundamentally altered. After the boundary, the oceans were apparently able to store much greater amounts of carbon, and the oceans withdrew large amounts of CO 2 from the atmosphere. In turn, more precipitation fell at low to middle latitudes; the resulting high-biomass vegetation formed a second major carbon reservoir to keep atmospheric CO2 low relative to the Late Cretaceous. Changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean-atmosphere system.
New Mexico Geological Society Annual Spring Meeting, Apr 24, 2015
The Upper Cretaceous McRae Formation was deposited in the Laramide (latest Cretaceous-Eocene) Lov... more The Upper Cretaceous McRae Formation was deposited in the Laramide (latest Cretaceous-Eocene) Love Ranch basin and is most widely exposed in the Cutter Sag, northeast of Truth or Consequences, south-central New Mexico. Primarily fluvial in origin, the McRae Formation is divided into the lower Jose Creek Member, which contains leaf fossil sites and at least 50 petrified stumps in growth positions, and the upper Hall Lake Member. A Maastrichtian age for the McRae has been based on the presence of two dinosaur fossils, which have poorly constrained stratigraphic positions in the Hall Lake Member because of faulting and Quaternary cover. Presented here are U-Pb-zircon dates from previously undated ash fall tuffs, including three in the middle and upper part of the Jose Creek Member and the "pink" tuff located nine meters above the base of the Hall Lake Member. The fine-grained, felsic tuffs were dated using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS). Between 11 and 17 zircons in each sample were dated, and no inherited cores were observed or analyzed. The stratigraphically lowest tuff yielded the oldest 206 Pb/ 238 Pb age (75.2 Ma) and the highest tuff yielded the youngest age (74.0 Ma), with the intermediate-level tuffs yielding ages of 74.7 Ma and 74.9 Ma. However, all four tuffs have the same age within the two-sigma uncertainty level (0.5-1.5 Ma). Taking into consideration the maximum uncertainties, the tuffs erupted between 73.0 and 76.7 Ma, making them late Campanian in age. These new dates for the lower McRae Formation indicate that the onset of Laramide sedimentation in the Love Ranch basin was contemporaneous with that in the Laramide Ringbone and San Juan basins in New Mexico, and they provide a more accurate comparison of the Jose Creek paleoflora with coeval paleoflora elsewhere in the Western Interior of North America.
Nature, Nov 1, 1986
... Vegetation, climatic and floral changes at the Cretaceous-Tertiary boundary. Jack A. Wolfe &a... more ... Vegetation, climatic and floral changes at the Cretaceous-Tertiary boundary. Jack A. Wolfe & Garland R. Upchurch Jr. US Geological Survey, MS-919, Box 25046, Federal Center, Denver, Colorado 80225, USA. ... 29. Brown, RW Prof. Pap. US geol. ... 39. Middleton, MD thesis, Univ. ...
Journal of Systematic Palaeontology, 2018
Phylogenetic analyses imply that monocots were a key group in the early radiation of angiosperms,... more Phylogenetic analyses imply that monocots were a key group in the early radiation of angiosperms, yet they are much rarer than other major clades in the Early Cretaceous macrofossil record. Here we describe a well-preserved leaf and several inflorescences related to the near-basal monocot family Araceae and abundant monocot leaves of uncertain affinities from two latest Albian localities in northeastern Spain. Orontiophyllum ferreri sp. nov. has a multistranded midrib, several orders of parallel-pinnate veins, two orders of transverse veins, and paracytic-oblique stomata. This suite of characters (but with both anomocytic and paracytic-oblique stomata) is characteristic today of Orontium in the near-basal araceous subfamily Orontioideae, and later Cretaceous and early Cenozoic leaves assigned to Orontiophyllum have similar architecture. Sedimentology and anatomy suggest a (semi)aquatic ecology. Other monocot leaves at the same locality are linear and parallel-veined but have similar stomata. Although anomocytic stomata have been proposed as ancestral in monocots, O. ferreri, the associated linear leaves, Albian-Cenomanian cuticles from Australia and Portugal, and extant data are consistent with the hypothesis that variable paracytic-oblique stomata are ancestral. Turolospadix bogneri gen. et sp. nov., from the other locality, includes spadices of ebracteate flowers with four tepals, a central gynoecium, and a long stipe (vs a spathe attached just below the fertile zone as in most Araceae). Phylogenetic analyses indicate that the character combinations seen in O. ferreri and T. bogneri are ancestral for Araceae, and they could be either sister to Araceae or nested within a basal grade of the family. Together with fossils from the Aptian-Albian of Brazil and Portugal, the Spanish fossils indicate that Araceae are among the oldest extant monocot families, but they were associated with diverse linear-leaved monocots of uncertain affinities.
Proceedings of the National Academy of Sciences of the United States of America, May 2, 2011
Paleobiology, 2011
The photosynthetic gas exchange capacities of early angiosperms remain enigmatic. Nevertheless, m... more The photosynthetic gas exchange capacities of early angiosperms remain enigmatic. Nevertheless, many hypotheses about the causes of early angiosperm success and how angiosperms influenced Mesozoic ecosystem function hinge on understanding the maximum capacity for early angiosperm metabolism. We applied structure-functional analyses of leaf veins and stomatal pore geometry to determine the hydraulic and diffusive gas exchange capacities of Early Cretaceous fossil leaves. All of the late Aptian-early Albian angiosperms measured possessed low vein density and low maximal stomatal pore area, indicating low leaf gas exchange capacities in comparison to modern ecologically dominant angiosperms. Gas exchange capacities for Early Cretaceous angiosperms were equivalent or lower than ferns and gymnosperms. Fossil leaf taxa from Aptian to Paleocene sediments previously identified as putative stem-lineages to Austrobaileyales and Chloranthales had the same gas exchange capacities and possibly leaf water relations of their living relatives. Our results provide fossil evidence for the hypothesis that high leaf gas exchange capacity is a derived feature of later angiosperm evolution. In addition, the leaf gas exchange functions of austrobaileyoid and chloranthoid fossils support the hypothesis that comparative research on the biology of living basal angiosperm lineages reveals genuine signals of Early Cretaceous angiosperm ecophysiology.
Proceedings of the National Academy of Sciences of the United States of America, Aug 1, 1987
Analyses of leaf megafossil and dispersed leaf cuticle assemblages indicate that major ecologic d... more Analyses of leaf megafossil and dispersed leaf cuticle assemblages indicate that major ecologic disruption and high rates of extinction occurred in plant communities at the Cretaceous-Tertiary boundary in the Raton Basin. In diversity increase, the early Paleocene vegetational sequence mimics normal short-term ecologic succession, but on a far longer time
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Papers by Garland Upchurch