Impact Ejecta Found at Paleocene-Eocene Boundary in New Jersey

Impact ejecta at the Paleocene-Eocene boundary

Authors:

Schaller et al

Abstract:

Extraterrestrial impacts have left a substantial imprint on the climate and evolutionary history of Earth. A rapid carbon cycle perturbation and global warming event about 56 million years ago at the Paleocene-Eocene (P-E) boundary (the Paleocene-Eocene Thermal Maximum) was accompanied by rapid expansions of mammals and terrestrial plants and extinctions of deep-sea benthic organisms. Here, we report the discovery of silicate glass spherules in a discrete stratigraphic layer from three marine P-E boundary sections on the Atlantic margin. Distinct characteristics identify the spherules as microtektites and microkrystites, indicating that an extraterrestrial impact occurred during the carbon isotope excursion at the P-E boundary.

discerning the Different Species of Cretaceous-Paleogene Multituberculate Genus Mesodma

Species Discrimination of Co-Occurring Small Fossil Mammals: A Case Study of the Cretaceous-Paleogene Multituberculate Genus Mesodma

Authors:

Smith et al

Abstract:

The mammalian fossil record is largely composed of isolated teeth and tooth-bearing elements. In vertebrate microfossil assemblages with closely related, co-occurring species of mammals, it can be difficult to identify isolated teeth to species level because morphological differences among species may be slight and based on a single tooth position. Here we investigate the utility of the allegedly diagnostic lower fourth premolar (p4) for species-level identification in the genus Mesodma (Multituberculata, Neoplagiaulacidae). We conducted linear and geometric morphometrics on 86 p4s representing four Cretaceous-Paleogene (K-Pg) species of Mesodma that are common in deposits of the western interior of North America. Although Mesodma has been extensively discussed in the literature, these four species overlap considerably in p4 size and shape, making species-level identifications challenging. Using linear measurements, landmarks, and semilandmarks, we quantified p4 size and shape to understand morphological variation across the genus and uncover practical sources of morphological differentiation among the species represented here. Our results indicate (1) size is more important than shape for identifying p4s of Mesodma species; p4 shape varies across the genus, but cannot be used alone to identify isolated p4s to species; (2) M. garfieldensis and M. thompsoni cannot be distinguished from each other using p4 size or shape; we therefore subsume M. garfieldensis within M. thompsoni; and (3) M. formosa increased in size across the K-Pg boundary. In light of these results, we recommend that taxonomic diagnoses relying on isolated teeth incorporate quantitative analyses of morphology whenever possible to increase the accuracy of species-level identifications and paleofaunal studies that employ them.

The Inner ear of Paleocene Paleogene Ungulate Protungulatum

The inner ear of Protungulatum (Pan-Euungulata, Mammalia)

Authors:

Orliac et al

Abstract:

We present new anatomical details about the bony labyrinth of Protungulatum based on micro CT-scan investigation of an isolated petrosal bone retrieved at the Puercan locality of Bug Creek Anthills and referred to Protungulatum sp. The exceptional state of preservation of the specimen allowed us to reconstruct the very fine details of the inside of the petrosal bone, including the bony labyrinth, the innervation of the vestibule and the innervation and vasculature of the cochlea. Estimation of the auditory capability of Protungulatum based on cochlear morphology indicate that Protungulatum was specialized for high-frequency hearing, with estimated low frequency limits above 1 KHz. Comparisons with Late Cretaceous non-placental eutherians and with early Tertiary pan-euungulates indicate that the bony labyrinth of Protungulatum is closer in general morphology to Mesozoic forms (low coiling and low aspect ratio of the cochlea, posterior orientation of the common crus, dorsal outpocketing of the cochlear fossula), and shares only a few characters with pan-euungulate and euungulate taxa. Interestingly, the bony labyrinth of Protungulatum also shares some morphological features with South American notoungulates and litopterns recently described from Itaboraí, Brazil. These new observations provide new morphological features of potential phylogenetic interest.

Purgatorius pinecreeensis: A New Omnivorous Species of Purgatoriid Plesiadapiform Primate From Paleocene Paleogene Saskatchewan, Canada

A new species of the basal plesiadapiform Purgatorius (Mammalia, Primates) from the early Paleocene Ravenscrag Formation, Cypress Hills, southwest Saskatchewan, Canada: further taxonomic and dietary diversity in the earliest primates

Authors:

Scott et al

Abstract:

The fossil record of the earliest primates, purgatoriid plesiadapiforms, has become increasingly well documented during the past two decades, but their dietary preferences remain poorly understood. While the available evidence, which consists mostly of isolated teeth and incomplete jaws with teeth, suggests that purgatoriids were insectivorous to omnivorous, we describe here a new species of Purgatorius, Purgatorius pinecreeensis sp. nov., that extends the range of purgatoriid dental disparity toward greater omnivory than had been known before. Purgatorius pinecreeensis sp. nov., from the early Paleocene (Puercan) Ravenscrag Formation of southwestern Saskatchewan, differs from other species of Purgatorius in having slightly lower crowned teeth with a lower trigonid relative to talonid, blunter and more swollen major cusps, more transverse lower molar paracristids, and m3 with a more robustly developed posterior lobe. Taken together, these specializations enhanced the capacity for crushing and grinding at the expense of orthal shear, and represent the first instance of a modest degree of bunodonty in the family. The discovery of P. pinecreeensis sp. nov., along with other recently reported basal plesiadapiforms from the Puercan and Torrejonian of the northern Western Interior, lends additional support to the notion of a significant primate radiation soon after the Cretaceous–Paleogene extinction event.

Alcidedorbingya inopinata: the Oldest Known Pantodont Eutherian From Danian Paleocene Paleogene Bolivia

Alcidedorbignya inopinata, a basal pantodont (Placentalia, Mammalia) from the early Palaeocene of Bolivia: anatomy, phylogeny and palaeobiology

Authors:

Muizon et al

Abstract:

The study of exceptional remains (several skulls and a complete skeleton) of a 65 MY old placental mammal from Bolivia, provides a good understanding of the cranial anatomy, biology and evolution of the first mammals which lived in South America just after the large dinosaurs disappeared, 66 MY ago. This mammal is a Pantodont named Alcidedorbingya, in honour of Alcide d’Orbigny, famous naturalist voyager of the Museum during the XIXth century. Pantodonts constitute a group of mammals from the beginning of the Tertiary, which disappeared 40 MY ago. They lived essentially in northern continents (China, North America, and Europe). They were of small (rabbit) to large size (cow) and were omnivorous. Alcidedorbignya is the only austral pantodont, the oldest, and the smallest known.

The CT scanner of the MNHN allows the authors, a reconstruction of the arterial and venous passageways of the basicranium, thus approaching an ancestral pattern of blood circulation of the first placental mammals. The complete skeleton of Alcidedorbignya, was also CT scanned, allowing virtual reconstructions of several life positions. Alcidedorbignya was terrestrial, but also capable of a bipedal position on its hind limbs and of climbing as is observed in the Recent squirels. This ability allowed Alcidedorbignya to escape the numerous crocodiles, which lived with it in a large Amazonian-like alluvial plain.

These results have been obtained thanks to the unprecedented completeness of the specimens, taking into account their geological age, in which the most common remains are only isolated teeth.

Evidence of Cold Snaps in the Paloecene Paleogene Paleoclimate of Antarctica

The Paleocene of Antarctica: Dinoflagellate cyst biostratigraphy, chronostratigraphy and implications for the palaeo-Pacific margin of gondwana

Authors:

Bowman et al

Abstract:

The Paleocene (66–56 Ma) was a critical time interval for understanding recovery from mass extinction in high palaeolatitudes when global climate was warmer than today. A unique sedimentary succession from Seymour Island (Antarctic Peninsula) provides key reference material from this important phase of the early Cenozoic. Dinoflagellate cyst data from a 376 m thick stratigraphical section, including the Cretaceous–Paleogene boundary, is correlated with biozones from New Zealand, the East Tasman Plateau and southeastern Australia. A detailed age model is suggested for the López de Bertodano (LDBF) and Sobral (SF) formations based on dinoflagellate cyst biostratigraphy and U-Pb dating of zircons, supported by correlated magnetostratigraphy and strontium isotope values from macrofossils. The top of the LDBF is confirmed as latest Maastrichtian to earliest Danian (~ 66.2–65.65 Ma) in age. The overlying SF is mostly Danian in age, with an inferred hiatus near the top overlain by sediments dated as? late Thanetian. Rare Apectodinium homomorphum first appear in the uppermost SF; the first in situ record from Antarctica. The distribution of marine and terrestrial fossils from uppermost Cretaceous to Eocene sediments in Patagonia, Antarctica, New Zealand and Australia required both sea and land connections between these fragments of Gondwana. Fossil evidence and reconstructions of Antarctic palaeogeography and palaeotopography reveals evidence for persistent embayments in the proto-Weddell and Ross Sea regions at this time. We conclude that a coastal dispersal route along the palaeo-Pacific margin of Gondwana could explain the fossil distribution without requiring a transAntarctic strait or closely spaced archipelago. A region in the West to East Antarctic boundary zone, elevated until the early Paleogene, perhaps acted as a site for high elevation ice caps. This supports fossil, geochemical and sedimentological evidence for cold climate intervals and significant sea level falls during the Maastrichtian and Paleocene.

Madagascar's Climate at the end of the Age of Dinosaurs was Wetter Than Previously Thought, Less Seasonal

Madagascar's climate at the K/P boundary and its impact on the island's biotic suite

Authors:

Ohba et al

Abstract:

The K/P boundary, 66 Ma, was a critical time in the history of the planet's biota. On the island of Madagascar, few Late Cretaceous species survived the associated extinction, and distance from the various mainland sources then acted as a strong filter for the number of over-water arrivees. Reconstructing the climate of the early Paleogene is vital for understanding the environments to which new colonizers landed and established a toe-hold on the island. Beginning with a “global” air-sea-coupled climate model simulation using the land–sea distribution at 66 Ma, we used dynamical downscaling to construct a scenario for how the atmospheric and oceanic fluid envelopes washed over and around the Madagascar at the start of the Paleocene. Dynamical downscaling of the global model yields a climate model with much finer resolution. We used this method to reconstruct the habitats for known fossil localities from that general period, better understand the ecological diversity of plants and animals that have been hypothesized to have then been present, and evaluate hypotheses regarding the evolutionary history of lemurs—a vast clade of primates endemic to Madagascar whose last common ancestor dates to this time. Our results show an island with a climate notably different from that of today, but not nearly as arid as others have suggested: the spiny thicket biome did not exist; temperatures were lower; rainfall less seasonal.

Splitter Attack! Late Cretaceous/Paleocene Eutherian Mammals Split, One Recognized at 'Ancestral' to Creodonts

A revision of the Late Cretaceous–Paleocene eutherian mammal Cimolestes Marsh, 1889

Author:

Fox

Abstract:

Cimolestes Marsh is a North American eutherian mammal primarily known from latest Cretaceous deposits in Alberta, Wyoming, Saskatchewan, and Montana. At present, five species of Cimolestes are considered valid, all Lancian in age; they include one of the largest North American Late Cretaceous therian mammals as well as one of the smallest, a size range far exceeding that within other genera of tribosphenic therians contemporary with Cimolestes, such as the leptictoid eutherian Gypsonictops Simpson or genera of alphadontid or pediomyid marsupials. Moreover, the species of Cimolestes display a disparity of dental morphology in addition to size well in excess of interspecific differences within these genera. Given these considerations, Cimolestes is clearly a grade-taxon, uniting species sharing an adaptively subzalambdodont dentition, but showing divergent specializations within this pattern that are inconsistent with monophyly of its presently included species. To correct these imbalances, this paper limits Cimolestes to Cimolestes incisus Marsh and Cimolestes stirtoni Clemens; Cimolestes magnus Clemens and Russell, Cimolestes cerberoides Lillegraven, and Cimolestes propalaeoryctes Lillegraven are reclassified in the new genera Altacreodus, Ambilestes, and Scollardius, respectively. Altacreodus magnus, having a massive shearing dentition, is reconfirmed as showing a relationship to some Tertiary ‘creodonts’ not shared by other species of Lancian cimolestids; Ambilestes cerberoides exhibits a distinctive molar wear pattern that emphasized horizontal grinding, not orthal shear; Scollardius propalaeoryctes, the smallest species in this revision and having hyper-faunivorous molars, was not ancestral to Paleogene Palaeoryctidae, as indicated in part by contradictions in premolar number and morphology.

Evidence of Increased Weathering, Volcanism During Paleocene-Eocene Thermal Maximum

Evidence for weathering and volcanism during the PETM from Arctic Ocean and Peri-Tethys osmium isotope records

Authors:

Dickson et al

Abstract:

Sudden global warming during the Paleocene–Eocene Thermal Maximum (PETM, 55.9 Ma) occurred because of the rapid release of several thousand gigatonnes of isotopically light carbon into the oceans and atmosphere; however, the cause of this release is not well understood. Some studies have linked carbon injection to volcanic activity associated with the North Atlantic Igneous Province (NAIP), while others have emphasised carbon cycle feedbacks associated with orbital forcing. This study presents the osmium isotope compositions of mudrocks that were deposited during the PETM at four locations (one from the Arctic Ocean, and three from the Peri-Tethys). The Os-isotope records all exhibit a shift of similar magnitude towards relatively radiogenic values across the PETM. This observation confirms that there was a transient, global increase in the flux of radiogenic Os from the weathering of continental rocks in response to elevated temperatures at that time. The tectonic effects of NAIP volcanic emplacement near the onset of the PETM is recorded by anomalously radiogenic Os-isotope compositions of PETM-age Arctic Ocean samples, which indicate an interval of hydrographic restriction that can be linked tectonic uplift due to hotspot volcanism in the North Atlantic seaway. The Peri-Tethys data also document a transient, higher flux of unradiogenic osmium into the ocean near the beginning of the PETM, most likely from the weathering of young mafic rocks associated with the NAIP. These observations support the hypothesis that volcanism played a major role in triggering the cascade of environmental changes during the PETM, and highlight the influence of paleogeography on the Os isotope characteristics of marine water masses.

Alluvial response to the Paleocene–Eocene Thermal Maximum

Alluvial response to the Paleocene–Eocene Thermal Maximum climatic event, Polecat Bench, Wyoming (U.S.A.)

Authors:

Kraus et al

Abstract:

The stratigraphic interval spanning the Paleocene–Eocene Thermal Maximum in the northern Bighorn Basin, Wyoming shows changes in the alluvial record that can be tied to a high resolution climate record. The complexity and stratigraphic spacing of paleosols change through the study section. Comparison to the climate record, reconstructed from paleosols, indicates the changes correspond to Paleocene–Eocene Thermal Maximum climatic fluctuations. In particular, the middle of the section contains thick, welded paleosols and thin avulsion deposits that link to times of well-drained floodplains and lower mean annual precipitation. Stratigraphic intervals below and above the main part of the Paleocene–Eocene Thermal Maximum interval correspond to times of less well drained floodplains and higher mean annual precipitation. These strata contain thinner paleosols and thick avulsion deposits.

Differences in paleosol complexity and spacing suggest that sediment flux to the depositional site varied in response to precipitation fluctuations associated with the Paleocene–Eocene Thermal Maximum. Welded paleosols and thin avulsion deposits indicate reduced floodplain accretion during deposition of the middle of the Paleocene–Eocene Thermal Maximum. Intervals with widely spaced paleosols indicate more rapid accretion. We hypothesize that drier episodes associated with warming caused reduced vegetation in source areas and promoted erosion and increased sediment yield. Because precipitation was reduced, much of that sediment was stored in upstream reaches of the fluvial system rather than moving to the depositional basin. Welded paleosols formed because of diminished sediment supply to the basin. With a return to wetter conditions during the recovery phase of the Paleocene–Eocene Thermal Maximum, upstream water flux increased, stored sediment moved to the basin, and vertically spaced, thinner paleosols developed. The results demonstrate how vertical sections of alluvial paleosols can provide information on how climate fluctuated through time and how the fluvial system responded to climate change.

Giant Bird Gastornis Was Herbivorous, Lived in Warm Dry Climate Like Modern Med Islands

Diet and climatic context of giant birds inferred from δ13Cc and δ18Oc values of Late Palaeocene and Early Eocene eggshells from southern France

Authors:

Angst et al

Abstract:

Abundant fragments from eggs laid by giant birds occur in the Palaeocene (Thanetian) and Eocene (Sparnacian) sedimentary deposits of southeastern France. In the Sparnacian, thick eggshell fragments, assigned to the oospecies Ornitholithus arcuatus, correspond to very large bird eggs that were most likely laid by Gastornis. The Thanetian thin eggshell fragments, assigned to Ornitholithus biroi, were presumably laid by a smaller, yet unidentified bird. In order to investigate ecology and environment of these egg-laying birds, stable carbon and oxygen isotope compositions of 125 fossil eggshell fragments were analyzed. After removing samples affected by diagenetic alteration of the calcitic shells, the measured range of δ13Cc values (− 11‰ to − 6‰ V-PDB) is interpreted as reflecting an herbivorous diet for these birds in a context of limited annual precipitation (≈ 500 mm y− 1). Stable oxygen isotope analysis of living ostrich eggshell calcite, along with that of the water extracted from their albumen and yolk, provided evidence to calculate isotopic fractionation factors between both calcite and body water (αcalcite–body water = 1.03041) and between body water and meteoric water (αbw–mw = 1.00399), using δ18O values of local meteoric waters identified as the source of the birds drinking water. Combined with the δ18O values of fossil eggshells, both isotopic fractionations provided calculated δ18O values of meteoric waters in the range − 9.5‰ to − 2.8‰ (V-SMOW) for the Thanetian, and in the range − 8.9‰ to − 1.7‰ (V-SMOW) for the Sparnacian. These large isotopic ranges likely reflect inter-annual temperature variations of the complete year, suggesting a year round egg-laying strategy. Corresponding Mean Air Temperatures (MAT) were comprised between 20 ± 4 °C and 22 ± 4 °C during the Thanetian, and between 23 ± 3 °C and 25 ± 3 °C during the Sparnacian. These giant birds likely lived under a warm and dry climate similar to that prevailing today in western Mediterranean islands.

Evidence of Reduced Export Productivity Supporting Living or Heterogeneous Ocean Hypotheses for KT/K-Pg mass Extinction

Evidence for reduced export productivity following the Cretaceous/Paleogene mass extinction

Authors:

Esmeray-Senlet et al

Abstract:

The Cretaceous/Paleogene (K/Pg) mass extinction was associated with a collapse in the carbon isotopic (δ13C) gradient between planktonic and benthic foraminifera and a decrease in bulk carbonate δ13C values. These perturbations have been explained by several hypotheses: global collapse of primary productivity (Strangelove Ocean); greatly reduced export but not primary productivity (Living Ocean); little or no reduction in export productivity (Resilient Ocean); and geographic heterogeneity in the change of export productivity (Heterogeneous Ocean). We tested primary vs. export productivity changes in the paleoshelf of New Jersey, where δ13C values and organic carbon accumulation rates can distinguish among different ocean responses. On the shelf, the K/Pg boundary is associated with a ~2.5‰ δ13C decrease in bulk carbonate, a ~0.8‰ δ13C decrease in organic carbon, a collapse of the surface to bottom δ13C gradient, and a drop in organic carbon percentage. We interpret an early Danian ~1.0‰ planktonic foraminiferal δ13C gradient, a ~0.75‰ cross-shelf benthic foraminiferal δ13C gradient, and a drop in carbon accumulation rates to reflect the presence of active primary but limited export productivity, consistent with the Living Ocean hypothesis. We evaluated interbasinal deep-sea benthic foraminiferal δ13C gradients between the Pacific (Site 1210) and the Atlantic (Site 1262) oceans as a proxy for changes in export productivity. The interbasinal δ13C gradient was reduced after the mass extinction, suggesting a reduction in global export productivity. Although our data support the Living Ocean hypothesis, evidence from paleo-upwelling zones shows significant export productivity, indicating spatial heterogeneity in the wake of the K/Pg mass extinction (Heterogeneous Ocean).

Why the Atlantic Ocean was More Acidified During the Paleocene Eocene Thermal Maximum

Around 55 million years ago, an abrupt global warming event triggered a highly corrosive deep-water current through the North Atlantic Ocean. The current's origin puzzled scientists for a decade, but an international team of researchers has now discovered how it formed and the findings may have implications for the carbon dioxide emission sensitivity of today's climate.

The researchers explored the acidification of the ocean that occurred during a period known as the Paleocene Eocene Thermal Maximum (PETM), when the Earth warmed 9 degree Fahrenheit in response to a rapid rise in carbon dioxide in the atmosphere and subsequently one of the largest-ever mass extinctions occurred in the deep ocean. They report their findings in today's (May 11) issue of Nature Geoscience.

This period closely resembles the scenario of global warming today.

"There has been a longstanding mystery about why ocean acidification caused by rising atmospheric carbon dioxide during the PETM was so much worse in the Atlantic compared to the rest of the world's oceans," said lead author Kaitlin Alexander, ARC Centre of Excellence for Climate System Science, University of New South Wales, Australia. "Our research suggests the shape of the ocean basins and changes to ocean currents played a key role in this difference. Understanding how this event occurred may help other researchers to better estimate the sensitivity of our climate to increasing carbon dioxide."

To get their results the researchers recreated the ocean basins and land masses of 55 million years ago in a global climate model.

During that time a ridge on the ocean floor existed between the North and South Atlantic that separated the deep water in the North Atlantic from the rest of the world's oceans. The ridge was like a giant bathtub on the ocean floor.

The simulations showed this ridge became filled with extremely corrosive water from the Arctic Ocean, which mixed with dense salty water from the Tethys Ocean and sank to the seafloor, where it accumulated. The sediment in this area indicates the water was so corrosive that it dissolved all the calcium carbonate produced by organisms that settled on the ocean floor.

When the Earth warmed as a result of a rapid increase in atmospheric carbon dioxide, it eventually warmed this corrosive bottom water. As this water warmed it became less dense and denser water sinking from above replaced it. The corrosive deep water was pushed up and spilled over the edge of the giant "bathtub" and flowed into the South Atlantic.

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Evidence the First Few Thousand Years After Chicxulub Impact the Climate Cooled

Palynological evidence for prolonged cooling along the Tunisian continental shelf following the K–Pg boundary impact

Authors:

Velekoop et al

Abstract:

The Cretaceous–Palaeogene (K–Pg) boundary mass extinction event is related to major global environmental changes resulting from a large extraterrestrial impact. Organic-walled cyst-producing marine dinoflagellates (dinocysts) survived the K–Pg mass-extinction relatively unscathed, making them ideally suited for reconstructing these environmental changes. So far, one of the best dinocyst records available is from the K–Pg boundary Global Stratotype Section and Point (GSSP) at El Kef (NW Tunisia). There, the dinocyst record shows major fluctuations across the boundary, likely reflecting strong responses to environmental changes. These fluctuations have so far not been confirmed by other studies. Therefore, in this study we performed a high-resolution marine palynological study on a closely spaced sample set from the Elles section, some 75 km south of El Kef, in order to generate a palaeoenvironmental and palaeoclimatic record across the K–Pg boundary to allow verification and refinement of earlier reported environmental changes. To better constrain the reconstructions based on qualitative biotic proxies we employed the quantitative sea surface temperature proxy TEX86. Unfortunately, the TEX86 proxy record of the studied section is compromised because of post-depositional oxidation. However, the diverse dinocyst assemblages at Elles show strong fluctuations similar to the El Kef record, therefore confirming the earlier recorded signals, showing rapid, regionally consistent changes. These records imply that the latest Cretaceous was characterized by a gradual cooling trend and the onset of relative sea level fall. Within the immediate post-extinction interval, in the first thousands of years after the impact, dinocyst assemblages reveal multiple incursions of higher-latitude dinocyst species implying repeated pulses of cooling. These results signify that the earliest Danian climatic and environmental conditions were relatively unstable across the Tunisian shelf.

Paleocene Paleogene Purgatorius was Arboreal, Close Basal Relative to Primates

Oldest known euarchontan tarsals and affinities of Paleocene Purgatorius to Primates

Authors:

Chester et al

Abstract:

Earliest Paleocene Purgatorius often is regarded as the geologically oldest primate, but it has been known only from fossilized dentitions since it was first described half a century ago. The dentition of Purgatorius is more primitive than those of all known living and fossil primates, leading some researchers to suggest that it lies near the ancestry of all other primates; however, others have questioned its affinities to primates or even to placental mammals. Here we report the first (to our knowledge) nondental remains (tarsal bones) attributed to Purgatorius from the same earliest Paleocene deposits that have yielded numerous fossil dentitions of this poorly known mammal. Three independent phylogenetic analyses that incorporate new data from these fossils support primate affinities of Purgatorius among euarchontan mammals (primates, treeshrews, and colugos). Astragali and calcanei attributed to Purgatorius indicate a mobile ankle typical of arboreal euarchontan mammals generally and of Paleocene and Eocene plesiadapiforms specifically and provide the earliest fossil evidence of arboreality in primates and other euarchontan mammals. Postcranial specializations for arboreality in the earliest primates likely played a key role in the evolutionary success of this mammalian radiation in the Paleocene.

Evidence of a Hyperthermal Caused Paleocene Paleogene Biotic Event

Terrestrial evidence for a two-stage mid-Paleocene biotic event

Authors:

Hyland et al

Abstract:

Marine records of the Paleocene indicate a series of hyperthermal events characterized by significant climatic and carbon cycle variability, but there are few comparable continental records. The mid-Paleocene biotic event (MPBE) is a recently described interval defined by a rapid negative carbon isotope excursion and major short-term changes in marine ecosystems, but it is as yet unclear whether the event was globally important. Here we present the first terrestrial paleoenvironmental record of the MPBE based on paleosols that document rapid and short-lived increases in temperature and precipitation and resultant shifts in plant assemblages concomitant with substantial carbon isotope excursions. The new record indicates that carbon cycle changes during the early late Paleocene may have resulted in a two-stage transient hyperthermal event that caused a significant perturbation to both the regional climate and terrestrial ecology of South America in addition to the major biotic event (MPBE) previously recognized in marine records. Overall, this suggests that the MPBE may have been a global climate event with far-reaching environmental impacts in both the marine and terrestrial realms.

Ursolestes perpetior: a new 'Giant' Purgatoriid Plesiadapiforme From Paleocene Paleogene Montana

A ‘giant’ purgatoriid (Plesiadapiformes) from the Paleocene of Montana, USA: mosaic evolution in the earliest primates

Authors:

Fox et al

Abstract:

Ursolestes perpetior gen. et sp. nov. is a large purgatoriid plesiadapiform primate from the middle/late Puercan (earliest Paleocene) Simpson Quarry, Montana, USA. It differs from Purgatorius Van Valen and Sloan, 1965, the only other known purgatoriid and the oldest discovered primate, in its substantially larger body size as inferred from the dimensions of the known parts of its dentition, while resembling Purgatorius in possessing a large lower canine, unreduced p1, and in the upper molars, a protocone twist and weakly developed postprotocone fold; moreover, the m3 of U. perpetior possesses an expanded, plesiadapiform-like posterior lobe of the talonid that supports the hypoconulid. The large lower canine and the greater development of trenchant molar crests suggest that U. perpetior was more insectivorous, differing appreciably from the omnivorous niche long hypothesized for Purgatorius and purportedly marking the insectivore–primate transition. Hence, U. perpetior adds significant new knowledge regarding the breadth of the adaptive zone occupied by purgatoriids in their position at the very beginnings of primate evolution.

New Pantolestid Mammals From Paleocene Paleogene Saskatchewan

New pantolestids (Mammalia, Eutheria) from the late Paleocene (late middle Tiffanian) Roche Percée local fauna, southeastern Saskatchewan, Canada

Author:

Rankin

Abstract:

The Pantolestidae are an extinct family of mammals known principally from the early Paleocene to late Oligocene (from approximately 64 to 30 million years ago) of North America and Europe. Although never particularly abundant, pantolestids are relatively well represented in the Eocene and Oligocene, with several taxa known from exceptionally well-preserved skulls and postcranial material. The early evolutionary history of the group, however, similar to that of many contemporaneous mammals, remains comparatively poorly known. The current study reports on several previously undescribed pantolestids from the early late Paleocene (late middle Tiffanian, Ti4) Roche Percée local fauna, Ravenscrag Formation, of southeastern Saskatchewan, Canada. Aatotomus placochton n. gen. n. sp. resembles the enigmatic pantolestid Paleotomus in having sectorial premolars with well-developed crests and tall, sharp molar trigonids, but differs principally in possessing narrow molar talonids. Besseocetor krausei n. sp. shares numerous similarities with B. thomsoni and B. septentrionalis but differs in being considerably smaller and less robust. Palaeosinopa reclusum n. sp., the oldest species of Palaeosinopa yet discovered, reveals a unique combination of primitive and derived pantolestid features, and supports previous suggestions of a close evolutionary relationship between Palaeosinopa and Bessoecetor. The new taxa document an unusually high diversity of pantolestids in the Tiffanian of western Canada and provide important new knowledge to the evolutionary history of this group during the Paleocene.

Evidences for a Paleocene Paleogene Marine Incursion in Southern Amazonia

Evidences for a Paleocene marine incursion in southern Amazonia (Madre de Dios Sub-Andean Zone, Peru)

Authors:

Louterbach et al

Abstract:

This article presents new biostratigraphic dating, facies analysis, organic geochemical data and Nd–Sr isotopic provenance from five outcrops of southern Amazonia (MD-85, MD-177 MD-184, MD-255 and MD-256) to document for the first time the presence of a shallow marine ingression in the Paleocene of southern Amazonia basin. The co-occurrence of a selachian assemblage encompassing Potobatis sp., Ouledia sp., and Pristidae indet. with the ostracod Protobuntonia sp. and the charophytes Peckichara cf. varians meridionalis, Platychara perlata, and Feistiella cf. gildemeisteri suggests a Paleocene age for the studied deposits (most likely Thanetian but potentially Danian). Fifteen facies have been recognized and have been grouped into three facies assemblages. Facies association A corresponds to the sedimentary filling of a tide-influenced meandering channel formed in the fluvial–tidal transition zone. Facies association B is related to more distal tidal-flats, little channelized tidal inlets and saltmarsh deposits. Facies association C corresponds to a stressed shallow marine environment such as a bay or a lagoon. The δ13CTOC value (− 23.4‰) of MD-184 is enriched in 13C compared to the other samples suggesting the presence of substantial amounts of marine organic matter in MD-184. The δ13CTOC values of samples from other outcrops (− 27.3 to − 29.8‰) indicate a mixed organic matter origin, from terrestrial to brackish environments. The analyzed sediments have similar Nd–Sr isotopic compositions as those of the Cenozoic sediments of the Altiplano (εNd(0) values from − 6.2 to − 10.7 and 87Sr/86Sr compositions from 0.712024 to 0.719026) indicating a similar volcanic source. This multidisciplinary dataset documents the presence of a tide-dominated estuary sourced by the proto-Western Cordillera debouching into a shallow marine bay during Paleocene times. This transgression might be explained by subsidence created in response to the proto-Western Cordillera loading. Similar to Miocene marine incursions affecting the Pebas megawetland, Paleogene marine incursions in the Amazonian foreland basin associated with Andean uplift may have played a role in the Neotropical biodiversity dynamics in favoring biogeographical isolation and promoting allopatric speciation for terrestrial organisms.

Evidence of Hypoxic Upper Ocean Waters During the Paleocene-Eocene Thermal Maximum (PETM)

I/Ca evidence for upper ocean deoxygenation during the Paleocene-Eocene Thermal Maximum (PETM)

Authors:

Zhou et al

Abstract:

Anthropogenic global warming affects marine ecosystems in complex ways, and declining ocean oxygenation is a growing concern. Forecasting the geographical and bathymetric extent, rate and intensity of future deoxygenation and its effects on oceanic biota, however, remains highly challenging because of the complex feedbacks in the earth-ocean-biota system. Information on past global warming events such as the Paleocene Eocene Thermal Maximum (PETM, ~55.5 Ma), a potential analog for present and future global warming, may help in such forecasting. Documenting past ocean deoxygenation, however, is hampered by the lack of sensitive proxies for past oceanic oxygen levels throughout the water column. As yet no evidence has been presented for pervasive deoxygenation in the upper water column through expansion of Oxygen Minimum Zones (OMZs). We apply a novel proxy for paleo-redox conditions, the iodine to calcium ratio (I/Ca) in bulk coarse fraction sediment and planktic foraminiferal tests from pelagic sites in different oceans, and compared our reconstruction with modeled oxygen levels. The reconstructed iodate gradients indicate that deoxygenation occurred in the upper water column in the Atlantic, Indian Oceans, and possibly the Pacific Ocean as well during the PETM, due to vertical and potentially lateral expansion of OMZs.