Transcript Document

Darwin called the evolution
of the Angiosperms a
“ Perplexing phenomenon”
…and in a letter to Joseph
Hooker he called them …
an “Abominable Mystery”
—Charles Darwin in a letter to Sir
Joseph Hooker, 1879.
QuickTime™ and a
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www.jdhooker.org.uk
90 million year old fossil
flowers (Fig. A- Clusiaceae and
B- related to the Heath Family)
already are highly developed
suggesting an earlier origin for
flowering plants.
(C) Phylogeny of living seed
plants based on morphological
characters. Note Gnetales and
Angiosperms clustered as the
Anthophytes..
(D) A contrasting phylogeny of
living seed plants based on
cpITS sequences. Note
support for the Gnetifer theory.
Crepet, William L. 1998. The Abominable Mystery. Science 282: 1653-1654
*
Reconstructions of three fossil flowers (Crepet et al., 1998. Am. J. Bot.91:1666-1682)
Paleoclusia
Microvictoria
(related to water
lilies)
Mabelia (monocot)
Location of
fossil finds of
Archaefructus
and Brachycera
flies
This has
changed our
view of early
angiosperms
Current Geography
Paleogeographic Map
showing Positions of
Modern Countries in
the Early Cretaceous
J=Japan, K=Korea,
Mon=Mongolia
NCB=North China,
SCB=South China, etc.
Archaefructus liaoningensis 1998
Archaefructus sinensis 2002
Non-Angiosperm Seed Plant? Early Angiosperms?
Or Specialized Early Angiosperm?
Archaefructus liaoningensis
1998
Archaefructus liaoningensis
Is a fossil angiosperm from the Jurassic (190136mya)-- the late Jurassic. It predates the
presumed Cretaceous (136-65 mya) origin for
the angiosperms.
(A) fruiting axes and remains of two subtending
leaves. (Scale bar, 5 mm).
(B) Enlarged view of the carpels showing
remains of the
adaxial (top) crest,
abaxial(bottom) venation,
seeds in each “carpel”, and
finger-like prominences.
(Scale bar, 5 mm).
(C) SEM of Portion of a seed removed from a
carpel (Scale bar, 25 µm).
Sun et al.1998 Science 282: 1692-1695.
Archaefructus sinensis
May, 2002
Archaefructus sinensis An aquatic herb!!
No petals or sepals! Protandrous?
Archaefructus sinensis
A. Whole specimen
B & C. Multiseed stalked
carpels and paired stamens.
D &I. Leaves (with swollen
leaf base).
Archaefructus liaoningensis
E. Two young fruits with
stamens below.
F & G Pollen (monosulcate)
J, K&L. Mature Fruits
Archaefructus sinensis
Fossil Reproductive Branch
Controversies:
Are they flowering plants?
Most likely- though this is
not definitive.
Are they the earliest
angiosperms to date?
Carpels
Could be but seems unlikely.
Are they dated accurately?
Initial dates were too old.
Stamens
Ovules
1
First 2 alternatives
for Archaefructus
placement:
1. Basal to all other
Angiosperms.
2. Specialized
genus in a clade
with aquatic plants.
2
Evidence:
1. Earlier dates (Late Jurassic >144mya) for this Yixian
formation (which includes the Jehol biota) were based on
flawed data. Recent data suggest this formation is about
125my old (early to mid Cretaceous). Other fossils of early
angiosperms date to this time.
2. Archaefructus lacks petals and sepals-- both found in most
bona fide Angiosperms. It shares features with some nonangiosperm seed plants-- making its position equivocal. We
have no data on ovule structure or evidence that the “carpels”
are derived from modified leaves.
3. Archaefructus may be a non-angiosperm seed plant group, a
basal angiosperm, or a specialized angiosperm. It may also
hint at the importance of an herbaceous, aquatic habitat, early
in the evolution of angiosperms.
1. Early estimates of age (Late Jurassic >144mya) for the Yixian
formation (including the Jehol biota) were flawed. New estimates
suggest this formation is about 125my old (early to mid
Cretaceous). Other fossils of early angiosperms date to this time.
Mammal
diversity
was high.
Plants
were also
diverse.
2. Archaefructus lacks petals and sepals-- both found in most bona fide
Angiosperms. It shares features with some non-angiosperm seed
plants-- making its position equivocal. We have no data on ovule
structure or evidence that the “carpels” are derived from modified
leaves.
Archaefructus may be 1. a non-angiosperm seed plant group, a
2. basal angiosperm, or 3. a specialized angiosperm. It may also
hint at the importance of an herbaceous, aquatic habitat, early in
the evolution of angiosperms.
Archaefructus
1
2
3
Protonemestrius jurassicus
(A) drawing of specimen
(B) photo of fly fossil
(C)
photo of proboscis
These fossil Brachycera flies were found in the same late rocks as
Archaefructus! They suggest the link between flies and flowers is old and
also may suggest an earlier origin for the angiosperms.
(Ren, D. 1998. Flower-associated Brachycera flies as fossil evidence for Jurassic angiosperm origins. Science 280: 85-88.)
(A) Drawing of specimen
(B) Photograph of body
(C) Photograph of proboscis
Palaepangonius eupterus-- another long tongued fly!
From Ren, D. 1998. Flower-associated Brachycera flies as fossil evidence for Jurassic angiosperm origins. Science 280: 85-88.
Initially the thought was that they were Jurassic-- but they are also
early to mid-cretaceous. Supporting and early Cretaceous origin for
flowers.
?
The Archaefructaceae were at one point considered basal with in the
angiosperms. But that view is being questioned and the search for the
earliest flowering plants continue.