Náttúrufræðingurinn - 1983, Blaðsíða 184

SUMMARY
Acer-leaves and samaras from
lcelandic deposits
by
Lic. scienl. Leifur A. Símonarson,
Raunvísindastofnun Háskólans,
Dunhaga 3,
107 Reykjavík, Iceland
and
Dr. rer. nat. Walter L. Friedrich,
Geologisk Institut,
Árhus Universitet,
C. F. M0llers Alleé 120,
DK-8000 Árhus C, Denmark.
In 1976 and 1982 the authors described
fossil Acer-leaves and samaras from seve-
ral Tertiary localities in Iceland and
pointed out that they are distinct from
recent and fossil species. There are two
different types of samaras, as well as
leaves, which seem to prove that there
were at least two Acer-species living in
Iceland in the Upper Miocene and
Pliocene.
Acer-samaras from the Hreðavatn area,
West Iceland, are different from recent
and fossil forms, especially due to their
large size (up to 90 mm), big locules (up to
30 mm) and the characteristic wing form.
We named them Acer askelssoni in 1976.
They compare with the fruit of the recent
species A. saccharinum from North Amer-
ica. Another type of Acer-samaras from
the Hreðavatn area, and several other
localities in West and Northwest Iceland,
is much smaller (up to 25 mm), with com-
parative larger locules (up to 10 mm) and a
different wing form, e. g. the tip of the
wing is more ovate. These samaras are
closely related to the modern species A.
rubrum from eastern North America. In
Iceland this latter type is always found
together with Acer-leaves closely related
to this species. The leaves are up to 15 cm
long and 13 cm broad, quinquelobat, with
the central lobe longer than the lateral
ones. The proximal part of the central lobe
has parallel margins. The angle between
the central lobe and the upper lateral lobes
is 38°—60° or 46,1° on average. The leaf
base is cordate. The margin has straight-
convex serration. The nervation is very
similar to that of A. rubrum, however, the
finest ends are not as often biforked. In
1982 we referred these leaves to a new
species, Acer islandicum, and tentatively
the smaller type of samaras is also referred
to this species. They are synonymous with
earlier described A. otopterix, A. crenati-
folium, A. crassinervium, A. tricuspida-
tum, A. rubrum and in part Vitis islandica
from Iceland.
Another type of Acer-leaves, up to 14
cm long and 18 cm broad, i. e. broader
than they are long, has been found
together with the samaras referred to as A.
askelssoni. These leaves are quinquelobat,
with the central lobe of similar length as
the upper lateral lobes. The proximal part
of the central lobe does not have parallel
margins. The angle between the central
lobe and the upper lateral lobes is 36°—50°
or 42° on average. The leaf base is cordate.
The margin has straight-straight serration.
These leaves seem closely related to the
modern North American species. A. sac-
charum and may belong to A. askelssoni.
Apparently Acer became extinct in Ice-
land 7 Ma ago. About 6 Ma ago the first
tillites were formed in Iceland, obviously
by local glaciations on mountain tops and
in inland areas. However, they represent
the worldwide climatic deterioration that
probably brought about the extinction of
Acer and other Tertiary thermophilic spe-
cies in Iceland.
168