Darwin called the evolution of the Angiosperms a

1
(No Transcript)
2
Darwin called the evolution of the Angiosperms
a Perplexing phenomenon and in a letter to
Joseph Hooker he called them
3
an Abominable Mystery Charles Darwin in a
letter to Sir Joseph Hooker, 1879.
www.jdhooker.org.uk
4
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
5
Reconstructions of three fossil flowers (Crepet
et al., 1998. Am. J. Bot.911666-1682)
Paleoclusia
Microvictoria (related to water lilies)
Mabelia (monocot)
6
Location of fossil finds of Archaefructus and
Brachycera flies This has changed our view of
early angiosperms
7
Current Geography
Paleogeographic Map showing Positions of Modern
Countries in the Early Cretaceous JJapan,
KKorea, MonMongolia NCBNorth China, SCBSouth
China, etc.
8
Archaefructus liaoningensis 1998
Archaefructus sinensis 2002
Non-Angiosperm Seed Plant? Early Angiosperms?
Or
Specialized Early Angiosperm?
9
Archaefructus liaoningensis 1998
10
Archaefructus liaoningensis Is a fossil
angiosperm from the Jurassic (190-136mya)-- 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.
11
Archaefructus sinensis May, 2002
12
Archaefructus sinensis An aquatic herb!! No
petals or sepals! Protandrous?
13
Archaefructus sinensis A. Whole specimen B C.
Multiseed stalked carpels and paired stamens. D
I. Leaves (with swollen leaf base). Archaefructu
s liaoningensis E. Two young fruits with stamens
below. F G Pollen (monosulcate) J, KL. Mature
Fruits
14
Archaefructus sinensis Fossil Reproductive
Branch Controversies Are they flowering
plants? Most likely- though this is not
definitive. Are they the earliest angiosperms to
date? Could be but seems unlikely. Are they
dated accurately? Initial dates were too old.
Carpels
Stamens
Ovules
15
1 2
First 2 alternatives for Archaefructus
placement 1. Basal to all other
Angiosperms. 2. Specialized genus in a clade
with aquatic plants.
16

• Evidence
• Earlier dates (Late Jurassic gt144mya) 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.
• 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.
• 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.

17

1. Early estimates of age (Late Jurassic gt144mya)
   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.
18

1. 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.

19
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.
1
2
3
Archaefructus
20
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.)
21
(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.
22
?
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.