SREERAJ E

BPS051318

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.

The Geological Time scale

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

How is a fossil formed?

1. SedimentAn 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. ErosionErosion from rain, rivers, and wind wears away the remaining rock layers. Eventually, erosion or people digging for fossils will expose the preserved remains.

2. LayersMore sediment layers accumulate above the animal’s/plant’s remains.

3. MovementMovement of tectonic plates, or rock slabs lifts up the sediments and pushes the fossil closer to the surface.

Remains of organisms that lived a very long time ago

Five main types of fossils

Petrified

Fossils

Molds and

Casts

Carbon

Films

Trace

FossilsPreserved

Remains

• 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.

Carbon film

FERN FOSSILThis carbon-film fossil of a

fern is more than

300 million years old.

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.

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.

• 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.

Furcula granulifera (upper Triassic)

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.

Archaefructus liaoningensis 1998 Archaefructus sinensis 2002

Non-Angiosperm Seed Plant? Early Angiosperms?

Or Specialized Early Angiosperm?

Archaefructus liaoningensis

1998

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

.

Archaefructus sinensis

May, 2002

Carpel

Stamen

Archaefructus sinensis, a125-million-year-old fossil

Artist’s reconstruction ofArchaefructus sinensis

5 cm

Archaefructus sinensis An aquatic herb?!

• 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.

Archaefructus

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.

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.

Pollen (The Lower and Mid Cretaceous period)

The earliest acceptable record of angiosperm is from lower cretaceous,Hautervianstrata 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.

Monocolpate pollen

Monocolpate pollen

Tricolpate pollenTricolpate pollen goes back approximately 127 MYA.

The diversification of pollen closely follows the diversification of leaf types.

Pollen

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

First angiosperm fossils --- sequence of diversification

The diversification of pollen closely follows the diversification of leaf types.

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.

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.

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.

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.

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

New CaledoniaFlower

Flowers of Amborella - carpels incompletely fused, no vessels