Kirk Johnson

• PhD
• Managing Director at Smithsonian Institution

Cycads are ancient seed plants (gymnosperms) that emerged by the early Permian. Although they were common understory flora and food for dinosaurs in the Mesozoic, their abundance declined markedly in the Cenozoic. Extant cycads persist in restricted populations in tropical and subtropical habitats and, with their conserved morphology, are often cal...

Over the past three centuries, people have collected objects and specimens and placed them in natural history museums throughout the world. Taken as a whole, this global collection is the physical basis for our understanding of the natural world and our place in it, an unparalleled source of information that is directly relevant to issues as divers...

Integration of the world’s natural history collections can provide a resource for decision-makers

Integration of the world's natural history collections can provide a resource for decision-makers.

Over the past three centuries, people have collected objects and specimens and placed them in natural history museums throughout the world. Taken as a whole, this global collection is the physical basis for our understanding of the natural world and our place in it, an unparalleled source of information that is directly relevant to issues as divers...

[This corrects the article DOI: 10.1371/journal.pone.0261397.].

The Chicxulub bolide impact has been linked to a mass extinction of plants at the Cretaceous—Paleogene boundary (KPB; ∼66 Ma), but how this extinction affected plant ecological strategies remains understudied. Previous work in the Williston Basin, North Dakota, indicates that plants pursuing strategies with a slow return-on-investment of nutrients...

The Upper Cretaceous (Campanian Stage) Kaiparowits Formation of southern Utah, USA, preserves abundant plant, invertebrate, and vertebrate fossil taxa. Taken together, these fossils indicate that the ecosystems preserved in the Kaiparowits Formation were characterized by high biodiversity. Hundreds of vertebrate and invertebrate species and over 80...

Leaves are the most abundant and visible plant organ, both in the modern world and the fossil record. Identifying foliage to the correct plant family based on leaf architecture is a fundamental botanical skill that is also critical for isolated fossil leaves, which often, especially in the Cenozoic, represent extinct genera and species from extant...

Presentation of the 2019 Harrell L. Strimple Award of the Paleontological Society to James L. Goedert - Volume 94 Issue 5 - Kirk R. Johnson

Geological samples must be archived for all if we are to solve the riddles of Earth’s complex history. Geological samples must be archived for all if we are to solve the riddles of Earth’s complex history.

The Cretaceous–Paleogene (K–Pg) boundary interval represents one of the most significant mass extinctions and ensuing biotic recoveries in Earth history. Earliest Paleocene fossil mammal faunas corresponding to the Puercan North American Land Mammal Age (NALMA) are thought to be highly endemic and potentially diachronous, necessitating precise chro...

Terrestrial record of recovery The extinction that occurred at the end of the Cretaceous period is best known as the end of the nonavian dinosaurs. In theory, this paved the way for the expansion of mammals as well as other taxa, including plants. However, there are very few direct records of loss and recovery of biotic diversity across this event....

The world's natural history collections represent a vast repository of information on the natural and cultural world, collected over 250 years of human exploration, and distributed across institutions on six continents. These collections provide a unique tool for answering fundamental questions about biological, geological and cultural diversity an...

The morphology of the early ontogenetic stages of cycad foliage may help resolve the relationships between extinct to extant cycad lineages. However, prior to this study, fossil evidence of cycad seedlings was not known. We describe a compression fossil of cycad eophylls with co-occurring fully developed leaves of adult specimens from the early Pal...

The Cretaceous-Paleogene (K-Pg) boundary interval represents one of the most significant mass extinctions and ensuing biotic recoveries in Earth history. Earliest Paleocene fossil mammal faunas corresponding to the Puercan North American Land Mammal Age (NALMA) are thought to be highly endemic and potentially diachronous, necessitating precise chro...

Taphonomic processes may filter in a biased manner the tiny fraction of leaves preserved as fossils. A common perception is that large leaves are underrepresented; this is based both on intuition (large leaves are more likely to break apart) and some observations of extant vegetation. Characterizing leaf area correctly is critical for reconstructin...

Proxy estimates of atmospheric CO2 are necessary to reconstruct Earth's climate history. Confidence in paleo-CO2 estimates can be increased by comparing results from multiple proxies at a single site, but so far this strategy has been implemented only for marine-based techniques. Here we present CO2 estimates for the well-studied early Paleocene Ca...

In this paper, I discuss issues of time resolution and time-averaging in fossil megafloras from Late Cretaceous (Cenomanian) to Oligocene age. The sites are predominantly from North America with some examples from other continents. The purpose of this paper is to explicate the methods used to resolve the age and duration of fossil floras and to dis...

Much of the current debate over the Cretaceous/Paleogene (K/Pg) mass extinction event revolves around the mechanism and tempo of the extinction of terrestrial vertebrates: gradual versus catastrophic. Hundreds of known fossil localities, otherwise floating data points, need to be time-correlated and tied to a biostratigraphic range for each taxa in...

Premise of research. A large number of floating aquatic aroid fossils have been recovered from pond sediments in the Hell Creek Formation (Upper Cretaceous) of South Dakota, providing valuable new data about aquatic vegetation of the uppermost Cretaceous, that are used to describe a new species of the genus Cobbania, and to evaluate associated repr...

The Cretaceous/Paleogene (K/Pg) mass extinction event is one of the best-studied mass extinction events. However there is still debate regarding the mechanism and tempo of the extinction for terrestrial vertebrates, particularly whether nonavian dinosaurs went extinct gradually or catastrophically. Here we use a high resolution GPS survey and GIS t...

The EARTHTIME Initiative was conceived by Sam Bowring and Doug Erwin in 2001 as a response to the advances being made in methods used to quantify time in the stratigraphic record. In the preceding decades the precision and resolution of radio-isotopic dating methods had improved significantly in parallel with increasingly quantitative analysis of t...

First a Discovery, Then Digging Like Mad Scalpel. Knife. Shovel. A bulldozer’s blade Cutting-edge science happens at a variety of scales, from the individual and intimate to the large-scale and collaborative. The publication of a special issue of Quaternary Research in Nov. 2014 dedicated to the scientific findings of the “Snowmastodon Project” hi...

Museums of science and natural history serve a critical role in preserving our past and educating the public about advances in our understanding of the world around us. Yet few appreciate the degree to which these seemingly timeless institutions have transformed to meet new challenges and evolving expectations. Kirk R. Johnson, director of the Smit...

In North America, terrestrial records of biodiversity and climate change that span Marine Oxygen Isotope Stage (MIS) 5 are rare. Where found, they provide insight into how the coupling of the ocean-atmosphere system is manifested in biotic and environmental records and how the biosphere responds to climate change. In 2010-2011, construction at Zieg...

Studies of terrestrial biotic and environmental dynamics of Marine Oxygen Isotope Stage (MIS) 5, also called the Last Interglacial Period, provide insight into the effects of long-term climate change on Pleistocene ecosystems. In North America, however, there are relatively few fossil sites that definitively date to MIS 5. Even fewer contain multip...

The few previously reported values of 187Os/188Os ratios from non-marine K–Pg boundary sections are distinctly higher than the range of 187Os/188Os ratios measured in chondrites and the range of ratios predicted by models of physical mixing between chondrites and upper crust. Here, Re–Os data from the West Bijou continental K–Pg boundary site, loca...

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 s...

Plant and associated insect-damage diversity in the western U.S.A. decreased significantly at the Cretaceous-Paleogene (K-Pg) boundary and remained low until the late Paleocene. However, the Mexican Hat locality (ca. 65 Ma) in southeastern Montana, with a typical, low-diversity flora, uniquely exhibits high damage diversity on nearly all its host p...

The geologic setting of the Ziegler Reservoir fossil site is somewhat unusual — the sediments containing the Pleistocene fossils were deposited in a lake on top of a ridge. The lake basin was formed near Snowmass Village, Colorado when a glacier flowing down Snowmass Creek Valley became thick enough to overtop a low point in the eastern valley wall...

AGATHIS is an iconic genus of large, ecologically important, and economically valuable conifers that range over lowland to upper montane rainforests from New Zealand to Sumatra. Exploitation of its timber and copal has greatly reduced the genus's numbers. The early fossil record of Agathis comes entirely from Australia, often presumed to be its are...

The Denver Museum of Nature & Science Annals (ISSN 1948-9293 [print], ISSN 1948-9307 [online]) is an open-access, peer-reviewed scientific journal publishing original papers in the fields of anthropology, geology, paleontology, botany, zoology, space and planetary sciences, and health sciences. Papers are either authored by Museum staff, associates...

During the summer of 2011, the Bighorn Basin Coring Project (BBCP) recovered over 900m of overlapping core from 3 different sites in late Paleocene to early Eocene fluvial deposits of northwestern Wyoming. BBCP cores are being used to develop high-resolution proxy records of the Paleocene–Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (...

Unlabelled: • Premise of the study: The early Eocene Laguna del Hunco caldera-lake paleoflora (ca. 52 Ma) from Chubut Province, Argentina, is notably diverse and includes many conifer and angiosperm lineages that are extinct in South America but extant in Australasian rainforests. No ferns have been previously described from Laguna del Hunco. We...

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 th...

We analyzed paleomagnetic samples and documented the stratigraphy from two sections near Miles City, Montana to determine the geomagnetic polarity stratigraphy and to constrain the age and duration of the Lebo and Tongue River Members of the Fort Union Formation in the northeastern Powder River Basin. The resulting polarity sequence can be correlat...

Strict consensus of 2 most parsimonious trees (length 288 steps, CI 0.69, RI 0.79) based on a phylogenetic analysis of 160 molecular sequence and indel characters for 17 extant taxa. (TIFF)

Strict consensus of 25 most parsimonious trees (length 85 steps, CI 0.62, RI 0.79) based on a phylogenetic analysis of 43 morphological characters for 17 extant taxa and the Patagonian fossils. (TIFF)

Morphological dataset. (TXT)

Combined morphology and molecular dataset (TXT)

Terminal names used in this study matched to terminal names used in the molecular analysis of Udovicic & Ladiges. (DOC)

Morphological character list. Characters and character states for the morphological matrix. (DOC)

The evolutionary history of Eucalyptus and the eucalypts, the larger clade of seven genera including Eucalyptus that today have a natural distribution almost exclusively in Australasia, is poorly documented from the fossil record. Little physical evidence exists bearing on the ancient geographical distributions or morphologies of plants within the...

Early Eocene land bridges allowed numerous plant and animal species to cross between Europe and North America via the Arctic. While many that were suited to prevailing cool Arctic climates would have been able to cross throughout much of this period, others would have found dispersal opportunities only during limited intervals when their requiremen...

Early Eocene land bridges allowed numerous plant and animal species to cross between Europe and North America via the Arctic. While many species suited to prevailing cool Arctic climates would have been able to cross throughout much of this period, others would have found dispersal opportunities only during limited intervals when their requirements...

• Paleobotanists have long used models based on leaf size and shape to reconstruct paleoclimate. However, most models incorporate a single variable or use traits that are not physiologically or functionally linked to climate, limiting their predictive power. Further, they often underestimate paleotemperature relative to other proxies. • Here we qua...

The Pampa de Jones fossil site, a stratigraphically isolated roadcut near the northeastern shore of Nahuel Huapi Lake in Neuquén Province, Argentina, holds a rich fossil biota including a macroflora, a microflora, insects, and most famously, an ontogenetic series of pipid frogs. The site exposes tuffaceous mudstone and sandstone beds of probable la...

The Letters by Archibald et al. , Keller et al. , and Courtillot and Fluteau question our conclusion that the Cretaceous-Paleogene mass extinction was caused by the asteroid impact at Chicxulub. All three Letters stress that Deccan flood basalt volcanism played a major role in the extinction. Keller

The cause and killing mechanisms for the two largest known extinctions in Earth history, the K/T and P/Tr, is the subject of much debate and controversy.

The Cretaceous-Paleogene boundary ~65.5 million years ago marks one of the three largest mass extinctions in the past 500 million years. The extinction event coincided with a large asteroid impact at Chicxulub, Mexico, and occurred within the time of Deccan flood basalt volcanism in India. Here, we synthesize records of the global stratigraphy acro...

The 51.9 Ma Laguna del Hunco (LH) and 47.5 Ma Río Pichileufú (RP) floras from Patagonia, Argentina are unusually rich, angiosperm-dominated assemblages with living relatives in the low-latitude West Pacific, neotropics, and temperate southern latitudes. The diverse gymnosperms in these floras are important for Gondwanan biogeographic history and pa...

Marine records of orbitally driven climate cycles have been used to create an astronomically calibrated timescale for the Neogene Period (0-23 Ma). Recent studies have attempted to extend this approach to the Paleogene Period (23-65 Ma), despite various uncertainties related to astronomical solutions this far back, climate sensitivity in a greenhou...

We document evidence of endophytic oviposition on fossil compression/impression leaves from the early Eocene Laguna del Hunco and middle Eocene Rio Pichileufu floras of Patagonia, Argentina. Based on distinctive morphologies and damage patterns of elongate, ovoid, lens-, or teardrop-shaped scars in the leaves, we assign this insect damage to the ic...