Early cretaceous fossil evidence for angiosperm evolution

Cenomanian angiosperm leaf megafossils, Dakota Formation, Rose Creek locality, Jefferson County, southeastern Nebraska

“…While some authors explained this situation by proposing extremely rapid evolution of flowering plants during the Cretaceous (Scott and others, 1960), others proposed an extensive period of diversification prior to the group's appearance in the fossil record, either in remote geographic regions (Seward, 1931) or in upland regions, where preservation of preTertiary sediments is minimal (Axelrod, 1952(Axelrod, , 1970. These concepts were consistent with occasional reports of pre-Cretaceous flowering plants (for example, Harris, 1932;Erdtman, 1948;Kuhn, 1955;Brown, 1956;Tidwell and others, 1970), now either discounted or considered problematic on morphological or stratigraphic grounds (Read and Hickey, 1972;Scott and others, 1972;Wolfe and others, 1975;Hickey and Doyle, 1977).…”

“…Sapindopsis has the most irregular vein organization of all taxa in the series, which implies that it represents the primitive end; this implies that compound leaves are primitive to many simple-leaved clades of Rosidae. Combined stratigraphic and phenetic evidence reinforces evidence from comparative morphology, because pinnately compound foliage of the Sapindopsis type is the most ancient and shows the closest morphological resemblance to angiosperm leaf taxa of Aptian to middle Albian ~ge (Doyle and Hickey, 1976;Hickey and Doyle, 1977;Hickey, 1978;Upchurch, 1984).…”

“…Magnoliales, which are considered the most primitive order of flowering plants by Cronquist (1968Cronquist ( , 1981 and Takhtajan (1969Takhtajan ( , 1980, are represented by fossils that show relatively low comparability with a single extant family and that show closest similarities to generally primitive extant taxa. For example, new genus A has the multistranded midrib and low venational regularity inferred to be primitive for the flowering plants as a whole (Hickey and Wolfe, 1975;Hickey and Doyle, 1977), plus a combination of features that is most similar to generalized magnolialean venation. "Ficus" macrophylla, a taxon originally described by Lesquereux (1892) from the Dakota Formation of Kansas, appears to represent a Late Cretaceous relative of the Ficophyllum complex, whose closest modern affinities lie with the primitive families Austrobaileyaceae, Magnoliaceae, and Winteraceae (Upchurch, 1983).…”

“…During this time, the angiosperms began their adaptive radiation, and major extant lineages at the level of subclass, order, and family made their first appearance. (See, for example, Wolfe and others, 1975;Hickey and Doyle, 1977;Dilcher, 1979;Upchurch, 1984;Walker and Walker, 1984. ) Associated with this adaptive radiation were progressive and broad-scale ecological displacements, wherein cycadophytes, ginkgophytes, and other dominant groups of gymnosperms declined in relative abundance and diversity and were replaced in most habitats and geographic regions by angiosperms, especially at lower and middle paleolatitudes (Doyle and Hickey, 1976;Hickey and Doyle, 1977;Retallack andDilcher, 1981, 1985;Crane, 1987;Upchurch and Wolfe, 1987b).…”

“…(See, for example, Wolfe and others, 1975;Hickey and Doyle, 1977;Dilcher, 1979;Upchurch, 1984;Walker and Walker, 1984. ) Associated with this adaptive radiation were progressive and broad-scale ecological displacements, wherein cycadophytes, ginkgophytes, and other dominant groups of gymnosperms declined in relative abundance and diversity and were replaced in most habitats and geographic regions by angiosperms, especially at lower and middle paleolatitudes (Doyle and Hickey, 1976;Hickey and Doyle, 1977;Retallack andDilcher, 1981, 1985;Crane, 1987;Upchurch and Wolfe, 1987b). Although some aspects of this transition have been elucidated by recent paleobotanical research, much remains unknown about this critical interval of Earth history, particularly with respect to the dynamics of angiosperm diversification and the establishment of major extinct and extant angiosperm lineages.…”