Jaelyn J. Eberle

Significantly warmer Arctic surface temperatures during the Pliocene indicated by multiple independent proxies

Temperatures in the Arctic have increased by an astounding 1 °C in response to anthropogenic forcing over the past 20 years and are expected to rise further in the coming decades. The Pliocene (2.6–5.3 Ma) is of particular interest as an analog for future warming because global temperatures were signifi cantly warmer than today for a sustained period of time, with continental confi gurations similar to present. Here, we estimate mean annual temperature (MAT) based upon three independent proxies from an early Pliocene peat deposit in the Canadian High Arctic. Our proxies, including oxygen isotopes and annual ring widths (MAT = –0.5 ± 1.9 °C), coexistence of paleovegetation (MAT = –0.4 ± 4.1 °C), and bacterial tetraether composition in paleosols (MAT = –0.6 ± 5.0 °C), yield estimates that are statistically indistinguishable. The consensus among these proxies suggests that Arctic temperatures were ~19 °C warmer during the Pliocene than at present, while atmospheric CO 2 concentrations were ~390 ppmv. These elevated Arctic Pliocene temperatures result in a greatly reduced and asymmetrical latitudinal temperature gradient that is probably the result of increased poleward heat transport and decreased albedo. These results indicate that Arctic temperatures may be exceedingly sensitive to anthropogenic CO 2 emissions.

Life at the top of the greenhouse Eocene world—A review of the Eocene flora and vertebrate fauna from Canada’s High Arctic

Early–middle Eocene (ca. 53–38 Ma) sediments of the Eureka Sound Group in Canada’s Arctic Archipelago preserve evidence of lush mixed conifer-broadleaf rain forests, inhabited at times by alligators, turtles, and diverse mammals, including primates, tapirs, brontotheres, and hippo-like Coryphodon. This biota reflects a greenhouse world, offering a climatic and ecologic deep time analog of a mild ice-free Arctic that may be our best means to predict what is in store for the future Arctic if current climate change goes unchecked. In our review of the early–middle Eocene Arctic flora and vertebrate fauna, we place the Arctic fossil localities in historic, geographic, and stratigraphic context, and we provide an integrated synthesis and discussion of the paleobiology and paleoecology of these Eocene Arctic forests and their vertebrate inhabitants. The abundance and diversity of tapirs and plagiomenids (both rare elements in midlatitude faunas), and the absence of artiodactyls, early horses, and the hyopsodontid “condylarth” Hyopsodus (well represented at midlatitude localities) are peculiar to the Eocene Arctic. The Eocene Arctic macrofloras reveal a forested landscape analogous to the swamp-cypress and broadleaf floodplain forests of the modern southeastern United States. Multiple climate proxies indicate a mild temperate early–middle Eocene Arctic with winter temperatures at or just above freezing and summer temperatures of 20 °C (or higher), and high precipitation. At times, this high precipitation resulted in freshwater discharge into a nearly enclosed Arctic Ocean basin, sufficient to cause surface freshening of the Arctic Ocean, supporting mats of the floating fern Azolla . Fluctuating Arctic Ocean sea level due to freshwater inputs as well as tectonics produced temporary land bridges, allowing land plants and animals to disperse between North America and both Europe and Asia.

Vertebrate faunal changes through Lancian and Puercan time in southern Wyoming

We summarize faunal changes through the thickest and one of the most complete records of terrestrial vertebrates spanning Lancian (∼latest Cretaceous) and Puercan (∼earliest Paleocene) ages, the type Ferris Formation in the Hanna Basin, southern Wyoming. Observed faunal changes predate tectonic definition of local Laramide basins. Nonmammalian vertebrates exhibit no major changes in taxonomic composition below the Lancian-Puercan boundary; diversity of non-avian dinosaurs remains high within uppermost levels of the Lancian section. Nevertheless, dinosaurian extinction was not necessarily “catastrophic” within a biologically relevant interval. Primitive condylarths appear locally above the highest known dinosaurs, probably as immigrants. At least in this part of the North American western interior, the first evolutionary radiation of condylarths was subsequent to the last appearance of dinosaurs, not synchronous with or prior to it. Niche-partitioning among condylarths is first recorded near the boundary between Puercan Interval-zones Pu1 and Pu2 (early and middle Puercan time, respectively), by which time the first great mammalian diversification of the Cenozoic had begun. Major experimentations in dental morphology and increasing ranges of body sizes had developed within 400,000 years of the Lancian-Puercan boundary. We recognize no evidence suggesting that placental mammals were “recovering” from events that led to demise of the dinosaurs. The true diversity of marsupials and condylarths precisely at the Cretaceous-Tertiary boundary, throughout the western interior, remains unknown. We cannot, therefore, evaluate extensiveness of competition, if any, at that time among members of the two groups.

Life in a temperate Polar sea: a unique taphonomic window on the structure of a Late Cretaceous Arctic marine ecosystem

As the earth faces a warming climate, the rock record reminds us that comparable climatic scenarios have occurred before. In the Late Cretaceous, Arctic marine organisms were not subject to frigid temperatures but still contended with seasonal extremes in photoperiod. Here, we describe an unusual fossil assemblage from Devon Island, Arctic Canada, that offers a snapshot of a ca 75 Myr ago marine palaeoecosystem adapted to such conditions. Thick siliceous biogenic sediments and glaucony sands reveal remarkably persistent high primary productivity along a high-latitude Late Cretaceous coastline. Abundant fossil faeces demonstrate that this planktonic bounty supported benthic invertebrates and large, possibly seasonal, vertebrates in short food chains. These ancient organisms filled trophic roles comparable to those of extant Arctic species, but there were fundamental differences in resource dynamics. Whereas most of the modern Arctic is oligotrophic and structured by resources from melting sea ice, we suggest that forested terrestrial landscapes helped support the ancient marine community through high levels of terrigenous organic input.

A new important record of earliest Cenozoic mammalian history Eutheria and paleogeographic/biostratigraphic summaries

We provide systematic description and discussion for each of 47 species of eutherian (“placental”) mammals from the type Ferris Formation of the western Hanna Basin, south-central Wyoming. All records are new for the basin, and for southern Wyoming in general. Although fossiliferous strata are both of Lancian (latest Cretaceous) and Puercan (earliest Paleocene) age, all but a few specimens (restricted to two genera) represent the Puercan. We describe five species of previously known genera as new, all of Puercan age. We also assign a previously described Puercan species to a new genus, to emphasize its distinctness. Ordinal categories are represented by Leptictida, Proteutheria, Condylarthra, and Cete. Except for fossils from lowest parts of the Puercan, the local early Paleocene fauna is biased taxonomically in favor of condylarths, animals of relatively large body size in early parts of the epoch. The taxonomic bias probably is due in part to fluvial size-sorting of specimens related to generally sandy, relatively high-energy depositional environments. The local Puercan mammalian fauna is of keen paleobiogeographic and biostratigraphic importance. Among the 59 species of Puercan mammals now known from the Hanna Basin (combining recently reported multituberculates and peradectians with eutherians considered here), at least 25 represent significant extensions of previously recognized geographic ranges (18 in northerly extent, 7 in southerly). Because many of those extended ranges involve major parts of the continent, confidence becomes greatly heightened in biostratigraphic utility of Puercan mammalian species for temporal correlations, even across vast distances of western North America. Composition of the Hanna Basin9s mammalian fauna confirms utility of most elements of the formalized interval-zones of Puercan time, established in the San Juan and Williston basins. We do, however, abandon use of Puercan Interval-zone Pu 0 as impractical, and use an expanded concept of Pu1 instead. Other than that adjustment, we strictly apply original faunal criteria for recognition of Puercan Interval-zones Pu1 through Pu3 to zonation of the type Ferris Formation. The unusually great thickness of Puercan parts of the formation, combined with our high density of sampled fossiliferous localities, has led to recognition of many extensions of temporal ranges beyond those known previously for individual species. The biostratigraphic importance of this section, therefore, becomes elevated for potential studies in: (1) long-distance temporal correlation of Puercan strata; and (2) many aspects of biological evolution across North America during earliest Cenozoic time. Basal parts of Interval-zone Pu2 in the Ferris Formation uniquely show persistence of some mammalian species known elsewhere only in Pu1. Faunal change within Interval-zone Pu2 greatly exceeds that observed between Pu2 and Pu3, although the evolutionary distinctiveness of Pu2 and Pu3 are confirmed in the present study. The newly discovered mammalian assemblages of Puercan age from southern Wyoming exhibit virtually no geographic endemism. Although they share species both from northern and southern fossil-bearing realms of the North American continent, composition of the Ferris assemblages clearly is more similar to southern than to northern faunas under comparison.

A new important record of earliest Cenozoic mammalian history :geologic setting, Multituberculata, and Peradectia

The type Ferris Formation of south-central Wyoming is thick, comparatively undeformed, and relatively fossiliferous. We documented more than 100 vertebrate-bearing, stratigraphically superposed fossil localities that span roughly 3,000 ft ( c. 900 m) of continental strata of Lancian (latest Cretaceous) and Puercan (earliest Paleocene) age. Fossil mammals were recovered from 39 of the localities, 32 or 33 of which represent Puercan time. The mammalian fossils allowed a detailed biostratigraphic zonation of the Puercan section, which is thicker, by nearly an order of magnitude, than any other known of that age. Preserved in a 1,763 ft- (537 m-) thick section are mammalian assemblages that represent all three Puercan Interval-zones ( i. e. , Pu1–Pu3), originally defined elsewhere from principally non-superposed strata. The local strata underwent only minor deformation, and that occurred late in the regional Laramide orogeny, not before the late Paleocene. On the basis of mammalian faunas, we place the Lancian-Puercan boundary at approximately 2,050 ft (625 m) above the base of the type Ferris Formation; remains of dinosaurs occur to just above that level, in absence of Puercan mammals. The lowest stratigraphic occurrence of Protungulatum donnae , a placental mammal diagnostic elsewhere of the earliest Puercan, exists at the 2,075 ft (632 m) level. Taxonomic composition of palynological samples is compatible with our placement of the Lancian-Puercan boundary. Previous workers assumed that advent of locally derived clasts in the Hanna Formation could be used to distinguish its outcrops from those of the underlying Ferris Formation. However, diverse pebbles from local sources also occur in the type Ferris Formation, even within its dinosaur-bearing parts. We have been unable to determine any combination of lithologic criteria that can be used reliably in the field to distinguish between outcrops of Ferris and Hanna Formations. We summarize important variations in depositional regime within Lancian-Puercan parts of the type Ferris Formation. We provide systematic description and discussion of multituberculate and peradectian components of the mammalian fauna. All reported taxa represent new records for the Hanna Basin and southern Wyoming in general, and the faunas help fill distributional gaps between species known to the north and south of central Wyoming. At least one species of multituberculate is recognized as new. Geographic range extensions include: (1) most southerly records of Cimolodon nitidus, Alphadon lulli, Mesodma ambigua, M. hensleighi, M. sp. cf. M. garfieldensis , and Catopsalis joyneri ; and (2) most northerly records of Ptilodus sp. cf. P. tsosiensis and Taeniolabis taoensis . Within the Hanna Basin, no genera of multituberculates or peradectians from the Ferris Formation have been documented in strata both of Lancian and Puercan age; several examples of pseudoextinction, however, may exist through taxonomic artifact. Temporal range extensions include first: (1) Puercan records of Mesodma hensleighi and Ectypodus spp.; (2) records within Puercan Interval-zone Pu3 of Ptilodus sp. cf. P. tsosiensis ; and (3) record in Puercan Interval-zone Pu2 of Catopsalis joyneri . In general, the Lancian multituberculate and peradectian faunas of the type Ferris Formation are similar to, although not nearly so diverse as, those from the type Lance Formation; the lower diversity almost certainly is an artifact of paucity of specimens available for study.

Arctic plant diversity in the Early Eocene greenhouse

For the majority of the Early Caenozoic, a remarkable expanse of humid, mesothermal to temperate forests spread across Northern Polar regions that now contain specialized plant and animal communities adapted to life in extreme environments. Little is known on the taxonomic diversity of Arctic floras during greenhouse periods of the Caenozoic. We show for the first time that plant richness in the globally warm Early Eocene (approx. 55–52 Myr) in the Canadian High Arctic (76° N) is comparable with that approximately 3500 km further south at mid-latitudes in the US western interior (44–47° N). Arctic Eocene pollen floras are most comparable in richness with todays forests in the southeastern United States, some 5000 km further south of the Arctic. Nearly half of the Eocene, Arctic plant taxa are endemic and the richness of pollen floras implies significant patchiness to the vegetation type and clear regional richness of angiosperms. The reduced latitudinal diversity gradient in Early Eocene North American plant species demonstrates that extreme photoperiod in the Arctic did not limit taxonomic diversity of plants.

A summertime rainy season in the Arctic forests of the Eocene

The discovery of exceptionally well-preserved fossil wood revealed that extensive forests existed north of the Arctic Circle during the Eocene (ca. 45–55 Ma). Subsequent paleobotanical studies led researchers to suggest eastern Asia as a modern analog, based on the distribution of nearest living relatives. During the last decade, proxy-based reconstructions of mean annual paleoprecipitation, productivity, and relative humidity have led workers to characterize the climate of the Arctic forests as similar to today9s temperate forests of the Pacific Northwest. Using a new model, we reconstructed the seasonal timing of paleoprecipitation from high-resolution intra-ring carbon isotope measurements of fossil wood. We showed that the Eocene Arctic forests experienced, on average, 3.1 times more precipitation during summer than winter, entirely dissimilar to the Pacific Northwest where summer precipitation is only one-half to one-sixth of the winter precipitation. This new result shows that although mean annual climate conditions may have been similar to the mean annual conditions the Pacific Northwest, consideration of seasonality implies that the temperate forests of eastern Asia represent the best overall modern analog for the Eocene Arctic forests.

Lower-latitude mammals as year-round residents in Eocene Arctic forests

The Arctic is undergoing rapid warming, but the impact on the biosphere, in particular on large terrestrial mammals, is not clear. Among the best deep time laboratories to assess biotic impacts of Arctic climate change, early Eocene (ca. 53 Ma ago) fossil assemblages on Ellesmere Island, Nunavut (~79°N), preserve evidence of forests inhabited by alligators, tortoises, and a diverse mammalian fauna most similar to coeval lower-latitude faunas in western North America. By analyzing carbon and oxygen isotope ratios of mammalian tooth enamel, we show that large herbivores were year-round inhabitants in the Arctic, a probable prerequisite to dispersal across northern high-latitude land bridges. If present-day warming continues, year-round occupation of the Arctic by lower-latitude plants and animals is predicted.

EARLY EOCENE BRONTOTHERIIDAE (PERISSODACTYLA) FROM THE EUREKA SOUND GROUP, ELLESMERE ISLAND, CANADIAN HIGH ARCTIC—IMPLICATIONS FOR BRONTOTHERE ORIGINS AND HIGH-LATITUDE DISPERSAL

Abstract The northernmost records of early Eocene brontotheres, fossils of cf. Eotitanops and Brontotheriidae gen. et sp. indet., are described here from late Wasatchian-aged strata of upper parts of the Eureka Sound Group on central Ellesmere Island (∼79°N). Although the fossils were initially tentatively identified on faunal lists as Lambdotherium, their larger size and dental morphology ally them more closely to mid-latitude Eotitanops and Palaeosyops. The Ellesmere Island specimens are dentally most similar to mid-latitude Eotitanops, but can be distinguished from the latter by derived characters on their premolars that are shared with the younger (i.e., Bridgerian) Palaeosyops. The presence of brontotheres in early Eocene strata on Ellesmere Island implies that the groups evolution was well underway early in its history at northern high latitudes, and is consistent with either an Asian or North American origin and trans-Beringian dispersal. While cf. Eotitanops from Ellesmere Island appears dentally too advanced to be ancestral to mid-latitude co-eval Eotitanops, it may be a suitable ancestor to Palaeosyops. The presence of cf. Eotitanops on Ellesmere Island may reflect a high-latitude lineage that subsequently dispersed to mid-latitudes during early middle Eocene (Bridgerian) time.