Southern South American Research Articles

Exotic sporomorpha as indicators of potential immigrant colonists in Antarctica

Abstract A brief account is given documenting the development of aerobiological research in the Antarctic. The results of the British Antarctic Survey's contribution to an international programme on long-distance dispersal of aeroplankton over the Southern Ocean are presented. This was achieved by collecting airspora deposited in Tauber traps and in surface snow at sites on South Georgia (sub-Antarctic) and Signy Island (maritime Antarctic). Although only a small number of the samples were analysed, the results provided ample evidence of a continuous immigration of exotic sporomorpha of southern South American provenance. The cause of this rain of biological material is attributed to the not infrequent easterly tracking storm events generated over the south-east Pacific Ocean. As they gain momentum over southern South America they become seeded with pollen and spores, and possibly by larger organelles such as invertebrates and seeds. These high winds may be deflected southwards by a blocking anticyclone over the South Atlantic Ocean, allowing a proportion of the sporomorpha to be deposited over land far to the south. The occurrence of such exotic sporomorpha in these remote and environmentally hostile regions is used here as evidence to support the hypothesis that there is a continuous input into the Antarctic biome of viable propagules from more northerly landmasses. While no exotic bryophyte or lichen spores have yet been detected in trapping experiments, the extremely rare occurrence of certain bryophytes associated only with geothermal sites in the Antarctic and in laboratory-cultured soils from barren ice-free terrain indicates that a pool of viable but dormant propagules is probably widespread in Antarctic soils and ice. However, germination and development in situ are possible only under exceptional environmental circumstances. An international programme is being planned to detect the main trajectories of long-distance transport of propagules into the Antarctic and to test their viability.

Alkaline magmatism within the segment 38°–39°S of the Plio‐Quaternary Volcanic Belt of the southern South American Continental Margin

In the segment 38°–39°S of the southern South American volcanic belt, the subalkaline central‐vent volcanoes that form the late Quaternary volcanic front of the Andean orogenic arc are located in the Main Andean Cordillera 30–80 km west of the centers that formed the Pliocene/early Pleistocene volcanic front. The Pliocene/early Pleistocene volcanic front was located along a precordilleran uplift that diverges southeast from the Main Andean Cordillera. During the Pliocene the centers along this uplift erupted subalkaline magmas similar to those currently being erupted along the late Quaternary front. In the early Pleistocene the centers at the southeast end of this uplift began to erupt alkaline magmas. By the late Pleistocene, magmatic activity in these centers had diminished, and the volcanic front had migrated westward to its current location, but alkaline back arc basaltic volcanism continued in the late Quaternary within the valleys flanking the precordilleran uplift on which the Pliocene/early Pleistocene arc had been situated. The early Pleistocene alkaline orogenic arc lavas and the late Quaternary alkaline back arc basalts have La/Yb higher than, but Ba/La and 87Sr/86Sr similar to, the subalkaline magmas erupted from centers of both the Pliocene and late Quaternary volcanic fronts. Their TiO2 and La/Nb are intermediate between subalkaline magmas erupted from both the Pliocene and late Quaternary volcanic fronts and alkaline basalts of the Patagonian plateau lavas south of 39°S which have intraplate oceanic island petrochemical characteristics. Compared with the subalkaline lavas of the current volcanic front, Quaternary alkaline arc and back arc lavas between 38° and 39°S formed by lower degrees of partial melting of a similar mantle source. This mantle had been modified by source region contamination processes related to dehydration of subducted oceanic lithosphere such as occur below the current volcanic front in the southern Andes.

Studies on the Genus Nephroma II. The Southern Temperate Species

AbstractThis paper reassesses the southern temperate South American and Australasian species of Nephroma, analyses their chemistry and provides a key to the 14 species and three varieties accepted. N. occultum from North America is also discussed due to its close relationship to N. microphyllum and N. papillosum. Three pairs of morphotypes are described for the first time: N. analogicum-N. chubutense, N. kuehnemannii-N. microphyllum and N. skottsbergii-N. papillosum. N. papillosum sp. nov. and N. skottsbergii sp. nov. from Chile and Argentina are newly described. N. lobuligerum and N. lepidophyllum are reduced to varietal rank. N. lyallii is placed in synonymy with N. plumbeum and a new combination N. plumbeum var. isidiatum (J. Murray) F. J. White & P. James is made.

The quaternary volcanic belt of the southern continental margin of South America: Transverse structural and petrochemical variations across the segment between 38°S and 39°S

In the segment between 38°S and 39°S of the southern South American continental margin volcanic belt, the volcanoes of the Quaternary “orogenic arc” may be divided into two groups: the first forming the volcanic front, which is located within the Cordillera Principal along a trend oriented 15° east of north; the second east of the volcanic front, occurring upon an uplifted precordilleran block that is east of the Bío-Bío/Aluminé fault system, trends west of north, and merges with the Cordillera Principal near 38°S. Quaternary “back-arc” plateau lavas, consisting of basalts erupted from small cones, occur in the valley east of this precordilleran block. Quaternary intra-arc and back-arc extension appear to be occurring in this section (38–39°S) of the southern South American volcanic belt and perhaps as far north as 34°S. South of 39°S, intra-arc extension is absent and the orogenic arc is restricted to the Cordillera Principal. Differences in the structural characteristics of the arc north and south of 39°S may be due to the change in age from older to younger oceanic lithosphere being subducted beneath, respectively, the two regions. Basalts erupted from both Quaternary arc and back-arc centers located east of the volcanic front between 38°S and 39°S have higher K 20, Rb, Ba, and LREE contents, and higher La/Yb but lower Ba/La ratios, than basalts erupted along the volcanic front. 87Sr/ 86Sr ratios for arc lavas from volcanic centers both within and east of the volcanic front range from 0.7038 to 0.7041 independent of their Si0 2 content, suggesting that more silicic compositions developed from basalts by crystal-liquid fractionation without significant crustal assimilation. Back-arc plateau basalts from the region 38–39°S have Sr isotopic compositions similar to those of the arc volcanoes. Basalts from both the arc and the back-arc centers between 38°S and 39°S may form by partial melting of a large-ion-lithophile-element-enriched mantle source similar to the source of mantle-xenolith-bearing Quaternary alkali plateau basalts from southern Patagonia (south of 39°S), further modified by the addition of alkali elements derived from subducted oceanic lithosphere.

FLIGHTLESSNESS IN STEAMER-DUCKS (ANATIDAE: TACHYERES): ITS MORPHOLOGICAL BASES AND PROBABLE EVOLUTION.

Flightlessness in Tachyeres is caused by wing-loadings in excess of 2.5 g·cm-2 , which result from the large body size and small wing areas of the flightless species. Reduced wing areas of flightless species are related to absolutely shorter remiges, and to relatively or absolutely shortened wing bones, although these reductions differ among species. Reduced lengths of the ulna, radius, and carpometacarpus are associated most strongly with flightlessness. Pectoral muscles and the associated sternal keel are well developed in all species of Tachyeres, largely because of the use of wings in "steaming," an important locomotor behavior. Relative size of these muscles was greatest in largely flighted T. patachonicus; however, sexual dimorphism in wing-loadings results in flightlessness in some males of this species. Proportions in the wing skeleton, intraspecific allometry, and limited data on growth indicate that the relatively short wing bones and remiges of flightless Tachyeres are produced developmentally by a delay in the growth of wing components, and that this heterochrony may underlie, in part, skeletal sexual dimorphism. Increased body size in flightless steamer-ducks is advantageous in territorial defense of food resources and young, and perhaps diving in cold, turbulent water; reductions in wing area probably reflect refinements for wing-assisted locomotion and combat. Flightlessness in steamer-ducks is not related to relaxed predation pressure, but instead was permitted selectively by the year-round habitability of the southern South American coasts. These conditions not only permitted the success of the three flightless species of Tachyeres, but at present may be moving marine populations of T. patachonicus toward flightlessness.

Paleogene Phytogeography and Climatology of South America

Paleogene, Maastrichtian, and Miocene floras are reviewed. They are located on continental margins, where several sedimentary basins developed. The affinities of the fossil genera to living ones allow the recognition of three paleofloras: Neotropical, Mixed, and Antarctic. These could be the forerunners, respectively, of the presently more humid dominions in Neotropical Region (Caribbean, Amazonic, and Guayano), of the drier ones (Chaquefto and Andino-Patagonico), and ofthe Subantarctic Dominion of the Antarctic Region. The South American climate, as indicated by the fossil floras, showed a trend to higher temperatures during the Paleocene and Lower Eocene, and a deterioration through the Middle and Upper Eocene. The purpose of the present work is to review the Paleogene taphofloras of South America and to analyze their paleophytogeographical and paleoclimatical significance. This problem has interested botanists and paleontologistsin the past. Berry (1921,1938,1940) published several reviews as a direct result of his work in the continent. More recently, Menendez (1964, 1969, 1971) detailed the taphofloras and the areas occupied by the different types of vegetation, and Volkheimer (1971) gathered evidence about the paleoclimatology of Argentina. Later, Archangelsky and Romero (1974) analyzed the environmental conditions based on the pollen record of the southern South American Paleogene, and Aragon and Romero (1984), Romero (1978), Romero and Arguijo (198 1b, 1982), and Romero and Dibbern (1984) analyzed some taphofloras of the same region. Therefore, much new geological, botanical, and paleontological evidence has been gathered, warranting a new review. The present paper is arranged in two parts. The first one reviews every published outcrop with impressions known to the author from the Paleogene of South America, complemented with information about fruit casts, petrified wood, and palynology. Data about some Maastrichtian and Miocene floras have been added to show more general trends in the changes. The age of the deposits was updated according to recent publications. The second part discusses the phytogeographical areas that could have existed during that time, and the climate under which they have developed. There is not an agreement on the terminology to be used in biogeographical discussions, especially among paleobotanists. I shall use a few of them, in an attempt to reach more accuracy and clarity, but without discussing their antecedents or convenience, which surpasses the limits of the present paper. They are: Flora. The list of the plants living together in a given area at a given moment. They may be fossil or living. Vegetation. Plant cover in a given area at a given moment, fossil or living. Their association, ecology, and life forms, rather than their taxonomic identity, are considered. Taphoflora. The list of the fossil plants preserved in a given outcrop. They represent the original flora, as affected by dispersal, burial in that place, diagenesis, and differential alteration. They are the smallest real evidence to be used in paleophytogeography. Paleoflora. A fossil flora that may be characterized by its systematic list, and so differentiated from other fossil floras. Each paleoflora may comprise several taphofloras. From the characteristic systematic list a characteristic plant association may be hypothesized, and so vegetational features suggested. A REVIEW OF THE PALEOGENE TAPHOFLORAS

Stratigraphy and geochemistry of accreted fragments of the ancestral pacific floor in southern south America

The outer Pacific archipelago of southern Chile has allochthonous fore arc rocks that were accreted prior to the Late Jurassic along the ancestral Pacific margin of the southern South American sector of Gondwana. The fore arc rocks in the Archipielago madre de Dios (50°-50° 47′S) are divisible into three assemblages: the Tarlton Limestone, a sequence of massively bedded Upper Carboniferous to Lower Permian limestone; the Duque de York Complex, a sequence of flysch-like sedimentary rocks; and the Denaro Complex, an association of pillow basalt, bedded chert, detrital calcareous rocks, and shale. The Denaro Complex is interpreted as a sequence of the late Paleozoic ancestral Pacific floor. The Tarlton Limestone may represent a shallow water carbonate platform also built on a basaltic substrate located within the ancestral Pacific realm. The basalt units of the Denaro Complex have tholeiitic major element patterns similar to those of modern day “MOR” and “within plate” basalts. Chemical data for the Denaro Complex allow for the partial discrimination of biogenic, hydrothermal, hydrogenous, and detrital components within the sedimentary units, and facilitate comparison with modern day sediments as well as with other ophiolite sequences. Chemical data together with stratigraphic and structural field relations suggest that the evolution of the Denaro Complex and Tarlton Limestone involved seafloor spreading, hydrothermal activity, seamount volcanism, carbonate reef development, and convergence of the oceanic realm with the margin of Gondwana.

Malaysian elements of the Southern South American mosses

Malaysian elements of the Southern South American mosses

A Revision of the Generic Classification of Certain Leptophlebiidae from Southern South America (Ephemeroptera)1

Southern South American genera of Leptophlebiidae are described in this paper from reared nymphs and adults. The genera Massartella, Atalonella , and Massartellopsis are redescribed. A type-species, A. ophis Needham & Murphy, is designated for Atalonella . Three new genera, PENAPHLEBIA, HAPSIPHLEBIA , and MERIDIALARIS are established for species previously placed in Australian genera. The status of Nousia and the possible synonymy of Atalonella with Nousia are discussed. The following new combinations are included: Penaphlebia chilensis (Eaton), P. fulvipes (Needham & Murphy), P. sepia (Thew), P. vinosa (Demoulin), Hapsiphlebia anastomosis (Demoulin), Meridialaris biobionica (Ulmer), M. chiloeense (Demoulin), M. diguillina (Demoulin), M. illapeli (Demoulin), M. laminata (Ulmer), M. patagonica (Lestage), and M. penai (Demoulin). Illustrated keys to the nymphs and adults of the genera are given. Preliminary studies on the relationships and phylogeny of these genera are presented.

A New Bolivian Trachysphyrus of the Imperialis Group (Hymenoptera, Ichneumonidae)

Entomologically, Bolivia is perhaps the least known part of Latin America. In 1967, when I published a monograph of the nearly 100 predominantly Andean and southern South American species of Trachysphyrus, I could include onty two records from that country, although adjacent Perú, Chile, and Argentina were each found to be major centers of abundance and diversity for Trachysphyrus. In March of 1968, however, when I was able to spend a week collecting near La Paz, I discovered an abundant and conspicuous new Trachysphyrus belonging to the group of T. imperialis Haliday, as defined in my earlier study (Porter 1967, p. 275).

STUDIES IN THE CAPPARIDACEAE. XI: CLEOME AFROSPINA, A TROPICAL AFRICAN ENDEMIC WITH NEOTROPICAL AFFINITIES

The Tropical West African‐Congolese spiny Cleome previously referred to the neotropical “C. spinosa” is the indigenous, distinct, here newly described C. afrospina, most closely related to the southern South American C. trachycarpa of the otherwise endemic neotropical Section Tarenaya. Early collections (from 1816) and widespread distribution in wet forests and riversides also indicate it to be indigenous and not adventive. Related also is the widespread Brazilian‐Argentinian C. hassleriana Chod. (“C. spinosa” auct. non Jacq.; “C. pungens” auct. non Willd.?), the commonly cultivated “Spider Flower,” once recently collected in the Congo (cultivated?). As the only indigenous spiny Old World Cleome, C. afrospina is a remarkable neotropical element in the African flora. Historical explanations for such disjunctions (continental drift, land bridges) are rejected. Avian long‐distance dispersal is indicated by semi‐aquatic successional habitats of high ecological receptivity, generally annual habit, other highly disjunct vicariads, and self‐compatibility within the group. Similar disjunctions occur in the distribution patterns of many aquatic birds (e.g., whistling ducks—Dendrocygna) and of various tropical plants of ecologically receptive “open” habitats.