Latitudinal Distance Research Articles

A review of the early and middle Tertiary mammal faunas of Mexico

ABSTRACT The early and middle Tertiary land-mammal record of Mexico includes five local faunas, two faunules and four isolated occurrences that range from ?late Paleocene to late Miocene and includes 10 orders, 24 families and 36 genera (both determined and inferred) from localities in eight states throughout the country. They show a mixture of endemic and non-endemic elements. This seems to result from the coexistence and interaction of two distinct biotic regions, North America proper and Middle America. Their degree of difference increases with latitudinal distance plus local environmental conditions. Northern Mexico has been a broad transitional zone. Throughout the Tertiary, Middle America probably functioned as a major center of evolution and differentiation of mammals that spread both north and south, appearing in the North American record as tropical immigrants, and in turn received northern elements because a measure of interchange remained possible during this period.

On the topographic coupling at the core-mantle interface

The mean tangential stresses at a corrugated interface between a solid, electrically insulating mantle and a liquid core of magnetic diffusivity λ are calculated for uniform rotation of both mantle and core at an angular velocity Ω in the presence of a corotating magnetic field B. The core and mantle are assumed to extend indefinitely in the horizontal plane. The interface has the form z = η( x, y), where z is the upward vertical distance and x, y are the zonal and latitudinal distances respectively. The function η( x, y) has a planetary horizontal length scale (i.e. of the order of the radius of the Earth) and small amplitude and vertical gradient. The liquid core flows with uniform mean zonal velocity U 0 relative to the mantle. Ω and B possess vertical and horizontal components. The vertical (poloidal) component B p is uniform and has a value of 5 G while the horizontal (toroidal) field B T = B p αz, where α is a constant. When |α| ⪡ 1, the mean horizontal stresses are found to have the same order of magnitude (10 −2 N m −2) as those inferred from variations in the decade fluctuations in the length of the day, although the exact numerical values depend on the orientation of Ω as well as on the wavenumbers in the zonal and latitudinal directions. The influence of the steepness (as measured by α) of the toroidal field on the stresses is investigated to examine whether the constraint that the mean horizontal stresses at the core-mantle interface be of the order of 10 −2 N m −2 might provide a selection mechanism for the behaviour of the toroidal field in the upper reaches of the outer core of the Earth. The results indicate that the restriction imposed on α is related to the value assigned to the toroidal field deep into the core. For example, if |α| ⪢ 1 then the tangential stresses are of the right order of magnitude only if the toroidal field is comparable with the poloidal field deep in the core.

HYBRIDIZATION BETWEEN SPECIES OF THE RANA PIPIENS COMPLEX IN CENTRAL TEXAS.

Widespread acceptance and application of the polytypic species concept in the 1930s and 1940s resulted in the taxonomic lumping of many allopatric nominal species on the basis of the assumption of conspecificity. Consequently, for many groups of organisms one can cite cases of what Vaurie (1955) called pseudo-subspecies-good species taxonomically confused as subspecies. The example provided by leopard frogs of the Rana pipiens complex is particularly important because of the prominent place they have had in relation to theories of intraspecific variation and the evolution of isolating mechanisms. Analysis of patterns of geographic variation in morphology and the ability of individuals from some widely separated areas to produce viable offspring in laboratory crosses led Moore (1944) to regard many forms of the Rana pipiens complex as members of one polytypic species. Moore's (1946a, 1946b, 1949a, 1949b, 1950) extensive and influential work on the effects of temperature on embryonic and larval development and on genetic compatibility between frogs from different areas was interpreted within the framework of intraspecific variation. His demonstration that degree of abnormality in embryonic development is related to latitudinal distance (and, to a lesser degree, longitudinal distance) between parental populations provided a model of the manner in which differences accumulate between conspecific populations along environmental gradients. As Moore's interpretation gained wide acceptance, Rana pipiens became a standard textbook

Solar wind plasma injection at the dayside magnetospheric cusp

Two mechanisms have been proposed for solar wind particle injection at the dayside magnetospheric cusps: magnetic merging and cross-field diffusion. These two mechanisms are experimentally distinguishable in that they produce different latitudinal distributions of particles penetrating to the low-altitude cusp. An examination of proton and electron measurements obtained by the AE-C satellite in the low-altitude dayside cusp reveals evidence of both types of injection processes. A majority of the injection events, especially the more intense fluxes, are best explained by a merging injection model in which cusp particles are confined to the poleward side of the last closed field line and have a characteristic energy that decreases with increasing latitudinal distance from the last closed field line. Less frequent and less intense injection events are better explained in terms of a diffusive injection of cusp particles onto closed dayside field lines with a characteristic energy that increases with increasing latitudinal distance from the last closed field line. Although diffusion appears to be quantitatively less important than merging in terms of the instantaneous particle injection rate, cross-field diffusion nevertheless appears to proceed at an unexpectedly fast rate, possibly exceeding the Bohm diffusion limit.

Preliminary observations on transplanting and a phenological index of seagrasses

Transplanting of seagrasses is a technique used to gain basic biological information on environmental tolerances to changes and extremes of water temperature and salinity, substrate, and chemical pollutants. Reciprocal transplants across tidal zones in one area or across latitudinal distances can be used to distinguish whether responses represent phenotypic plasticity or ecotypic differentiation. Transplanting also represents the ability to maintain, create, or recreate seagrass meadows in an inshore coastal environment where human activity is increasing, often with inimical effects on the marine environment. A variety of transplanting techniques have been developed, using vegetative and sexual stages of tropical and temperate North American seagrasses. Some show preliminary promise of successful transplanting. It is important to know the phenology of seagrasses used in transplanting. A preliminary phenological index is given. By identifying a phenological index and correlating stages with a planting method best suited for the stage, it should become possible to ensure the greatest possible use of the seagrass ecosystem with the least adverse effects.

Regional Comparisons of Cottontail Reproduction in Missouri

First conceptions of the year for 196 female cottontails (Sylvilagus floridanus) collected in 1962 on five study areas in Missouri occurred from late January to late March. In all areas except one, most first conceptions centered about February 12-14. The latitudinal distances between areas were as great as 125 miles. Collections made in southwestern Mississippi, nearly 600 miles south of our northernmost area, also showed that the first wave of conceptions peaked about midFebruary. Thus, a southerly location does not necessarily lead to earlier breeding by cottontails. Mean litter sizes (second litters only) were larger to the north, increasing from 3.5 (southwestern Mississippi) to 4.8 (southeastern Missouri) and 5.6 (northern Missouri). Specimens from southeastern Missouri showed that postpartum breeding was the rule. The length of the breeding season there would allow ample time for at least seven litters per female per year. Collections for the entire study in Missouri totalled 606 female cottontails.

The relationship of total atmospheric ozone to the sunspot cycle

For the 27-year period 1933–1959 inclusive, highly significant negative correlation is found between the relative sunspot number and the worldwide average of total atmospheric ozone. Peak correlation with respect to the present-day 10-year sunspot cycle is found at a lag of 1½ to 2 years of the sunspots relative to ozone. The peak correlation of total atmospheric ozone with the mean latitudinal distance from the solar equator of the total area of sunspots is almost identical in magnitude to that with sunspot number. However, the peak correlation with sunspot latitude is found at a lag of less than 6 months of the ozone relative to sunspot latitude, in the opposite direction to that with sunspot number. This phase difference of the negative correlation suggests that atmospheric ozone is much more sensitive to sunspot latitude than to sunspot number.

Breaks in the Indian summer monsoon as a phenomenon of interaction between the easterly and the sub-tropical westerly jet streams

The present paper contains the results of the study of a synoptic situation over India during a period of 8 days in which normal monsoon conditions were followed by a break and were further followed by a return to normal monsoon. This study has shown that during breaks in the monsoon, a trough in the middle latitude westerlies with a jet embedded in it increases considerably in its amplitude and gets retarded as it moves into the Tibetan Plateau on account of its entering a region of weaker basic current. The large-amplitude trough weakens or destroys completely the Tibetan high at the 500 mb level and appreciably weakens the easterlies at the higher levels to the south of the Himalayas. Protruding into India and Pakistan, the large amplitude trough contributes to the development of heavy rainfall along and near the foot of the Himalayas which is characteristic of the break conditions. The southward protrusion of the trough and its subsequent movement eastward, is also indirectly responsible for a corresponding shift of the high over Iran and Arabia, which, in its turn, seems to lead to the formation of a secondary jet core in the easterlies west of 80° E between 20° N and 25° N. Consequent on the above developments, the westerly jet which had retreated to the north of the Himalayas at the time of the onset of the monsoon reenters the Indo-Pakistan sub-continent during the breaks. Thus we see during break conditions, the remarkable spectacle of two jets of entirely different types-the easterly and the sub-tropical westerly—within a short latitudinal distance of each other and dynamically interacting with each other.
 The above detailed study, supplemented by a general examination of the monthly mean 700 mb charts for the northern hemisphere for a period of 10 years, suggests that active monsoon over India is closely associated with high index circulation in middle latitudes over Asia and neighbourhood, while weak monsoon is closely associated with low index circulation over the same region.

Mother Lode, 1949

MOTHER LODE, 1949* Ruth E. Baugh University of California, Los Angeles The year 1949 marks the centennial of a momentous migration to the newly discovered gold fields of California and the settlement of the mining country known as the Mother Lode. Certainly not great among CaIifornian regions, nor currently outstanding in economic productivity, the Mother Lode possesses an individuality unmatched among the minor regions of the State for its picturesque beauty and its literary and histori cal associations. Located off the beaten track, the area preserves a good deal of the flavor of early days. Brick and adobe buildings constructed along simple, mid-nineteenth century lines are numerous in the surviving towns. Many retain the heavy iron doors and shutters, essential for protection against devastating fires which so frequently razed the early communities. Balconies of frame and ornamental iron work overhang narrow trail-like streets. In dozens of hamlets strung along the Lode structures erected in the 'fifties still house a few families or perhaps the village store or post office, while the ubiquitous and substantial Wells Fargo building is a prominent reminder of the part played by the express companies in the days before the establishment of banks. But a modern overlay, particularly in the large communities, almost obliterates the earlier landscape. Such towns as Sonora, Jackson and Placerville affect the new look in modernistic lines of the recent architecture, in chain stores and neon lights; but their origin as mining camps is apparent in their outmoded, hemmed-in sites and the narrow, sinuous streets that serve as main highways. A single exploitive industry laid the economic foundation during the pioneer period when the Mother Lode occupied an isolated frontier location . Recent years have witnessed a quickening of economic life in the utilization of long dormant resources. The diversification of economy and its improved stability parallel the trend noted in adjacent regions of California. (Note: See map of Mother Lode Country, p. 58.) THE TERM MOTHER LODE, GEOLOGIC AND GEOGRAPHIC The term Mother Lode, as used by the geologist, denotes the system of metalliferous veins in quartz and other rocks that occur in the folded and faulted formations underlying the lower slopes of the western Sierra Nevada. A more or less continuous belt of quartz veins occupies a fault zone approximately one mile wide, extending from Mariposa on the south to Georgetown north of Placerville, a latitudinal distance of one hundred twenty miles. It is from this system of rocks that all the gold of the western Sierra is derived—the surface placers worked during the ?Presidential address of the Association of Pacific Coast Geographers, Vancouver, British Columbia, June 16, 1949. 4 Yearbook of the AssociationVOL. 11 first decade after the discovery; the older Tertiary auriferous gravels exploited by hydraulicking; and particularly the deep lode mines that maintained California's gold production until the second World War. Attention was early directed to the massive outcrops of quartz in the placer zone, and a theory grew up that a single vein, "a mother lode, " the ultimate source of all the gold, extended from one end of the belt to the other. The origin of the term points to early Mexican miners to whom the veta madre was familiar in many of the Mexican mining districts. According to Knopf, the first gold-quartz vein was discovered and opened in August 1849 on Colonel Fremont's Mariposa grant, but ". . .the term was first applied to the veins worked at Nashville, twelve miles south of Placerville, El Dorado County, in the latter part of 1850, or early in 1851. "' The original belief of a single great persistent quartz vein traversing the state from end to end gave way in time to the established fact that the Mother Lode ". . . must not be considered as a continuous vein, but rather as a belt of parallel though some times interrupted quartzfilled fissures. "* On the other hand the term Mother Lode as applied to the geographical region is far more extensive than the mile-wide belt of auriferous rocks. In a general way the region overlies the Lode and its branching veinlets, but here and there it expands, reaching back into adjacent foothills or running out toward...