Cretaceous and Paleogene Fagaceae
from North America and Greenland: evidence
for a Late Cretaceous split between Fagus
and the remaining Fagaceae
1 | University of Vienna, Department of Palaeontology, Althanstraße 14 (UZA II), 1090 Vienna, Austria |
2 | Swedish Museum of Natural History, Department of Palaeobiology, P.O.Box 50007, 10405 Stockholm,
Sweden |
Online publication date: 2016-12-13
Publication date: 2016-12-13
Acta Palaeobotanica 2016; 56(2): 247–305
ABSTRACT
Modern lineages of the beech family, Fagaceae, one of the most important north-temperate families
of woody flowering plants, have been traced back to the early Eocene. In contrast, molecular differentiation
patterns indicate that the Fagus lineage, Fagoideae, with a single modern genus, evolved much earlier than the
remaining lineages within Fagaceae (Trigonobalanoideae, Castaneoideae, Quercoideae). The minimum age for
this primary split in the Fagaceae has been estimated as 80 ± 20 Ma (i.e. Late Cretaceous) in recently published,
time-calibrated phylogenetic trees including all Fagales. Here, we report fagaceous fossils from the Campanian
of Wyoming (82–81 Ma; Eagle Formation [Fm]), the Danian of western Greenland (64–62 Ma; Agatdal Fm), and
the middle Eocene of British Columbia (ca 48 Ma; Princeton Chert), and compare them to the Fagaceae diversity
of the recently studied middle Eocene Hareøen Fm of western Greenland (42–40 Ma). The studied assemblages
confirm that the Fagus lineage (= Fagoideae) and the remainder of modern Fagaceae were diverged by the middle
Late Cretaceous, together with the extinct Fagaceae lineage(s) of Eotrigonobalanus and the newly recognised
genus Paraquercus, a unique pollen morph with similarities to both Eotrigonobalanus and Quercus. The new
records push back the origin of (modern) Fagus by 10 Ma and that of the earliest Fagoideae by 30 Ma. The earliest
Fagoideae pollen from the Campanian of North America differs from its single modern genus Fagus by its
markedly thicker pollen wall, a feature also seen in fossil and extant Castaneoideae. This suggests that a thick
type 1 foot layer is also the plesiomorphic feature in Fagoideae although not seen in any of its living representatives.
The Danian Fagus pollen of Greenland differs in size from those of modern species but is highly similar
to that of the western North American early Eocene F. langevinii, the oldest known beech so far. Together with
the Quercus pollen record, absent in the Campanian and Danian formations but represented by several types
by the middle Eocene, this confirms recent dating estimates focussing on the genera Fagus and Quercus, while
rejecting estimates from all-Fagales-dated trees as too young. The basic Castaneoideae pollen type, still found
in species of all five extant genera of this putatively paraphyletic subfamily, represents the ancestral pollen type
of most (modern) Fagaceae (Trigonobalanoideae, Castaneoideae, Quercoideae).