James R. Couper

Bio: James R. Couper is an academic researcher. The author has contributed to research in topics: Pollen. The author has an hindex of 1, co-authored 1 publications receiving 363 citations.

Fossil pollen records of extant angiosperms.

Abstract: The fossil record for angiosperm pollen types which are comparable to recent taxa is evaluated, following a similar survey published in 1970. Special attention is paid to the dating of the sediments. Evidence for 139 families is considered to be reliable, for others the records are cited as provisional, pending the accumulation of more evidence. Some published records are shown to be erroneous.

Early cretaceous fossil evidence for angiosperm evolution

Abstract: Morphological, stratigraphic, and sedimentological analyses of Early Cretaceous pollen and leaf sequences, especially from the Potomac Group of the eastern United States, support the concept of a Cretaceous adaptive radiation of the angiosperms and suggest pathways of their initial ecological and systematic diversification. The oldest acceptable records of angiosperms are rare monosulcate pollen grains with columellar exine structure from probable Barremian strata of England, equatorial Africa, and the Potomac Group, and small, simple, pinnately veined leaves with several orders of reticulate venation from the Neocomian of Siberia and the basal Potomac Group. The relatively low diversity and generalized character of these fossils and the subsequent coherent pattern of morphological diversification are consistent with a monophyletic origin of the angiosperms not long before the Barremian. PatuxentArundel floras (Barremian-early Albian?) of the Potomac Group include some pollen and leaves with monocotyledonous features as well as dicotyledonous forms. Patuxent angiosperm pollen is strictly monosulcate and has exine sculpture indicative of insect pollination. Rare Patuxent-Arundel angiosperm leaves are generally small, have disorganized venation, and are largely restricted to sandy stream margin lithofacies; the largest are comparable to and may include ancestors of woody Magnoliidae adapted to understory conditions. Patapsco floras (middle to late Albian?) contain rapidly diversifying tricolpate pollen and several new complexes of locally abundant angiosperm leaves. Ovate-cordate and peltate leaves in clayey pond lithofacies may includeancestors of aquatic Nymphaeales and Nelumbonales. Pinnatifid and later pinnately compound leaves with increasingly regular venation which are abundant just above rapid changes in sedimentation are interpreted as early successional “weed trees” transitional to but more primitive than the modern subclass Rosidae. Apparently related palmately lobed, palinactinodromous leaves which develop rigidly percurrent tertiary venation and become abundant in uppermost Potomac stream margin deposits (latest Albian-early Cenomanian?) are interpreted as riparian trees ancestral to the order Hamamelidales. Comparisons of dated pollen floras of other regions indicate that one major subgroup of angiosperms, tricolpate-producing dicots (i.e., excluding Magnoliidae of Takhtajan) originated in the Aptian of Africa-South America at a time of increasing aridity and migrated poleward into Laurasia and Australasia. However, the earlier (Barremian) monosulcate phase of the angiosperm record is represented equally in Africa-South America and Laurasia before marked climatic differentiation between the two areas. These trends are considered consistent with the hypothesis that the angiosperms originated as small-leafed shrubs of seasonally arid environments, and underwent secondary expansion of leaf area and radiated into consecutively later successional stages and aquatic habitats after entering mesic regions as riparian “weeds,” as opposed to the concept that they arose as trees of mesic forest environments.

Late Cretaceous and Tertiary vegetation history of Africa

Abstract: Twenty-five years have elapsed since Moreau (1952) completed his outstanding essay, ‘Africa since the Mesozoic: with particular reference to certain biological problems’. This valuable synthesis resulted from his interest in a major problem raised by the avifaunas. They reveal great differences between the four principal habitats of the continent: the arid regions, savanna, lowland evergreen forest, and montane evergreen forest. Since two or more of these ecosystems regularly are contiguous over wide areas, the coexistence of distinct avifaunas in them for a long period of time requires explanation, as does the existence of the different vegetation zones themselves.