Eocene Fossil Research Articles

The systematic relationships of the snake genus Anomochilus

Phylogenetic analysis of 38 skeletal characters, 12 muscular characters and 15 visceral characters in 17 major snake clades plus Anomochilus suggests that Anomochilus is the sister taxon of all other living alethinophidian snakes. However, skeletal, muscular and visceral character sets analysed separately or in pairs give four groups of nonconcordant tree topologies. Based on the cladogram derived from the total evidence, two families are erected to prevent the existing family Uropeltidae from becoming parapbyletic: Anomochilidae, for the Malaysian and Indonesian genus Anomochilus , and Cylindrophiidae, for the Sri Lankan, Southeast Asian and Indonesian genus Cylindrophis and the Upper Eocene fossil Eoanilius .

The systematic relationships of the snake genus Anomochilus

Phylogenetic analysis of 38 skeletal characters, 12 muscular characters and 15 visceral characters in 17 major snake clades plus Anomochilus suggests that Anomochilus is the sister taxon of all other living alethinophidian snakes. However, skeletal, muscular and visceral character sets analysed separately or in pairs give four groups of nonconcordant tree topologies. Based on the cladogram derived from the total evidence, two families are erected to prevent the existing family Uropeltidae from becoming parapbyletic: Anomochilidae, for the Malaysian and Indonesian genus Anomochilus , and Cylindrophiidae, for the Sri Lankan, Southeast Asian and Indonesian genus Cylindrophis and the Upper Eocene fossil Eoanilius .

Fossils Tell of Mild Winters In an Ancient Hothouse

Fossil evidence from the Eocene points to a warmer winter climate in the continental interior (e.g. North Dakota) than that predicted by computer models. Paleobotanists have been able to quantify approximate winter mean temperatures by using leaf characteristics. As one example, leaves from colder climates have toothed edges. Leaf structure was correlated with modern climate regimes, and these relations were then applied to Eocene fossils. They found cold-month mean temperatures of 1-8[degrees]C in Wyoming and Montana, well above model predictions. Climate models can be manipulated to reproduce these temperatures, but not without overheating the entire globe. The problem could be that the Eocene atmospheric circulation was different from today, something not accounted for well by climate models.

The attraction of paleomagnetism

AbstractThe majority of fossil primates and human archeological sites are recovered from sedimentary rocks, but obtaining radioisotopic dates directly from rocks of this type is generally difficult. Paleomagnetism offers an alternative dating approach. Specific applications of paleomagnetism in the field of anthropology range from dating late Eocene fossil anthropoids to determining human archeological site use and occupation. This single dating technique is not restricted to a specific time range, but can be used across the entire span of primate evolution. When linked with other dating techniques, such as radioisotopic or astrochronologic methods, paleomagnetism offers a high level of temporal resolution in unraveling questions of the past.

Variation in the shape of the palate in adapis (Eocene, Adapiformes) compared with living primates

This study is a quantitative analysis of the variation of palate shape inAdapis, an Eocene fossil primate. The observed coefficients of variation of palate dimensions inAdapis are statistically greater than in most living primate species. The histogram of the index (palate width/palate length) emphasizes the great heterogeneity in the fossil species.

Paleo-Historical Fluctuations in Paleogeography, Depositional Environment, and Chemistry of Eocene Fossil Lake

Fossil Butte National Monument contains within its boundaries a significant portion of the world's best preserved and most complete ancient lake deposit, known in the scientific literature as the Fossil Butte and Angelo Members of the Green River Formation (Oriel and Tracy 1970). Fossil Lake, the Eocene depository of these members of the Green River Formation, occupied a north-south trending structural basin within the Wyoming Thrust Belt known as Fossil Basin. Within Fossil Basin one can follow individual time horizons or rock units from lake center to margin with relative ease and great accuracy. Those rock units have faithfully recorded lake center to lake margin differences in lake depth, turbidity, salinity, alkalinity, temperature, and faunal elements. Areal changes in thickness and lithology (rock type) can be measured and mapped revealing details of lake shape, geography, and regional differences in lake depth and chemistry. Details concerning location and size of fluvial inlets and deltas, variations in lake bottom gradient and sediment type, and how these relate to flora and fauna can be discerned. An understanding of these aspects of the ancient lake system are essential if paleontologists are to put together a complete picture of the lake's fish fauna, which is the focal point of the monument. A variety of basin analysis maps derived from data collected in the field and laboratory will be used to make paleoenvironmental and paleogeographical interpretations of Fossil Lake through time.

Paleo-Historical Fluctuations in Paleogeography, Depositional Environment, and Chemistry of Eocene Fossil Lake

Fossil Butte National Monument contains within its boundaries a significant portion the world's best preserved and most complete ancient lake deposit, known in the scientific literature as the Fossil Butte and Angelo Members of the Green River Formation (Oriel and Tracy 1970). Fossil Lake, the Eocene depository of these members of the Green River Formation, occupied a north-south trending structural basin within the Wyoming Thrust Belt known as Fossil Basin. Within Fossil Basin one can follow individual time horizons or rock units from lake center to margin with relative ease and great accuracy. Those rock units have faithfully recorded lake center to lake margin differences in lake depth, turbidity, salinity, alkalinity, temperature, and faunal elements. Areal changes in thickness and lithology (rock type) can be measured and mapped revealing details of lake shape, geography, and regional differences in lake depth and chemistry. Details concerning location and size of fluvial inlets and deltas, variations in lake bottom gradient and sediment type, and how these relate to flora and fauna can be discerned. An understanding of these aspects of the ancient lake system are essential if paloontologists are to put together a complete picture of the lake's fish fauna, which is the focal point of the monument. A variety of basin analysis maps derived from data collected in the field and laboratory will be used to make paleoenvironmental and paleogeographical interpretations of Fossil Lake through time.

Eocene Fossil Algae from the Subcrops of the Bengal Basin

Eocene Fossil Algae from the Subcrops of the Bengal Basin

Paleo-Historical Fluctuations in Paleogeography, Depositional Environment, and Chemistry of Eocene Fossil Lake

Fossil Butte National Monument contains within its boundaries, a significant portion the world's best preserved and most complete ancient lake deposit, known as the Fossil Butte and Angelo Members of the Green River Formation (Oriel and Tracy 1970). Fossil Lake, the Eocene depository of these members of the Green River Formation, occupied a north-south trending structural basin within the Wyoming Thrust Belt known as Fossil Basin. Within Fossil Basin one can follow individual time horizons or rock units from lake center to margin with relative ease and great accuracy. Those rock units have faithfully recorded lake center to lake margin differences in lake depth, turbidity, salinity, alkalinity, temperature, and faunal elements. Areal changes in thickness and lithology (rock type) can be measured and mapped revealing details of lake shape, geography, and regional differences in lake depth and chemistry. Details concerning location and size of fluvial inlets and deltas, variations in lake bottom gradient and sediment type, and how these relate to flora and fauna can be discerned. An understanding of these aspects of the ancient lake system are essential if paleontologists are to put together a complete picture of the lake's fish fauna, which is the focal point of the monument. A variety of basin analysis maps derived from data collected in the field and laboratory will be used to make paleoenvironmental and paleogeographical interpretations of Fossil Lake through time.

Chronostratigraphy of Upper Eocene Microspherules

Impact-glass microspherules occur at numerous localities in rocks that can be dated as late Eocene. There is debate as to whether the discovered microspherule layers are the result of two or three impact events. Standard biostratigraphic techniques have been employed to date the microspherule layers. However, analysis of the available data indicates that zonal biostratigraphy has been insufficient for the task, particularly if practiced with only one taxonomic group. A chronostratigraphic framework model constructed using the Graphic Correlation technique is used with calcareous and siliceous microfossil data to determine the position in time of the microspherule layers. The results indicate that there are not two or three different layers, but at least six and possibly more. There are at least three and probably more eastern American microspherule layers. There are three Indo-Pacific layers that do not seem to correlate with any of the American layers. All of the proven layers (not possibly the result of contamination) are spread out over a one-million-year period in the middle and upper Globigerinatheka semiinvoluta Biochronozone. A chronostratigraphic table contains correlations of various upper Eocene fossil and stratigraphic events.

Stratigraphy and Vertebrate Biostratigraphy of Lower Eocene Regina Member, San Jose Formation, Sandoval County, San Juan Basin, New Mexico: ABSTRACT

The Regina Member of the San Jose Formation is a nonmarine fluvial deposit well known as a source of early Eocene (Wasatchian) fossil vertebrates. It is particularly well exposed along the Continental Divide south of Canada Largo on the Jicarilla Apache Indian Reservation in Sandoval County. Seventeen sections were measured in an area encompassed by Secs. 2 and 3 of T21N, R3W; Secs. 3, 10, 15, 16, 17, 21, and 28 of T22N, R2W; and Secs. 27, 34, 35, and 36 of T23N, R2W. In this area, the Regina Member is approximately 80 m thick, overlies the Cuba Mesa Member of the San Jose Formation, and is overlain by the Llaves Member of the San Jose Formation. It consists of about 40% sandstone, 30% siltstone, and 30% mudstone. Typical lithologies are yellowish gray (5 Y 8/1) subarkosic sandstone that is poorly sorted, trough-cross-bedded, well indurated, and calcareous; greenish gray (5 GY 5/2), grayish red (5 R 4/2), and yellowish gray (5 Y 8/1) variegated siltstone; and light olive (10 Y 4/2), pale yellowish brown (10 YR 5/4) and very dusky red-purpose (5 RP 2/2) variegated mudstone. Through extensive surface prospecting in this area, 1,192 specimens of fossil vertebrates from 211more » localities have been recovered. Fossils tend to occur in variegated mudstones and siltstones and are often associated with carbonate concretions. Fossils are confined to three relatively narrow zones: (1) about 70 to 75 m below the base of the Llaves Member; (2) about 40 to 50 m below the base of the Llaves Member; and (3) about 18 to 25 m below the base of the Llaves Member. The mammalian fauna from all three of these zones suggest a middle Wasatchian (Lysitean) age.« less

Paleoenvironmental Constraints Controlling Deposition of Oil Shale in Eocene Fossil Lake, Wyoming: ABSTRACT

The shoreward increase in sedimentation of precipitated calcite with its consequent dilution of organics was the primary paleoenvironmental constraint controlling the deposition and richness of oil shales in Eocene Fossil Lake (Fossil Butte Member of the Green River Formation). Kerogen-rich laminated calcimicrite (oil shale) was deposited as a result of a continuous rain of organic matter that was periodically interrupted by calcite precipitation. Precipitation was in response to the inflow of calcium-rich waters that also transported varying amounts of detrital mud-flat dolomite and fluvial siliciclastics. Organic input significantly exceeded sediment deposition, resulting in dark reducing sediments. Kerogen-poor laminated calcimicrite formed midway toward the basin margins because higher sedimentation rates closer to inflow areas diluted the organic matter. The higher sedimentation also resulted in less reducing conditions, thus allowing bioturbation. Massive or bedded calcimicrites were deposited near the lake margins where organic input was most diluted and bioturbators were uninhibited. Lateral variations in sedimentation rates seem to be a primary constraint on oil shale deposition. Evidence for this constraint includes the shoreward decrease in kerogen content matched by a shoreward thickening of micrite between tuff beds (time markers), a shoreward increase in bioturbation structures, a shoreward increase in siliciclastics, and anmore » increase in probable eolian quartz in the richest oil shales.« less

A New Species of the Early Tertiary Rodent Thisbemys

A new species of the early Tertiary rodent Thisbemys is described and compared with other species of the genus. The new species is derived from the lower Bridgerian (middle Eocene) species Thisbemys plicatus, but does not lie on the main lineage to later species of the genus. In the late 1940's and early 1950's, Robert W. Wilson and field crews from the University of Kansas, Museum of Natural History actively collected Paleocene and Eocene fossil mammals from western North America. Among the large number of middle Eocene (Bridgerian) mammals that were collected are several specimens referable to the paramyid rodent genus Thisbemys. The majority of the specimens are referred to T. plicatus and T. corrugatus; however, one specimen, University of Kansas, Museum of Natural History (KUVP) number 14233 is not referable to either of these species or any other known species of Thisbemys and therefore represents a new species.

Rb [sbnd]Sr dating of the Kohistan arc-batholith in the Trans-Himalaya of north Pakistan, and tectonic implications

The Kohistan arc-batholith in northern Pakistan is situated between the Indus Suture and the Northern Suture. It belongs to the Trans-Himalayan belt which continues eastwards as the Ladakh arc-batholith in northwest India and the Kangdese batholith in southern Tibet. In Kohistan the island arc consists (upward sequence) of the Chilas stratiform complex of norites, noritic gabbros and chromite-layered dunites which formed in the sub-arc magma chamber, plutons of tonalite and diorite, one of which has a Rb Sr isochron age of 102 ± 12 Ma, the Chalt volcanics of basaltic tholeiites succeeded by andesites to rhyolites, and the Yasin Group sediments which formed in overlying intra-arc basins and which contain Albian-Aptian faunas. All these rocks were deformed by major fold structures which are correlated with the formation of the Northern Suture. NE-SW trending basic Jutal-Nomal dykes (north of Gilgit) cross-cut all the above structures and have a 39Ar/ 40Ar hornblende age of 75 Ma. Thus the Northern Suture must have formed in the period 102 ± 12 to 75 Ma. With the island arc attached to the Eurasian plate, further northward subduction of the Tethyan plate gave rise to an Andean-type batholith, two plutons of which have Rb Sr isochron ages of 54 ± 4 Ma and 40 ± 6 Ma. The Dir-Utror Group of calc-alkaline lavas (and sediments with Eocene fossils) are remnants of the volcanic cover of the Andean-type batholith. We suggest that late Cretaceous blueschists formed during subduction under the active continental margin, and that continental collision and formation of the Indus Suture was in the Eocene. The batholith was intruded by layered aplite-pegmatite sheets at 34 ± 14 Ma and 29 ± 8 Ma (Rb Sr ages) in post-collisional times. The 87Sr/ 86Sr initial ratios of all the dated rocks range between 0.7039 and 0.7052.

Seamounts as recorders of hot-spot epeirogeny

Observations in the central Pacific suggest that older seamounts are uplifted if plate motion carries them over mantle hot spots. A depth-anomaly map of the area reveals several volcanic chains now located on younger hot-spot swells. Uplift is estimated by comparing the observed depth of a seamount summit or the observed stratigraphic section in an atoll with that predicted assuming standard subsidence of the sea floor after the seamount formed. Cretaceous seamounts on the margin of the Hawaiian Swell have standard summit depths, whereas those on the crest of the swell are at least 1,100 m shallower. Summit depth correlates with sea-floor depth anomaly, implying that the Hawaiian Swell has caused the uplift. Eocene fossils are exposed at the surface in the Tuamotu Atolls, whereas, according to the standard subsidence relation, Eocene deposits should be covered by 1,000 to 2,000 m of more recent material. The inferred uplift is consistent with the atoll9s present position atop the Society Swell. Possible evidence for 600 m of uplift in the Southern Cook Islands, however, is unexplained by swell height. The observed uplifts of the Cretaceous seamounts near Hawaii and of the Tuamotu Atolls put a limit on when the Hawaiian and Society Swells formed at their present locations of maximum elevation. The swells must have developed within the past several million years and probably formed at the same time as did the younger volcanic edifices on their summits.

Dietary Correlates of the Origin and Radiation of Snakes

Stomach analyses of living families and of a fossil containing prey were used to address possible dietary correlates of the history of snakes. Aniliids, morphologically primitive among living snakes, feed on relatively heavy, elongate vertebrates. Large aniliids eat larger prey than do small individuals but, as in advanced snakes, they also take small items. Living boids, structurally intermediate between aniliids and advanced snakes, feed on relatively heavy prey of a much greater variety of shapes than do aniliids. An Eocene fossil that might be a boid contains a relatively large crocodilian in its gut. These findings, previous studies, and morphological considerations suggest that very early snakes used constriction and powerful jaws to feed on elongate, heavy prey. This would have permitted a shift from feeding often on small items to feeding rarely on heavy items, without initially requiring major changes in jaw structure relative to a lizard-like ancestor. Subsequent morphological changes could then have allowed boids to utilize a broad range of prey types, including many of those currently eaten by advanced snakes. More recent dietary themes include the consumption of even heavier prey by highly venomous elapids and viperids, and frequent feeding on relatively small items by some other advanced snakes.

Starch Grain Casts and Moulds in Eocene (Tertiary) Fossil Mangrove Hypocotyls

Starch Grain Casts and Moulds in Eocene (Tertiary) Fossil Mangrove Hypocotyls

CHATTAWAYA (STERCULIACEAE): A NEW GENUS OF WOOD FROM THE EOCENE OF OREGON AND ITS IMPLICATIONS FOR XYLEM EVOLUTION OF THE EXTANT GENUS PTEROSPERMUM

A new sterculiaceous wood, Chattawaya paliformis gen. et sp. n., was collected from a Middle Eocene locality in the type area of the Clamo Formation of north central Oregon. The wood differs from all known extant woods in having very large and irregularly shaped tile cells. However, other features of the xylem indicate a close natural relationship between Chattawaya and the extant paleotropical genus, Pterospermum. It is suggested that the xylem organization of the Eocene fossil represents a more primitive condition than that observed in Pterospermum. Comparative xylotomy indicates three evolutionary trends within the complex to which Chattawaya and Pterospermum belong: development of storied structure, increased uniformity in shape and size of tile cells and loss of multiseriate rays. Chattawaya is part of a growing body of paleobotanical evidence indicating that the Sterculiaceae was well differentiated by the early Tertiary, but that the lineages leading to extant genera have undergone an appreciable amount of evolutionary change since the Eocene.

Presbyornis and the Origin of the Anseriformes (Aves: Charadriomorphae)

Olson, Storrs L., and Alan Feduccia. Presbyornis and the Origin of the Anseriformes (Aves: Charadriomorphae). Smithsonian Contributions to Zoology, number 323, 24 pages, 15 figures, 1980.•Evidence purportedly allying the Anseriformes with the Galliformes is discredited. The discovery of vestigial lamellae in the Anhimidae, in addition to the characters these birds share with the anomalous Australian Magpie Goose (Anseranas), proves their anseriform relationship; within the order Anseriformes, the Anhimidae are highly derived and not representative of the ancestral condition in the order. The abundant Eocene fossil Presbyornis combines the body of a shorebird with a duck-like head and shows the Anseriformes to have evolved from the Charadriiformes. The unique filter-feeding apparatus of Presbyornis and the Anatidae was the key adaptation that led to the radiation of the order Anseriformes. The skull o[ Presbyornis has its greatest similarity to that of the living Australian duck Stictonetta, which on other grounds has been considered primitive. This suggests that a rearrangement of the subgroups of Anatidae may be needed. The fossil record shows that no certain Anseriformes are known before the early Oligocene, indicating a probable mid-Tertiary date for the major radiation of Anatidae. The ancestors of ducks were Charadriiformes that adapted originally for life in shallow saline lakes, where selection pressure for filter-feeding would have been strong. The Anseriformes should be maintained as a separate order following the Charadriiformes. Presbyornis is considered still to have had a charadriiform grade of morphology and for the present is retained in the Charadriiformes. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The coral Montastrea cavernosa (Linnaeus). Library of Congress Cataloging in Publication Data Olson, Storrs L Presbyornis and the origin of the Anseriformes (Aves, Charadriomorphae) (Smithsonian contributions to zoology ; no. 323) Bibliography: p. 1. Anseriformes•Evolution. 2. Presbyornis•Evolution. 3. Birds•Evolution. L Feduccia, J. Alan, joint author. IE Title. IIL Series: Smithsonian Institution. Smithsonian contributions to zoology ; no. 323. QL1.S54 no. 323 [Q,L696.A5] 591s [568'.3] 80-607065

Chattawaya (Sterculiaceae): A New Genus of Wood from the Eocene of Oregon and Its Implications for Xylem Evolution of the Extant Genus Pterospermum

A new sterculiaceous wood, Chattawaya paliformis gen. et sp. n., was collected from a Middle Eocene locality in the type area of the Clamo Formation of north central Oregon. The wood differs from all known extant woods in having very large and irregularly shaped tile cells. However, other features of the xylem indicate a close natural relationship between Chattawaya and the extant paleotropical genus, Pterospermum. It is suggested that the xylem organization of the Eocene fossil represents a more primitive condition than that observed in Pterospermum. Comparative xylotomy indicates three evolutionary trends within the complex to which Chattawaya and Pterospermum belong: development of storied structure, increased uniformity in shape and size of tile cells and loss of multiseriate rays. Chattawaya is part of a growing body of paleobotanical evidence indicating that the Sterculiaceae was well differentiated by the early Tertiary, but that the lineages leading to extant genera have undergone an appreciable amount of evolutionary change since the Eocene.