This document summarizes key aspects of paleobotany and the fossil record relating to early angiosperms. It describes how fossils are formed, the main types of fossils, and outlines the geological timescale. Regarding early angiosperms, it discusses Archaefructus fossils from the Early Cretaceous as possibly the earliest examples. It notes the sudden appearance and rapid diversification of angiosperms in the fossil record during the Early Cretaceous, as evidenced by leaves, pollen, and plant families. Amborella is presented as the most basal living angiosperm based on DNA analysis.

1. SREERAJ E
BPS051318

2. Introduction
• A branch of botany dealing with fossil plants.
• Includes the study and classification of plants of the
geological past as well as the study of their relationship with
each other and with extant plants.
• Palynology : the study of pollen
• Paleobotany and paleozoology are usually joined in the
science of paleontology.

3. The Geological Time scale
Geological Time scale describes the timing and relationships
between events that have occurred throughout Earth’s history.

4. How is a fossil formed?
Remains of organisms that lived a very long
time ago
1. Sediment
An animal/plant is
buried by sediment,
such as volcanic ash or
silt, shortly after it
dies. It is protected
from rotting by the
layer of sediment.
4. Erosion
Erosion from rain,
rivers, and wind wears
away the remaining
rock layers. Eventually,
erosion or people
digging for fossils will
expose the preserved
remains.
2. Layers
More sediment layers
accumulate above the
animal’s/plant’s
remains.
3. Movement
Movement of tectonic
plates, or rock slabs
lifts up the sediments
and pushes the fossil
closer to the surface.

5. Five main types of fossils
Petrified
Fossils
Molds and
Casts
Carbon
Films
Trace
Fossils
Preserved
Remains

6. Carbon film
• All living things contain an
element called carbon.
• When an organism dies and is
buried in sediment, the
materials that make up the
organism break down.
• Eventually, only carbon
remains.
• The thin layer of carbon left
behind can show an organism’s
delicate parts, like leaves on a
plant.
FERN FOSSIL
This carbon-film fossil of a
fern is more than
300 million years old.

7. Angiosperm origin: fossil record
• Darwin with reference to the origin of flowering plants,used the phrase the
"Abominable Mystery".
• Angiosperms appear suddenly in the fossil record with no obvious ancestors for a
period of 80-90 million years before their appearance.
• Clarifying the origin and diversification of angiosperms poses fascinating challenges to
evolutionary biologists
• The lack of fossils has been attributed to the idea that angiosperms arose in dry,
upland areas that were not optimal for fossilization.
• The earliest definite angiosperm fossils are from the Cretaceous, approximately 130
MYA. Angiosperms dominated the flora by 90 MYA, and most existing families were
present by 75 MYA.
• During the late Mesozoic, the major branches of the clade diverged from their
common ancestor.

8. The Pre-Cretaceous record of presumed angiosperms
• There is no good evidence in the fossil record of presumed angiosperm
remains that suggests that they had a pre-cretaceous origin.
• The first valid evidence does not appear until the Lower Cretaceous.
• Furcula granulifera (upper triassic) provides an excellent example of
fossil leaf remains that combine characteristics of angiosperms.

9. Furcula granulifera (upper Triassic)
• Leaf
Bifurcated lamina
A forked midrib from which dichotomizing secondary veins arising.
The intercostal veins between the secondary veins joins to form a
reticulam.
Stomata is syndetocheilic with surface of the guars cells thinly cutinized.
The stomata are oval and only slightly sunken.
The charecterestics of venation and stomata are those of angiosperms.
But the forking lamina is like that of certain cycadophytes,for this reason it
still not completely classified as an angiosperms.

10. The Lower and Mid Cretaceous record
• The origin and rapid diversification of angiosperms occurred in the lower
cretaceous.
• This conclusion is based in part on comprehensive studies of leaf
compression-impression and dispersed pollen types from the Potomac
group of the Lower Cretaceous in the US.

11. Archaefructus liaoningensis 1998 Archaefructus sinensis 2002
Non-Angiosperm Seed Plant? Early Angiosperms?
Or Specialized Early Angiosperm?

12. Archaefructus liaoningensis
1998

13. Archaefructus liaoningensis
It is a 125 MY old fossil angiosperm
(A) fruiting axes and remains of two subtending
leaves.
(B) Enlarged view of the carpels showing
remains of the
adaxial (top) crest,
abaxial(bottom) venation,
seeds in each “carpel”, and
finger-like prominences.
(C) SEM of Portion of a seed removed from a
carpel
.

14. Archaefructus sinensis
May, 2002

15. Carpel
Stamen
Archaefructus sinensis, a
125-million-year-old fossil
Artist’s reconstruction of
Archaefructus sinensis
5 cm
Archaefructus sinensis An aquatic herb?!

16. Archaefructus
• Archaefructus lacks petals and sepals-- both found in most Angiosperms.
• It shares features with some non-angiosperm seed plants-- making its
position equivocal.
• There is no data on ovule structure or evidence that the “carpels” are
derived from modified leaves.
• 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. Leaves (Cretaceous period)
There is rapid increase in diversity of angiosperm leaf types higher in the cretaceous.
The percentage of angiosperm leaf remains increase dramatically to as much as 25%
in the lower cretaceous.
These tend to be dominated by members of the palmately lobed
Araliaephyllum,Araliopsoides etc.
Pinnately compound leaves of Sapindopsis and leaves exhibiting a diversification of
monocot and dicot types also make their appearance.

18. Angiosperm Pollen
• Vascular plant pollen and spore walls contain one of the most stable and decay-resistant
biopolymers known to man.
• Palynologists can extract pollen from rocks using some of the strongest acids
know, without damaging the pollen.
• Spores and pollen get trapped in fine-grained rocks, usually when they settle out
of a column of lake or ocean water into bottom muds.
• which later become compressed into rock as more layers of sediment
accumulate above them.

19. Pollen (The Lower and Mid Cretaceous period)
Monocolpate pollen
The earliest acceptable record of angiosperm is from lower cretaceous,Hautervian
strata of England.
Early Angiosperms had pollen grains with one aperture (slit or pore, termed
monocolpate), as do cycads and Ginkgo.
Found here are grains with an angiospermous sporoderm comprising a tectum that
covers columellae and continueous inner layer of the exine.
Some of the grains are boat-shaped monocolpate type that could belong to either
monocots or some magnoliaceous dicots.
The occurrence of these pollen types correlates well with the presence of monocot
and dicot leaf types in this era.

20. Monocolpate pollen
Tricolpate pollen
Pollen
Tricolpate pollen goes back approximately 127 MYA.
The diversification of pollen closely follows the
diversification of leaf types.
Colpi are any thinning, thickening or other modification of the wall of pollen or spores that serve as an exit for
its contents or to allow shrinking and swelling of the grain in response to changes in moisture content

21. First angiosperm fossils --- sequence of diversification
The diversification of pollen closely follows the diversification of leaf types.

22. Evolution of the angiosperm flower
• (a) cone of the Jurassic bennettitalean Williamsoniella, showing the female fertile structure, the ovule,
contained in a central receptacle, and surrounded by the male fertile structures, the microsporophylls;
(b) flower of the gnetale Welwitschia, showing the central ovule, and surrounding male elements; and
(c) flower of the angiosperm Berberis, showing the same pattern, but with the seed enclosed in a
carpel.

23. Bevhalstia pebja - the world’s oldest flower (130 MYA)
Carpels in primitive angiosperms were imperfectly fused, and make a
physical intermediate between a folded leaf and fused pistil.

24. 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.)

25. (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.

26. Rapid radiation of the angiosperms during the Cretaceous
Rapid radiation of the angiosperms during the Cretaceous, shown by the rise in the
number of angiosperm families, from none at the beginning of the Cretaceous to
more than 35 by the end of the period. Neocom, Neocomian;
B, Barremian; Ce, Cenomanian; T, Turonian.

27. Basal Angiosperms:Amborella
• Analysis of DNA reveals this genus is the most primitive flowering plant.
• Found only on island of New Caledonia in the South Pacific.
• Understory shrub; plants dioecious
• Flowers with moderate number of petals.
• Flowers are imperfect (separate male and female gametophytes).
• Leaves simple, evergreenFlowers small, unisexual: ♀ apocarpous, with stigmatic crests; ♂
with laminar stamens
• No vessels in wood
Flower New Caledonia

28. Flowers of Amborella - carpels incompletely fused, no vessels