A reappraisal of the systematics, biogeography, and evolution of fossil horses

Paleobiology ◽  
1982 ◽  
Vol 8 (4) ◽  
pp. 315-327 ◽  
Author(s):  
M. O. Woodburne ◽  
Bruce J. MacFadden
Keyword(s):  
United States ◽  
Fossil Record ◽  
Evolutionary Rates ◽  
Western United States ◽  
Vertebrate Paleontology ◽  
Evolutionary Trends ◽  
Evolutionary Pattern ◽  
Major Mode ◽  
The Rich

The founders of North American vertebrate paleontology, F. V. Hayden, Joseph Leidy, E. D. Cope, O. C. Marsh, and their colleagues, collected and described the first suites of fossil mammals obtained from the rich Tertiary successions of the western United States. Among them were remains of fossil horses, and subsequent study of these resulted in an interpretation that supported the concept of Darwinian gradualism as the major mode of evolution. The fossil record of horses also contributed importantly to the demise of orthogenesis as an evolutionary pattern, and to the evaluation of evolutionary rates and long-term evolutionary trends in a major phyletic group of organisms.

scholarly journals Redescription ofCalyptosuchus(Stagonolepis)wellesi(Archosauria: Pseudosuchia: Aetosauria) from the Late Triassic of the Southwestern United States with a discussion of genera in vertebrate paleontology

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e4291 ◽  
Author(s):  
William G. Parker
Keyword(s):  
United States ◽  
Phylogenetic Analysis ◽  
Fossil Record ◽  
Phylogenetic Analyses ◽  
Western United States ◽  
Late Triassic ◽  
Vertebrate Paleontology ◽  
Unique Combination ◽  
Epistemological Problem ◽  
Chinle Formation

Calyptosuchus wellesiis a medium-sized desmatosuchian aetosaur common in Adamanian (early to middle Norian) age rocks from the Chinle Formation and Dockum Group of the Western United States. Known chiefly from osteoderms, this taxon has never been fully described and non-osteoderm material assigned toCalyptosuchushas been done so based on questionable criteria. Mapping of aetosaurian elements from thePlaceriasQuarry allows for the recognition of associated material providing support for referrals of non-osteoderm material. Furthermore, another previously undescribed specimen from the Chinle Formation of Arizona provides more details about this taxon. PresentlyCalyptosuchuslacks discrete autapomorphies, but can be distinguished from other aetosaurs based on a unique combination of characters supported by a phylogenetic analysis.Calyptosuchusis one of the most common aetosaurians in the Western United States and an index taxon of the early Adamanian biozone. The nameCalyptosuchusis retained and encouraged as the applicable genus name for the specieswellesirather than the often usedStagonolepisbecause assignments of taxa to multi-species genus names are problematic and in this case provides a proposed taxonomic relationship that cannot be unambiguously supported, even by phylogenetic analyses. Because of the inherent limitations of the fossil record, referral of specimens and species to species and genera respectively is an epistemological problem in vertebrate paleontology.

Warming is Driving Decreases in Snow Fractions While Runoff Efficiency Remains Mostly Unchanged in Snow-Covered Areas of the Western United States

2018 ◽  
Vol 19 (5) ◽  
pp. 803-814 ◽  
Author(s):  
Gregory J. McCabe ◽  
David M. Wolock ◽  
Melissa Valentin
Keyword(s):  
United States ◽  
Time Series ◽  
Winter Precipitation ◽  
Western United States ◽  
Balance Model ◽  
Winter Temperatures ◽  
Long Term Trends ◽  
Monthly Water Balance ◽  
Surface Water Supply

Abstract Winter snowfall and accumulation is an important component of the surface water supply in the western United States. In these areas, increasing winter temperatures T associated with global warming can influence the amount of winter precipitation P that falls as snow S. In this study we examine long-term trends in the fraction of winter P that falls as S (Sfrac) for 175 hydrologic units (HUs) in snow-covered areas of the western United States for the period 1951–2014. Because S is a substantial contributor to runoff R across most of the western United States, we also examine long-term trends in water-year runoff efficiency [computed as water-year R/water-year P (Reff)] for the same 175 HUs. In that most S records are short in length, we use model-simulated S and R from a monthly water balance model. Results for Sfrac indicate long-term negative trends for most of the 175 HUs, with negative trends for 139 (~79%) of the HUs being statistically significant at a 95% confidence level (p = 0.05). Additionally, results indicate that the long-term negative trends in Sfrac have been largely driven by increases in T. In contrast, time series of Reff for the 175 HUs indicate a mix of positive and negative long-term trends, with few trends being statistically significant (at p = 0.05). Although there has been a notable shift in the timing of R to earlier in the year for most HUs, there have not been substantial decreases in water-year R for the 175 HUs.

scholarly journals Variability of Cloudiness over Mountain Terrain in the Western United States

2017 ◽  
Vol 18 (5) ◽  
pp. 1227-1245 ◽  
Author(s):  
Edwin Sumargo ◽  
Daniel R. Cayan
Keyword(s):  
United States ◽  
Large Scale ◽  
Spatial Scales ◽  
High Elevation ◽  
Empirical Orthogonal Functions ◽  
Western United States ◽  
Spatial And Temporal Variability ◽  
Regional Patterns ◽  
Cloud Albedo

Abstract This study investigates the spatial and temporal variability of cloudiness across mountain zones in the western United States. Daily average cloud albedo is derived from a 19-yr series (1996–2014) of half-hourly Geostationary Operational Environmental Satellite (GOES) images. During springtime when incident radiation is active in driving snowmelt–runoff processes, the magnitude of daily cloud variations can exceed 50% of long-term averages. Even when aggregated over 3-month periods, cloud albedo varies by ±10% of long-term averages in many locations. Rotated empirical orthogonal functions (REOFs) of daily cloud albedo anomalies over high-elevation regions of the western conterminous United States identify distinct regional patterns, wherein the first five REOFs account for ~67% of the total variance. REOF1 is centered over Northern California and Oregon and is pronounced between November and March. REOF2 is centered over the interior northwest and is accentuated between March and July. Each of the REOF/rotated principal components (RPC) modes associates with anomalous large-scale atmospheric circulation patterns and one or more large-scale teleconnection indices (Arctic Oscillation, Niño-3.4, and Pacific–North American), which helps to explain why anomalous cloudiness patterns take on regional spatial scales and contain substantial variability over seasonal time scales.

Long-Term Aridity Changes in the Western United States

Science ◽  
2004 ◽  
Vol 306 (5698) ◽  
pp. 1015-1018 ◽  
Author(s):  
E. R. Cook
Keyword(s):  
United States ◽  
Western United States

scholarly journals Ecological opportunity and the rise and fall of crocodylomorph evolutionary innovation

2021 ◽  
Vol 288 (1947) ◽  
Author(s):  
Thomas L. Stubbs ◽  
Stephanie E. Pierce ◽  
Armin Elsler ◽  
Philip S. L. Anderson ◽  
Emily J. Rayfield ◽  
...  
Keyword(s):  
Fossil Record ◽  
Evolutionary Biology ◽  
Evolutionary Dynamics ◽  
Evolutionary Rates ◽  
Apex Predators ◽  
Ecological Opportunity ◽  
Evolutionary Innovation ◽  
Great Heterogeneity ◽  
Living Species

Understanding the origin, expansion and loss of biodiversity is fundamental to evolutionary biology. The approximately 26 living species of crocodylomorphs (crocodiles, caimans, alligators and gharials) represent just a snapshot of the group's rich 230-million-year history, whereas the fossil record reveals a hidden past of great diversity and innovation, including ocean and land-dwelling forms, herbivores, omnivores and apex predators. In this macroevolutionary study of skull and jaw shape disparity, we show that crocodylomorph ecomorphological variation peaked in the Cretaceous, before declining in the Cenozoic, and the rise and fall of disparity was associated with great heterogeneity in evolutionary rates. Taxonomically diverse and ecologically divergent Mesozoic crocodylomorphs, like marine thalattosuchians and terrestrial notosuchians, rapidly evolved novel skull and jaw morphologies to fill specialized adaptive zones. Disparity in semi-aquatic predatory crocodylians, the only living crocodylomorph representatives, accumulated steadily, and they evolved more slowly for most of the last 80 million years, but despite their conservatism there is no evidence for long-term evolutionary stagnation. These complex evolutionary dynamics reflect ecological opportunities, that were readily exploited by some Mesozoic crocodylomorphs but more limited in Cenozoic crocodylians.

Using long-term datasets to study exotic plant invasions on rangelands in the western United States

2013 ◽  
Vol 95 ◽  
pp. 65-74 ◽  
Author(s):  
C. Morris ◽  
L.R. Morris ◽  
A.J. Leffler ◽  
C.D. Holifield Collins ◽  
A.D. Forman ◽  
...  
Keyword(s):  
United States ◽  
Plant Invasions ◽  
Western United States ◽  
Exotic Plant

The Last Drops

2008 ◽  
Author(s):  
Howard G. Wilshire ◽  
Richard W. Hazlett ◽  
Jane E. Nielson
Keyword(s):  
United States ◽  
Native American ◽  
Native Americans ◽  
Western United States ◽  
Environmental Groups ◽  
National Environmental Policy Act ◽  
Boom And Bust ◽  
The Face ◽  
The Rich ◽  
Groundwater Basins

The western United States has low overall rainfall and snowfall levels, few rivers, and many deep groundwater basins. Small Native American populations once lived within the restraints of aridity by seeking harmony with nature. But owning land in such an arid region means little or nothing without a supply of fresh water. Instead of limiting population growth in the face of scarce and unpredictable rainfall, however, the west’s aridity challenged the newcomers to redirect water supplies and make the rich desert soils bloom. The region’s localized precipitation, generally doled out on boom-and-bust schedules, has made water “the most essential and fought over resource in the western United States.” Raising a lone voice of warning in 1893, western explorer John Wesley Powell foresaw that irrigating western lands would pile up “a heritage of conflict and litigation over water rights for there is not sufficient water to supply the land.”2 That Powell was right about conflicts goes without saying, for the west’s bitter heritage of water wars speaks for itself.3 Invading Americans used legal doctrines of first appropriation and “beneficial use” to take water from Indians’ lands and then turned to taking it from each other, oblivious to the effects on wildlife and natural habitats. Today’s depleted river flows and overpumped groundwater basins indicate that Powell probably was right about water supply limits, too. Expanding populations and increasing water contamination have strained supplies of fresh, clean water, even as per capita water demands decrease. By the 1970s, degraded natural settings, rising water pollution, and disappearing native fauna had lowered the quality of western life and built a constituency for environmental protection. But the 1970 National Environmental Policy Act and 1973 Endangered Species Act simply pitted environmental groups and courts against irrigators, cities, and states. In an ironic reversal, recently enriched Native Americans are poised to exercise their primary legal claims to many western rivers.

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